By: Virrujan Sribaskran 213566807

Thane Higgins 212199451

Rohan Kaicker 212927232

Akash Oommen 213725437

Table of Contents I. Team Statement of Participation ............................................................................................... 1

II. Executive Summary ................................................................................................................... 2

III. Planning and Clarification .......................................................................................................... 3

i. Background ......................................................................................................................... 3

ii. Design Specifications ...................................................................................................... 3-4

Comments and Corrections(Design Specifications) ........................................................... 4

iii. Functional Structural Diagram ............................................................................................ 5

Comments and Corrections(Functional Structural Diagram .............................................. 5

IV. Conceptual Design ................................................................................................................... 6

i. Morphological Chart ........................................................................................................... 6

ii. Conceptual Design Selection............................................................................................ 7-9

Comments and Corrections(Conceptual Design Selection) ............................................. 10

V. Embodiment Design ................................................................................................................ 10

i. Preliminary Layout ....................................................................................................... 10-13

ii. Design Analysis ................................................................................................................. 14

Comments and Corrections (Design Analysis) .............................................................. 15

VI. Design Implementation ......................................................................................................... 15

i. Manufacturing ............................................................................................................. 15-16

ii. Prototype Analysis ........................................................................................................... 16

Comments and Corrections (Prototype analysis) ..................................................... 16-17

iii. Final Design .................................................................................................................. 17-18

Appendix A: Functional Structure Diagram Report ................................................................. 19-24

Appendix B: Conceptual Design Report ................................................................................... 25-29

Appendix C: Selected Conceptual Design Report .................................................................... 30-37

Appendix D: Embodiment Design Report ................................................................................ 38-58

Appendix E: Prototype Report ................................................................................................. 59-65

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II. Executive Summary :

The purpose of this project was to create a car that would have the lightest possible

weight and gain input energy from either stretching or compressing and effectively convert that

input energy to yield the largest possible run distance. To achieve these goals we need to go

through several phases. The first phase was to create a functional structure diagram this would

clearly state the purpose of the project and state the objectives of our design. Then we had to

create a requirements list to that would lead to the success of achieving our goals. The next

phase was to create a morphological chart, which would lead to the development of conceptual

designs, we had each team member create a conceptual drawing. After this stage, we now

need to create a criterion to rank each of our conceptual designs against based on ease of

manufacturing, aerodynamics, distanced travelled and weight. Then we made a weight

scheme, which would give us a final numeric value based on our criteria, this would tell us,

which of our designs was the best. One we selected our design we had to figure out the

dimension of each component, and the entire layout of our car. Next, we made free-body

diagrams to see how the forces travelled throughout the car. Once we figured out the forces,

we made strength calculations to theoretically see which components of the car had a risk of

failing. Now it time to make a CAD model and do a final check to see if part were interfering,

and also to see if our final car design would fit in the loading mechanism. Then we started to

build our prototype and test runs. Here we encountered many problems and had 3 re-builds

until we finally designed a car that was finally running.

In this report, we will be going over background of this project and discussing the scope,

stakeholders, and goals of the project. We will also be going into detail about the errors we

made, which led to failure of our initial designs. From our initial planning stages we will be

comparing between our past and corrected changes from the functional structure diagram,

design analysis, and etc. which leads to our final and working design.

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III. Planning and Clarification

i. Background

Scope

The scope of the problem was to create a car that would have the lightest possible weight and gain input energy from either stretching or compressing a spring and effectively convert that input energy to yield the largest possible run distance. Stakeholders

The stakeholders of our project are our group. We are the principal stakeholders for obvious reasons. We hold a vested interest in this project because the success of our car directly impacts our final grade, and we want to achieve the best grade possible. Goals The goals of the project were to create a car that could travel the maximum possible distance

from stored spring energy, while trying to keep the car as light as possible.

ii. Design Specifications : Requirement List

CATEGORY DEMAND OR WISH REQUIREMENT Geometry Demand Size has to be within

24”x20”x20”

Kinematics Demand Type of motion will be rotary motion

Direction of motion must be straight

Forces Demand Weight will either be 2.5 or 5 lbs, and the direction will be down

Weight will induce a tension force in the spring, parallel to the direction of motion

Energy Demand Able to gain gravitational energy from a 2.5 or 5lb load

Store elastic energy Convert elastic energy to

kinetic energy

Signal Demand Compatible with the loading mechanism

4

Ergonomics Wish Aesthetically pleasing Schedule Demand Get things done by the

required deadline

Material Demand Build the car with the materials provided and 3d printed parts

Production Demand Build the car within the maximum dimensions (24 x 20 x 20 in) provided.

