kun shan university mechanical engineering undergraduate...

Kun Shan University

Mechanical Engineering

Undergraduate Program

Detachable bicycle dynamo generator

Student: Tanya Parham (唐雅)

ID: 4000H257

Advisor: PhD. Wang Song Hao

May 2015

Detachable bicycle dynamo generator Kun Shan University

I

ABSTRACT

The law of conservation of energy states that energy cannot be created or destroyed; it can only

change forms or be transferred from one object to another. Today, so many forms of energy are

being used to do drive the everyday activities of human beings. We need energy to drive our cars,

wash our clothes, light up our homes at night, and to cook our food. If this energy that we're

speaking of cannot be created or destroyed, one might wonder, why do we need to pay for it?

This is where the concept of free energy comes in.

Free energy is energy from sources that do not require an input which has to be paid for. A

nuclear power plant would not fit in this category since the steam that drives the turbine

generators needs energy to be produced. The energy needed to turn water into steam has to be

paid for. A windmill, on the other hand, would be considered free energy because the wind(input)

that drives the turbines is free.

Free energy is all around us, from the sun, the wind, the waves, and even from our everyday

activities. We waste a lot of energy doing activities such as walking, running and riding. This is

the reason I have dedicated my project to creating a mechanism that can harness the wasted

energy from the turning motion of a bicycle wheel. Although the energy needed to turn the

bicycle wheel is indirectly paid for (through food that the rider eats), the wasted energy can be

considered free energy.

This project aims to develop a device that can be attached to the rear wheel of a bicycle and

harness the wasted energy produce from the turning motion of the wheel. It will utilize the

concept of Faraday's Law which states that the turning a coil of wire inside a magnet will induce

an electromotive force. This same concept holds true for a magnet spinning inside a coil of wire.


II

ACKNOWLEDGEMENT

Looking back four years ago, I can honestly say that I am not the same person I was when I first

came to Taiwan. I can proudly say that I have grown academically, socially and spiritually due to

the invaluable experience I have gained throughout my studies in this amazing country.

First, I would like to thank ICDF for providing me with this once in a lifetime opportunity to

further my studies in what I enjoy while getting to learn a new culture and language.

To the staff at the Kun Shan University International Office, you all did a fantastic job in

welcoming us to Taiwan and helping us get situated on our arrival. You have been there for me

throughout the past four years helping in whatever way you can to make my stay more

comfortable and enjoyable. Life in Taiwan would be much more difficult without your generous

support. For all this, I say a big thank you.

To my advisor, Dr. Wang Song-Hao, I would like to thank you for your guidance and

encouragement to my classmates and me over the past four years. Thank you also for your

insight and knowledge in helping me to complete this project. Lastly, congratulations on your

retirement, and I wish you all the best in your future endeavors after Kun Shan.

I would like to extend a big thank you and appreciation to all my professors as well. You all have

done an exceptional job in teaching us in a language different from your mother tongue. You

have successfully relayed valuable information to that will help throughout my future career. The

knowledge I have gained from you all has been very useful in helping me complete my final

project.

To my mom and dad, and my entire family who have shown me nothing but love, support and

encouragement; a big thank you. You all made it possible for me to be where I am today.


III

To my friends, classmates and colleagues; thank you for sharing your companionship,

knowledge, and insight. It has been a pleasure meeting and knowing you all and learning about

new cultures and countries.

Lastly, I would like to thank all the Taiwanese people who have made my stay in their country a

little brighter whether it be helping me find the train station, filling out forms, or mailing a

package. You are a very hospitable and friendly nation of people. I have learned a lot from your

way of life and especially your work ethic, which I plan to take home with me.

