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FRONT SUSPENSION OPTIMISATION FOR UJ SOLAR CAR, ILANGA I

By

JULES DAVID DE PONTE - 200901524

A design project submitted to the Faculty of Engineering and the Built Environment in partial

fulfilment of the degree of

BACCALAUREUS INGENERIAE

In

MECHANICAL ENGINEERING SCIENCE

At the

UNIVERSITY OF JOHANNESBURG

SUPERVISOR: N. Janse van Rensburg

October 2012

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Anti-Plagiarism Declaration

I, Jules David de Ponte, hereby declare that this design Report is wholly my own work and has not

been submitted anywhere else for academic credit by myself or another person. I understand what

plagiarism implies and declare that this mini-dissertation is my own ideas, words, phrases, arguments,

graphics, figures, results and organisation except where reference is explicitly made to another‟s

work.

I understand further that any unethical academic behaviour, which includes plagiarism, is seen in a

very serious light by the University of Johannesburg and is punishable by disciplinary action.

Sign: Date:

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“Scientists dream about doing great things. Engineers do them.”

– James A. Michener

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Acknowledgements

I would like to thank the following people, without whom, this project would have been unsuccessful.

- God – For the ability, intellect and strength of will to complete this project.

- My Family – For motivating and encouraging me, and also financial support during my

degree.

- N. Janse van Rensburg – Whose efforts has made the UJ Solar Team a reality. Also, for

providing practical advice on how to best complete this project.

- The UJ Solar Team – I would like to acknowledge the good job that was done during the

2012 Sasol Solar Challenge. May the 2014 race be even better for us. Thanks to the masters‟

students for their advice during the design phase of this project, and to the rest of the

undergraduate students who assisted in building and completing Ilanga I.

My deepest gratitude goes out to these individuals.

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Executive Summary

This Report will document the process untaken to design the updated suspension system for the UJ

solar car, Ilanga I. The need is identified as a suspension system, which is stronger, lighter, more

aerodynamically efficient and more practical than the solution currently employed. In order to

facilitate this, the suspension will be constructed from AISI4130 chrome-moly. This material is

stronger than the aluminium currently used, but it is also heavier. Therefore, to reduce weight, the

system will be optimised as much as possible; any non-essential members have been removed.

In order to perform these optimisations, literature on suspension designs was reviewed. This gave

valuable insight into the various systems currently in use, as well as what sort of practical design

aspects have to be considered. After reviewing the literature, the selection criteria for the concepts

could be chosen. This would provide a semi-quantitative answer as to which concept is better; rather

than merely a subjective selection. The concepts were generated such that they would fulfil the design

requirements. The literature was also used extensively in devising practical solutions. The concepts

were evaluated using a pair-wise comparison, and the best concepts were chosen for further

development. The selected concepts were double wishbone suspension, with a pushrod and rocker.

The conventional steering swivel was chosen, instead of a bicycle fork arrangement.

With the selected concept in mind, the design calculations were performed. The design process was an

iterative one, where various geometries were altered. After the geometry was altered, a performance

simulation was conducted. The geometry was changed slightly and re-evaluated. The best solution

from multiple iterations was carried forward for further development. The Performance Simulation in

Section 8 shows the final performance simulations. The strength of materials calculations was

performed to validate the design. A finite element analysis was conducted on one of the components;

this was done, in a large part, to illustrate the concept of finite element analysis. A review on material

properties was conducted in Section 9, and the most appropriate material was selected; AISI4130.

The manufacturing involved laser cutting of certain components, welding and assembly. Plates were

cut for the steering swivels, pushrod rocker arms, and parts of the suspension box. The suspension box

consists of plates and tubes; these were welded together, as were the suspension control arms. The

unit was assembled, and bolted onto the chassis.

While the suspension was being designed, other members of the Solar Team were optimising the

chassis. The new chassis, dubbed Ilanga I-I, would be used in the South African Solar Challenge.

After assembly, the car was tested. Driver feedback was positive, with the drivers stating that the

handling was good.

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Table of Contents

Anti-Plagiarism Declaration ................................................................................................................... 2

Acknowledgements ................................................................................................................................. 4

Executive Summary ................................................................................................................................ 5

Table of Contents .................................................................................................................................... 6

List of Figures ......................................................................................................................................... 9

List of Tables ........................................................................................................................................ 11

Definition of Terms ............................................................................................................................... 12

1. Introduction ................................................................................................................................... 13

2. Needs Identification ...................................................................................................................... 15

3. Operating Environment, Functional Analysis and Mission Analysis ........................................... 16

3.1 Operating Environment and Functional Analysis ................................................................. 16

3.2 Mission Analysis ................................................................................................................... 17

3.2.1 Sponsors ........................................................................................................................ 17

3.2.2 Technical Obligations ................................................................................................... 18

4. Contextual Background................................................................................................................. 19

4.1 Introduction ........................................................................................................................... 19

4.2 Types of Suspension Systems ............................................................................................... 19

4.3 Castor Angle ......................................................................................................................... 21

4.4 Scrub Radius and Steering Angle Inclination ....................................................................... 22

4.5 Camber .................................................................................................................................. 22

4.6 Springs and Dampers ............................................................................................................ 23

4.7 Ackermann Angle ................................................................................................................. 25

4.8 Centre of Gravity, Roll Centre and Roll Axis ....................................................................... 26

4.9 Toe Settings .......................................................................................................................... 27

4.10 Bump Steer ............................................................................................................................ 27

4.11 Legal, Health and Patent and Other Considerations ............................................................. 28

4.11.1 Legal ............................................................................................................................. 28

4.11.2 Health and Safety .......................................................................................................... 28

4.11.3 Patents ........................................................................................................................... 29

4.11.4 Social, Environmental and Other Considerations ......................................................... 30

4.11.5 Conclusion .................................................................................................................... 31

5. Product Design Specification ........................................................................................................ 32

6. Selection Criteria .......................................................................................................................... 33

6.1 Criteria Governing the Steering Swivel Arm ........................................................................ 34

6.2 Criteria Governing the Suspension System........................................................................... 35

7. Concept Generation and Selection ................................................................................................ 36

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7.1 Design considerations ........................................................................................................... 36

7.1.1 Existing Bodywork ....................................................................................................... 36

7.1.2 Existing Suspension Geometry and Front Wheels ........................................................ 36

7.1.3 Existing Steering Rack .................................................................................................. 36

7.2 Alternative Design Concepts ................................................................................................ 37

7.2.1 Front Fork Arrangement ............................................................................................... 38

7.2.2 Steering Swivel Arm ..................................................................................................... 39

7.2.3 Pushrod Suspension with Rocker Arm ......................................................................... 41

7.2.4 Pushrod Suspension without Rocker Arm .................................................................... 42

7.2.5 MacPherson Strut .......................................................................................................... 43

7.2.6 Using the Lower control Arm as a Rocker .................................................................... 44

7.3 Conclusion ............................................................................................................................ 46

8. Performance Simulations and Design Calculations ...................................................................... 47

8.1 Performance Simulations ...................................................................................................... 48

8.1.1 Change in Track Length vs. Suspension Travel ............................................................ 49

8.1.2 Change in Camber due to Steering Input ...................................................................... 50

8.1.3 Ackermann Steering Geometry ..................................................................................... 50

8.2 Design Calculations .............................................................................................................. 51

8.2.1 Control Arm and Pushrod Force Calculations .............................................................. 51

8.2.2 Pushrod Rocker Stress Calculations.............................................................................. 54

8.2.3 Axel Bending Stress Calculations ................................................................................. 56

8.2.4 Control Arm Pivots Force Calculations ........................................................................ 57

8.3 Conclusion ............................................................................................................................ 57

9. Material Selection ......................................................................................................................... 58

9.1 Material Science .................................................................................................................... 58

9.1.1 Metals ............................................................................................................................ 58

9.2 Material Properties ................................................................................................................ 60

9.2.1 AISI 4130 Chrome-Moly .............................................................................................. 61

9.2.2 6063-T6 Aluminium ..................................................................................................... 62

9.3 Side-by-Side Comparison ..................................................................................................... 62

9.4 Calculations ........................................................................................................................... 63

9.4.1 Control Arm and Pushrod Material Calculations .......................................................... 63

9.4.2 Pushrod Rocker Material Selection ............................................................................... 64

9.4.3 Suspension Box Structure ............................................................................................. 64

9.5 Conclusion ............................................................................................................................ 64

10. Manufacturing Process .............................................................................................................. 65

10.1 Laser Cutting ......................................................................................................................... 66

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10.2 Welding ................................................................................................................................. 67

10.3 Standard Parts ....................................................................................................................... 68

10.4 Manufacturing ....................................................................................................................... 68

10.5 Assembly............................................................................................................................... 69

11. Maintenance .............................................................................................................................. 73

11.1 Wheels – Bearings and Brakes .............................................................................................. 73

11.2 Bushes ................................................................................................................................... 73

11.3 Brake Lines ........................................................................................................................... 73

11.4 Shock Absorbers ................................................................................................................... 74

11.5 Tie Rod Ends ......................................................................................................................... 74

11.6 Conclusion ............................................................................................................................ 74

12. Conclusion ................................................................................................................................ 75

Bibliography ......................................................................................................................................... 76

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List of Figures

Figure 1-1 – Ilanga I-I, the rendering of the updated UJ solar car [1] .................................................. 14

Figure 3-1 – Route for the South African Solar Challenge 2012 [3] .................................................... 16

Figure 4-1 – Double Wishbone Assembly [6] ...................................................................................... 20

Figure 4-2 – MacPherson Strut Assembly [6] ...................................................................................... 20

Figure 4-3 – Pushrod Suspension Assembly [7] ................................................................................... 21

Figure 4-4 – Positive Castor Angle and Restoring Moment ................................................................. 21

Figure 4-5 – Steering Axis Inclination and Scrub Radius [10] ............................................................. 22

Figure 4-6 – Negative vs. Positive Camber .......................................................................................... 23

Figure 4-7 – Types of Damping ............................................................................................................ 24

Figure 4-8 – Visualisation of the Ackermann Principle........................................................................ 26

Figure 4-9 – Roll Centre [18] ................................................................................................................ 27

Figure 6-1 – Fourth Design Concept ..................................................................................................... 33

Figure 8-1 – Suspension Geometry ....................................................................................................... 49

Figure 8-2 – Suspension Travel vs. Track Length Change ................................................................... 49

Figure 8-3 – Steering Input vs. Camber Change ................................................................................... 50

Figure 8-4 – Ackermann Steering, wheels Straight .............................................................................. 51

Figure 8-5 – Ackermann Steering, Wheels Steered .............................................................................. 51

Figure 8-6 – Upper Control Arm .......................................................................................................... 52

Figure 8-7 – Lower Control Arm .......................................................................................................... 53

Figure 8-8 – Suspension geometry with Pushrod ................................................................................. 54

Figure 8-9 – Pushrod/Rocker/Shock Absorber assembly ..................................................................... 55

Figure 8-10 – Load bearing sections (a), stresses experienced by the components (b) ........................ 56

Figure 8-11 – Axel acting as a cantilever ............................................................................................. 56

Figure 9-1 – Microscopic Image of Low Carbon Steel Grains [27] ..................................................... 59

Figure 9-2 – Microscopic Image of High Carbon Steel Grains ............................................................ 59

Figure 10-1 – Final Suspension System ................................................................................................ 65

Figure 10-2 – CAD Model of the Steering Swivel ............................................................................... 66

Figure 10-3 – Lower control Arm Alignment Jig ................................................................................. 67

Figure 10-4 – Lower Control Arm Pivot Bracket ................................................................................. 67

Figure 10-5 – Rocker Arm, Right and Left Steering Swivels, taped up, ready to be sent to the welder

.............................................................................................................................................................. 68

Figure 10-6 – Pushrod Rockers and brackets after being welded ......................................................... 69

Figure 10-7 – Steering Swivel after being welded ................................................................................ 69

Figure 10-8 – Steering Swivel and Brake Calliper with the wheel attached ......................................... 70

Figure 10-9 – Full Assembly before being bolted onto the Chassis ..................................................... 71

Figure 10-10 – Full Assembly Bolted onto the Chassis ........................................................................ 71

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Figure 10-11 – Front Right Corner of the Car, Fully Assembled and Operational ............................... 72

Figure 10-12 – Ilanga I-I, with the updated suspension, and members of UJ Solar, ready to participate

in the Solar Challenge ........................................................................................................................... 72

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List of Tables

Table 4-1 – Environmental Data of 25CrMo4 ...................................................................................... 30

Table 6-1 – Selection Criteria for the Steering Swivel Arm ................................................................. 34

Table 6-2 – Selection Criteria for the Suspension System .................................................................... 35

Table 7-1 – Ease of Design and Manufacture ....................................................................................... 40

Table 7-2 – Ability to set up the car for a desired handling characteristic ........................................... 40

Table 7-3 – Compliance of the design within existing parameters ....................................................... 40

Table 7-4 – Ease of incorporating the rest of the suspension system with the steering swivel arm ..... 40

Table 7-5 – Aerodynamic Efficiency .................................................................................................... 45

Table 7-6 – Incorporation of design within existing parameters .......................................................... 45

Table 7-7 – Design uses available resources or equipment .................................................................. 45

Table 7-8 – Design provides the opportunity to tune the suspension if desired ................................... 45

Table 7-9 – Weight ............................................................................................................................... 46

Table 8-1 – Suspension Parameters ...................................................................................................... 48

Table 9-1 - AISI 4130 Steel, normalized at 870°C (1600°F) Properties [29] ....................................... 61

Table 9-2 - 6063-T6 Properties [30] ..................................................................................................... 62

Table 9-3 - Side-by-Side Comparison between AISI 4130 and 6063-T6 ............................................. 62

Table 10-1 – Selection of Standard Parts .............................................................................................. 68

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Definition of Terms

Throughout this Report, there will be several terms which may be unfamiliar to the reader. Some of

these will be defined here:

Term Definition

Centre of Gravity Point at which all of the mass/forces of the car is said to act.

CVT: Constantly

Variable

Transmission

An alternate means of transmitting power from a motor to the driving wheels. A

pulley system where the diameters of the pulley are varied to change the gear

ratios.

FIA: Federation

Internationale de

l‟Automobile

The governing authority for the South African Solar Challenge 2012

Ilanga I, I-I, II

Ilanga is the isiZulu word for „sun‟. Ilanga I and Ilanga II are two solar powered

cars being design and built by the University of Johannesburg. Ilanga I-I is the

updated version of Ilanga I.

Pair-wise

Comparison

A method used to evaluate the worth of the design selection criteria as well as the

design alternatives.

PDS: Product

Design

Specification

The design specifications to which the design must measure up.

Pushrod Rocker

In the pushrod suspension design, the rocker is a pivot point which transmits the

up-and-down motion of the wheel to the shock absorber. Using the principle of

leverage, the force acting on the shock can be increased or decreased.

Roll Centre Point around which body roll will occur during cornering.

SASC 2012:

South African

Solar Challenge

2012

An alternative fuel race around South Africa, governed by the FIA.

UJ

University of Johannesburg.

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1. Introduction

The University of Johannesburg (UJ) has endeavoured to partake in the South African Solar

Challenge 2012. This is a race of over 5 100 km around South Africa and is open to universities from

around the world. The entrants are required to design, build and race a solar powered vehicle through

harsh environments, such as the Karoo and as well as through the Drakensburg Mountain range.

The University entered the competition in 2010 with a petrol-electric hybrid vehicle, which came first

in its class. In 2011, UJ built 3 alternative fuel vehicles; the effort was filmed and broadcast under the

name „Fuel Duel‟ on the Mindset Learn Channel. Of the three cars to be designed, one was a solar car.

The car was called Ilanga, which is the Zulu word for Sun. The upper side of the body is covered

with solar cells, which collects electromagnetic radiation from the sun, and uses it to charge batteries.

This energy is used to power the motor and drive the vehicle. The University has since undertaken a

project to build a second car, Ilanga II. Both Ilanga I and Ilanga II are expected to be race-worthy in

time for the South African Solar Challenge which starts in mid-September 2012, and runs for two

weeks.

Ilanga I was built by [then] final year students, in 2011, which have now graduated and are doing their

Master‟s degree; they are now designing the flagship Ilanga II solar car. Currently, the task of

ensuring Ilanga I is race worthy has fallen to a group of final year students from both mechanical and

electrical engineering. This group will work closely with the Master‟s students in ensuring that all

design tasks are completed to the required specifications. Additionally, the Master‟s students will

assist the final year students in terms of offering advice.

Ilanga I has already been built, and at the time of writing, has a rolling chassis. There are however, a

few key concerns with the vehicle in its current state. The front suspension which was designed did

not conform to the requirements. Therefore, the front suspension has to be redesigned; this is the

scope of this text. The other concerns include the rear suspension, which also has to be redesigned,

allowing for the correct placement of the constantly variable transmission (CVT). The steering

column must be redesigned to be collapsible during an impact, while the steering rack must be

modified such that it will accommodate the changes to the front suspension. Other research and

design areas remain, but are not relevant to the scope of this text.