Design Criteria 5-Excellent, 4-Very Good, 3 -Good, 2-Satisfactory,1-Poor

Design Criteria Weighting Design 1 Design 2 Design 3 Weight 0.35 3 4 2

Distance 0.50 3 2 3 Ease of

Manufacturin

g

0.05 5 4 2

Aerodynamics 0.10 2 4 3

Total 1.00 3 3 2.6

Comments and Corrections(Design Specifications):

Requirement list

The final design of our project managed to meet all the demand requirements we listed in our

requirement list. For our geometry requirement it was within the dimension restrictions, for

kinematics, forces, and energy; the motions was rotary and straight, able to withstand the

weighted loaded of 5lbs, and able to convert the gravitational energy to elastic potential

energy. It was compatible with the loading mechanism thus completing the signal

requirement, designed and completed on schedule to meet the deadlines, and built only using

the materials provided.

Criteria

A criteria for aerodynamics was not really necessary. Initially we thought of reducing the air

drag force by making our car more aerodynamic. But the air drag force for such a small car is

very minimal and can be easily neglected. So the criteria for aerodynamics was not really

required for such a small car. Instead of aerodynamics we could have considered a criteria for

removing friction. As towards the end if the project, friction was one of the main obstacles we

had to deal with.

Our final design did meet most of the criteria. It did fulfil our 2 main criteria which was the

weight and distance criteria. We did move the car a certain distance and also made it as light as

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possible. The last two criteria of aerodynamic and ease of manufacturing did not really affect

our final design.

iii. Functional Structural Diagram:

Comments and Corrections(Functional Structural Diagram):

Our functional structure diagram included everything that was required, the only thing that was not required was the second block in the materials tab which included spring accepting compression from the hook. This was not required as this is more of a energy transformation than materials. But we did also mention this in the energy transformation tab.

Our Final design included almost all the functions. The only function that was missing was the

use of a trigger pin to keep our spring compressed/tensioned. During the final stages of our

project we realised that using our hand as a locking mechanism to keep the spring

compressed/tensioned was much more practical.

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IV. Conceptual Design

i. Morphological Chart :

7

ii. Conceptual Design Selection :

Design Criteria Weighting Design 1 Design 2 Design 3 Weight 0.35 3 4 2

Distance 0.50 3 2 3 Ease of

Manufacturin

g

0.05 5 4 2

Aerodynamics 0.10 2 4 3

Total 1.00 3 3 2.6

Weight

Design 2(Best)

Our group felt that Design # 2 was the best design we had in term of weight, but we gave it

a rating of 4/5 because felt like the weight component can be optimized even further. Some

of our ideas to optimize the weight were to cut down on the housing (or frame) of the car.

But this was your best deign in terms of weight because compared to design 1 and 3 we

figured this would be the lights because it uses less materials and components.

Design 2(Good)

Design # 1 was given a rating of 3/5 for weight because relative to design # 2 this design

featured a slightly larger frame for the car and it also feature larger wheels, which would

add more mass to the car.

Design 3(Bad)

Design # 3 was given a rating of 2/5 for because this design looked aesthetically pleasing but

to compensate for the more was added on to this design. This design featured a really large

frame for the car, and this would add on a ton of unnecessary mass that would affect the

performance of the cart. This turned out to be our least favourable design because it

weighed much more than the rest of our designs.

Aerodynamic

Design 2(Best)

Design 2 got a rating of 4/5 for aerodynamics because the car's front wheels were closer

together, so it featured a front end that was narrow. Then the rest of the body sloped

upwards towards the end of the car, and the reasoning behind this was to guide the streams

of air above the car smoothly. The body of the car also sloped outward (horizontally) to

guide the streams of air along the sides of the car as well. Overall, this design would best

deal with the air drag force due to its slopes and curves.

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Design 3(Good)

Design 3 got a rating of 3/5 for aerodynamics because the framework of the car was slightly

better than Design 2. Design 3 featured a pointed front end, which would cause air to split,

to both sides of the car, causing a smooth flow of air throughout the body of the car.

However this cars aerodynamic rating fell behind Design 2 because the height of this design

was relatively larger compared to design 2 and 3, causing more contact between the car and

air, which as a result will increase the drag force.