Sincerely,

Tanya Parham


IV

Table of Contents

Abstract..................................................................................................................................... I

Acknowledgement.................................................................................................................... II

Project Description................................................................................................................... 1

1. Introduction.......................................................................................................................... 2

1.1 Faraday's Laws.............................................................................................................. 2

1.2 Dynamo Generator........................................................................................................ 3

1.3 Processing of ac current................................................................................................. 4

1.4 Gear Mechanism............................................................................................................ 6

1.5 SolidWorks Premium 2012........................................................................................... 9

1.6 Rapid Prototyping......................................................................................................... 10

2. Procedures............................................................................................................................ 11

2.1 Design of Generator Casing.......................................................................................... 11

2.2 Gear Design................................................................................................................... 13

2.3 Dynamo Design............................................................................................................. 16

2.4 Electrical Circuit............................................................................................................ 17

2.5 Rapid Prototyping.......................................................................................................... 18

3. SolidWorks Design............................................................................................................... 19

3.1 Case and Cover.............................................................................................................. 20

3.2 Gear Mechanism............................................................................................................ 22

3.3 Dyanamo........................................................................................................................ 24

3.4 Tapped Holes................................................................................................................. 26

4. SolidWorks Drawings.......................................................................................................... 28

5. SolidWorks Assembly.......................................................................................................... 34

6. Results.................................................................................................................................. 35

7. Discussion............................................................................................................................. 38

8. Conclusion............................................................................................................................ 41

9. References............................................................................................................................ 42


1

PROJECT DESCRIPTION AND

RELEVANCE

In the past, people used bicycles as a means of transportation to get them from point A to point B.

Today, there are so many different styles of bicycles depending on the needs of the riders. Many

people use bicycles for leisure activities such as mountain biking or for riding cross-country.

This project aims at developing a device to harness the wasted mechanical energy from the

turning motion of the wheel of a mountain bicycle. The device will be able to attach and detach

on the rear axle between the wheel and the frame. The driving gear will then be connected to the

spokes of the rear wheel to harness the wasted energy. This gear will connect to an idle gear and

a pinion gear to turn a magnet inside a coil of copper wire. This copper wire will be connected to

an electric circuit, which will convert the ac current induced by the dynamo into usable output

current.

The current produced can be used to charge batteries and small devices such as smart phones,

portable media players and LED lights. This is especially useful for bikers who spend long hours

on the road hiking or doing cross country, etc.

The purpose of this project is to employ the concepts and knowledge that I have gained in my

mechanical engineering studies in order to make something meaningful and practical. These

include Computer Aided Drawing (Solidworks), Rapid Prototyping, Mechanisms and Electricity

and Magnetism.


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1. INTRODUCTION AND BACKGROUND

1.1 Faraday's Law of Electromagnetic Induction

1. Faraday's First Law

Faraday's first Law of Electromagnetic Induction states that any change in the magnetic field

near a conductor (such as a coil of wire) will induce an electromotive force (emf) in the

conductor [1]. This conductor, when connected to a closed electric circuit, will allow an induced

current to flow through it. The emf can be induced by various ways such as:

1.) Moving the magnet towards or away from the coil.

2.) Moving the coil towards or away from the magnet.

3.) Rotating the magnet relative to the coil.

4.) Rotating the coil relative to the magnet.

2. Faraday's Second Law

Faraday's Second Law of Electromagnetic Induction states that the induced emf is equal to the

rate of change of flux linkages. The flux linkage is the product of turns of the coil, N, and the

magnetic flux, Φ, associated with it [2].

dt

dNE

, where BA [3]

B = Magnetic Field Strength

A = Area of coil

E = Induced emf

According to this equation, the induced emf from the generator can be increased by:

1.) Increasing the number of turns in the coil

2.) Increasing magnetic field strength (of the magnet)


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3.) Increasing rate of change by increasing the speed of the motion between the coil and magnet.

1.2 Dynamo Generator

Dynamos are generators that convert mechanical energy into electrical energy using Faraday's

Law of Electromagnetic Induction. Most dynamos use either a magnet spinning inside a coil of

wire or spinning a coil of wire inside a magnetic field.

