final presentation v final

1Dartmouth Formula Racing 1

Dartmouth Formula RacingDrivetrain and Driver InterfaceGroup 11: Samuel Axelrod, Joshua Bary, Zachary Currier, Ermira Murati


Background Information

FSAE Student Design

Formula Hybrid

Background

Formula Hybrid CompetitionPresentation 100

Design 200Acceleration 150

Autocross 150Endurance 400

201174

185DNFDNF123

2012 Goal

WIN

201085

18211877

105

200991

192124DNFDNF

200810012715095

110

200799

200DNFDNF108


Introduction

FALL TERM FOCUS

• Understanding the Car

• Designing Systems

• Fabricating components

WINTER TERM FOCUS

• Installation, Implementation, Assembly

• Rules Compliance

• Driving, Testing, Troubleshooting


The 2011 Dartmouth Formula Hybrid racecar does not possess a reliable or

robust mechanical system that interfaces well with the driver

Problem Statement


DFR needs to win the 2012 Formula Hybrid Competition.

Our group needs to design a functional drivetrain and integrate all mechanical systems by January to allow for optimization, so that the team can complete all events at competition.

Need Statement


Deliverables

Primary Deliverables:

1. Implement a mechanism to start the racecar every time

2. Design a system that can shift consistently

3. Redesign the drivetrain to eliminate complexity and allow for improved alignment

4. Work with the Electrical Powerplant and Data Management groups to install and test their systems on the racecar


Design Overview - Design Objectives

Simplicity — Time is our scarcest resource

Reliability — Failure rate must be very near zero

Durability — We plan for extensive testing and driving

Modularity — They will thank us next year

Transparency — Feedback critical for testing


CostThe DFR budget is not unlimited, and our combined activities and purchases (including other 89/90 groups and DFR team projects) cannot exceed the collected funds of $8,000.

SizeThe overall size of the frame has been finalized, so every component must be designed to a specific size that will fit well in the assembly.

Rules ComplianceWe cannot race if we break any of the Formula Hybrid rules.

SafetyAs aspiring engineers, rules of ethical conduct require us to put the safety of all individuals above any other considerations.

Design Overview - Constraints


• True dynamic loads are hard to predict

• All power is transmitted through the chain

• First part to fail should be the easiest to replace

• Design components so the chain is first to fail

Design Overview - Failure Strategy


Previous design and reasons:‒ Fuel-injected internal combustion engine‒ Easy engine mapping and tune-ability ‒ No cutting out through corners‒ Problem: depended on high-voltage to start

Needed to design a mechanism to start the engine:‒Honda CRF250X with built-in electric starter‒Start with high voltage system‒External starter motor on the CRF 250R‒Mechanical linkage

Engine/Starter - Overview

http://twostrokemotocross.com/wp-content/uploads/2009/12/Keihin_PWK.jpg


Engine/Starter - Specifications

Specification Justification Quantification Baseline Target

Cost DFR has a limited budget and numerous systems that must be improved

Price ($) <$1000 <$500

Weight A lighter car will perform better, all else equal

Pounds 10% increase from 2011

0% increase from 2011

Reliability The car must start every time, immediately. We cannot race if our car does not start.

Number of times engine starts out of 20

Starts 75% of the time


Durability Our starter mechanism must be durable enough to handle testing and competition. We do not want to worry whether our starter could fail

Number of broken parts during spring testing

No failures during testing


Size The starter must be small enough to leave room for the other systems on the car

Volume 10% increase from 2011



Engine/Starter - Decision Matrix

Starter

Specification WeightHigh

VoltageStarter Motor

Internal Starter

Mechanical Linkage

Cost 0.00% 1 0 1 0

Weight 15.00% 1 0 1 0

Reliability 37.50% -1 1 1 0

Durability 25.00% -1 1 1 1

Size 22.50% 1 -1 1 0

-0.25 0.4 1 0.25


• Design mounts and mount the engine

• Alter wiring harness to match the 2005 CRF250X

• Make and run new cooling hoses

• Design and fabricate new angled air filter

Engine - Methodology, Work Accomplished


Engine - Finite Element Analysis

Factors of Safety: Front 4.5; Middle 1.1; Rear 1.9


• Testing engine on the bench mounted in the car

• Drove the car on several track days

– Racecar started quickly both hot and cold

Engine/Starter - Testing


Engine/Starter - Specifications

Specification Quantification Baseline Target Actual

Cost Price ($) <$1000 <$500 ~$300

Weight Pounds 10% increase from 2011


<5% increase

Reliability Number of times engine starts out of 20



Starts >95% of the time

Durability Number of broken parts during spring testing




Size Volume 10% increase from 2011


0% increase


Shifter Overview

• 2011 team designed a pneumatic paddle-shifting system

• Clutch-less upshifts and downshifts using spark cut

• Tested only on the dynamometer

• Mounted on the car with universal joints, in a different location than designed