Design 1(Bad)

Design 1 got a rating of 2/5 for aerodynamics because the overall framework of the body

was a solid rectangular body with no curves, which was the worst case due to the fact the

rectangular body’s tend to increase drag force from air.

Ease of Manufacturing

Design 1(Best)

We believed that the first design was the easiest to manufacture. It had simple planar walls,

and two axles, which would be relatively simple to make with SolidWorks and a 3-D printer.

The gears, gear rack, and the wheels would be easily made with a laser cutter and acrylic

sheets. It would definitely take a lot less time to produce and make when compared to the

more complex shapes from the second and third designs. The majority of tolerance would

go into making sure the axles and the wheels fit tightly, as well as ensuring the gears and the

rack are properly dimensioned.

Design 2(Good)

We believed that the second design was relatively easier to make when compared to the

third design, since it involved no complex curves, rather it still had similar planar walls such

as the first design. However, in an attempt to make this more aerodynamic, drawing

inspiration from formula-1 cars, we changed the simple rectangular planar walls to more

diagonal, which would allow air to flow more easily off the top of the car. However, this

design would still be relatively simple because there are no curves and all parts (except the

wheels), were still straight. We could again simply laser cut the wheels from acrylic sheets,

and 3d print the body/lever, and put it all together. Again, the majority of the tolerance

would go into making sure that axles and the wheel fit.

Design 3(Bad)

The third design was not so good in terms of manufacturability. There are a lot more moving

parts in this design, which include the moveable plate, the two racks, the axles/wheels. We

would be required to heavily tolerance these parts in ensuring that everything runs

smoothly in the operation of this car. If for example, the moving plate wasn't

9

dimensioned/tolerance properly, and it was far too wide, then when the car is let go, the

plate won’t be able to move. This in turn will hinder the ability of the racks to turn the

gears, and hence the wheels, which would mean our car wouldn't move at all. The

production and manufacturing of this car will take far too long to be considered feasible.

Distance

Design 1 (Good)

For the 1st design we gave it the score of 3 based on its gear and rack system which we believe

is the one out of the two designs with the most effective ways of transferring force. The gear

and rack system of design 1 directly spins the wheels of the kart due to the position of the gears

on the axel which decreases the amount energy loss that would come from having multiple

components interacting with each other . Also by using a tension spring instead of the

compression springs in the design, the amount of energy able to "deform" the tension spring

will be lower than that of using the compression springs because of the lower spring

constant(k). Translating to greater displacement of the rake on the gears and more rotation of

the wheels allowing the kart to travel further.

Design 3(Good)

The 3rd design received a weighted score of 3. This is due to the design having the same gear

and rack set up as design 1 with the gear and rack positioned on the axel. Like design 1, it uses a

limited number of parts to load the spring reducing the amount of energy transfer loss. The

difference is design 3 uses a compression spring instead a tension spring, it would be lighter in

total mass, and it would be a more aerodynamic cutting down the wind resistance applied to

the kart as it moves. With the last two traits incorporated in the design, it would make up for

compression spring not being "deformed" enough to generate the needed displacement on the

gear and rack system. Giving design 3 the same score as design 1.

Design 2(Bad)

Design 2 was given the weight score of 2 because it incorporated an important design

component in the form of a lever to multiple the force applied on the spring but had an

infeasible idea of using a string to rotate the axel. Because of using this extra material not

permitted in the design process, we could not give it a higher score than the other two designs

being compared.

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Comments and Corrections(Conceptual Design Selection) :

Our original designs would not have worked because our design consisted of only one spur gear

and a inverted rack over it. But later we realized that the torque produced was too much for

one pair of gears to handle and also realized that they way we at first design the rack and gears

to interact did not work the way we thought it would work. Also the force produced by the 5lbs

load was not that much , so we had to include a force multiplier to multiply the force provided.

Our selected conceptual design was not close to our final design. It was very different as we

included a number of compound gears interacting as a gear train to reduce the torque from the

loaded spring and force multiplier. We also placed the rack to move along the bottom of gears

instead of the top as it was easier to stay aligned this way. Finally we had to increase the length

of the car to fit all the compound gears aligned in the gear train which would further increase

our weight.