This spinning motion is usually powered from some source of mechanical energy such as falling

water, wind, oscillation of waves, or steam. The diagram below shows a simple magnet rotating

in a coil arrangement:

Figure 1.1 Simple dynamo generator [4]

The induced emf of this generator can be increased by increasing the rotation speed of the

magnet, increasing the strength of the magnet or increasing the number of turns in the coil of

wire.

There are two main types of generators; DC and AC generators. In theory, the emf induced by

any dynamo (generator) produces an alternating current (ac). This alternation current is not


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useful current and needs to be changed to direct current for practical use. The DC generators use

a commutator to change the current from ac to direct current (dc). This process is called

rectification [6]. A rectifier attached the electrical circuit in ac generators will eventually convert

the induced ac current to dc current for usability.

1.3 Processing of AC current

The AC current produced by the dynamo needs to be processed for several reasons:

1.) Alternating current need to be converted to direct current for it to be usable

2.) Constantly changing voltage need to be regulated to keep output voltage constant

3.) The current need to be smoothed out especially for generators where the rotation is not

constant

1. Bridge Rectifier

A bridge rectifier is an arrangement of four or more diodes in a bridge circuit configuration

which provides the same output polarity for either input polarity [7]. In other words, a bridge

rectifier is used to convert ac current to dc current using an arrangement of diodes. The following

diagram shows a four diode bridge rectifier and how it is connected to the circuit:

Figure 1.2 A bridge rectifier

Alternating current from the dynamo is arbitrarily connected to the ac input in the picture and the

diodes converts this to a direct current output as shown.


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There are many types of bridge rectifiers depending on the average rectified current and the

induced voltage.

2. Voltage Regulators

A voltage regulator is a device used to turn incoming changing voltage into a steady output

voltage. The wheel of a bicycle does not turn at a constant rate and will slow down or speed up at

a very fast pace causing spikes in the induced voltage or causing the voltage to drop too low. The

voltage regulator helps to keep the output voltage constant regardless of the induced voltage

produced by the generator. This also helps to protect the circuit especially when there is a high

induced voltage.

3. Capacitors

A capacitor is a device used in an electrical circuit that charges when powered up and discharges

when power is turned off. Capacitors are used in circuits for many reasons such as:

1.) Storing energy: An example of this is in a camera. A large amount of electricity is needed for

the flash and cannot be provided by the circuit alone. The flash needs a large charge of electricity

for it to work. Another example is in to prevent our computers from suddenly shutting off when

power is disrupted.

2.) Timing circuits: For example flashing LED on and off.

3.) Reducing electrical noise: When there is not a constant flow of voltage, capacitors are placed

together in parallel, called decoupling capacitors, to smooth out the electric current passing

through loads in the circuit. For example, when the power supply requires a change from ac to dc

current, this causes a constantly changing voltage thus, without capacitors, the current will not be

stable [8].

In the case of an ac generator with constantly changing voltage, a decoupling capacitor is needed

to smooth out the induced current. Decoupling capacitors usually consist of a large capacitor

(called the bulk capacitor) and one or more much smaller capacitors, depending on the number of


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loads in the circuit. The bulk capacitor is usually placed near the power supply and the smaller

capacitor is placed in parallel between the bulk capacitor and the first load. After this, another

small capacitor can be placed in parallel between the first and second load, etc.

1.4 Gear Mechanism

Gears are "toothed wheel" that are very useful in mechanical design to increase or decrease

rotation speed and torque and to reverse direction of rotation. There are many types of gears

depending on the outcome that is needed. Many machines we use in our everyday lives such as

vehicles, bicycles, wind-up toys, clocks and watches use gear mechanisms. For the dynamo, the

type of gear that is most suitable is the spur gear. Spur gears are the most common type of gears.

When designed correctly, spur gears can transmit high power transmission efficiency, offer

constant velocity ratio, and they are easy to install [9]. When it comes to the bicycle dynamo, the

velocity ratio of the spur gear mechanism is most important since the primary purpose of the

gears will be to transfer the spinning motion of the wheel to the magnet.