This Report will serve as the Design Report for the suspension reconfiguration/optimisation. The

subsequent sections will cover the project request in detail. Further, an in depth Literature Review will

be conducted to familiarise the reader with all the relevant concepts and terminology involved in

suspension design. The Design Description will cover topics such as the operating environment of the

finished product, legal, social and patent considerations, and the financial side of the project.

Thereafter, the concept generation will be presented where, based off of established design criteria,

the most effective design will be selected. Performance simulations of the selected design will follow,

giving a baseline, from which actual real world results may be determined. The manufacturing

processes necessary to complete the design will follow. This section will provide details and

instructions to ensure that the finished product meets an acceptable standard. Finally, some

conclusions of the design process will be made, summing up the experience, and the final product.

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Figure 1-1 – Ilanga I-I, the rendering of the updated UJ solar car [1]

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2. Needs Identification

The design request is as follows:

“Redesign/reconfiguration of the front suspension, braking system and nose section of Ilanga I within

existing design parameters. Also, considerations must be made for quick tyre change under race

conditions. All design considerations must be made to FIA specifications.”

The suspension governs how a car behaves during cornering, and over bumpy roads. It is arguably

one of the most important aspects of the design to do correctly; thus the need to optimise the current

suspension system. The design request was provided by the Master‟s students who designed and built

Ilanga I. The design request can be further dissected to glean more detail:

1. Optimise/Reconfiguration of the front suspension: The current solution is a type of

double wishbone and pushrod assembly, though not the conventional sort. This solution

has the pushrod on the upper control arm, instead of the lower one. This uses more space,

which requires more extensive modifications to the body of the car. Furthermore, the

current wheel track is too wide for the body. Bicycle wheels were used, which do not

have the required strength to support the weight of the chassis, batteries, bodywork and

driver. These, therefore have to be changed. 2. Brakes: The current braking system uses a disc brake from a bicycle. The problem is that

the brake discs cannot sustain braking for extended periods. These will have to be

upgraded to a hydraulic braking system from a motorcycle. The new brakes have already

been designated. A steering swivel arm has to be designed to accommodate these new

brakes, i.e. callipers and discs. 3. Nose Section: The nose section of the vehicle has to be designed to conform to the FIA

Crash Test Regulations. The current nose section is adequate, in terms of strength;

however, it is built in, and is an integral part of the current front suspension which will be

redone. The nose section presents an interesting research project; it can be simulated

using Finite Element Analysis. 4. Existing Design Parameters: The body of Ilanga I has been designed and built. There is

very little, if any, room for modifications to the body. Therefore, all designs must be

made to fit the bodywork.

These specifications have been determined based on consultations with the Master‟s students and

during meetings. The minutes of the meetings have been added in Appendix A. The minutes cover

topics pertaining to how each of The Team members is faring with their respective tasks. Most of the

detail in the above request was given by Warren Hurter, one of the Master‟s students. He has set out

very specific guidelines as to how the design should be done, and some product design specifications

(PDS). The PDS is deferred to a later section.

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3. Operating Environment, Functional Analysis and Mission Analysis

This section will describe the functions the updated suspension system must accomplish. This will be

facilitated by identifying the operating environment that the system must work in. The information

presented in this, and the preceding section will be used as a basis for the Product Design

Specification in Section 4. The mission analysis will focus on the goals of the project as a whole, i.e.

what the University wants to achieve in the SASC 2012. This also includes contractual obligations to

sponsors, obligations to the University and personal pride.

3.1 Operating Environment and Functional Analysis

According to [2], the SASC will be run from Pretoria, down the N1, N4 Rustenburg, N14 through

Vryburg, Upington and Springbok to Cape Town. From there, the route will move up the coast to East

London. Assuming that the vehicle has travelled 1 800km by East London, the team can choose to

travel to Bloemfontein along the N6 via Queenstown and Aliwal North, and then down to Durban

along the N5 and N3. Thereafter, the cars head north to Nelspruit, along the N2, R33, N17 (E), R38

and R40. From Nelspruit, the race heads back towards to Pretoria along the N2. Figure 3-1 shows the

router for the 2012 edition of the South African Solar Challenge.

Figure 3-1 – Route for the South African Solar Challenge 2012 [3]

A conservative estimate of the length of the course is 5 100km. This route takes the competitors

through some harsh environments. The stint through the desert – Upington to Springbok – is perhaps

the most severe for the driver and the car. The elevation changes are also substantial; from the

Highveld, down to reef altitude and over a mountain range.

The front suspension will have to be designed in such a way as to limit the possibility of dirt and

grime interfering with the moving components. The materials must also be corrosion resistant, as a

fair deal of the race is along the coast, which has a humid atmosphere. Another consideration is the

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condition of the South African roads. Experience has shown that especially in the smaller towns along

the route, the roads are often poorly maintained, with many potholes. The National Roads are in better

condition though. Nevertheless, the suspension must be of such a nature that if the driver were to

drive over a pothole, the shock would be absorbed, with little ill effects on the car, equipment or

driver. The route along the National Roads has been set out by the FIA in [2], however, the route

through the urban areas has not. Due to the fact that almost all of the race will be conducted on the

Nation Roads, the suspension will be set up for the best straight line ability; cornering performance is

not critical.

The following functions that the suspension must accomplish can be summarised thus:

- Straight line performance: The vehicle will be travelling in a straight line for most of the

journey. Therefore, the suspension must be set up in a way to ensure the car is easy to steer in

a straight line for long distances, i.e. with minimal driver input. This way, the drive can drive

for a longer stint without fatiguing, saving time on driver changes throughout the race.

- Resistance to dirt: Dirt is the bane to many mechanical components. Since the vehicle will

be traversing through harsh environments, it must be able to cope. The wheel fairings will

provide some protection against dirt and dust. Nevertheless, the suspension must have a fair

tolerance for dirt. This can be achieved by ensuring that the tolerances on the moving

components are such that if dirt is trapped in the system, it will not end up damaging it.

Furthermore, allowance should be given to facilitate easy cleaning of the system.

- Performance over bumps/during cornering: The shock absorbers for Ilanga I have already

been specified. They are gas filled units with only 5cm of travel, and are generally fairly stiff.

However, the unit‟s stiffness can be adjusted, thus optimal performance over bumpy terrain

can be accounted for. Another consideration is that the more stiffly sprung the shock

absorbers are, the less body roll will be present during cornering. An optimisation must then

be reached between cornering performance and acceptable ride quality.

- Corrosion Resistance: The suspension will be manufactured from either AISI 4130 chrome

moly or 6063-T6 aluminium alloy. Both of these are corrosion resistance. The fasteners must

also be corrosion resistant, to ensure they do not rust together, making them difficult undo.

- Fatigue Life: Fatigue may turn out to be a problem, especially if an aluminium alloy is used.

The race is over a long distance, and the interior of the car is expected to be hot, in the region

of 50° C, due to the hot motor and motor controller, and limited ventilation. The fatigue life of

aluminium is dependent on temperature, and the suspension will be subjected to cyclic

loading. Therefore, the material selection must take these factors into account.

3.2 Mission Analysis

The University has received funding from many organisations, both from within the engineering

community and from without. There is a lot of money at stake, as well as the pride and reputation of

the University. The design and manufacturing stages of the vehicle will be televised on three

channels, putting UJ on display to the rest of the country. Therefore, it is imperative that the

University completes the SASC 2012 and does well. Therefore, there are several aspects The Team

must accomplish.

3.2.1 Sponsors

The project is sponsored by some leading corporations in the industry. Some of which include [4]:

- Eskom

- Arrow Altech

- ProductONE

- Altium

- Technopol

- Milled and Shaped Profiles

- MTN

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These sponsors have sponsored the labs where the cars are being built, design software, technical

assistance and money. Their logos will be displayed on the body of the solar cat and the support

vehicles during the race, as well as being displayed on national television. Therefore, the university

has an obligation to them to do well, and showcase their brands in a professional manner. The

following contractual obligations and agreements are between UJ and the Technology Innovation

Agency, although much of these obligations remain the same with the other sponsors.

The contract states some general terms and gives definitions thereof. The contract states

commencement and duration of the agreement, in this case, the agreement ends on the 31st day of

December 2012. The monies and/or resources provided will be used to design and build Ilanga I for

participation in the south African Solar Challenge 2012. UJ agrees to display the trademarks of the

sponsors in a manner which is mutually acceptable for both parties. UJ also agrees to inform the

sponsor of any upcoming promotional event in which the cat or Team is showcased. UJ is also to

inform the media/broadcasting organisations about the sponsor‟s involvement, and at all times, where

applicable, display the sponsor‟s trademark by means of branding and/or team gear agreed upon by

both parties.

In addition to the issues of displaying the sponsor‟s trademarks where applicable, the contract protects

both parties, wherever possible, with regards to intellectual property (IP) rights and privacy. Any IP

belonging to a party before the agreement was entered into would remain the property of that party.

Any IP created during the design and construction of the solar car, using the sponsor‟s money, would

be the property of UJ. UJ will have full possession of the solar car. Any information which one party

discloses to another, which is not in the public domain, will remain private.

Furthermore, the contract delves into the details of breach of contract, termination, warranties and

indemnities. The main focus of the sponsors who enter into an agreement with UJ is that of

advertising and branding. The contracts are fairly straight-forward and do not bog the reader down in

legal jargon.

3.2.2 Technical Obligations

The South African Solar Challenge begins on the 15th of September 2012. The vehicle must pass

scrutineering by the FIA officials. This implies that all the designs must be within the regulations set

out by the FIA. The specific goals to be accomplished are presented below:

- Design the front suspension according to the FIA regulations, thus making the car eligible to

participate in the South African Solar Challenge 2012. The regulations have rules set out

governing the front suspension. These include ensuring that the car is able to turn within an

eight meter turning radius, curb to curb. They also restrict the type of steering rack to a rack

and pinion type. Therefore, no other types of steering mechanisms (steering box,

reciprocating ball screw, level type steering) are allowed. The front wheels must also be

fitting with breaks.

- Ensure that the design meets the criteria of the PDS. The PDS gives the designer a

specification to work towards. The PDS is dictated largely by the operating environment in

which the system will work. Meeting the PDS (which also incorporates the regulations) will

ensure that the design will provide a competitive addition to the solar car.

- Ensure that all the components are designed and manufactured well before the start of the

SASC, to allow for testing. Testing the system is important. Should any changes have to be

made, there would be time to do so, if test is started early. If testing were started closer to the

start of the event, then a botch solution would have to be found, should the system not

perform as expected. This is why the planning and design phase are so critical; to minimise

the possibility of system performing inadequately. Nevertheless, testing should begin as soon

as possible, to cover all possibilities.

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4. Contextual Background

4.1 Introduction

When designing a suspension and steering system, there are various aspects one needs to consider in

order to ensure its efficacy. Firstly, one has to consider the type of vehicle and the environment in

which it will be used. With this information, the appropriate performance objectives can be set. With

this overarching theme in mind, specifics of the design can be finalised. Some of these specific details

are:

- Type of suspension system, i.e. independent, wishbone, etc.

- General suspension geometry, such as castor angle, steering axis inclination and scrub radius.

- Calculating the forces acting upon the suspension, both in cornering as well and over bumps

and static loading.

- Calculating what spring rates are required.

- Determining what sort of damping system is required.

- Determining the necessity of torsion bars.

- Optimising the system to have the best performance during cornering, in terms of Ackermann

and camber angles.

- Selecting wheels and tyres which will meet the space requirements of a solar car.

- Designing the uprights which will accommodate the wheels and tyres, allow for the

positioning of the braking system and integrate seamlessly with the suspension design.

- Optimising the design to ensure it meets strength and budget constraints.

This Literature Review will focus on each of the abovementioned points. Using this information, the

design of the suspension system can be carried out. In each subsection of the Literature Review, the

relevant literature will be discussed. Following this will be a paragraph describing how the

information is pertinent to the UJ solar car, Ilanga I.

NOTE: The information outlined in this Literature Review is, for the most part, an introduction to the

abovementioned concepts. It merely gives a broad description of the various aspects and

nomenclature encountered in suspension design. The more detailed calculations will be presented and

referenced in the Design Calculations section.

4.2 Types of Suspension Systems

Only independent front suspension will be considered, not dependent suspension. Dependent

suspension fell out of favour years ago, as independent suspension provides better steering and

improves comfort [5].

One type of design of front suspension is the double wishbone, so called, because the control arms

resemble a wishbone, or A-frame. The broad side of the wishbone is attached to the chassis of the

vehicle, while the narrow end is attached to the steering swivel member, via a ball joint. The forces

that the suspension members are subjected to due to acceleration and braking act along the car,

meaning that a triangular shape, or A-frame, is required to withstand these loads. The control arms

can be parallel and of equal length. In this case, the wheel will not tilt, but move directly up and down

over bumps. This causes the track length (the distance between the left and right wheels) to shorten,

adversely affecting tyre life. Furthermore, since the weight of the car moves to the outside when

cornering, the outside tyre – which carries the greater load - will lean slightly outwards, which

diminishes cornering performance. For these reasons, the wishbones are neither parallel, nor of equal

length. The bottom control arm is longer than the top one. This means that it will follow a wider arc

when the wheel passes of a bump – the wheels will tilt inwards in this case. This gain in negative

camber increases the cornering forces the tyres are subjected to [5].

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Figure 4-1 – Double Wishbone Assembly [6]

The other popular choice of suspension design is the MacPherson strut assembly. In this

configuration, there is a lower wishbone, with a telescopic strut, anchored at the top via a flexible

mounting. The lower end of the strut is mounted via a transverse-link. This system helps the vehicle

follow irregularities in the road, and is mechanically simpler. It does not cause a substantial change in

camber when cornering [5].

Figure 4-2 – MacPherson Strut Assembly [6]

Another type of suspension design is the pushrod system. This type is used in most modern racing

cars. This is also the type used on the current iteration of the UJ Solar Car. Pushrod suspension

follows the same principles as those of the double wishbone. However, instead of the damper and coil

spring, a pushrod is used. It is connected to the damper and wishbone by means of a mechanical

linkage, called a rocker arm. This is favoured in open wheel racers because it is more aerodynamically

efficient. It is also slightly more complex. It is questionable whether this type of suspension is strictly

necessary in a solar car. If the suspension is closed off to the environment then the aerodynamic gains

for open wheel cars will be nullified.

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Figure 4-3 – Pushrod Suspension Assembly [7]

4.3 Castor Angle

The castor (or caster) is defined as the angle between the normal to the road and the pivot axis of the

steering swivel member [8,9]. If the top of the steering swivel arm is further towards the rear of the

vehicle than the bottom, this is called positive castor. If the top of the steering swivel arm is further

forward than the bottom, it is called negative castor. If the top and bottom of the steering swivel arm

are normal to the ground, it is termed neutral castor [9]. The castor angle can affect the stability of the

vehicle, positively, or adversely. The direction of the castor which generates more stability depends

on whether the car is front or rear wheel driven. Rear wheel drive cars reap the benefits from a

positive castor angle. When a car has a positive castor, the axis of the steering swivel member

intersects the road in front of the tyre‟s contact patch. When the steering wheel is turned, the contact

patch of the wheel is on the outside of the point where the steering swivel arm axis intersects the road.

This creates a restoring moment, which tends to return the wheels to a forwards facing position. Thus,

the car tends to travel in a straight line with minimal driver input. Front wheel drive cars are more

stable with a negative castor [9]. Since the UJ solar car is rear wheel drive, the most stable option will

be a positive castor angle. Figure 4-4 below shows a rear wheel drive car with a positive castor. When

the wheel is turned to the right, it can be seen that the contact patch is on the outside of the turning

axis. The bottom arrow shows the restoring moment which tends to straighten the front wheels out.

This increases the stability of the vehicle.

Figure 4-4 – Positive Castor Angle and Restoring Moment

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4.4 Scrub Radius and Steering Angle Inclination

When viewed straight on, the scrub radius is the distance between the steering swivel member axis

and the tyre‟s contact patch on the ground. When viewed from the front, the steering axis inclination

(SAI) is the angle that the steering swivel member axis makes with the ground. It will become clear

how the SAI and the scrub radius are related [10].

Figure 4-5 – Steering Axis Inclination and Scrub Radius [10]

When the front wheel steers the vehicle, it would naturally want to pivot around the wheel‟s central

axis. However, the wheel actually pivots around the steering axis, which is slightly offset from the

wheel‟s central axis. Therefore, when the wheel turns to steer the car, it scrubs along the ground. The

SAI reduces the scrub radius. The SAI also causes the car to lift slightly as the steering wheel is

turned. Therefore, the mass of the car is used to restore the front wheels to a straight ahead position,

increasing stability [10]. This type of self-centring steering is advantageous compared to the castor

angle, as this configuration provides the same benefits without the drawbacks.