V. Embodiment Design

i. Preliminary Layout

11

12

13

14

ii. Design Analysis

Loading Arm bending stress analysis

Gear strength analysis

15

Comments and Corrections (Design Analysis)

From our final design the most important components to analyze was the force multiplier and the compound gears. Firstly regarding the force multiplier, it was essential that the force multiplier creates a larger force to transfer to the rack so that a sufficient force is provided to obtain the most longest run distance. Secondly regarding the compound gears, because it was vital to obtain a optimal gear ratio so that a reduced torque could be supplied to the back axle (driving axle) to ensure that the wheels do not spin. Our initial strength calculations held true so we didn't to have to redo much of the calculation,

which includes the strength calculations for part such as gears, force multipliers, wheels, axle

and spring. So the strength of our main components were able to handle the stress being

applied on them.

VI. Design Implementation

i. Manufacturing

Our designs consisted of components that were made out of both acrylic and PLA. Since we wanted our car to travel the longest possible distance we wanted to go with acrylic entirely, but we were limited to only two sheets of acrylic that were 24”x24”, so we had to use acrylic for some components. Also to cut acrylic we could use the laser cutter, which was very reliable with slight errors so we used it to make out chase since we need the holes on both sides of the chase to line up. To use PLA we could only use the 3-D printers which had a error of about 2mm, which was too high for our case.

Firstly, the dominant form of manufacturing for most of our car was laser cutting. This is because acrylic was used for the majority of our car. This includes the force multiplier, sides, front, body, and washers. The washers were used to keep the gears in place along the axle. Acrylic was chosen for these parts because it was known that laser cutting would allow fast manufacturing, whereas if we had used PLA, the manufacturing time would have been much longer. To create the axles for our wheels and gears, we simply used the aluminum rods we were given. We then marked off locations, with permanent marker, in order to cut it down to the lengths we needed. To cut the rods, we clamped it down to the table, and used a handsaw. For the gears, they were manufactured through creating a 3D model in SolidWorks, then converted that to an STL file, in order to 3D print it with the MakerBots. This allowed us to vary the face width of the various gears, which we would be unable to do if we chose acrylic, although we could glue two acrylic sheets together, but this would bring error in the shaft hole placement. Corner brackets, to hold the body together, were 3D printed. Then to put the entire car together, superglue was used.

Most of our car parts were manufactured in the same way through our various iterations,

except for the gears. Initially in our first two iterations we had made them through acrylic, but

one of the errors we found with this was that the shaft holes had to perfectly line up, and we

16

found this feat to be difficult. Therefore, in our final iteration, we decided to just simply 3D

print all the gears, even the compound ones, so we wouldn’t have to worry about lining up the

gear shaft holes so that the axle would line up. Everything else was manufactured in the same

way as previous iterations.

ii. Prototype Analysis

Trial # Displacement

1 6 inches

Unfortunately, the testing stage of our prototype did not go as planned. Almost immediately of

testing the design, it was evident that our prototype was not going to travel a testable distance.

Loading the spring and releasing only managed a 6 inch displacement which was mostly due to

the recoil of the spring. After 1 trial it was determined that not further trials would be performed

under the current design as it was not moving by the method it was designed to travel.

Comments and Corrections (Prototype analysis) Our prototype did not work as expected. It had a couple of problems. The most important problem was the compound gears, our gear train was not working properly as we needed more gears to reduce the torque. Also we did not have enough length to add a lot of gears , but eventually we decided to increase the length of the car and add in more gears. furthermore, we

17

did not consider clearance fits , so some of our tight fits turned out to be loose fits. These were the main reasons our prototype tests failed.

Yes, we did make a working prototype of the car in SolidWorks. This proved effective since not only could we have a 3D model of the design to view from different angles, but also it allowed us to form interactions within the program for the gears, rack, and force multiplier to see how they would mesh and interact once loaded and released.

Yes it would have been better if we spent a bit more time in modelling and analyzing the design

before we built it. Because after manufacturing our car and testing it ,we realized that the lock

for the force multiplier could have been at more optimal positions. Furthermore, it would have

been optimal for us to model the car in such a way for it to be modular ,just like our final

design. This would have allowed us to potentially add in more gears if the torque was still too

high.

iii. Final Design

CAD Model

18

Photos of Final Design

For the changes we made from the prototype design, we decided to not only add another

set of gears to the gear train, but to also manufacture all the gears out of PLA material

instead of acrylic. The rate of which the torque being applied to our gear train system and

thus our wheels, needed to be reduced in order to prevent the wheels from spinning in

place. It was determined the best way to accomplish this was to increase the thickness of

each gear and add another set of gears to the system which would help reduce the rate. We

had used acrylic for the gears and glued multiple sheets together to increase the thickness.