Let us look at the how the spur gears work to transfer rotation speed. For the sake of convenience,

the teeth on the wheels are omitted in the figure below:

Figure 1.3 Two parallel shafts A and B connected at the ends by two spur gears [10]

I figure 1.3 the velocity ratio of the smaller gear to the larger gear is 24:48 which is 1:2. This

means that for every one turn for gear B, gear A will turn twice. Depending if you want to


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increase or decrease rotation speed, the gear that connects to the source of rotation is called the

driver and the gear that receives rotation from the driver is called the driven gear.

1. Gear Meshing

Connecting two gears with the same amount of teeth sounds simple enough; however there are

some specifications needed to design the gears in order for them to mesh and spin properly

without grinding. When designing a gear manually, many specifications need to be taken into

consideration. However, I will design the gears using SolidWorks drawing software. Four main

factors need to considered when designing gears in SolidWorks:

1.) Module: For gears to mesh their modules, m, need to be equal. This indicates the tooth size

and is the number of mm of pitch circle diameter (p.c.d.) per tooth [11]. The gear ISO standard in

SolidWorks is based on this value.

2.) Pitch Circle Diameter: This is the reference diameter, d, of the circumference of the gear

where circles with the same module value will transmit the same velocity ratio by friction [11].

The pitch circle diameter can be calculated using the formula m X N = d. For example a gear

with a module of 2 and 30 teeth will have a pitch diameter of 2 X 30 = 60 mm.

3.) Pressure angle: The pressure angle refers to the angle through which forces are transmitted between

meshing gears [12]. For gears to mesh properly, this value also has to be equal for all the gears. The

pressure angle is usually 20 degrees for most gears.


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Figure 1.4 Diagram of meshed gears [13]

Figure 1.4 shows how to mesh spur gears using the three specifications mentioned above. As

shown in the diagram, the pitch circles are tangent to each other and their pressure angles are

equal.

2. Idler gears

In real life situations, the driver gear might not be close to the driven gear and will require a bit

of help to transfer the mechanical advantage to the final (driven) gear. This is where an "idler

gear" comes in. The idler can be used to transmit power, torque, rotation speed, or simply change

the direction of rotation without disrupting the overall ratio of the gears. For example, a driver

gear of 80 teeth and a driven gear of 20 teeth will have a gear ratio of 1:4. This means that for


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every turn of the driver the driven gear will turn four times. Placing an idler gear of 40 teeth

between the gears will create a ratio of 1:2 driver to idler and 1:2 idler to driven gear. This means

that for every turn of the driver, the idler will spin twice and for every turn of the idler, the driven

gear will spin twice. So, in both cases, a turn ratio of 1:4 will be transmitted.

Figure 1.5 An idler Gear used to keep rotation direction constant between two gears [12]

In figure 1.5 the idler gear keeps the direction of rotation constant but doesn't change the gear

ratio.

1.5 SolidWorks Premium 2012

Solidworks is a 3D CAD design software that allows users to design, assemble, analyze, and

even run motion analysis on products, among many other features. It allows users to get a real

life image of how the product will look before making a hard copy. When using SolidWorks, or

any other computer aided drawing software, the drawings can be saved for easy retrieval to make

changes if necessary. This is very useful and saves a lot of time.

In addition to allowing users to make accurate drawings, the program also comes with a large

built in library of tools to make it easier to create standardized tools instead of designing from

scratch.

When design is complete the drawings can be exported from SolidWorks for rapid prototyping.


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1.6 Rapid Prototyping

Rapid prototyping is a technique used to quickly fabricate a model of a part or assembly with the

help of 3D CAD drawing [14]. This is an effective, inexpensive and fast way to take a look at a

product, fix mistakes, and make changes before manufacturing. In some cases, where large scale

manufacturing is not intended, it could also be used to create a finished product. This is usually

in cases where material choice of the product is not an issue; since the material used in rapid

prototyping is usually plastic and not very strong.

The methodology of rapid prototyping is as follows:

1.) The model is created in a 3D CAD software, in this case, SolidWorks Premium 2012.