The front suspension can either have zero scrub radius, positive of negative scrub radius. When the

SAI line intersects the contact patch, the car will have zero scrub radius. This is also called centre

point steering. This situation causes the steering to lack feel, and feel unstable during cornering [11].

When the SAI line and the normal to the contact patch intersect below the road surface, a positive

scrub radius is present. If the SAI line and the normal to the contact patch intersect above the road

surface, negative scrub radius results. Positive scrub radius provides more steering feel, but also

increases the steering effort required. Negative scrub radius decreases steering feel, but in the case of

a tyre blow out, less force will act on the steering wheel, thereby ensuring the vehicle is safer [11].

Ilanga I will have a negative scrub radius for the following reasons. Firstly, steering feel is less

important when navigating straight roads. Second, in the event of a blowout, the car must still be

controllable, both to ensure the safety of the driver, and to preserve the car.

4.5 Camber

Camber is viewed front the front of the vehicle, and it is the angle at which the tyre tilts. When the top

of the tyre is tilted away from the car, the camber is positive. When the top of the tyre is tilted towards

the car, the camber is negative. In Figure 4-5 above, the camber is positive. A positive camber serves

to shorten the scrub radius. Additionally, it also serves to offset vehicle loading. In terms of stability, a

negative camber may be desired. This is easy to visualise; when the car turns a corner, the weight is

transferred to the outside wheel, which will tend to „stand up‟, i.e. become more perpendicular to the

ground [10]. Thus, the more perpendicular the tyre is, the greater the contact patch on the ground, and

the higher the cornering forces will be.

The camber for the solar car will be slightly negative. This will provide some lateral stability during

cornering, with little expense to directional stability. A negative camber angle of 1° will be used for

Ilanga I.

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Figure 4-6 – Negative vs. Positive Camber

4.6 Springs and Dampers

Coil springs are the only option under consideration of this vehicle. Important considerations include

the spring rate, i.e. their stiffness, number of coils, diameter and the configuration of the springs and

dampers, e.g. coil-over shocks. The equation for spring stiffness is given as [12]:

(4.1)

Where:

- k = Spring Stiffness

- d = Diameter of the wire

- D = Diameter of the coil spring

- N = Number of turns of the spring

The number of turns depends on the end condition of the spring. The end condition refers to the

whether the spring is cut, ground, or has a closed end. When the spring has a closed end, those coils in

the end are not active, and therefore do not behave as the rest of the coils would [12].

It is instructive to elaborate on how different spring rates would affect balance of the car. Increasing

the spring rate of the front springs will increase responsiveness. It will also, however, decrease grip on

bumpy surfaces and increase tyre wear. Decreasing stiffness will increase grip on bumpy surfaces,

reduces tyre wear, but also reduce responsiveness. One can only reach the best compromise when the

route of the SASC has to be known. This includes both the type and quality of road surfaces, as well

as whether there will be many corners or not.

Elementary mechanics tells us that a mass attached to s spring will oscillate back and forth if the

spring is displaced from its equilibrium point. In the real world, this oscillation will not continue

indefinitely, since there is always friction. The oscillation is said to be damped. There are three types

of damping available to engineers when designing a damping system; they are: over damped, under

damped and critically damped.

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Figure 4-7 – Types of Damping

The equation governing damped oscillatory motion is [13,14]:

(4.2)

Where:

- m = Mass attached to the spring

- k = Spring constant, i.e. stiffness

- b = Damping Coefficient

- x = Direction of motion

- t = Time

Solving this equation yields [14]:

√

√

(4.3)

Where:

- = b/m = damping factor, multiplied by two

- = k/m = Natural Frequency squared

The variables defined above are so defined for mathematical convenience.

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If: - ; the system is said to be over damped. The roots to the characteristic equation of

(4.2) are real and distinct [14].

If: - ; the system is critically damped. The roots of the characteristic equation of (4.2) are

real and equal. Therefore, the solution to (4.2) in this case is [14]:

(4.4)

If: - ; the system is under damped. The roots are complex and distinct. Manipulating the

equation using Euler‟s Equation yields the following solution for (4.2) [14]:

√ √ (4.5)

The mass of the car still has to be determined before any real calculation of the spring rate or damping

coefficient can be completed. Driver preference as well as the road conditions and route layout will all

play a part in determining the required damping.

The ultimate goal of this vehicle is for stability. As in open wheel racing, little thought is given to

driver comfort when designing suspension. The car must be stable, balanced and drivable; it is

assumed that the driver will be fit enough to endure a stint of approximately two hours behind the

wheel.

4.7 Ackermann Angle

When a car turns a corner, the front wheels would naturally want to maintain pure rolling motion, free

from tyre scrub. True rolling motion can only be achieved if each front wheel is perpendicular to the

centre of the turn. The centre of the turn will lie somewhere along the rear axle‟s centre line, since it is

fixed in relation to the vehicle. Each front wheel is a different distance away from the centre of the

turn, and they therefore have to follow different arcs through the turn; the inside wheel follows a

smaller turning radius than the outside wheel. For this reason, the inside wheel has to be steered

through a greater angle than the outside wheel. The Ackermann Principle is used here to achieve this

[15].

There are three possible outcomes to consider when designating the Ackermann Angle. These are

zero toe on turn in, toe out on turn in and toe in on turn in. In the first case, the tyre is aligned with the

turning curvature and thus rotates with true rolling motion. In the other two cases, the wheel scrubs as

it turns the corner [15]. In order to obtain this optimal scenario of true rolling motion during

cornering, the steering swivel arm has to be angled such that its projections intersect the centre of the

rear axle.

The rear axle of Ilanga I has been designed, as is located 2 260mm behind the front wheels.

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Figure 4-8 – Visualisation of the Ackermann Principle

4.8 Centre of Gravity, Roll Centre and Roll Axis

The centre of gravity (CG) is the point of the car through which all of its mass essentially acts. If one

could balance the car on one single point, the centre of gravity would be it. The CG is important in

suspension design for several reasons. The position of the CG (both fore and aft, and top to bottom)

has an effect on the balance. If the CG is too far towards the back, the steering will be less responsive,

increasing understeer, but if the CG is to far forward, the rear will feel „light‟, and oversteer is likely

to occur. The higher the CG is positioned, the more the chassis will tend to roll when cornering.

The roll centre (RC) is the point around which the chassis will roll during cornering, with respect to

the ground [16]. This point is different for the front and rear of the vehicle, and is based upon

suspension geometry. Suppose the vehicle has double wishbone suspension, and the car is being

viewed from the front. The RC can be found by projecting a line of the upper and lower wishbones

until they intersect at a certain point (A, in Figure 4-9). This point is called the instant roll centre, and

is important in determining the angle of the front steering tie rod. A line from the centre of the contact

patch of the wheel in question (C) is drawn to this intersection point. The RC is located where this

new line intersects the mid-line of the car [17].

When cornering, the forces of inertia act through the centre of gravity of the vehicle. Since the CG

and the RC are generally not in the same location, a moment is set up. This is what causes the body to

roll during cornering. As seen in Figure 4-9, the RC can be located higher or lower (and by

implication, nearer to or further from the CG), depending on the suspension geometry. The general

idea would be to limit body roll, thus, the RC would have to be near to the CG.

This has a bearing on Ilanga I in the following way: The car will be set up for straight line

performance. The location of the roll centre is one of the few design considerations which can make

the car more stable during cornering, with sacrificing directional stability. An intelligent choice of the

roll centre, with respect to the centre of gravity may make a significant difference to the handling of

the car.

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Figure 4-9 – Roll Centre [18]

4.9 Toe Settings

Toe refers to the direction the front wheels are pointed. If the wheels are pointed inwards, towards

each other at the front, this is called toe in. If the wheels are pointed outwards, this is called toe out. If

the two front wheels are exactly parallel, this is called zero toe. Toe affects three primary performance

characteristics of the vehicle: Tyre wear, straight line ability and cornering performance. If the toe

angle is too great – in or out – the tyres will wear excessively on the outboard or inboards edges,

respectively [16].

For improved directional stability, the suspension should be set up for toe in. Toe out creates and

improved steering response. Therefore, toe in creates a lazy, or dull steering response and toe out

tends to make the vehicle directionally unstable. The toe setting chosen by the engineer depends

largely on the intended application. Cars that will be travelling in straight line, predominantly, will

have more toe in. Race car drivers navigating tight circuits will tend to sacrifice directional stability

for improved response and feel during cornering [16].

The implication for the SASC 2012 is that the car will be set up for more toe in. The national routes

are straight, with little need for a very sharp steering response. The driver will also benefit for having

a car with more directional stability; he will have to make less steering inputs to keep the vehicle in a

straight line.

4.10 Bump Steer

Bump steer is caused by improperly designed steering linkages. When the steering linkage is not the

correct length, the front tyres tend to steer themselves, without driver input, when traversing rough

ground. This effect also occurs under braking or cornering, although during cornering, the unwanted

steering effect is called roll steer. The cause is when the steering tie rod is too short, say, and a wheel

passes over a bump. The movement in the suspension cannot be followed precisely by the steering

linkage without it creating a moment on the steering swivel arm and steering the wheels [19]. This is

because the steering tie rod does not follow the same arc as the suspension control arms when the car

passes over a bump.

Simply designing the front suspension correctly will nullify the effect of bump steer. If one where to

draw a line from the top control arm pivot point to the bottom one, the tie rod end should intersect that

line. In a similar fashion, if one where to draw a line from the top to the bottom ball joints on the

steering swivel arm, the other tie rod end should intersect that line. A line project along the tie rod

should intersect with the instant centre, point A in Figure 4-9.

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4.11 Legal, Health and Patent and Other Considerations

In addition to completing the design, one must also be aware of the legal, health and social

implications of the design. In terms of the legal aspects, one must be careful to not copy another

design, or infringe on patents. The must also be safe; the components should be designed to

incorporate a reasonable safety factor. It is also important to know what the other safety concerns are;

i.e. those which do not directly affect the present design. Each team member should have some

knowledge of the other team members‟ duties, in order to spot potential safety oversights. The social

impact of the project should also be considered. This project is to aid in the research of alternative

energy, so it is important to investigate this aspect. Additionally, sourcing materials from local

suppliers can increase the local economy, which is a point for consideration. Finally, the

environmental impact should be assessed. The next few pages will investigate these aspects.

4.11.1 Legal

There are several legal responsibilities that the University has to fulfil while undertaking this project.

The first, and probably most important, is the responsibility towards the sponsors. The second legal

issue revolves around the University‟s participation in the SASC 2012. This includes meeting all the

requirements set out by the FIA, obtaining the correct temporary licence for the vehicle and obeying

all of the road‟s regulations while competing. A third issue is centred on the manufacturing of

components. Should a part require specialised welding, such as aluminium or stainless steel, then

qualified and certified personnel should be sought to do the job. This section will take a brief look at

some of the specifics regarding these issues.

The sponsors of The Team are providing support primarily by means of monetary contributions.

Others are providing services free of charge. There are two issues of importance concerning the

sponsors; the sponsors each have their own contractual obligations, and the event will be televised.

The contractual obligations have to be fulfilled. This may include displaying the sponsor‟s logos and

trademarks at all public events, or being barred from using competitors‟ products. The event is also

being televised, putting UJ and the sponsors on show for the rest of the country. The Team thus has to

maintain professional conduct at all times in front of the cameras, and display the relevant sponsors‟

signage when and where required.

Each entrant into the SASC 2012 will have to pay the entry fee, and ensure that their vehicle is

registered with the relevant authorities [2]. There are regulations concerning how the race is run. More

specifically, the regulations detail how many support cars the entrant requires, the running order of the

support vehicles, the following distances and overtaking protocols. Although these are not technically

„legal‟ issues (in terms of national law), they have been set out by the FIA, and must be observe to

ensure the safety of the entrants. Additionally, not observing the regulations will result in penalties

and/or exclusion from the event.

Certified welders are required by law for certain tasks. For example, a welder must undergo

continuous training and re-evaluation if he to weld a pressure vessel. There are certain materials that

are very difficult to weld and hence require a specialised and certified welder to complete the task.

This includes aluminium and stainless steel welders. Certified welders will guarantee a standard of

work that a non-certified welder will. Further, if the certified welder‟s work does not meet a certain

standard, then the customer can rightfully demand that the work be redone at the welder‟s own

expense.

4.11.2 Health and Safety

The driver‟s health and safety are primary issues of importance. This section will focus on the various

aspects that have to be considered in order to ensure that the driver is safe during the race. This also

extends to the people working on the car. Although this Report is about the suspension design, this

section will look at aspects such as electrical considerations, warning devices and requirements as

stated in the regulations.

Page | 29

As mentioned previously, driver fatigue is a concern, so the following courses of action are necessary

(These are stated in the PDS). Driver inputs into the steering wheel to keep the car going straight must

be kept a minimum to reduce the risk of driver fatigue. According to the regulations [20], adequate

ventilation must be ensured inside the cockpit. The scrutineers require a simulation of the airflow

within the driver‟s compartment. This simulation is to be done using software such as StarCCM+.

Other regulations include ensuring that all sharp edges within the driver compartment must be cover

up, or filed smooth. This extends to the presence of sharp edges anywhere on the vehicle. All wires

must be properly insulated to avoid the risk of the driver being shocked. All electrical components

must comply with the IEEE standards. Where the vehicle operates with a voltage higher than 32V,

warning labels must be fixed to the cars, and it must be demonstrated that it is impossible for the

driver to touch a live wire. The scrutineers also require a drawing of the power circuits and electrical

equipment with specifications. The vehicle must be fitted with lights and indicators which must be

visible from 30m in daylight. Importantly, all entrants must have rear brake lights fitted. All vehicles

must have a horn, hooter or some audible warning device fitted.

In the event of a front end collision, the solar array must be deflected away from the driver

compartment. It is required to show the scrutineers a simulation of this. The vehicle will be fitted with

a collapsible steering column; the column will use a shear pin which will shear off under a certain

loading condition, i.e. a high load experienced during a collision. The seat must be approved by the

FIA, along with a five point harness. Ilanga I will use a six point harness. There is a maximum time

limit that the driver has to exit the vehicle. From a driving position, with all safety equipment in place

and with the safety harness attached, the driver should be able to exit the vehicle in 7 seconds or less.

The driver compartment should be able to be opened both from inside and outside the vehicle. The

handles on the outside of the vehicle must be painted red, orange or yellow; a colour which is clearly

distinguishable from the rest of the bodywork. Furthermore, a person unfamiliar to the vehicle should

be able to open the driver compartment should he need assistance.

The brakes must be able to achieve a deceleration of 5.8m/s2. The front steering swivel arms will have

to be designed such that they accommodate the callipers and brake discs. The swivel arms and the

suspension control arms should be able to withstand the forces imposed on them due to braking. This

is a critical aspect of the design, as the braking forces are severe. The brake discs will also have to be

of an appropriate specification. If they are too thin, the will warp under the braking loads.

As mentioned, ventilation to the driver is very important. Ilanga I has two slots for ventilation in the

front, with several placed where the air can exit, out the back. Nevertheless, the cockpit is expected to

reach upwards of 50°C, due to the hot motor and motor controller. This is in addition to the fact that

the driver is required to wear a fire-retardant overall, gloves and helmet. Therefore, a drinks bottle

will have to be added into the car to keep the driver hydrated. The maximum stint a driver can expect

to manage is 45 minutes.

4.11.3 Patents

Many patents have been approved with regards to front suspension design of automobiles. These

patents include the use of active systems, that is, suspension the firms- or softens up depending on the

road and/or other conditions. Other patents investigate designs for specific conditions, such as off-

road, or suspension for snow vehicles. Yet others examine various methods of stabilisation. This

section will investigate some of these patents. Reviewing patents can stimulate thought and help

improve one‟s own design.

The invention patented by R.H. Kress in [21] aims to optimise ride height characteristics of heavy

vehicles, both laden and unladen. Kress mentions that a design that optimises ride height of a fully

loaded truck may not be the correct design for an unloaded truck. Thus the characteristics of the

suspension may be a compromise between the two extremes. The invention aims to optimise the

suspension characteristics by providing a system where the vehicle load is supported by a

compressible fluid. The pressure of this fluid is largely controlled by the driver.

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More recently, active suspension systems have become increasingly popular. The Williams FW14

Formula One car incorporated active suspension, which took Nigel Mansell to World Championship

title in 1992. In [22], R.I. Davis patented an electrically powered active suspension for a vehicle. The

purpose of the invention was more sophisticated than the one presented in [21], which merely

optimised ride height. R.I. Davis‟ invention sought to maintain the ideal relationship between the

suspension control arms and the chassis in real time, by the use of electric motors. The types of

motors employed to power this active suspension may either be permanent magnets, synchronous,

variable reluctance or an induction motor. The motor can either be linear or rotary. It is clear that

Davis sought a general, all-encompassing solution.

Although it is instructive to know about these more advanced types of suspension systems, their

existence bears little influence on the current task. The suspension to be used on Ilanga I will be a

passive system, with no possibility of active ride height control and the like. These systems are

expensive and require a lot of time to develop. They will also add significantly to the weight of the

vehicle, with little redeeming value.