But this proved difficult as the alignment of gears did not always line up which made the

rotation of the gear train almost impossible to turn. By making the gears out of PLA, and 3D

printing the thickness, this method allowed the gear train to rotate without inconsistencies

and gave us the needed reduction in the rate of which the torque being applied to our gears

and wheels.

During the competition, the distance and weight of each team's car was measured and

recorded. The goals of the project was to have your design weight the lightest and travel

the furthest. For our design the total weight and longest distance travelled were (put weight

number here) and (put distance number here) respectively.

19

Abstract

Appendices

By: Thane Higgins

Rohan Kaicker

Akash Oommen

Virrujan Sribaskaran

This document goes over the Introduction, Requirements List and Functional Structure Diagram for the project.

20

Contents Introduction ........................................................................................................... 2

Objectives .............................................................................................................. 2

Objective Diagram .............................................................................................. 2

Requirements List .................................................................................................. 3

Functional Structure Diagrams............................................................................... 4

21

Introduction In today’s world, with ever-rising fuel costs, and rising levels of pollution, Allied Springs Systems

has hired Hot Wheels (our team+) to design a car that will be solely powered by springs.

Through alternative fuel source, our impact on the environment will be minimized. Our design

must be able to travel the maximum distance achievable, while still being as light as possible.

Furthermore, we have to take into consideration, the fact that it must be compatible with the

supplied loading mechanism and able to bear the 2.5 or 5 lbs.

Objectives The objectives of the design are:

a. Able to achieve the maximum distance (Displacement)

b. Lightest possible design construction

c. Fnishing by the deadline dates

Objective Diagram

22

Requirements List

CATEGORY DEMAND OR WISH REQUIREMENT

Geometry Demand Size has to be within 24”x20”x20”

Kinematics Demand Type of motion will be rotary motion

Direction of motion must be straight

Forces Demand Weight will either be 2.5 or 5 lbs, and the direction will be down

Weight will induce a tension force in the spring, parallel to the direction of motion

Energy Demand Able to gain gravitational energy from a 2.5 or 5lb load

Store elastic energy Convert elastic energy to

kinetic energy

Signal Demand Compatible with the loading mechanism

Ergonomics Wish Aesthetically pleasing Schedule Demand Get things done by the

required deadline

Material Demand Build the car with the materials provided and 3d printed parts

Production Demand Build the car within the maximum dimensions (24 x 20 x 20 in) provided.

23

Functional Structure Diagrams

24

25

Conceptual Design Report

By:

Thane Higgins

Rohan Kaicker

Akash Oommen

Virrujan Sribaskaran

26

Morphological Chart

27

Conceptual Designs Design 1: For our first design, the path we chose, based on our morphological chart was {3-3-1-2}.

28

Design 2: For our second design, the path we chose, was {1-3-1-4}.

29

Design 3:

For our third design, the path we chose was {4-3-1-3}.

30

Selected Design Report

By: Virrujan Sribaskaran, Akash Oommen, Rohan Kiacker

and Thane Higgins This document goes over the process and criteria we used to select of final design.

31

Ta b l e of Con t en t s

Sketches For Each Design ........................................................................................................ 3

Criteria Selection and Weighting ............................................................................................. 4

Ratings ............................................................................................................................. ................ 4 Importance ...................................................................................................................................... 4

Select a Conceptual Design ..................................................................................................... 5

Weight ............................................................................................................................. ................ 5 Aerodynamics ............................................................................................................................. ..... 5 Ease of Manufacturing ...................................................................................................................... 6 Distance ............................................................................................................................. .............. 7

Final Design ............................................................................................................................ 8

32

Ske t c he s Fo r Eac h D e si gn

Design 1 Design 2

Design 3

33

Cr i t er i a S el ect i on a n d W ei g h t i n g

Ra t i n g s

5-Excellent, 4-Very Good, 3 -Good, 2-Satisfactory,1-Poor

Design Criteria Weighting Design 1 Design 2 Design 3

Weight 0.35 3 4 2

Distance 0.50 3 2 3

Ease of

Manufacturing

0.05 5 4 2

Aerodynamics 0.10 2 4 3

Total 1.00 3 3 2.6

Im p o r ta n c e We i g h t

Based on our project’s grading criteria, “Weight” is one of the 2 main aspects that will be marked for

testing the cart. It is worth 1/3 of the total grade on testing performance. Since this directly impacts our

grade we decided to give it one of the higher weightings. As it is one of our major goals to make the

lightest car we decided to give it a weighting of 0.35.