2.) The model is then exported to STL format and sent to the Rapid Prototyping machine to be

processed.

3.) The machine creates the product in predefined layers, and the model is lowered after every

layer to accommodate the new layer of printing.

4.) After the printing is complete, the finished product is cleaned of residues.


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2.PROCEDURES

2.1 Design of the generator casing

Apart from the electrical components, SolidWorks Premium was used to design all the

mechanical parts of the generator. The dimensions of the casing was made to fit on a 17 inch

frame Giant mountain bicycle. Shown below:

Figure 1.6 Bicycle used to design the dynamo generator

The generator is made to be detachable to the rear axle of the bicycle where the driver gear will

connect to the spokes to be able to turn:

Figure 1.6 The picture shows where the generator will be attached

When designing the case a number of factors were taken into consideration:

1.) Ergonomics - It should be easy to attach to the bicycle and easy to be taken off.


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2.) Size - It should not be too bulky or heavy since this will add to the weight of the bicycle and

cause the rider to have to use more power to peddle the wheel. It should also be big enough to

hold all the components, such as the gears, the dynamo, and the electric circuit.

In addition, all dimensions of the case and all the drawings are to be no less than 1.5 mm to

accommodate for the limitations of the 3D printer.

3.) Aesthetics - The shape of the case should look appealing as well as the color and texture of

the material.

The final shape of the case is shown below:

Figure 1.7 Diagram showing the outer casing of the dynamo generator


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Figure 1.8 Diagram showing how the generator will attach to the wheel and axle (color-

coding for easy distinguishing)

2.2 Gear Design

Due to size constraints, the driver gear could not directly connect to the driven gear without

interference with the dynamo and the case. Therefore, an idler gear was placed in between them

to transfer the rotation.

1. Driver Gear:

All the gears were designed using

SolidWorks ToolBox. The dimensions for

the driver gear are as follows:

Module: 1.75 mm

Number of teeth: 30

Pressure Angle: 20

Face Width: 2mm

The dimensions will ensure that the teeth

are wide enough for 3D printing without

breaking and the number of teeth can

provide a 3:1 gear ratio.


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2. Driven Gear

3. Idler Gear

To ensure a 1:3 ratio, the driven gear was designed

to have 10 teeth. The dimensions are as follows:

Module: 1.75 mm

Number of teeth: 10

Pressure Angle: 20

Face Width: 2 mm

This gear will be connected to the magnet for

rotation inside the coils of copper wire.

For simplicity, the idler gear was assigned 15 teeth

with the following dimensions:

Module: 1.75 mm

Number of teeth: 15

Pressure angle: 20

Face width: 2 mm

The idler gear will be placed between the driver and

driven gear to transfer the mechanical advantage.

For every turn of the driver gear, this gear will turn

twice, and the driven gear will turn three times.


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4. Gear Meshing

In order for the gears to mesh, the pressure angle and the module must be the same for all gears.

The module in this case is 1.75 mm and the pressure angle is 20 degrees.

In addition to this, the reference circle, also known as the pitch circle, of each connecting gear

must be tangent to each other. This diameter of this circle is calculated as follows for each gear:

A. Driver Gear

Reference diameter = Number of teeth X Module = 30 X 1.75 mm = 52.5 mm

B. Idler Gear


C. Driven Gear


Figure 1.9 Meshing of the gear train


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Figure 2.0 Gears designed and assembled together in solidworks.

Figure 2.5 shows the gears meshed in solidworks assembly option. Shafts of 2mm diameter will

be placed inside the holes for the idler and third gears. The third gear will fully supported by the

dynamo cover. The top part of the idler gear axle will be placed in an added support in the case

covering. Likewise, the covering will add top support to the driver gear.

2.3 Dynamo Design

There two main components of the dynamo design:

1.) Coil of wire

For the coil, 0.29 mm diameter copper wire was used since copper has a high conductivity. The

wire was wrapped around each coil core around 200 times. In the actual dynamo, one of the coils

was taken out due to size constraints.