A final comment about patents; while doing the review, it was found that a lawyer in Australia, John

Keogh patented what he called a “circular transportation facilitation device”; more commonly referred

to as “the wheel” [23]. Apparently, Keogh wanted to test new patent system introduced in Australia.

4.11.4 Social, Environmental and Other Considerations

The environmental and social factors of this project cannot be overlooked. This section will look at

some of the environmental impacts this project could have both in terms of manufacturing the vehicle,

and also what impact the research the project facilitates, will have in the future. The social benefits of

the project will be looked at in terms of the immediate and distant future.

The vehicle is manufactured from aluminium, steel alloys, fibre glass with the addition of rubbers,

adhesives, spray paints and the like. To extract materials such as iron, aluminium and their alloying

agents will impact negatively on the environment. Certain steel/aluminium suppliers disclose the

amount of carbon that is released into the atmosphere during the manufacturing of the product but

most others do not. The following table discloses the environmental data for the manufacturing of

25CrMo4 Chrome Moly [24]. 25CrMo4 is essentially the same material as AISI 4130, which is one of

the materials considered in the design.

Table 4-1 – Environmental Data of 25CrMo4

Quantity Value Unit

Eco Indicator 95 4.409 mPt

EPS 9040 mELU

Ex(in)/Ex(out) 3.697841727 MJ/MJ

GER 23.7 MJ

Raw Materials Input 3.17460524 kg

Solid 0.0122822 kg

Eco Indicator 99 0.0938 Pt

Environmental Remarks: Environmental data for the production of 1 kg crude steel from SPIN.

Transport is added. The coal comes for 65% from Canada, 23% Australia, 12% from the EEC. Iron

ore comes for 37% from Brasil, 21% Australia, 31% Europe and the remaining 11% from elsewhere.

Page | 31

Lime is imported from Belgium. Metallic alloy elements are assumed to be added in the required

percetages. The production and emission data are for 1989 [25].

The social implications of this project are fantastic. The Team itself consists of members from every

background; white, black, Asian, English, Afrikaans. Therefore, The Team is exposed to different

cultures and ethnicities which instil the values of tolerance and acceptance. The Team is also exposed

to a realistic working environment, while completing their degree. This serves to prepare The Team

for the challenges encountered outside of University. Thus the members will emerge better prepared

than their colleagues. UJ strives to produce top quality engineers, and this project serves to

accomplish just that. Better engineers mean better possibilities for those engineers themselves, as well

as the communities in which they work.

Furthermore, the research into alternative energy vehicles will have an impact on society in the future.

Solar energy in one of its various guises may provide cheap, clean energy, thus even impoverished

communities will benefit. The environmental and social implications of this project make it worth

pursuing by themselves.

Care must be taken when selecting solar panels. Although they produce no emissions, solar panels

production can in some cases, be environmentally unfriendly [26]. The irony is that solar panels

require electricity to manufacture, and thus, during their construction, solar panels indirectly lead to

greenhouse gas emissions. However, the University of Johannesburg‟s Physics Department has

developed a new solar cell technology. Professor Vivian Alberts has created a thin-film solar cell [27].

The cells are cheaper, easier to make and more efficient than conventional photo-voltaic cells.

According to the University‟s website, these panels can produce 60kW of power for only R650 [28].

This is precisely the point of projects such as the UJ solar car. Research into various fields will

ultimately lead to technological improvements for society.

The manufacturing of batteries is another cause for environmental concern. According to a study

conducted by Notter, D.A., ET. Al. [29], the impact on the environment due to personal mobility is

predominantly caused by the operation phase, and not the manufacturing phase. So while the

production of batteries may not be environmentally friendly, the clean operation of the vehicle

mitigates this fact. With time and more research, the production of these batteries may become

cleaner.

4.11.5 Conclusion

The legal and health considerations are to be kept in mind as the project progresses. It is a good idea

to refer back to the literature regularly to find out if there is something more one could do to increase

safety, or to ensure one does not wander into the realm of infringing on patents, and inadvertently

copying others‟ work.

The future environmental impact the project presents cannot be stated with a high degree of certainty.

Many companies and universities are looking to develop alternative energy, and solar energy is just

one of the possibilities. UJ itself is exploring two other avenues, namely hydrogen fuel cells and

turbo-electric power. Although it is impossible to know what the future holds, it is certain that the

research into these projects can only have a positive effect.

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5. Product Design Specification

Both quantitative and qualitative aspects arise when compiling a Product Design Specification (PDS)

for this project. All qualitative concerns will be presented in plain text, while quantitative concerns

will be displayed in italics.

1. As the front suspension linkages will be outboard, and open to the oncoming wind flow, the

suspension should employ a more aerodynamically efficient pushrod suspension. 2. The front tack length should be such that the wheels will fit the current body. The front track

length should be 1500mm. 3. The ride height of the car’s bodywork should be 150mm. 4. The front wheels must be structurally sound to support the weight of the vehicle. The weight

carried by the front wheels is approximately 75kg each. 5. The front brakes should be capable of locking the front wheels. The deceleration target for

the front brakes is 4m/s2.

6. A hydraulic system must be used for the front brakes. As such, the steering swivel members

must be able to accommodate the callipers and brake discs. 7. Body roll of the car should be kept to a minimum. As such, the roll centre will be as close to

the centre of gravity as possible. The maximum allowable body roll will be 5° 8. The suspension must be set up for predominantly driving in a straight line. High performance

cornering ability is not of primary import. 9. The vehicle must be able to drive over South African roads safely. This implies a reasonable

tolerance for bumps and potholes. This implies sufficient bump damping for the driver to

ensure acceptable ride comfort. The Suspension travel will be 50-70mm. 10. The camber angle should be chosen to offer the best stability during cornering. The camber

angle will be 1° 11. The castor angle should be such as to offer the driver self-centring steering, without the

steering being too heavy. The castor angle will be 8° 12. The steering axis inclination angle should offer the driver self-centring, without the steering

being too heavy. The steering axis inclination angle will be 10° 13. The Ackermann Principle should be applied to the steering swivels. The optimum

Ackermann Angle will be determined by geometry, once the rear suspension has been

designed, and the rear axel‟s position is known.

14. The turning radius will be 8-9m

15. The entire system must be as light as possible. The weight limit for the suspension and nose

section is 30kg.

16. The vehicle must be critically damped.

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6. Selection Criteria

Different design concepts will be generated to ensure most possibilities are considered. The quality of

each concept will be measured based upon selection criteria. The pair-wise selection method will be

used. A brief description of the pair-wise method of selection follows.

A certain number of criteria are selected; these must be pertinent to the goal of the project. These

criteria can be: speed, accuracy, corrosion resistance and the like. Essentially, any performance

characteristic of the product can be chosen. Once a list of criteria has been determined, the

importance, or weight of each criterion can be evaluated. An matrix is set up with each criterion

plotted along a single row and column (Assuming n criteria). Each criterion is compared against every

other criterion. When two criteria are compared against each other, the criterion with the higher

priority is assigned a value of 1, and the lower priority criterion is assigned a value of 0. If the priority

of the two cannot be distinguished, they are each awarded a value of 0.5 each. This way, the most

important criteria are determined, and they are assigned the most weight.

After the criteria have been selected, the alternative design options can be compared. An m

matrix is set up, for each criterion (Assuming m alternative designs). The design concepts are plotted

along a single row and column. The designs are compared against one another – in a similar fashion

as mentioned above – in terms of a particular criterion. This is done for each criterion.

The alternative design which has obtained the highest score for a particular criterion is multiplied with

the weight of the criterion. Thus, one design solution may have fared the best in one particular

comparison, but that criterion may not have the highest priority. This way, the alternatives are

compared on a level playing field, and the design solution that fared the best, in the most important

comparisons will end up being the design that is chosen.

In the case where a criterion fails to score a point during the criteria evaluation process, it will be

assigned a value of „1‟. All other criteria have an additional point added to them. This is important

when evaluating the design alternatives. This is so that, if a criterion does fail to score a point, it does

not mean that it is completely unimportant; it simply means that it has a lower priority than the other

criteria against which it is being compared.

The pair-wise comparison method was chose to select the design criteria for the following reasons: It

is a powerful method to determine qualitatively, when the conditions the design alternative must

adhere to. It also provides a way to quantify which selection criteria have priority, over their

counterparts. The design alternatives can be compared using this method as well. Thus, the pair-wise

selection method is useful in determining both the selection criteria, as well as the best design

alternative.

There are two distinct aspects of the suspension design that can be identified. The first is the design of

the steering swivel arm, and the second is the type of suspension system used. Based on consulting

with W. Hurter, there are two possible solutions for the steering swivel arm – fork design and a

conventional steering swivel. There are four possibilities for the suspension system itself –

MacPherson Strut, Pushrod suspension with rocker arm, and pushrod suspension without rocker arm.

A fourth concept was devised later on; it entails incorporating a sort of rocker onto the lower control

arm. This idea is displayed in Figure 6-1. As the control arm is displaced due to bumps or cornering,

the shock absorber is also displaced. More detail on these can be found in Section 7.

Figure 6-1 – Fourth Design Concept

Each one of these two design aspects has their own set of design criteria; for example the steering

swivel arm is housed inside the wheel fairing. Therefore it does not have to be aerodynamically

PIVOT POINT

CONTROL ARM

SHOCK ABSORBER

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efficient, but is must be compact. The suspension system is licked by the airstream, and thus must by

aerodynamically efficient. The criteria for these two design aspects are present below with a brief

description. The criteria have an abbreviated form in brackets. These abbreviations will be used in the

selection criteria tables.

6.1 Criteria Governing the Steering Swivel Arm

- Ease of design and manufacture (EoD): The system must preferably be easy to design and

manufacture. Simple designs are often elegant, lighter and cheaper. A simple design also

affords leeway to the designer if some aspect of the design should be altered, based on new

information.

- Ability to set up the car for a desired handling characteristic (HC): In order for the design

to be successful, it should enable to vehicle to perform well in the intended application. The

steering swivel arm design plays a large role in determining the rode characteristics of the

vehicle.

- Compliance of the design within existing parameters (Comp): The steering swivel will

have to fit inside the wheel fairings. Thus, they have to work effectively within these design

constraints.

- Ease of incorporating the rest of the suspension system with the steering swivel arm

(Incorp): The fork design presents a different challenge in terms of designing the rest of the

system; this is a different challenge to that faced when considering the conventional steering

swivel arm.

Table 6-1 – Selection Criteria for the Steering Swivel Arm

EoD HC Comp Incorp

EoD X 1 1 1

HC 0 X 1 1

Comp 0 0 X 0.5

Incorp 0 0 0.5 X

Totals 1 2 3.5 3.5

The two most important criteria are “Compliance of the design within existing parameters” and “Ease

of incorporating the rest of the suspension system with the steering swivel arm”. This is a logical

conclusion, because, if the system is to work at all, it must be enclosed by the wheel fairings and it

must be able to be incorporated into the rest of the design. The criterion “Ability to set up the car for a

desired handling characteristic” was third in priority, because, which ever design is chosen, that

design will be done in a way as to ensure the desired handling characteristics are achieved. The final

criterion “Ease of design and manufacture” failed to score a point in the process, but it is still awarded

a point, merely to prevent it from having a value of zero. This criterion is not unimportant; it simply

has a lower priority than the other criteria. It is still a valid design concern which should be

considered.

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6.2 Criteria Governing the Suspension System

The criteria governing the suspension system itself will now be considered. These are different from

those presented in the previous section, as there are different factors to consider. Once again, these

criteria have an abbreviation used in Table 6-2. The criteria are:

- Aerodynamic Efficiency (AE): The design must present the least possible resistance to the

air as possible. The bodywork was designed with a heavy focus based on aerodynamics, and it

would be nonsensical to not consider this aspect in the design. It is worth noting that the

control arms and/or other linkages will be in the airstream, and will be subject to aerodynamic

drag.

- Incorporation of design within existing parameters (Incorp): The design will have to

accommodate the existing bodywork. The nose section of the vehicle – to which the front

suspension is bolted – will be redesigned, but the prospects of changing the design

substantially are low. Thus any changes that need to be made to the bodywork and/or chassis

should be kept to a minimum. This is also to save costs.

- Design uses available resources or equipment (Avail): The first Ilanga I design team has

sourced components which are to be used in the reconfiguration of the suspension. These

include the shock absorbers, wheels and brakes. The new design must incorporate these new

parts in order to keep costs down.

- Design provides the opportunity to tune the suspension if desired (Tune): The design

should allow some aspect of flexibility. It would be detrimental to design a system which

cannot be set up to achieve the desired handling characteristics.

- Weight (W): Different solutions will differ in terms of mass. Weight savings are important,

especially in this type of vehicle. Everything else being equal, the weight of the system will

be the deciding factor.

Table 6-2 – Selection Criteria for the Suspension System

AE Incorp Avail Tune W

AE X 0.5 1 0 0

Incorp 0.5 X 1 0 0

Avail 0 0 X 0 0

Tune 0 0 1 X 0

W 1 1 1 0 X

Totals 1.5 1.5 4 0.5 0.5

The criterion “Design uses available resources or equipment” was ranked the most important. The

equipment available must be used in the design, and there is no way around this. The two criteria

“Aerodynamic Efficiency” and “Incorporation of design within existing parameters” were tied for

second. The bodywork can be modified to a small extent; therefore incorporating the new design into

the existing bodywork can be achieved. Aerodynamic efficiency is an important goal in this project.

The lower the wind resistance, the less power the batteries will have to provide to drive the car.

Finally, “Design provides the opportunity to tune the suspension if desired” was ranked with the

lowest priority, along with “Weight” These two conditions are still important, but in terms of

completing the design within budget, they assume a lower priority. In this case, no criterion scored a

value of zero, unlike the situation in Table 6-1.

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7. Concept Generation and Selection

This section will deal with the design considerations for the suspension. This will include various

concepts for different components, and concepts fort the suspension system as a whole. It will also

document the design challenges and constraints that have to be circumvented in order to produce a

decent design.

7.1 Design considerations

Since Ilanga I has been built, there are some real challenges to consider before design work can begin

in earnest. These include:

7.1.1 Existing Bodywork

Half way through the design phase of the solar car, it was decided that a second solar car, Ilanga I-I

would be built. Ilanga I-I would be the race vehicle used in the solar challenge, and Ilanga I would be

used as a promotional vehicle. I-I would be designed with four wheels, and would use the updated

suspension discussed in this Report. Ilanga I-I is set to use the same bodywork as Ilanga I, with one

exception; the wheel fairings of Ilanga I-I would be mounted to the steering swivels and turn with the

wheels. This eliminates the problem of having the wheels fit and turn within the wheel fairings. This

will allow for a greater range of steering angles for the front wheels, thus reducing the turning circle.

The regulations state that the turning circle diameter must be 16m curb-to-curb, which will easily be

achieve with Ilanga I-I. The updated car is also set to use hub motors, instead of the CVT solution

currently employed. The issue with using imported hub motors is that they have a long delivery time;

once they have arrived, there will only be three or four weeks to test them in the updated car.

The Team has to consider the possibility that the hub motors will not be delivered in time. In this case,

Ilanga I will have to be fit to race; it has to conform to all the technical regulations. Therefore, the

concept generation, design and implementation of this project will assume that Ilanga I will be the

race vehicle for UJ. This way, all the bases will be covered, and UJ will have a race-ready car for the

solar challenge. No further mention of Ilanga I-I will be made, as the design of that car has been left

to the senior Solar Team members.

The front fairings for Ilanga I have been fitted, and the range of steering angles of the front wheels has

been assessed. It was noted that the wheels interfere with the wheel fairing before the wheels have

been steered to full lock. In the updated suspension design, the front wheels have been replaced with

motor cycle wheels, more specifically, those from a Honda CBR125. These new wheels have a

smaller diameter than the bicycle wheels currently on the car. The smaller diameter should allow the

wheels to steer to a grater angle before touching the wheel fairing.

7.1.2 Existing Suspension Geometry and Front Wheels

Since the chassis was designed around the front wheels being 711mm in diameter, the suspension

could be designed accordingly. However, the new wheels, having a smaller diameter, have their axles

located closer to the ground. This imposes a serious limitation of the available suspension control arm

angles that can be attained (the angle between the suspension control arm and the ground). The

bodywork of the car must remain 150mm off the ground due to aerodynamic reasons. The limited

scope for changing the control arm angles also placed a restriction on the position of the roll centre.

Thus, the roll centre will almost certainly not be located on top of the centre of gravity, as was

initially intended.

7.1.3 Existing Steering Rack

The updated Ilanga I must use the existing steering rack. Although it can be altered slightly, to change

the tie rod length, not much more can be done to it. Therefore, the suspension must be designed

around it. This imposes yet another limitation as to where the control arm pivot points can be located;

this is due to ump steer reason, as mentioned in Section 4.10. By implication, this also limits the

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available lengths of the control arms, relative to one another, and it also influences the steering axis

inclination. The steering rack was designed as an off-centre system, although this will be changed to a

central system.