D is t a n c e

Distance was given a weighting of 0.50, higher than all the other aspects because distance travelled is

the main aspect we will be graded on and it accounts for 2/3 of the competition marks. The criterion

was given the highest weighting because the distance travelled directly correlates to the winner of the

competition.

Eas e o f M anuf ac t ur i ng

We gave this criterion 0.05 weighting because we felt that manufacturing was a one-time effort and the

complexity of it will not impact the success of the design. But we still included this in our criteria,

because we had to take into consideration our collaborative skills and build a car that is feasible.

Ae r o d y n a m i c s

We felt that this is an important secondary criterion that directly influences the potential distance that

our car could travel. Also we felt that this is something that we could easily design and reduce the air

drag force as much as we can.

34

Se l e c t a C o nc e pt ual Des i g n

We i g h t Design 2 (Best)

Our group felt that Design # 2 was the best design we had in term of weight, but we gave it a rating of

4/5 because felt like the weight component can be optimized even further. Some of our ideas to optimize

the weight were to cut down on the housing (or frame) of the car. But this was your best deign in terms

of weight because compared to design 1 and 3 we figured this would be the lights because it uses less

materials and components.

Design 1 (Good) Design # 1 was given a rating of 3/5 for weight because relative to design # 2 this design featured a

slightly larger frame for the car and it also feature larger wheels, which would add more mass to the car.

Design 3 (Bad) Design # 3 was given a rating of 2/5 for because this design looked aesthetically pleasing but to

compensate for the more was added on to this design. This design featured a really large frame for the

car, and this would add on a ton of unnecessary mass that would affect the performance of the cart.

This turned out to be our least favourable design because it weighed much more than the rest of our

designs.

Ae r od y n a m i c s Design 2 (Best)

Design 2 got a rating of 4/5 for aerodynamics because the cars front wheels were closer together, so it

featured a front end that was narrow. Then the rest of the body sloped upwards towards the end of the

car, and the reasoning behind this was to guide the streams of air above the car smoothly. The body of

the car also sloped outward (horizontally) to guide the streams of air along the sides of the car as well.

Overall, this design would best deal with the air drag force due to its slopes and curves.

Design 3 (Good)

Design 3 got a rating of 3/5 for aerodynamics because the framework of the car was slightly better than

Design 2. Design 3 featured a pointed front end, which would cause air to split, to both sides of the car,

causing a smooth flow of air throughout the body of the car. However this cars aerodynamic rating fell

behind Design 2 because the height of this design was relatively larger compared to design 2 and 3,

causing more contact between the car and air, which as a result will increase the drag force.

Design 1 (Bad)

Design 1 got a rating of 2/5 for aerodynamics because the overall framework of the body was a solid

rectangular body with no curves, which was the worst case due to the fact the rectangular body’s tend

to increase drag force from air.

35

Ease of Manufacturing Design 1 (Best)

We believed that the first design was the easiest to manufacture. It had simple planar walls, and two

axles, which would be relatively simple to make with SolidWorks and a 3-D printer. The gears, gear rack,

and the wheels would be easily made with a laser cutter and acrylic sheets. It would definitely take a lot

less time to produce and make when compared to the more complex shapes from the second and third

designs. The majority of tolerance would go into making sure the axles and the wheels fit tightly, as well

as ensuring the gears and the rack are properly dimensioned.

Design 2 (Good)

We believed that the second design was relatively easier to make when compared to the third design,

since it involved no complex curves, rather it still had similar planar walls such as the first design.

However, in an attempt to make this more aerodynamic, drawing inspiration from formula-1 cars, we

changed the simple rectangular planar walls to more diagonal, which would allow air to flow more easily

off the top of the car. However, this design would still be relatively simple because there are no curves

and all parts (except the wheels), were still straight. We could again simply laser cut the wheels from

acrylic sheets, and 3d print the body/lever, and put it all together. Again, the majority of tolerance

would go into making sure that the axles and the wheels fit.

Design 3(Bad)

The third design was not so good in terms of manufacturability. There are a lot more moving parts in this

design, which include the moveable plate, the two racks, the axles/wheels. We would be required to

heavily tolerance these parts in ensuring that everything runs smoothly in the operation of this car. If,

for example, the moving plate wasn’t dimensioned/tolerance properly, and it was far too wide, then

when the car is let go, the plate won’t be able to move. This in turn will hinder the ability of the racks to

turn the gears, and hence the wheels, which would mean our car wouldn’t move at all. The production

and manufacturing of this car will take far too long to be considered feasible.