2.) Magnet

Two small magnets big enough to fit inside the third gear axle were fastened unto to the axle.


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Figure 2.1 SolidWorks Design of the Generator Dynamo

Figure 2.6 shows the design of the generator dynamo in SolidWorks. The third gear will be

attached to the axle to spin the magnet inside the coils of wire thus generating an induced emf.

The magnets will be fastened to the third gear axle using electrical tape.

2.4 Electrical Circuit

For the electrical circuit to process the induced ac current from the dynamo, the circuit will need

a Bridge Rectifier, Capacitors and a voltage regulator. The full bridge rectifier is used to change

the dynamo current from ac to dc. Just rectifying the current is not enough, however. We need to

account for voltage spikes, which is where a voltage regulator comes in. The voltage regulator

used has an constant output of 5V. While it is not necessary, adding capacitors in the circuit will

help to smooth out the current and also store current to accommodate for when the bicycle wheel

is turning too slow to produce a large enough voltage.


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Fig. 2.2 Schematic Diagram of electrical circuit

Figure 2.3 Actual circuit on circuit board

2.5 Rapid prototyping

The solidwork design of the parts were all converted to STL format and sent to the 3D printer for

printing. When using a 3D printer for rapid prototyping, one has to keep in mind the output

quality and accuracy of the printer and design the parts according to this. In this project, the

minimum thickness or hole diameter was set to 2mm so that the part will be strong enough and

don't break easily. Also, undercuts were kept to a minimum to lower the time taken to print the

parts and to minimize the amount of material used.


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Figure 2.4 3D printing the dynamo cover

3. SOLIDWORKS DESIGN

The parts in solidworks were designed with three things in mind:

1.) 3D printing: The parts were designed keeping in mind the limitations of 3D printing. 3D

printing method is used mainly for rapid prototyping and not for actual products. This is because

of the manufacturing time and the quality, and material constraints. All the parts were designed

with a minimum of 1.5-2mm thickness for durability. In addition, keeping the design as simple

as possible was very important for easy printing and minimizing undercuts. The fitting and hole

tolerance was set to 0.5 mm.

2.) Space saving: One of the aims of the design was for it to be effective with the smallest

dimensions possible. This is to prevent a bulky and heavy final product. The generator was

designed to have a very small amount of unused space.


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3.) Practicality and durability

All the parts were designed with practicality in mind. For example, in SolidWorks Assembly, a

3D printed gear shaft would work perfectly but in reality that is not the case. It would break

easily considering that it is only 2mm in diameter. Therefore, the gears were designed with a

hole so that store bought 2mm diameter metal shafts could be used.

There are three main areas of design in making the generator:

1.) Case

2.) Gear mechanism

3.) Dynamo

4.) Tapped holes

All four of these designs are dependent on each other so that everything fits together perfectly.

3.1 Case and cover

Figure 2.5 Diagram of inside of case


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Figure 2.6 Cover and its functions


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Figure 2.7 Attachment to fasten generator to the rear wheel axle

3.2 Gear Mechanism

1. Driver gear

The driver gear has no shaft but instead will be supported by being placed firmly between the

case and the cover. This gear will be attached to the rear wheel axle and tying wire will connect

it to the spokes of the bicycle so that the gear can turn.


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Figure 2.8 Driver Gear

2. Idler Gear

The idler gear was placed in between the driver gear and the driven (third gear) at a position

where the pitch circle diameters are all tangent to each other.

Figure 2.9 Idler Gear


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3. Third Gear (Driven Gear)

The third gear could not be design all in one part because it would be difficult to print on the 3D

printer. Therefore it was designed in two separate parts. One is the gear itself and the other part is

to hold the magnets.

Figure 3.0 Third Gear with magnet holder

3.3 Dynamo

The design of the dynamo has three parts:

1.) Coil core

2.) Magnet axle

3.) Dynamo Cover

1. Coil Core

The coil core's primary function is to provide a support for the coil of copper wire. It was

designed for ease of use by making it rectangular. To make use of the space, it was most

practical to put four coil cores around the spinning magnet.