7.2 Alternative Design Concepts

The design of the front suspension involves two parts. Firstly, one has to consider the steering swivel

and its possible configurations. Secondly, the type of suspension, and by implication, the geometry

has to be considered. Each of these has their own design criteria and thus, will be considered

separately. Two design options are considered for the steering swivel arm and four alternatives are

considered for the suspension system. For the sake of clarity, each concept will be presented on a new

page.

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7.2.1 Front Fork Arrangement

After consulting with the senior members of The Team, the idea of a front fork assembly was

considered. The basic description is thus; the new front wheels have been designed such that the brake

discs bolt directly to them. Therefore, to facilitate quick tyre changes, a front fork may be a viable

solution, since the wheel can slip in/out of the fork, and the brake disc can slip easily in/out from

between the callipers. Ilanga II will most likely have a front fork arrangement.

7.2.1.1 Evaluation against the Functional Requirements

- Straight line performance: The fork can be designed to incorporate a suitable caster angle,

which will provide self-centring steering capabilities. The wheels will have centre point

steering which is inherent of forks. In this case centre point steering may not be desirable,

because it causes the steering to lack feel, and may require additional steering inputs to keep

the wheels pointing in a straight line. This may increase driver fatigue.

- Resistance to dirt: In this case, the fork system has some advantages. Many mountain bikes

and all off road dirt bikes have front disc brakes. Therefore, designing the front suspension

using this system will be resistant to the ill effects that dirt poses. The CBR125 from Honda is

a road bike, which will have a slightly lower tolerance to dirt than a dirt bike.

- Performance over bumps/during cornering: This can only be determined with respect to

the entire suspension design. Many fork designs incorporate suspension. Mountain bikes and

dirt bikes often have substantial suspension travel and thus, good performance over bumps. In

another situation, the front fork may be rigid, and the suspension movement is provided by

control arms and the like, in the conventional manner. Cornering performance is too complex

a matter to evaluate definitively without testing the system.

- Corrosion Resistance: If an off-the-shelf product is used, it will likely have good anti-

corrosion properties. If a solution has to be designed and manufactured, then a suitable

corrosion resistant material should be employed. As mentioned in Section 3.1, AISI 4130 or

6063-T6 are viable materials.

- Fatigue Life: This depends on the material used for the fork, and also if the fork incorporates

suspension. An off-the-shelf product will also likely have favourable fatigue characteristics.

From the above, it can be seen that the front fork may be a viable solution. If it were to be used, it is

recommended that a high quality, off-the-shelf product is used. This will reduce the amount of design

work and manufacturing involved, which will likely save money. The front fork will also have the

necessary mounts for the brake callipers. The downside to using an existing fork would be that the

fork more than likely will not conform to the space constraints of the bodywork.

7.2.1.2 Advantages

- With this solution, it would be easy to change the front wheel is race conditions.

- The wheel fairings would not have to be altered to change wheels. The car could simply be

raised to the required height, and the front wheel could be removed.

- It is a simple solution in terms of attaching the wheel and brake to the fork.

- The axle in this case will act as a simply supported beam with two supports, and one load in

the middle. This is a stronger solution than the conventional swivel arm, where the axle is

subjected to bending, such as that found on a cantilever.

7.2.1.3 Disadvantages

- It is a complex solution in terms of attaching the fork to the chassis.

- A front fork requires more space than a conventional steering swivel arm. With the already

strict space constraints, this may prove to be a real challenge.

- In order to replace a wheel quickly under race conditions, the ole wheel must be removed, the

hot brake disc taken off and bolted to the new wheel, which can then be put back in place.

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7.2.2 Steering Swivel Arm

This will be a conventional swivel arm arrangement. This solution will require some additional design

work and/or modifications to the new front wheels. The additional design work will involve designing

a mechanism to locate the wheels with respect to the brakes, while still ensuring that the wheel can be

removed without having to remove the brake disc with it. This could be achieved by using a sort of

wheel hub and stud arrangement.

7.2.2.1 Evaluation against the Functional Requirements

- Straight line performance: Using this sort of arrangement, the suspension can be set up for

any type of steering/cornering performance. The steering can be light, thus enabling quick and

nimble cornering, or the steering can be heavier, providing better directional stability for

straight line performance. To increase straight line performance, the castor angle should be

increased, as well as the scrub radius.

- Resistance to dirt: This solution may have a slightly lower tolerance for dirt, considering the

additional components which have to be designed for the hub/stud arrangement. Nevertheless,

many off-road and road vehicles use this type of suspension arrangement. Assuming the

components are properly designed and manufactured, dirt should not pose a serious problem.

- Performance over bumps/during cornering: As was mentioned earlier, this suspension can

be set up for improved cornering performance, or directional stability, depending on the

requirements. The cornering will be improved if the shocks are set slightly stiffer, and the ride

quality will suffer somewhat. Thus, an optimisation between cornering ability and

performance over bumps can be reached during testing.

- Corrosion Resistance: Not much more can be said on the topic of corrosion resistance. A

material with anti-corrosion properties will be used.

- Fatigue Life: This also depends on the material. Chrome moly has better fatigue

characteristics than aluminium, but a design calculation and material selection will determine

the type of material to be used.

The conventional steering swivel arm provides the designer with more flexibility than the fork

arrangement. In this arrangement, the axle will act as a cantilever, which implies that the axle material

must be very strong and hard; does not deform to an appreciable degree under the applied loads.

7.2.2.2 Advantages

- Provides flexibility to the designer; offers more choice pertaining to the best solutions for the

rest of the suspension system.

- It takes up less space than a fork arrangement.

- This solution will enable quicker tyre changes than the fork arrangement during race

conditions. This also satisfies the design request.

- It will use less material than a fork, which will make it lighter.

7.2.2.3 Disadvantages

- The bodywork will have to be modified to facilitate a wheel change during the race.

- Potentially more difficult to design, particularly with respect to the mechanism that locates

the wheel to the brake.

- Material selection is more critical, especially for the front axle.

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7.2.2.4 Pair-wise Comparison and Selection of Steering Swivel Arm

Table 7-1 – Ease of Design and Manufacture

Conventional Steering Swivel Front Fork Arrangement

Conventional Steering Swivel X 1

Front Fork Arrangement 0 X

Table 7-2 – Ability to set up the car for a desired handling characteristic

Conventional Steering Swivel Front Fork Arrangement

Conventional Steering Swivel X 1

Front Fork Arrangement 0 X

Table 7-3 – Compliance of the design within existing parameters

Conventional Steering Swivel Front Fork Arrangement

Conventional Steering Swivel X 1

Front Fork Arrangement 0 X

Table 7-4 – Ease of incorporating the rest of the suspension system with the steering swivel arm

Conventional Steering Swivel Front Fork Arrangement

Conventional Steering Swivel X 1

Front Fork Arrangement 0 X

Totals:

- Conventional Steering Swivel = 4

- Front Fork Arrangement = 0

The conventional steering swivel wins the pair-wise comparison outright. The front fork arrangement

was considered only as it was a suggestion made by the Masters‟ students.

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7.2.3 Pushrod Suspension with Rocker Arm

This system was discussed in Section 4.2. It is essentially the same as a double wishbone suspension;

however, instead of having the shock absorber from the bottom control arm to the chassis, there is a

pushrod in this case. The pushrod acts against a rocker arm which then acts upon the shock absorber.

This system can be seen in Figure 4-3. The design considerations for this solution involves decided

where and how to attach the rocker and the shock absorber. Additionally, the angle of the pushrod,

and therefore, the stresses acting on it will have to be calculated.

7.2.3.1 Evaluation against the Functional Requirements

- Straight line performance: The straight line performance of the vehicle is determined, in a

large part, by the type of steering swivel arm that is used. The conventional type of steering

swivel arm has been selected, and thus will be designed and optimised for this type of

performance. After all of the pertinent properties have been established (castor, camber and

steering axis angles), the pick-up points for the control arms will be determined. Designing

the double control arm around the conventional steering swivel arm is rather straightforward.

- Resistance to dirt: Nylon bushes can be used for all of the pivot points, thus ensuring a low

friction surface and limiting the amount of dirt that can impede the performance of the

moving components. Additionally, the shock absorber will be enclosed within the bodywork.

The resistance to dirt is high for this design. The bearings of the rockers will have to be sealed

to maintain their integrity.

- Performance over bumps/during cornering: Pushrod suspensions have generally been used

on racing cars. The system can thus be optimised for cornering performance. The car will be

set up for straight line performance, however, if the system is designed properly, it is believed

that the cornering performance will be acceptable. Performance over bumps can be

compensated for by the design of the rocker arms. These can artificially stiffen of soften the

suspension by increasing/decreasing the moment arms.

- Corrosion Resistance: Not much more can be said on the topic of corrosion resistance. A

material with anti-corrosion properties will be used.

- Fatigue Life: The pushrod will be subjected to compression, and parts do not yield due to

fatigue when subjected to compression. Buckling may be of concern in this case, but this will

be dealt with by selecting an adequate material for the pushrod. The control arms and tie rod

ends will have to be designed carefully though to ensure they have an acceptable fatigue life.

The rocker mounting point will also be subject to fatigue, and will have to be considered

carefully.

7.2.3.2 Advantages

- The system presents less frontal area to the on-coming airstream.

- The rocker arm provides some additional scope for tuning the suspension, i.e. alter the forces

acting of the shock absorber.

- It is easy to determine the location of the roll centre and other pertinent points based on the

geometry.

- Once the geometry has been determined, designing the system will be fairly straight forward.

7.2.3.3 Disadvantages

- The rocker may add weight to the system, as it needs to be mounted using a bearing.

- The shock absorbers are physically small, which is less conducive to being used as part of a

pushrod assembly.

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7.2.4 Pushrod Suspension without Rocker Arm

This solution is similar to that which is being used on Ilanga I currently. Ilanga I has a pushrod on the

upper control arm. This alternative proposes to use the pushrod on the lower control arm; the pushrod

will be connected directly to the shock absorber. Since the shock absorbers are small, they may fit

well with this type of system. A push rod system with a rocker has the advantage of being more

flexible, in terms of design and performance optimisation. The pushrod without the rocker has an

advantage in terms of being lighter. Otherwise, the two systems are identical.

7.2.4.1 Evaluation against the Functional Requirements

- Straight line performance: See Section 7.2.3.1. The characteristics of these two systems are

quite similar.

- Resistance to dirt: See Section 7.2.3.1

- Performance over bumps/during cornering: This system will have less scope for

configurability than the pushrod with a rocker. The damping effect of the shock absorber will

be determined by the gas pressure inside of the unit. Nevertheless, the system can be designed

and optimised for performance over bumpy roads, as and when required.

- Corrosion Resistance: Not much more can be said on the topic of corrosion resistance. A

material with anti-corrosion properties will be used.

- Fatigue Life: See Section 7.2.3.1.

7.2.4.2 Advantages

- The system presents less frontal area to the on-coming airstream.

- The lack of a rocker saves on weight.

- It is easy to determine the location of the roll centre and other pertinent parameters based on

the geometry.

- Once the geometry has been determined, designing the system will be fairly straight forward.

- Since the shock absorbers are small, they will be fairly simple to incorporate into the design.

7.2.4.3 Disadvantages

- The lack of a rocker limits the scope for performance optimisation, i.e. cannot alter the forces

acting on the shock absorber.

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7.2.5 MacPherson Strut

The MacPherson Strut was discussed in Section 4.2. In this situation, there is only a lower control arm

connected to a steering swivel arm, and then to the shock absorber. This may seem like the simplest

solution in terms of design; however, certain considerations have to be taken into account: Based on

the physical size of the shock absorber, there is no real way to use the shock absorber as a strut.

Assuming this problem did not exist, the shock would be in the airstream, which would provide a lot

of wind resistance. Regardless, this is still a design alternative so the rest of the design analysis will

determine this concept‟s worth.

7.2.5.1 Evaluation against the Functional Requirements

- Straight line performance: It is less straightforward to determine the roll centre for this sort

of design. Additionally, the physical constraints (size of the shock absorber, existing

bodywork) make this even more challenging. Inherently however, this solution is more suited

to straight line performance, rather than cornering.

- Resistance to dirt: If the shock is used as a strut, it would more than likely be place outside

the vehicle, exposed to the elements. Thus, it will be more vulnerable to dirt impacting on its

performance.

- Performance over bumps/during cornering: Camber does not change substantially during

cornering. This would mean less stability in the corners, which is undesirable. Performance

over bumps is dictated, once again, by the gas pressure within the shock absorber unit.

- Corrosion Resistance: Not much more can be said on the topic of corrosion resistance. A

material with anti-corrosion properties will be used.

- Fatigue Life: The material selection is important here, and well as a proper design of the

control arms and designation of the tie rod ends. Unlike the pushrods, nothing in this design is

subjected to what may be considered to be a buckling load.

7.2.5.2 Advantages

- Simple design, in theory, i.e. less components.

7.2.5.3 Disadvantages

- The shock absorber is small, and is not conducive to this design.

- The shock absorber would be in the airstream, causing substantial drag.

- The car was not designed around this type of suspension system, which implies that trying to

design a MacPherson strut assembly would be more effort than what it‟s worth.

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7.2.6 Using the Lower control Arm as a Rocker

This design concept is displayed in Figure 4-3.. It uses the basic premise of the rocker used in the

pushrod, however, this rocker in this concept is incorporated into the control arm; i.e. the control arm

itself acts as a rocker. When the control arm is displaced by bumps or during cornering, the

rocker arm displaces the shock absorber. The goal of this idea is to save weight, and also introduce

less components into the airstream, thus cutting down on drag.

7.2.6.1 Evaluation against the Functional Requirements

- Straight line performance: The straight line performance (or performance characteristics in

general) of this design will be similar to both pushrod concepts already discussed.

- Resistance to dirt: Due to the small number of components in this design, and due to the fact

that the shock absorber is enclosed inside the bodywork, means that there is less of a chance

of dirt influencing the performance.

- Performance over bumps/during cornering: See Section 7.2.3.1

- Corrosion Resistance: Not much more can be said on the topic of corrosion resistance. A

material with anti-corrosion properties will be used.

- Fatigue Life: The rocker on this control arm will have to be designed correctly to take fatigue

into account.

7.2.6.2 Advantages

- Very simple design.

- Saves on weight, due to less components in general.

- Reduces drag, due to less components being present in the airstream.

- This solution presents the design with the added flexibility due to the presence of a „rocker‟.

7.2.6.3 Disadvantages

- Since this is a new design, it is untested and unfamiliar.

- The force acting on the shock absorber may be large due to the small moment arm of the

rocker.

Page | 45

7.2.6.4 Pair-wise Comparison of the Suspension System

Table 7-5 – Aerodynamic Efficiency

Pushrod w/ rocker Pushrod w/o rocker MacPherson Rocker on A-Arm

Pushrod w/ rocker X 0.5 0 1

Pushrod w/o rocker 0.5 X 0 1

MacPherson 1 1 X 1

Rocker on A-Arm 0 0 0 X

Totals 1.5 1.5 0 3

Table 7-6 – Incorporation of design within existing parameters

Pushrod w/ rocker Pushrod w/o rocker MacPherson Rocker on A-Arm

Pushrod w/ rocker X 0 0 0

Pushrod w/o rocker 1 X 0 0.5

MacPherson 1 1 X 1

Rocker on A-Arm 1 0.5 0 X

Totals 3 2 0 1.5

Table 7-7 – Design uses available resources or equipment

Pushrod w/ rocker Pushrod w/o rocker MacPherson Rocker on A-Arm

Pushrod w/ rocker X 0.5 0 0

Pushrod w/o rocker 0.5 X 0 0.5

MacPherson 1 1 X 1

Rocker on A-Arm 0 0.5 0 X

Totals 2.5 2 0 1.5

Table 7-8 – Design provides the opportunity to tune the suspension if desired

Pushrod w/ rocker Pushrod w/o rocker MacPherson Rocker on A-Arm

Pushrod w/ rocker X 0.5 0 0.5

Pushrod w/o rocker 0.5 X 0 0.5

MacPherson 1 1 X 1

Rocker on A-Arm 0.5 0.5 0 X

Totals 2 2 0 2

Page | 46

Table 7-9 – Weight

Pushrod w/ rocker Pushrod w/o rocker MacPherson Rocker on A-Arm

Pushrod w/ rocker X 1 1 1

Pushrod w/o rocker 0 X 1 1

MacPherson 0 0 X 1

Rocker on A-Arm 0 0 0 X

Totals 0 1 2 3

Now, to determine the most feasible design alternative, the totals in each comparison must be

multiplied with the corresponding weight for that criterion. Thus

Pushrod w/ rocker = 1.5(1.5) + 3(1.5) + 2.5(4) + 2(0.5) + 0(0.5) = 17.75

Pushrod w/o rocker = 1.5(1.5) + 2(1.5) + 2(4) + 2(0.5) + 1(0.5) = 14.75

MacPherson = 0(1.5) + 0(1.5) + 0(4) + 0(0.5) + 2(0.5) = 1

Rocker on A-Arm = 3(1.5) + 1.5(1.5) + 1.5(4) + 2(0.5) + 3(0.5) = 15.25

7.3 Conclusion

From the preceding sections, the following conclusions can be drawn:

The conventional steering swivel arm was far and away the superior concept. The front fork

arrangement was considered on the advice of the Masters‟ Students. Although it may be a reasonable

concept to employ, based on the current design constraints, it is not feasible.