36

Di s t a n ce

Design 1 (Good)

For the 1st design we gave it the score of 3 based on its gear and rack system which we believe

is the one out of the two designs with the most effective ways of transferring force. The gear

and rack system of design 1 directly spins the wheels of the kart due to the position of the gears

on the axel which decreases the amount energy loss that would come from having multiple

components interacting with each other. Also by using a tension spring instead of the

compression springs in the design, the amount of energy able to "deform" the tension spring

will be lower than that of using the compression springs because of the lower spring

constant(k). Translating to greater displacement of the rake on the gears and more rotation of

the wheels allowing the kart to travel further.

Design 3 (Good)

The 3rd design received a weighted score of 3. This is due to the design having the same gear

and rack set up as design 1 with the gear and rack positioned on the axel. Like design 1, it uses a

limited number of parts to load the spring reducing the amount of energy transfer loss. The

difference is design 3 uses a compression spring instead a tension spring, it would be lighter in

total mass, and it would be a more aerodynamic cutting down the wind resistance applied to

the kart as it moves. With the last two traits incorporated in the design, it would make up for

compression spring not being "deformed" enough to generate the needed displacement on the

gear and rack system. Giving design 3 the same score as design 1.

Design 2 (Bad)

Design 2 was given the weight score of 2 because it incorporated an important design

component in the form of a lever to multiple the force applied on the spring but had an

infeasible idea of using a string to rotate the axel. Because of using this extra material not

permitted in the design process, we could not give it a higher score than the other two designs

being compared.

37

Fin al Design

38

EMBODIMENT DESIGN REPORT

This document goes over the layout of out vehicle, free-body diagram

analysis, strength calculation, the revised design and the CAD model of the

vehicle.

B y :

V i r r u j a n S r i b a s k a r a n

R o h a n K a i c k e r

T h a n e H i g gi n s

A k a s h O o m m e n

39

Contents Layout............................................................................................................................................................ 2

Dimension for Each Part ........................................................................................................................... 2

Force Multiplier Frame (Acrylic) ........................................................................................................... 2

Force Multiplier Frame (Steel Rod) ....................................................................................................... 2

Axle to Support Force Multiplier (Steel Rod) ........................................................................................ 3

Front Wheels (Acrylic)........................................................................................................................... 3

Rear Wheels (Acrylic) ............................................................................................................................ 4

Wheel Axles (Steel Rod) ........................................................................................................................ 4

Gear Rack (Acrylic) ................................................................................................................................ 5

Gears (Acrylic) ....................................................................................................................................... 5

Body of Cart (Acrylic) ............................................................................................................................ 6

Free Body Diagrams ...................................................................................................................................... 0

Strength Calculations .................................................................................................................................... 3

Collected Data on the Model .................................................................................................................... 3

Strength of the Materials.......................................................................................................................... 4

Magnitude of Forces ................................................................................................................................. 4

Determining Wheel Spin ......................................................................................................................... 10

Review and Revise ...................................................................................................................................... 11

CAD Models................................................................................................................................................. 12

Figure 1: Unloaded Cart .......................................................................................................................... 12

Figure 2: Loaded Cart .............................................................................................................................. 13

40

Layout Note: All numerical values are in centimeters

Dimension for Each Part

Force Multiplier Frame (Acrylic)

Force Multiplier Frame (Steel Rod)

Axle to Support Force Multiplier (Steel Rod)

41

Front Wheels (Acrylic)

Axle to Support Force Multiplier (Steel Rod)

42

Rear Wheels (Acrylic)

Wheel Axles (Steel Rod)

Gear Rack (Acrylic)

43

Gears (Acrylic)

Gear Rack (Acrylic)

44

Body of Cart (Acrylic)

Gear Rack (Acrylic)

45

Free Body Diagrams

Gear Rack (Acrylic)

46

Gear Rack (Acrylic)

47

Gear Rack (Acrylic)

48

Strength Calculations Collected Data on the Model

Gear Rack (Acrylic)

49

Strength of the Materials

Material Young's Modulus (GPa) Ultimate Tensile Strength (MPa) Acrylic 3.2 70

PLA 3.5 50 Aluminum 6061-T6 70 300

Magnitude of Forces

Gear Rack (Acrylic)

50

Gear Rack (Acrylic)

51

Gear Rack (Acrylic)

52

Gear Rack (Acrylic)

53

Gear Rack (Acrylic)

54

All of the above stresses were below the yield strengths for the respective part.