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Figure 3.1 Coil core

2. Magnet Axle

The magnet axle is the same as in figure 3.5 so there is no need to show it again. It is placed right

in the center of the coils and it was designed keeping in mind the size of the magnet and making

sure it will spin freely without interference but not too much wasted space.

3. Dynamo Cover

The purpose of the dynamo cover is to hold the coil cores in place and to be a top support for the

third gear shaft.


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Figure 3.2 Dynamo Cover

3.4 Tapped holes

Since the fastening screws are really small and the material used for printing is soft, the screw

holes are not made with threading but instead a "tapped hole" was made for the screws. The

diameter of the screw is 2mm for all the fastening screws required. The dimensions of the tapped

holes are as follows:

Standard: ISO

Size: M2

Depth: 5 mm


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Figure 3.3 1.6mm diameter tapped holes in screw holes


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4.

SOLIDWORKS

DRAWINGS


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30


31


32


33


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5. SOLIDWORKS ASSEMBLY

Figure 3.4 Final assembly of solidworks parts after interference check

Figure 3.5 Final Assembly with case on


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6.RESULTS

Figure 3.6 Final 3D printed parts

The printing of all the parts took a long

time with the case taking around 7

hours to complete. It was difficult

removing the supports for the

undercuts while trying not to break the

part. The hardest materials to remove

were the ones inside the shaft holes

and the tapped holes in the case.

Figure 3.7 Grinding

Even after tolerance fitting

was accounted for in the

solidworks designs, a lot of

grinding needed to be

done for the parts to fit

together without rubbing

on each other.


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Figure 3.8 Final Assembly

In the first picture, one of the coils was removed due to size constraints when the wire coil was

added. The magnets were attached to the driven gear axle and fastened using electrical tape. In

the last picture the driven gear (third gear) is fastened by the case at the bottom and the dynamo

cover at the top. The idler gear is fastened at the bottom by the case and at the top by the

generator case cover. The driver gear is fastened at the bottom by the case and at the top by the

generator case cover.


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Figure 3.9 Final Assemble with screws. Red tape to keep the case shut tight

Figure 4.0 Broken Part

Some of the inside dimensions in the generator fastener were too small for 3D printing and so the part

broke.

While trying to remove material from inside the small holes in the driver gear, the part connecting to the

bicycle wheel broke.


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Because of the quality of the 3D printer the final parts were not accurate. The finished parts had

inaccuracies of about 0.2 - 0.5 mm depending on the part. This made it difficult for fitting and

for gear meshing. The gears did not properly mesh because of the added material on the teeth.

This caused interference when turning the gears and a lot of noise since the driver gear kept

rubbing against the walls of the case.

7. DISCUSSION

When designing a gear mechanism, many factors need to be considered: the material, machining

process and the purpose. From the results of this project, the importance of the machining

process in designing was very important.

When using rapid prototyping there are many advantages but some disadvantages too.

Some of the advantages are:

1.) Fast and cheap machining

2.) Able to see how the design will look in real life and make changes as necessary

Some Disadvantages:

1.) The material used is plastic and may break easily.

2.) The printing is inaccurate therefore the design has to have a high tolerance to accommodate

for these inaccuracies.

3.) The size constraints when printing too large or too small parts.

After completion of this project I have learned a lot about rapid prototyping and how it could be

helpful and the ways in which I have to make changes to my designs so that it could be printed.

It helped me get a good idea of how the part will look in real life and allowed me to see where

changes need to be made for a better part.

After putting everything together I have seen all the areas that need changes or improvements:

1.) Gear design and meshing: One thing I found out when putting the gears together is that the

gears didn't fit properly because the teeth were small and a small inaccuracy as 0.2 mm will

make it difficult to mesh. While it is difficult to make changes to the gear design itself, the

location for the idler gear could be changed. The actual idler gear will remain with the same

dimensions but it's position will change using a reference circle of a bigger diameter:


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2.) Idler gear not stable: When spinning the gears the idler gear tend to tilt a little bit making it

hard to turn the gears. Adding some support at the top (on the cover), to help keep the gear

horizontal will minimize this problem.