The pushrod with the rocker is the concept that will be developed. The added weight of the rocker

assembly will be mitigated by the fact that it has the highest likelihood of working correctly. The

pushrod without the rocker offers the designer limited flexibility in terms of the forces acting on the

shock absorber. The forces acting on the shock absorber may be too great for the shock, and may end

up damaging it. The same is true for the control arm which incorporates the rocker. The MacPherson

Strut was considered for the sake of completeness, but was never really a viable design option.

Page | 47

8. Performance Simulations and Design Calculations

This section will primarily focus on the design calculations employed to design the suspension. More

specifically, some performance simulations will be presented. These simulations will include

measuring the track length change with respect to suspension travel, determining the Ackermann

Angle, determining the turning radius and the like. The geometry of the suspension must be

determined first, and then the material selection can be conducted. The material selection is based

upon the forces present in the system. Therefore, the geometry will be determined, and justified by

means of the performance simulations, and afterwards, the materials required to achieve the

performance goals will be designated by means of strength of materials calculations. This will be

done in Sections 9 and 10. First however, the design methodology will be discussed, to give the reader

a sense of the thought processes involved.

Section 7.1 explains some of the challenges faced to complete this design. Essentially, the main

challenge is that the bodywork was designed and built around a completely different suspension setup

and wheels to the ones that are being considered for this design. The following factors have had an

effect on the design:

- Size and shape of the wheel fairings.

- Length of the steering rack.

- Required ride height of the body.

- The fact that smaller wheels are being used.

After conducting the pair-wise comparison in Section 7, the components chosen for the design are the

conventional steering swivel arm and the pushrod suspension with rocker. The design software used

was SolidWorks Academic Edition 2011-2012. The first order of business was to reverse engineer the

steering rack. As was mentioned in Section 4.10, the steering rack dimensions must be known in order

to account for bump steer in the design. Some simple suspension geometry was drawn as a starting

point. The steering rack was inserted into the model, and its height above the reference plane (ground

plane) was adjusted such that its tie rod ends‟ centres intersected the line joining upper and lower

control arm pivot points. After this, the wheels were inserted into the model and planes were created

to define the wheels‟ final positions. Based on the Literature Review and consulting with the senior

students, the geometry was refined.

Some mock steering swivel arms were modelled based on the suspension geometry. Its position was

defined, in the process, defining the scrub radius. With this in place, the turning circle was determined

next. The wheel was steered to the left/right and stopped just before intersecting the body work. The

track length was adjusted so that the inner wheel could turn through a smaller arc than the outer one.

Once the maximum steering angles were found (by implication, the turning circle), the Ackermann

angles were determined.

The above design process was an iterative one. Various parameters were tested, and the most

promising values were brought to light. These values are tabulated below:

Page | 48

Table 8-1 – Suspension Parameters

Parameter Value Unit

Steering Axis Inclination 10 Degrees

Castor Angle 8 Degrees

Camber Angle 1 Degree

Toe In Angle 1 Degree

Lower Control Arm Angle 11 Degrees

Upper Control Arm Angle 9 Degrees

Scrub Radius 48 mm +

Length between upper and

lower control arm pivots

280 mm

Steering rack Length 581.5 mm

Lower Control Arm Length 563 mm

Upper Control Arm Length 352 mm

Turning Circle Radius 8 780 mm

8.1 Performance Simulations

As was previously mentioned, the design process was iterative. Values for the various parameters

were selected, based on the physical geometry of the vehicle. The system was analysed using the

performance simulations presented in the subsequent pages. The values were altered slightly, and re-

evaluated. After multiple iterations, the values seen in Table 8-1 were determined. The suspension

geometry, as it was selected is shown in Figure 8-1. The figure also depicts the mock steering swivel

arm and the steering rack. The performance simulations presented below will discuss matters

previously seen in the Literature Review. See Appendix B for the spread sheets used to generate the

graphs presented in this section.

Page | 49

Figure 8-1 – Suspension Geometry

8.1.1 Change in Track Length vs. Suspension Travel

Figure 8-2 below shows how much the track length changes for a given amount of suspension travel.

The change in track length for the droop (negative suspension travel) is more pronounced than that of

the bump (positive suspension travel). Over a range of 70mm of suspension travel, the track length

changed by 10mm. A point to note is that the shock absorbers being used have only approximately

50mm of travel, so the maximum expected track length change is 6mm (the positive portion of the

graph). As mentioned in Section 6.2, the control arms must be non-parallel and of unequal lengths so

as to minimise track length change for a given amount of suspension travel.

Figure 8-2 – Suspension Travel vs. Track Length Change

-6

-4

-2

0

2

4

6

8

-30 -20 -10 0 10 20 30 40 50 60

Trac

k Le

ngt

h C

han

ge [

mm

]

Suspension Travel [mm]

Suspension Travel vs. Track Length Change

Page | 50

8.1.2 Change in Camber due to Steering Input

Camber was discussed in Section 6.5. Due to the castor angle and the steering axis inclination, the

camber angle changes during cornering. This is desired, especially since motorcycle tyres are being

used, as they were designed to navigate corners while having high camber angles. Figure 8-3 below

shows that the change in camber due to a change in the steering angle can be approximated by a

straight line. The data represented in the graph is for the right wheel; a positive value for the steering

input indicates turning left and a negative value is indicative of the wheel turning right. The results

shows that when the wheels are steering to take a corner, the wheels tend to „lean in‟ slightly. This is

consistent with theory.

Figure 8-3 – Steering Input vs. Camber Change

8.1.3 Ackermann Steering Geometry

The Ackermann Angle was discussed in Section 6.7, where it was mentioned that wheels going

around a corner want to rotate with pure rolling motion, i.e. no scrubbing. This section describes how

the Ackermann Principle was applied to this vehicle. The wheels were steered to full lock, and their

angles were measured, relative to the straight ahead position. The inside wheel‟s angle was 19.8° and

the outside wheel‟s angle was 16.8°. Using the „blocks‟ feature in SolidWorks, the angles of the

steering arms and tie rods were determined. The blocks feature allows the user to draw a sketch and

move it in real time. This is a useful tool to analyse the motion of mechanisms. Incidentally, blocks

were also used to analyse the motion of the suspension geometry. The top view of the suspension can

be seen in Figure 8-4. Although it is difficult to see in this image, the front wheels have a 1° toe-in

setting. This geometry was finalised using a trial-and-error approach – in conjunction with

SolidWorks „blocks‟ – to achieve proper Ackermann Steering.

y = -0.1387x + 88.81

85

86

87

88

89

90

91

92

-25 -20 -15 -10 -5 0 5 10 15 20

Cam

be

r C

han

ge

Steering Input

Steering Input vs. Camber Change

Page | 51

Figure 8-4 – Ackermann Steering, wheels Straight

Figure 8-5 – Ackermann Steering, Wheels Steered

Figure 8-5 above shows the wheels steered to the left. Again, it is difficult to see, but at full lock, the

inner wheel is steered approximately 4° more than the outer wheel. This is also a convenient, as the

steering rack is mounted onto the same mounting structure as the shock absorbers; all of the

components (pushrods, shock absorbers, steering rack) therefore line up, thus mitigating the need for

additional mounting structures.

8.2 Design Calculations

The performance of the suspension system was analysed in SolidWorks during the design phase. An

additional consideration is that of the strength of the structure itself. The design must be able to

withstand the rigors of testing and the race, as outline in the Operating Environment section. This

section will look at some strength of materials calculations for the control arms, pushrods, axels and

the structure of the suspension box.

8.2.1 Control Arm and Pushrod Force Calculations

The control arms support the mass of the car in the vertical direction, as well as being subjected to

longitudinal loads, due to acceleration and braking. Solar cars‟ rates of accelerate are generally quite

low; however, solar cars do need the capability of stopping quickly when required. Thus, the main

longitudinal force acting on the suspension is due to braking. This force is simply Newton‟s Second

Law (NII):

Steering Rack

Steering Swivel Arms

Steering Linkages

Page | 52

(8.1)

Where:

- F = Longitudinal force acting on the suspension

- m = Mass of the car

- a = Required braking acceleration

The regulations stipulate that the required braking force is 5.8m/s^2 [20]. The mass of the car is

(including driver and batteries) 250kg. Thus applying NII:

This force will have to be withstood by four control arms, so the actual force acting on each of the

control arms is 362.5N. Assuming a factor of safety of 3, the force acting on each member is

approximately 1 100N (conservatively rounding up). The control arms are of an A-Arm configuration.

Figure 8-6 – Upper Control Arm

The control arms were a compromise between attaining the best geometry of the A-Arm to ensure the

lowest possible forces act on the members, and ensuring that they fit inside the bodywork. Figure 8-6

shows the values for angles Alpha and Beta. A simply truss analysis was carried out to determine the

loading condition on these control arm members. The following two equations were derived:

(8.2)

(8.3)

Where F is the load due to braking.

With the known angles, and using equations 8.2 and 8.3, the forces acting on the control arm members

are: 1214N on the member acting in tension, and 1064N on the member acting in compression.

Page | 53

A similar analysis was done for the lower control arms:

Figure 8-7 – Lower Control Arm

The results yielded 1737N on the compression member, and 1917N on the tension member. The cross

member seen in Figure 8-7 has been added for extra rigidity of the control arm, as the lower control

arm is considerably longer than the upper one.

Page | 54

Figure 8-8 – Suspension geometry with Pushrod

A similar truss analysis for the suspension geometry itself (including pushrods) will yield the forces

present on the structure due to the mass of the vehicle. The car (including driver, etc.) weighs 250kg.

Approximately 126kg acts on the front wheels, thus, 63kg on each wheel. The forces present due to

this loading condition where found after deriving the following two equations and solving

simultaneously:

(8.4)

(8.5)

Thus, the forces present are 950N in compression on the pushrod, and 600N on the lower control arm.

This is due to a force of 630N acting on the steering swivel arm. The upper control arm carries very

little load; so little in fact, it can be neglected.

8.2.2 Pushrod Rocker Stress Calculations

The shock absorbers can only withstand approximately 80kg or 800N load. Thus, the pushrod rocker

has to decrease the force acting on the shock absorber. This is done by having a ratio of 2:1, the shock

Page | 55

absorber side to the pushrod side. The geometry of the rock has been designed in such a way that the

pushrod acts perpendicularly to the rocker, which in turn acts perpendicularly to the shock absorber.

This is the case when the car is standing stationary, and the suspension has not travelled. As the

suspension travels up or down, the angle between the pushrod and rocker, and between the rocker and

shock absorber changes slightly, but this change is on the order of 2 degrees, which has very little

effect on the suspension system itself.

Figure 8-9 – Pushrod/Rocker/Shock Absorber assembly

The centre line shows the lines of action of the respective forces.

As a larger amount of force is acting on the rockers, a finite element analysis of the rockers was

conducted to ensure they will operate as desired. Refer to Appendix C for the full finite element

analysis report of this component. The following two images show were the load is carried by this

component, and what the stress on this component is.

(a)

Page | 56

(b)

Figure 8-10 – Load bearing sections (a), stresses experienced by the components (b)

The images in Figure 8-10 shows that the load is carried by the two sides, thus justifying the large

hole in the middle of the plate. The maximum stress on the plate is approximately 60MPa, which is

well within the yield strength for this material, AISI4130.

8.2.3 Axel Bending Stress Calculations

The bearings used by the CBR125 wheels have a bore of 12mm. Thus, a 12mm diameter axel has to

be used. This axels acts as a cantilever, therefore, it is subjected to a large bending moment, and a

comparatively small shear moment.

Figure 8-11 – Axel acting as a cantilever

Page | 57

The length of the axel supporting this load is 97mm. Using the bending moment equation yields:

(8.6)

Where:

- M = 0.097×630 = 61Nm

- y = 0.006m

- I = πd4/64 = π(0.012

4)/64 = 1.0179×10

-9m

4

Thus:

This stress is fairly significant, thus, an appropriate material must be used.

8.2.4 Control Arm Pivots Force Calculations

The control arm pivots are subjected to some large forces, especially the lower control arms. From the

calculation from equations 8.4 and 8.5, it is seen that the force acting on the lower control arm is

approximately 600N. This is acting on the A-Arm, which is essentially a truss. The maximum force

acting on the members is 860N (found from simple truss analysis). The bolt holding the control arm

also acts as its pivot. The force acts on the bolt in double shear. Once again, the bending moment

applies a greater stress than the shear stress. Grade 8.8 bolts have been selected for the suspension. If

M12 bolts are used, the bending stress on them would be:

Where:

- M = 0.038×860 = 32Nm

- y = 0.006m

- I = πd4/64 = π(0.012

4)/64 = 1.0179×10

-9m

4

The yield strength of the bolts is 660MPa [12], thus, the bolts will be strong enough.

8.3 Conclusion

The results obtained in this section will show their true worth when it comes to selecting the

appropriate materials. When selecting the materials, a minimum safety factor of 8 will be aimed for.

This high safety factor includes the different load cases the design will be subjected to during

operation.

Page | 58

9. Material Selection

The preceding section on the design calculations provides a tangible sense of the loads each of the

components will experience. Using this information, the materials for these components can be

selected. There are some additional material selection criteria to consider, which include cost and ease

of manufacture. This section will deal firstly with the most suitable materials to use for the design, in

terms of strength; thereafter, the other considerations will be taken into account. After all the available

information has been analysed, the material will be selected. Before delving into the material

selection, it would be appropriate to conduct a brief review of material science to provide a starting-

off point for the later selection. Most of the literature surveyed with regards to material selection

comes from [25]. This source demonstrates material selection for the design. That is, it demonstrates

that the design can be conducted, and the material will be selected to suit the design, and not

designing the product to suit a particular material. The present design was conducted with the same

philosophy as outlined in [25].

Ilanga I was built using 6063-T6 aluminium, thus this material will be under consideration for the

design. The other alternative is to use AISI4130 chrome-moly. This steel is used for aircraft, and is

approximately three times stronger than the aluminium (ultimate tensile strength); it is also three

times heavier. The most appropriate material will be selected from these two front runners.

9.1 Material Science

According to [25], there are five fundamental engineering materials. These are: Ceramics, Metals,

Polymers, Elastomers and Glasses. These materials can be combined together if certain proportions to

obtain some hybrid material. These groups of materials are known as families. Each member of a

certain family of materials will have certain traits in common with the other members. Each one of

these families can be subdivided into classes, sub-classes, and members [25,26]. These members have

attributes specific to it. It is these attributes that are important when selecting a material. Certain

materials have attributes in common with others, but each individual material will have a combination

of properties. When selecting a material, it is important to select the material which offers the best

compromise of attributes. In the following sub-section, the „metals‟ family will be looked at; a metal

product will be used for the components.

9.1.1 Metals

Metals generally have a high modulus of elasticity, that is, they are generally stiff. Unless alloyed

with some agent, pure metals will deform quite easily, meaning that they have a low yield strength.

The yield strength can be increased by alloying, or by heat treating. Despite this, under standard

conditions (not extremely low temperatures), the material will remain ductile, thus alloying to yield a

certain amount before failing/fracturing. The resistance the material has to fracturing in called

toughness. Metals will generally corrode if not protected, either by some surface treatment, of by the

introduction of some alloying agent [25]. Metals have many properties that are appealing to an

engineer. A wide range of treatments can be conducted on them to increase strength, corrosion

resistance, electrical conductivity and the like. A full review of the mechanical properties of metals is

beyond the scope of this review, so only some pertinent aspects will be discussed.

9.1.1.1 Grain Structure

Metals are cast when they are in the liquid phase. As the metal begins to cool, the molecules of the

metal start forming bonds with each other. This yields a grain of an almost perfect crystal. This

happens at different locations within the cast at the same time. Eventually, the metal will contain

hundreds of these crystals within it. The lattice structure of these crystals has a different orientation

from one grain to the next. The yield strength of a material is based largely of the size, shape and

orientation of these grains [26]. The grain itself has a very high yield strength, but the weakness of the

material lies in the grain boundaries. A crack will propagate along grain boundaries much faster than

it would propagate through the grain itself.

Page | 59

Alloying was mentioned earlier. What some alloying agents, like magnesium, do is promote grain

refinement [26]. What this means is that the grains in the metal become much smaller, increasing the

amount of grain boundaries. It seems counter-intuitive that this would make the metal stronger, but it

does. With smaller grains, the number of grain boundaries increase, thus increasing the number of

discontinuities, which would hinder crack propagation [26].