• Shifted inconsistently

• Could not find neutral


Shifter - Specifications



Price ($) < $1000 <$500


Pounds 5lbs more than last year

No weight increase over last year

Reliability The driver will be required to shift numerous times per lap and must be able to depend on the shifter working when actuated. The shifter must be able to shift up, down and find neutral without missing shifts

Consistency of shifting and finding neutral

Shifts 98%, finds neutral 50%


Durability The shifter should last through testing and competition without failing





Shifter - Specifications (Continued)


Size The car has limited space. A new shifting system should not take up more space that the current pneumatic system

Volume Same size as last year

10% smaller than last year

Power Requirement

The shifter may require power to function. If so, it must be a low enough requirement so that the power does not run out during the endurance race

Power draw (W) 36W (last year’s system)

No increase in power draw

Speed The system must quickly execute shifts to improve acceleration and decrease lap times

Time per shift 0.2 seconds 0.1 seconds


Shifter - Decision Matrix

Shifter

Specification WeightElectric

SolenoidPneumatic (existing

system) Mechanical

Cost 3.57% -1 0 0

Weight 4.76% 1 0 0

Reliability 26.19% 0 0 0

Durability 17.86% 0 1 1

Size 10.71% 1 0 -1

Power Requirement 16.67% -1 -1 1

Speed 20.24% 1 1 -1

0.1547 0.2143 0.0358


Shifter - Design Overview

• Last year – open-loop pneumatic system

• Adjustments:– How long air flows into cylinder– Pressure in tank– Pressure at regulator

Schematic of last year’s shifting system

CompressorPressure Switch

Air tank

Paddles Solenoids Cylinder

Regulator

VCU


Shifter - Design Overview

• This year – closed-loop pneumatic system

• Adjustments:– How far cylinder travels– Pressure in tank– Pressure at regulator

Schematic of new shifting system

CompressorPressure Switch

Air tank

Paddles Solenoids Cylinder

Regulator

VCU


Shifter - Methodology, Work Accomplished

• Cylinder Sizing– Measured force and distance required to shift– Purchased Bimba Position-Feedback cylinder

• Power consumption– Air compressor draws 20A at 12V so 240W if

running continuously– Rated for 15% duty cycle – 36W on average– 14Ah battery – will last at least 0.7 hours (longer

than endurance race)

• Mounting– Solid mount to secure the cylinder position– Eliminates lateral motion


Shifter - Methodology, Work Accomplished

• Shifter control– Moved from Arduino to Vehicle Control Unit (VCU)– VCU already weatherproofed– Eliminated the problem of wires falling out

• Spark cut– Program to cut engine spark for time of cylinder travel– Removes all load on transmission to ensure

consistent shifting– VCU triggers a relay to ground the kill input on the

ignition control module– Will trigger as soon as a paddle is pressed


• Bench test– Ran through the gears in sets of 20– Listened for shift and monitored

wheel speed

• Track day tests– Shifting without spark cut – Shifting with spark cut

• Neutral– Found neutral on bench at least

50% of the time

Shifter - Testing



Cost Price ($) < $1000 <$500 $350

Weight Pounds 5lbs more than last year

No weight increase over last year

No increase

Reliability Consistency of shifting and finding neutral



100% bench, >95% outside




No failures

Size Volume Same size as last year

10% smaller than last year

Same as last year

Power Requirement

Power draw (W) 36W (last year’s system)

No increase in power draw

Same as last year

Speed Time per shift 0.2 seconds 0.1 seconds 0.1 – 0.4 secs

Shifter - Specifications


Drivetrain - Overview

Last year’s rear drive configuration

• Last year’s configuration was designed to allow the electric motor to start the internal combustion engine

• Incorporated a “launch clutch” to disengage the electric motor and engine from the wheels

• Chain between engine and motor and belt from motor to differential

• Misaligned and difficult to adjust

Clutch


Drivetrain - Specifications



Price ($) <$1000 <$500


Pounds No increase in weight

10% decrease over 2011

Reliability Must be able to operate consistently. The system should not lose alignment or constantly require adjustment