3.) The driven gear had problems to turn because it had interference with the top support. When

turning it was rubbing against the top of the dynamo cover. I used the grinder to smooth the part

of the dynamo cover in contact with the gear to minimize this. Fixing this in SolidWorks would

be a problem since the thickness is already 1.5mm and making it smaller would make printing

more difficult.

4.) The wheel connection for the driver gear broke when trying to remove material from the hole.

This is difficult to fix because it is impossible to make this part bigger because it would cause

interference when connected to the bicycle. One solution is to totally redesign this gear using a

different mechanism to connect to the wheel spokes.

5.) The case did not fit securely enough so I had to use electrical tape to help secure it. If the case

cover isn't securely fastened to the case, it would cause the idler gear shaft to slip out of the top

support which is attached to it. Using the case as the top support for the idler gear was not a good

idea because it is not secure. and also, testing how the gears turn is difficult because the cover

has to be placed securely on so we can't see how well the gears turn in this situation. One way to

fix this is to redesign the case to make more space so that a support could be added on top of the

idler gear similar to that of the driven gear.

Figure 4.1 Sketch of location for idler gear

In the sketch on the right, the driver gear and

the driven gear pitch diameter are used as

reference for the location of the idler gear. By

making the reference diameter bigger for the

driven gear and the idler gear, the location can

be moved a little further to the left so when

assembling the printer parts the gears would

mesh better.


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6.) The attachment to fasten the generator to the rear wheel broke because the inside dimensions

were too small. Suggestions for improvement could be to remove the polygon edges and just

make it a complete circle and use a CNC machine to machine a metal part. This would be better

and stronger to hold the generator until the rear wheel without it moving when then bicycle is on

the road.


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8. CONCLUSION

After finishing this project, I have acquired a better understanding of the factors that comprise

mechanical designing and Rapid Prototyping.

Although the parts did not fit together properly to produce an outcome, I have gained a better

idea on how and where improvements need to be made.

When making a mechanical design, a great deal of consideration need to be made concerning the

machining process. In this case, it is necessary to make a design that could be easily 3D printed

and strong enough for its purpose using a plastic material. Some ways to make the product better

when 3D printed are:

1.) Adding in small features such as chamfers, filets, and ribbing can help to increase the

sturdiness of the product.

2.) Adding a 0.5mm tolerance for fitting and for the gears to turn properly.

3.) For parts with small dimensions, increase the overall dimension of the parts so that the

smallest thickness or hole is 1.5mm - 2.0 mm.

When designing the gear mechanism, one change I would make is to redesign the case so that the

driver gear connects directly to the driven gear. This will greatly reduce problems caused by

friction and inaccurate meshing. Since the 3D printer cannot print parts with dimensions less

than 1.5 mm, it would be better to increase the diameter of the gears so that the teeth size and

module could be larger. By doing this, the acceptable error when printing is bigger. For example,

the gears would still mesh properly if 0.1 mm of material were added after printing.

All in all, the project gave me great insight and practical experience in mechanical design and

rapid prototyping. Energy is all around us, we just have to figure out innovative and efficient

ways of harnessing this energy for practical use. The results of this project is inconclusive but is

a great platform for anyone interested in alternative energy and has a lot of room for

improvement.


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10. Zhang, Yi. "Introduction to Mechanisms." Chapter 2. Mechanisms and Simple Machines.

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11. "Gear Tooth Nomenclature." Gear Tooth Nomenclature. Web. 31 May 2015.

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13. "Spur Gears." Spur Gears. Web. 31 May 2015.

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14. "Rapid Prototyping: An Overview." Rapid Prototyping: An Overview. Web. 31 May 2015.

<http://www.efunda.com/processes/rapid_prototyping/intro.cfm>.

kun shan university mechanical engineering undergraduate...

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