Figure 9-1 – Microscopic Image of Low Carbon Steel Grains [27]

Figure 9-1 above shows the microscopic grain structure. This image shows a low carbon steel. High

carbons steels have a grain structure as shown in Figure 9-2. The dark areas are graphite flakes

imbedded in the metal.

Figure 9-2 – Microscopic Image of High Carbon Steel Grains

9.1.1.2 Strain Hardening

Metals can be strain hardened. This means that if a metal undergoes strain, or a deformation, it will

become harder and stronger [25,26]. The reason for this is that the grains within the metal become

deformed. Thus, the grain boundaries will once again contain discontinuities and impede crack

propagation. The amount a metal will strengthen is depended upon a quantity known as strain

Page | 60

hardening index. Thus, a material can be processed (cold rolled) to increase strength. For a more in-

depth study of this topic, refer to either one of the following references [12,25,26].

9.1.1.3 Alloying

Alloying is a key concept in material science. It offers the designer some properties that he otherwise

would not have had. The steel, AISI4130 has the following constituents: 0.5-0.95% Chromium, 0.12-

0.2% Molybdenum [28]. The Chromium serves to increase corrosion and oxidation resistance, it

increases hardenability, increases high temperature strength, and can combine with carbon to form

hard, wear resistant micro-structures [28]. Molybdenum promotes grain refinement, and improves

high temperature strength [28]. Steels can be combined with many other alloying agents, such as

silicon, vanadium, nickel and others to produce these and other characteristics. Aluminium can be

alloyed in much that same way.

9.1.1.4 Conclusion

The preceding paragraphs provide a very cursory view of metals. For further information, the reader

may consult references [25,26,28]. The purpose of the above sections is to demonstrate the range of

possibilities, and material properties available when choosing a material. The focus was given to

metals, as a metal will be used to construct the components; at this stage however, it is uncertain as to

which metal will be chosen. The following sections will present a list of material properties and

selection criteria. After which, calculations will be made and the most appropriate material will be

selected.

9.2 Material Properties

The two possibilities for the material are 6063-T6 aluminium, and AISI 4130 chrome-moly. The

reasons for these choices are based on availability and convenience. The UJ Solar Team is designing

and building an update solar car, Ilanga I-I. The selected material for the new chassis is AISI 4130.

The current car, Ilanga I has been built using 6063-T6 aluminium, and some spare material is

available to be used for the front suspension components. Thus, whichever material is chosen, there

will be now problems concerning availability, as there may have been is a different material entirely

was chosen.

Page | 61

9.2.1 AISI 4130 Chrome-Moly

Table 9-1 - AISI 4130 Steel, normalized at 870°C (1600°F) Properties [29]

AISI 4130 Steel, normalized at 870°C (1600°F)

Physical Properties Metric English

Comments

Density 7.85 g/cc 0.284 lb/in³

Mechanical

Properties

Metric

English

Comments

Hardness, Brinell 197 197

Hardness, Knoop 219 219

Hardness, Rockwell

B

92 92

Hardness, Rockwell

C

13.0 13.0

Tensile Strength,

Ultimate

670 MPa 97200 psi

Tensile Strength,

Yield

435 MPa 63100 psi

Elongation at Break 25.5 % 25.5 % in 50 mm

Reduction of Area 60.0 % 60.0 %

Modulus of

Elasticity

205 GPa 29700 ksi

Bulk Modulus 140 GPa 20300 ksiT

Poissons Ratio 0.290 0.290 Calculated

Izod Impact 87.0 J 64.2 ft-lb

Machinability 70 % 70 % Annealed and cold drawn

Shear Modulus 80.0 GPa 11600 ksi

Page | 62

9.2.2 6063-T6 Aluminium

Table 9-2 - 6063-T6 Properties [30]

Aluminum 6063-T6

Physical

Properties

Metric English Comments

Density 2.70 g/cc 0.0975 lb/in³

Mechanical

Properties

Metric English Comments

Hardness, Brinell

Hardness, Knoop

73

96

73

96

500 g load; 10 mm ball

Hardness, Vickers 83 83

Tensile Strength,

Ultimate

241 MPa 35000psi

Modulus of

Elasticity

68.9 GPa 10000

Ultimate Bearing

Strength

434 MPa 62900 psi

Bearing Yield

Strength

276 MPa 40000 psi

Poissons Ratio 0.330 0.330

FatigueStrength

Machinability

68.9MPa

50 %

10000 psi

50 %

@# of Cycles 5.00e+8

Shear Modulus 25.8 GPa 3740 ksi

Shear Strength 152 MPa 22000 psi

9.3 Side-by-Side Comparison

Table 9-3 - Side-by-Side Comparison between AISI 4130 and 6063-T6

Property AISI 4130 Value 6063-T6 Value AISI 4130/6063-T6

%

Yield Strength 435MPa 214MPa 203%

Ultimate Strength 670MPa 241 278%

Modulus of Elasticity 205GPa 68.9GPa 297%

Density 7.85g/cc 2.7g/cc 291%

Table 9-3 above shows that the steel is nearly three times as dense as the aluminium, while offering

only twice the strength. If the weight-to-strength ratio was the only consideration, aluminium would

be the preferred material. Since this ratio is not the only factor, we have to investigate what sort of

loads each respective material can handle. The following two sections were recommended for each

respective material:

- AISI 4130: 19.05×1.25mm

- 6063-T6: 31.76×3.18mm

The following sub-section will use the values obtained in Section 8 to determine the stresses acting on

these members.

Page | 63

The AISI 4130 is also far easier to weld than the aluminium. This is according to the welder. The

welder‟s personal preference, and area of expertise is welding AISI 4130 structures, which adds

another tick for the steel alloy.

9.4 Calculations

Using

(9.1)

Where:

- A = Cross-sectional Area.

- D = Outer diameter of the tube.

- d = Inner diameter of the tube.

The cross-sectional areas of the two sections are:

- AISI 4130: 6.964×10-5

m2

- 6063-T6: 2.855×10-4

m2

This means that the area of the steel section is 24% of that of the aluminium section. Thus, for unit

length, the respective masses of the sections are calculated using:

(9.2)

Where:

- m = Mass per unit length.

- = Material density.

- = Volume per unit length.

The mass per unit lengths are thus:

- AISI 4130: 0.5467kg/m

- 6063-T6: 0.7709kg/m

These values agree with the values given by SolidWorks. So, despite the aluminium having the lower

density, because a smaller section of AISI4130 is being used, the steel alloy is actually lighter.

9.4.1 Control Arm and Pushrod Material Calculations

The forces acting on the upper control arm members are shown in Figure 8-6. The two forces present

on the arm are:

- 1 214N - Tension

- 1 064N - Compression

The stress these forces would impart on the structural members are calculated using:

(9.3)

Where:

- = Stress imparted on the member. - = Resultant force.

- Cross-sectional area of the member.

The stresses on the upper control arms‟ members are thus:

- AISI 4130:

o Where F = 1 214N, = 17.43MPa - Tension

o Where F = 1 064N, = 15.28MPa - Compression

Page | 64

- 6063-T6

o Where F = 1 214N, = 4.25MPa - Tension

o Where F = 1 064N, = 3.72MPa - Compression

The forces acting on the lower control arm members are shown in Figure 8-7 and Figure 8-6. The two

forces present on the arm are:

- 1 917N - Tension

- 1 737N – Compression

The stresses on the lower control arms‟ members are thus:

- AISI 4130:

o Where F = 1 917N, = 27.5MPa - Tension

o Where F = 1 737, = 24.9MPa - Compression

- 6063-T6

o Where F = 1 917N, = 6.6MPa - Tension

o Where F = 1 737N, = 6MPa - Compression

Thus, the stresses induced on the members are very small, and the factors of safety are very high,

about 16 for the steel, and 36 for the aluminium. Thus, based on strength, it does not matter which of

these two materials are used. Therefore, the lighter of the two will be chosen, the steel.

9.4.2 Pushrod Rocker Material Selection

The FEM analysis done of the pushrod rocker shows a stress of about 60MPa under static conditions.

This stress will increase as the car goes over bumps, or hits a pothole. Additionally, the fatigue stress

of the aluminium is 68.9MPa. A factor of safety of four is being employed throughout the design.

Thus, to avoid fatigue failure, or failure due to shock loading, the steel will be chosen.

9.4.3 Suspension Box Structure

The material used for the suspension box is the steel alloy. Once again, the sections are lighter per

meter than the aluminium ones, while offering more than acceptable strength. An internal truss-type

construction will ensure that the structure can withstand the forces imparted on it.

9.5 Conclusion

The material chosen for all the components is AISI 4130 chrome-moly. There are several reasons for

this: The sections are lighter than the aluminium sections currently in use. The steel offers high

strength, affording more than acceptable safety factors. The welder prefers to work with AISI 4130,

thus ensuring high quality workmanship. The new car, Ilanga I-I will use this material for its chassis.

Thus, the material will be ordered in bulk by the University. Therefore, for economic reasons, it

would be beneficial to use this material for the present design. So for the reasons of strength, weight,

economics and time, it will be beneficial to use the AISI 4130.

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10. Manufacturing Process

Manufacturing of the components consists of two parts, the first is cutting of the materials (laser

cutting for the sheet metal, and cutting of the tubes) and the second part consists of welding these

parts together. The material chosen for all of the components is AISI 4130. The welder to be used is

Carl Johnson, from Johnson‟s welding. The welder specialises in welding this specific grade of metal,

which was consideration in choosing the steel alloy over the aluminium one. This section will

investigate the parts to be laser cut, the pipes to be cut and the welding to be done. Additionally, off-

the-shelf products are also used in this design, such as the brakes, steering rack and bearings.

Before looking at the manufacturing processes in depth, it would be appropriate to insert an image of

the final design, so the reader has a good idea of what the suspension system looks like.

Figure 10-1 – Final Suspension System

The system consists of the following components:

- Suspension box: This bolts to the rest of the chassis. All other suspension components attach

to the suspension box. It consists of the front and rear plates, and an internal structure of tubes

to bear the loads. The front and rear plates have holes to accommodate the pivot points for the

upper and lower control arms. It has a central cross bar to which the rockers and shock

absorbers mount. The front and rear plates have a series of holes cut out to save on weight;

the pattern of the holes was chosen such as to not compromise the plates‟ load bearing

capabilities.

- Control Arms: The upper and lower control arms attach to the steering swivel arms. The

pushrod comes up from the lower control arm towards the rocker. The lower control arm is

subject to more force than the upper one, and it is longer as well. Therefore, it has a

strengthening brace partway along its length.

- Steering Swivels: These members are pivoted by ball joints at the top and bottom, to allow

them to steer, and to allow range of motion in the vertical direction. The brake callipers

mount to the steering swivels. Therefore, they should be strong enough to withstand the

torque imparted on them under braking. They also support the load from the axels.

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10.1 Laser Cutting

Most of the parts used in the design, such as the steering swivel arms, brackets and mounts are all flat

plates welded together. These plates are best cut using a computer controlled laser cutter, to ensure

high accuracy and precision. The parts were designed in such a way that they fit together like a three

dimensional puzzle. Thus, the part, the steering swivel, for example, can be assembled, and held

together by masking tape. This reduces the workload for the welder. He would simply have to tack

weld the assembled part, remove the tape and continue with full length welds.

All of the plates to be laser cut, where ever possible, had holes cut out to reduce the weight. The holes

were cut in a specific pattern such that portions of the part which did not carry a high load would be

cut away.

(b)

Figure 8-10 demonstrates this. FEM analysis was done on these components to ensure their safety.

Figure 10-2 below shows the steering swivel; here you can see the holes to reduce weight.

Figure 10-2 – CAD Model of the Steering Swivel

Sheets of the appropriate thickness AISI 4130 were ordered. The flat plates were arranged using Creo

(another design package) to fit on these sheets, with minimal wastage. These layups have been added

as an appendix. These parts were all designed using SolidWorks. Once designed, they can be saved in

a certain file format, which the laser cutting machine can read. Thus, intricate shapes can be cut, and

working drawings for these parts are not strictly necessary. Nevertheless for the sake of completeness

working drawings of the assembled components are given.

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10.2 Welding

As mentioned, the plates to be welded can be pre-assembled and then given to the welder. The tubes

to be welded are also fairly straight forward. Alignment jigs were designed and built. These jigs serve

to position the tubes correctly, so the welder can simply weld them.

Figure 10-3 – Lower control Arm Alignment Jig

Figure 10-3 shows one of these jigs. A jig was made for the upper and lower control arms, as well as a

structural section of the suspension box itself.

The suspension box itself is also fairly easy to weld. The plates which were laser cut (such as the

control arm pivot brackets) all have a flat surface, which can be made level using a spirit level.

Figure 10-4 – Lower Control Arm Pivot Bracket

These flat surfaces can be

measured and made level using a

spirit level.

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All welds are to be 3mm filet welds. Since the material is inherently corrosion resistant, it will not

need to be painted. Painting also adds weight, which is undesirable. All of the components are easy to

manufacture, with the possible exception of some of the internal suspension box members. These will

have to be cut to a specific profile in order to fit. Apart from that, this will be an easy project for an

experienced artisan.

10.3 Standard Parts

The standard parts in the design consist of the wheels, tyres, braking system, nuts and bolts, bearings,

tie rod ends and shock absorbers. The standard parts list follows:

Table 10-1 – Selection of Standard Parts

Part Name Supplier Quantity

CBR125RW8 2008 Graphite Black Honda 2

CBR125W8 Brake Master Cylinder (including braking lines) Honda 2

CBR125W8 Brake Caliper Honda 2

DT Swiss M210 Shock Absorber DT Swiss 2

IKO POS 12A[5] Tie rod ends IKO 8

Hex Bolt, M12 × 50 long UJ 20

Hex Bolt, M10 × 50 long UJ 20

Hex Bolt, M12 × 30 long UJ 20

Hex Nut, M14 UJ 10

Hex Nut, M12 UJ 20

Hex Nylock Nuts, M12 UJ 20

Hex Nut, M10 UJ 20

Washers, M14 UJ 80

Washers, M12 UJ 120

Washers, M10 UJ 80

Steering Rack (unknown make and model) 1

10.4 Manufacturing

Some images of the components in various stages of production will now be shown.

Figure 10-5 – Rocker Arm, Right and Left Steering Swivels, taped up, ready to be sent to the welder

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Figure 10-5 shows the parts which returned from the laser cutters, General Profiling. The plates were

assembled and taped together, ready to be sent to the welder. At the time these pictures were taken,

certain plates had not yet arrived, which delayed production of these parts by a few days.

Figure 10-6 – Pushrod Rockers and brackets after being welded

Figure 10-7 – Steering Swivel after being welded

10.5 Assembly

Assembly of the components is arguably the easiest phase of the project. The suspension box will be

attached to the chassis by means of seven bolts. The suspension control arms will be attached

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(pivoted) by two bolts, with a bush. The steering swivel arms, suspension pushrods and steering arms

will all have tie rod ends screwed into inserts (designed by another team member). The steering rack

will be held on by four bolts, and it will be attached to the steering column by means of a universal

joint.

Figure 10-8 – Steering Swivel and Brake Calliper with the wheel attached

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Figure 10-9 – Full Assembly before being bolted onto the Chassis

Figure 10-10 – Full Assembly Bolted onto the Chassis

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Figure 10-11 – Front Right Corner of the Car, Fully Assembled and Operational

Figure 10-12 – Ilanga I-I, with the updated suspension, and members of UJ Solar, ready to participate in the Solar

Challenge

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11. Maintenance

Maintenance of the system should be fairly straightforward. The South African Solar Challenge is a

long race however, so although it may be straightforward, it should not be overlooked. Several

components should be inspected on a regular basis (each evening after the day‟s running during the

race), and cleaning and/or replacing necessary components should take place. This includes the

bearings, bushes, brake lines and shock absorbers. This section will take a brief look at each of these

components.

11.1 Wheels – Bearings and Brakes

The wheels, the Honda CBR125 front wheels are purchased with bearings already seated. These have

dust seals, and so should be fairly robust. These bearings would be difficult to inspect directly; one

would have to remove the wheel and brake assembly. Thus, the check would be simply raising the

front end of the car, and spinning the wheel. It is easy to hear and see if the wheel is binding; it will

slow down far sooner than a wheel which is not binding. If the bearings do not seem to be turning

freely, it would be best to remove the wheel and replace the bearings. This is a simple task with the

CBR125‟s wheels; the bearings are held in place with a circlip. As previously stated, sealed bearings

should be used as they are more resilient to dirt than non-sealed bearings.

It is also important to check that the front wheel it not binding due to the brakes. Even when the

brakes are not applied, it is difficult to get rid of all interaction between the brake disc and pad. Some

subtle interaction between them is acceptable, but it should be reduced as much as possible. If there is

a lot of binding, them the calliper should be removed from the mount, and reattached using some

washers as spacers, where applicable. Another alternative is to reposition the wheel on the axel, using

washers as spacers.