Service time required between track days (hours)

<2 hours <1 hour

Durability Must be able to operate through testing and competition without failure




Size Must leave room for other components that will be installed on the car

Volume No increase in size

10% decrease over 2011


Drivetrain - Decision Matrix

Drivetrain

Specification Weight Current SystemSwitch Belt to

ChainClutch-less

SystemParallel Chains

Cost 0.0% 1 0 0 -1

Weight 8.3% -1 -1 1 0

Reliability 21.4% -1 0 0 0

Durability 13.1% -1 0 0 0

Size 11.7% -1 -1 1 0

-1 -0.35 0.35 0


Drivetrain - Alternatives

1. Hybrid Type – Series or Parallel2. Belt or Chain3. Drivetrain Component Geometry

Engine

Electric Motor

Transmission

Differential / Wheels

Chain

Engine

Electric Motor

Transmission


Chain

Chain

Engine

Electric Motor

Transmission


Chain

One Chain Two Parallel Chains Two Chains in Series


Chain Tensioning

Adjustable motor and differential


Drivetrain - Motor Shaft

Electric Motor Assembly Motor Shaft

• Splined Shaft - Elegant design- Interchangeable sprockets- Extra expense and machining

time

• Shaft with welded sprockets- Simple- Machinable

Alternatives


Drivetrain - Chain Guards

• 0.125” x 2½” Stock• Combine to cover both chains entirely• Mount to frame and rear engine mount


Drivetrain - FEA Analysis

Electric Motor Shaft


• Analyzed the welds between the motor shaft and the sprockets

• Static Analysis– Factor of Safety = 1

• Fatigue Analysis– Welds fail due to large bending stresses created by the maximum tension

force of the chain of 7000lbf

– Calculations demonstrate that no possible weld size, weld material, or shaft material will fix this problem

• Future Plan– Conduct a three-point bending stress test to determine at what bending

stress the weld will fail

– Investigate the problem further and fabricate two to three motor shafts with welded sprockets as reserves

Weld Analysis


Bearing Mount



Motor Mount



Drivetrain - Differential

• Taylor Race Engineering - 4:1 Automatic Torque Biasing (ATB) Differential

• One wheel can have up to 4X the torque of the other wheel

• Output Range of 220 hp

• 17 lbs including the differential housing and oil

Current Differential


Drivetrain - Specifications Evaluation


Cost Price ($) <$1000 <$500 $478.32

Weight Pounds No increase in weight 10% decrease over 2011

No increase in weight

Reliability Service time required between track days (hours)

<2 hours <1 hour <15 min





Size Volume No increase in size 10% decrease over 2011

No increase in size


Did we improve over previous designs?

– Easy, lasting chain tensioning– No alignment issues– Less space used overall– No custom parts– February completion

Drivetrain - Overall Evaluation


Subassemblies Price Manufactured Price

Shift Mechanism

$865.50 $479.02

Engine $5,381.15 $2,926.37

Drivetrain $3,427.32 $2,085.32

Total $9,673.97 $5,490.71

Economic Analysis – Market Analysis

• Target Market : Amateur weekend racecar drivers

• SCCA has over 55,000 members that compete in over 2000 events every year

• NASA has more than 10,000 members in 15 chapters nationwide

• Secondary Market: Hybrid industry, FSAE and Formula Hybrid teams, motorcycle and dirt bike enthusiasts

• Followed FSAE rules to price components for 1,000 unit per year production


• Final Drive Ratio– Will choose a final drive ratio after more driving, with a better understanding

of traction and engine performance

• Pedal Package

• Gas Tank– Design will be guided by simplicity, the need to place it above the engine,

and need to install in it a level sensor

• Steering Wheel

• Engine Tuning and Efficiency Testing– Carburetor re-jetting and fuel efficiency testing

• Manuals and Competition Presentations

Future Design Work


Deliverables

1. Installed the CRF250X with an electric starter so that our racecar starts every time

2. Improved the pneumatic system so that we can shift consistently

3. Redesigned the drivetrain to eliminate complexity and allow for improved alignment

4. Worked with the Electrical Powerplant and Data Management groups to install and test their systems on the racecar

Moving Picture


- Professors Douglas Van Citters and John Collier- Douglas Fraser- Jason Downs- Christian Ortiz- Graham Keggi- Review Board Members

Thank you!


Questions?

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