11.2 Bushes

As with bearings, bushes are meant to reduce rotational friction and support loads. The bushes used in

the present design are used to support the control arms and the pushrod rocker. The bushes must also

be kept clean, although this is not as big a concern as with the bearings in the wheels. The main

concern with the bushes is that they might deform due to a load in a particular direction. The material

used for the bushes is vesconite, for the control arms, and aluminium, for the pushrod rocker. Should

these bushes become deformed, the easiest solution would be to replace them. Thus, at least three

spares of each bush should be manufactured.

11.3 Brake Lines

While inspecting the car, it would harm nothing to check the brake lines. Part of the brake lines would

likely be in the open, exposed to possible rocks, glass, etc. Although the brake lines are made from a

very tough material, The Team should check for leaks, and test the brakes to ensure they are in

working order.

Another point to note is that the brakes should be bled once they have been installed, or any work

happens to the brakes/brake lines. In order to bleed the brakes, the following procedure should be

followed:

a. Locate the bleeding nipple on the brake calliper, find out what sort of brake fluid is used and

locate the master cylinder. Pour some clean brake fluid into a bottle, and have a pipe (some

fish tank pipe) running from the bleeding nipple into the bottle. Ensure that the end of the

pipe is submerged in the brake fluid. This prevents air from being sucked back into the brake

system.

b. Top up the master cylinder with brake fluid. Have an assistant pump the brakes, until they

feel firm.

c. Once the brakes feel firm, open the bleeding nipple with a spanner. The brakes will feel soft

once again, as brakes fluid – and some air bubbles – leave the calliper, and enter the bottle.

Page | 74

d. Top up the master cylinder. Do not let the master cylinder run too, otherwise, air will enter

the system, and the process would have to be restarted.

e. Repeat steps b. to d. until no more air come out of the system. Repeat for the other wheels.

11.4 Shock Absorbers

The DT Swiss Shocks are air filled. If they operate under a certain loading condition, they should be

filled to a certain air pressure. These specifications can be found in the data sheet which accompanies

the shock absorbers. It would be well to check the pressure before setting out on a day‟s run, to guard

against failure of the shock absorber during the race. These pieces of equipment are expensive

(approximately £584.99 or R7 585 each); The Team cannot afford to damage one of them.

11.5 Tie Rod Ends

Servicing tie rod end may be a bigger job than is first appears. Depending on its function within the

design, other components would have to be disassembled first in order to get to the tie rod end. The

IKO tie rod ends have to be serviced occasionally. This is done by using a grease gun to inject grease

into the brass bush through the grease nipple. The Team may have found another supplier, who

provides service free tie rod ends. Either way, the tie rod ends are not subjected to high rotational

velocities, and should be robust.

11.6 Conclusion

The system was designed to be low maintenance from the start. The concepts selected were the one

which presented the lowest possibility of the adverse effects of dirt and grime. The scale of

maintenance can required can only be assessed in earnest, once the system is operational. The

information provided in this section serves as a guideline; recommending the best solutions to

possible problems that may arise. If the system is used sensibly, there should be no problems in terms

of maintenance.

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12. Conclusion

This Report detailed the process of designing and manufacturing the updated front suspension of the

UJ Solar Car, Ilanga I. The task started out by identifying the need which was to be fulfilled. The need

was to optimise the front suspension of Ilanga I, such that it would be able to cope with the rigors of

the South African Solar Challenge. The operating environment was identified; the environment

consists of desert, coast lines, potholed roads and dirt. The system has to cope with all of these

conditions.

The mission analysis was conducted. The Team has an obligation towards the sponsors and technical

obligations in order to participate in the race. The obligations towards the sponsors include upholding

their good reputation, and displaying their logos at all public events. The technical obligations

consisted of safety concerns, by and large, as well as practical aspects, such as, ensuring the car can

make a full U-turn in 16 meters.

A study of the available literature concerning suspension designs was conducted. This gave a valuable

insight into all of the technicalities of designing suspensions. The importance of properly designed

suspension geometry was discovered. The literature study also helped in formulating the product

design specification. It also ensured that seemingly obscure concepts were kept in mind while the

design was undertaken.

The product design specifications were established. All the technical aspects of the design had to

conform to the specifications set out in Section 5. The main concern was safety, and the second one

was weight. The steering axis inclination was set to 10 degrees and the camber and toe were set to 1

degree negative and toe in, respectively. These angles, as well as the geometry of the control arms,

were calculated so, such that the car would be safe to drive. The current geometry ensures the car is

still controllable after a tyre blowout, while still affording the driver good feedback, and cornering

ability.

Selection criteria were formulated in order to compare concepts against one another. Two sets of

criteria were established. One to determine what type of design should be used for the control arms,

and what type of design should be used for the steering swivels. With this being completed, the design

concepts were considered.

Two concepts were generated for the steering swivels, and four were generated for the control arms.

After conducting the pair-wise comparison, the concepts selected were the conventional steering

swivel arm, and the double wishbone suspension, with a pushrod. These were selected based on the

selection criteria, as well as the practical aspects of implementing the designs within the constraints

set out in Section 7.1.

Performance simulations were run to develop and optimise the design. The design process was an

iterative one. A certain parameter for a particular component was selected, and that component‟s

behaviour was evaluated, with respect to the rest of the design. The parameter was changed and re-

evaluated. This process was follow when design the suspension geometry, the steering geometry, the

shape of the steering swivels and the shapes of the upper and lower control arms.

The performance simulations gave the first representative indication of the loads and forces acting on

the system. With this in mind, the materials were selected. The choice of materials was limited, based

on available resources. AISI 4130, chrome-moly was selected to construct the suspension.

The manufacturing and maintenance of the system used up the most time, but they were the easier

aspects of this project. The manufacturing section of the Report contained many pictures of the

various components as they had been laser cut, welded and assembled. All of the components fit

together very intuitively; the manufacturing aspect was simply. The maintenance aspect is equally

simple. One should merely inspect the design regularly (every night after a the day‟s race), to check

for leaks in the break lines, air leaks in the tyres, and ensure the shock absorbers are still functioning.

Page | 76

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Appendix A – Minutes of The Team Meetings

This Appendix will include the minutes of The Team meetings. In these meetings, the performance

and characteristics of every component was discussed. This includes the electrical and mechanical

design considerations.

Page | 79

UJ Solar Team Meeting

2 March 2012 – Minutes

1. Add project description on Trello for Ilanga 1 students. To be done before Monday.

2. Electricals to submit project proposal to Electrical Master‟s.

3. Revise the generalised time table.

4. Group members are to define the auxiliary roles, i.e. finances, logistics, etc.

5. Find a suitable time for smaller team meetings, for undergrads

6. Find a good venue for smaller team meetings, perhaps the engineering corridor.

7. UJ Solar Society E-Mail address to be set up.

8. Speak with faculty heads in connection with UJ Solar Society.

9. Events to promote the UJ Solar Society. Perhaps coupled with the launch of the Prospective

Engineer‟s Student Council.

10. Each person to post something about the car each week via Facebook or Twitter, or other

social media.

11. The Solar Team should make an effort to attend some of UJ‟s events, like the Varsity

Cup.

12. Undergrads to determine deadlines and project plan for Ilanga 1.

13. Go to www.ganttchart.org if you do not have access to Microsoft project.

14. Note that Creo is available from the Master‟s. They will be able to enable the product

keys such that we can use Creo off campus.

15. Altium will likely be available. They want more exposure from UJ Solar first.

16. TomTom meeting on Wednesday, 7 March, 2-3PM. Be there if you‟re available. Confirm

Venue with Mrs Janse van Rensburg

17. E-Mail address for UJ Solar Team team@ujsolar.ac.za

18. JP has some role in sponsorship, TBC.

19. Group Dynamics course, Saturday, 10 March 2012.

20. Results of personality profile to be sent to njvr@uj.ac.za

21. For more info on the solar car project, go to www.ujsolar.ac.za

22. Ilanga 1 is in the Challenge Class, in the FIA regulations.

23. See FIA regulations, and consult with Master‟s if in any doubt.

24. Speak to Winston? Regarding regulations.

25. Warrick to speak to Master‟s regarding locking mechanism.

26. Use Mendeley as a PDF database.

27. Create drop box for undergrad group.

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Solar car meeting

9 March minutes

Recommended that the electrical undergrads upload their first section of their design reports

Ilanga I to be running on 16 March, 16H00

Concerning the meetings, there is no need to work together as this is unproductive. Just meet

and catch everyone up.

Leave about three months for manufacturing for mechanicals

Electricals to use Altium when it becomes available

Theran is responsible for understanding and being familiar with the electrical regulations

Jules is responsible for understanding and being familiar with the mechanical regulations

See F1 dictionary – Mechanicals

Updates up to 9 March

Vincent – Has been doing research

Jules – Modelled mock up suspension geometry. Needs steering rack dimensions

Rob – Looked at different collapsible steering shafts, shear pin seems to be the

desired option.

Bafana – Chapter 1 of report. Consider off the shelf products for his particular

product

Geoff – Chapter 1. Rese4arch battery management and chip programming

Theran – Chapter 1. Research into different lights, such as Audi LED lights, etc.

Warrick – Literature Review

Palesa – Literature Review. Must look at fibre glass encapsulation, EVA, Solaris

Charles – Wanted to use KERS (Kinetic Energy Recovery System – Regenerative

Braking), although car already has it. Look at mounting points for brake callipers, and

design new pedal box

JP – Concept has been generated. Has done CAD drawings

Ishmael – Must revise chapter 1.

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Solar car meeting

16 March minutes

Rear wheel for Ilanga I will now be a HUB motor. JPO should adjust his design

Electricals take note, the battery will be changed from 48V-96V bus. This has a particular

effect5 on Bafana‟s work

The solar panels need to be rewired to output 60V.

Undergrads to post a paragraph on how far they are, and what they still need to do and

possible time lines as well.

The above should be posted on Trello.

Undergrads to set 3 hours aside each week to work on Ilanga i.

Work Updates – Not much was done as everyone had tests/assignments to complete

Palesa – Read through Warren‟s report on encapsulation, and Solaris.

Ishmael – Must speak to David to gain clarity on what exactly needs to be done.

Geoff – Will find schematics on motor controllers

Rob – Has plans laid out. Waiting for the 23rd

of March to disassemble the steering

rack to draw it up.

Theran – Reviewed concepts for LED‟s and looked at the required specs for the

lighting system.

Charles – Sifting through GrabCAD files.

Vincent – Will learn how to use/optimise/program the current motor controller from

Hayden.

Jules – Drawn the new nose. Plans are laid out for the suspension. Waiting for the

23rd

of March to disassemble the steering rack to draw it up.

Ilanga I – Bodywork has been bolted to the chassis. The CVT was repaired and

placed back on the car. The car can now run.

Look at DropBox for the HUB motor drawings.

1st June, likely to be a seminar where the undergrads must present their section of work on the

car.

If you want to add anything to drop box, search for Jules de Ponte. I believe most of the

undergrads have joined DropBox.

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Friday, 30th of March

Solar Challenge Meeting – Minutes

Discussions:

1. Undergrad Concept presentation

2. Sponsorship update from the study-leaders and masters students

3. Budget update

Tasks:

4. NB! Undergrads need to generate an updated and detailed project plan in MSP(micro-soft

planner)

5. Undergrads need to check if they are available for the race in September ie. No tests,

major hand-ins or unmissable classes during those two weeks

6. Undergrads need to form a clear picture of optimizing

define Optimizing i.t.o:

◦ how

◦ what

◦ when

7. Undergrads need to attend a Company meeting/information session. It will most likely be on

a Saturday. Further details will be given in the near future.

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20 April Minutes

1. Mechanical‟s to E-Mail Jules the Project Plan

2. 17 July is the date for the next mechanical‟s submission

3. 2May is the date for t eh next electrical‟s submission

4. Presentation of the Solar car project is on the 1st of June

5. Ilanga 1.1 is going to be competing in the challenge class

6. Epsilon Engineering is going to do the moulding of the bodywork for Ilanga 1.1. Warrick‟s

design will change as a result of the changed bodywork

7. Ilanga I will race in the SASC 2012. It will be used as a promotional vehicle, training vehicle,

etc.

8. Each driver needs 10 hours of experience in the car to race for the SASC 2012. Thus, the car

will be run on weekends.

9. The undergrads need to find out if they can race. Therefore, they must e-mail Mrs J. van

Rensburg their timetables for next semester.

10. Ilanga 1.1 needs 22-24% efficiency cells. Battery packs have been organised.

11. Undergrads must find out when exams start.

12. Monday, 23 April, the other two heel fairings are to be made.

13. Work that still needs to be completed on Ilanga I:

a. Windscreen – Epsilon Engineering will likely be able to do this.

b. Front Suspension – See Jules‟ Progress report.

c. Method of attaching the nose must be devised.

d. Back wheel faring mould must be delivered. JP must see to this.

e. Lights for Ilanga I and Ilanga 1.1 must be finalised. See Therean‟s Progress report.

f. Steering – See Rob‟s progress report.

g. Swing Arm – See JP‟s Progress report.

h. Locking mechanism – See Warrick‟s progress report.

i. Brakes.

14. For the team meetings, the undergrads are to have PowerPoint Presentations to display

progress reports.

15. UJ Solar Society will have a big launch. Geoff is in charge of marketing.

16. Use Google calendar instead of Trello

Page | 84

25 May Minutes

1. 29/05 Eskom Presentation

2. 30/05 Marketing Day

3. Gauteng Motor Show on 2 and 3 June at Zwartkops.

4. Electrical‟s must work on the encapsulation.

5. Undergrads to send weekly e-mails to masters, especially electrical‟s.

6. Ron to find out about heat treatment and gear cutting.

7. JP to find pipe benders.

8. Based on project plans, the completion dates are 21 august for mechanicals and 11 July for

Electricals.

Absentees:

Charles

Page | 85

Appendix B – Performance Simulation Spread Sheets

This Appendix presents the spread sheets used to conduct the performance simulations of Section 8.

Suspension Travel vs. Change in Track Length

Suspension Travel [mm]

Track Length Change [mm]

-20 -4.092

-18 -3.641

-16 -3.2

-14 -2.768

-12 -2.345

-10 -1.931

-8 -1.527

-6 -1.131

-4 -0.745

-2 -0.368

0 0

2 0.359

4 0.709

6 1.05

8 1.382

10 1.705

12 2.019

14 2.323

16 2.619

18 2.906

20 3.184

22 3.453

24 3.713

26 3.964

28 4.206

30 4.439

32 4.664

34 4.879

36 5.085

38 5.283

40 5.471

42 5.651

44 5.822

46 5.984

48 6.137

Page | 86

50 6.281

Steering Input vs. Camber Change

Steering Input

[degrees] Camber

[degrees]

18.86 91.2

16.63 90.95

14.38 90.75

12.21 90.52

10.87 90.38

6.27 89.84

-1 89

-3.26 88.56

-7.66 87.87

-9.95 87.48

-14.04 86.71

-17.83 85.99

Page | 87

Appendix C – Finite Element Analysis

Page | 88

Appendix D – Drawings Register

Page | 89

Number Description Drawing Number

1 FRONT SUSPENSION OIP4000-A000

2 SUSPENSION BOX ASSEMBLY OIP4000-100

3 SUSPENSION BOX AISI 4130 OIP4000-101

4 LONGITUDINAL MEMBERS OIP4000-001

5 SQAURE CROSS BAR OIP4000-002

6 CROSS TIE 1 OIP4000-003

7 INNER V OIP4000-004

8 OUTER V OIP4000-005

9 CROSS TIE 2-3 OIP4000-006

10 LOWER TENSION MEMBER OIP4000-200

11 LOWER COMPRESSION MEMBER OIP4000-201

12 CONTROL ARM TIE ROD END OIP4000-202

13 UPPER TENSION MEMBER OIP4000-203

14 UPPER COMPRESSION MEMBER OIP4000-204

15 CONTROL ARM PIVOT OIP4000-205

16 LOWER A-ARM OIP4000-206

17 UPPER A-ARM OIP4000-207

18 LEFT LOWER CONTROL ARM OIP4000-208

19 RIGHT LOWER CONTROL ARM OIP4000-209

20 CONTROL ARM BUSH OIP4000-210

21 STEERING SWIVEL RIGHT OIP4000-300

22 STEERING SWIVEL LEFT OIP4000-301

23 TOP OIP4000-302

24 BOTTOM OIP4000-303

25 BACK 1 OIP4000-304

26 LEVER ARM TOP OIP4000-308

27 LEVER ARM BOTTOM OIP4000-309

28 LEVER ARM SIDE OIP4000-314

29 STEERING TIE ROD END OIP4000-315

30 AXEL OIP4000-316

31 ROCKER ASSEMBLY OIP4000-A400

32 PUSHROD OIP4000-400

33 ROCKER BUSH OIP4000-401

34 SHOCK SHIM OIP4000-402

35 ROCKER PLATE OIP4000-403

36 404 ROCKER SIDES OIP4000-404

37 PUSHROD MOUNT OIP4000-405

38 PUSHROD BRAKCET OIP4000-406