Gear Rack (Acrylic)

55

Determining Wheel Spin ���� ����� = ��

��� ����� = (0.60)(0.94��)(32.2)

���� ����� = 18.16��

��� ����� − �� � ����� = ��

���� − �� ����� = 7.5��

(0.60)(0.94��)(32.2) − �� ����� = 7.5��

�� ����� = 10.36��

���� �����

Ftraction

Ffriction

To prevent slip = 2 ���� �����

���� ����� 18.16

= ( ) = 1.75 �� �����

10.36

Gear Rack (Acrylic)

56

Review and Revise A problem we encountered was that our force multiplier increased the initial force due to the 5lb weight too much that the spring went over the

maximum extendible length of 4.1” (8.1”-4”). To fix this problem we considered using the 2.5lb weight to create the initial force.

The 15lb force is produced as a result of our force multiplier and was directly transferred to our spring, the calculation followed as such:

Failed Approach ������� = 15��

������� = �∆

��������� �� ��� ∆

�������

12cm

5 lb

∆ =

∆ =

�

15��

2.93

15lb

4cm

Axle

∆ = 5.11 � > 4.1 � ( ��� ��� �� � ����������)

Successful Approach

*the forces were calculated in the pervious section

To solve this problem, we decided to go with the 2.5 lb weight instead of the 5 lb weight, the calculations are as follows;

To find the force in the Spring, we can take moment about the axle,

�� ���� = 0

0 = (2.5��)(12��) − ( ������� )(4��)

������� = 7.5��

Gear Rack (Acrylic)

57

CAD Models

Figure 1: Unloaded Cart

Gear Rack (Acrylic)

58

Figure 2: Loaded Cart Acrylic is the transparent Material

All the Axles used are made of 5mm 6061-T6 Aluminum Rods

Gear Rack (Acrylic)

58

PROTOTYPE REPORT

This document goes over images of our prototype vehicle, testing analysis,

and possible improvements that can be made.

B y :

V i r r u j a n S r i b a s k a r a n

A k a s h O o m m e n

T h a n e H i g g i n s

R o h a n K a i c k e r

Gear Rack (Acrylic)

60

Contents Prototype Images .......................................................................................................................................... 2

Testing Analysis............................................................................................................................................. 4

Potential Improvements ............................................................................................................................... 6

Prototype Images

61

Figure 1: Isometric View

Figure 2: Front View

Prototype Images

62

Figure 3 Side View

Testing Analysis

63

Unfortunately, the testing stage of our prototype did not go as planned, but we did

manage to learn a lot from our mistakes. Once the spring was fully loaded, and all the locking

mechanisms were in place (in the rack and the force multiplier), we set the prototype car down,

and released the locking mechanisms. Almost immediately, one of our side panels sheared right

off, and the car only moved approximately 6 inches. This is shown below, in Figure 4. This side

panel was responsible for holding the force multiplier in place, which in turn was directly

connected to the tension spring. So as soon as this side panel broke, all the spring energy was

lost as the spring compressed back. We realized multiple reasons for this. Firstly, we did not

consider that the right angles at which the side panels are designed at are critical points of

weakness. It is clear to us now that if we were to implement this type of design that we should

have used filets to round out the corners, ultimately decreasing the stress. However, since we

did not use filets, this critical area almost immediately failed.

Furthermore, as shown from the previous images, our design did not consist of any

compound gear system, and therefore, the entire torque was entirely on one gear, which had a

tight fit connection to the back-wheel axle. We realized now, through our test run, that even if

our side panel had not broken, it is quite possible that our back wheels would have slipped. This

is one of the major issues we had to take into consideration in figuring out how to improve our

design.

Another major problem we discovered while testing our vehicle was that there was

nothing stopping our gear rack from flying up off of the gear, ultimately rendering our gear

system useless. As will be discussed in the next section, we decided to have the rack on the

bottom of the car in order to circumvent this issue entirely. Along with this, there was nothing

stopping our gear from moving along the axle, and so we’ve realized the need to have some

sort of a bearing, on the axle, restricting the movement.

Trials 2 through 5 were unable to be completed because the car was broken, as stated

above.

Testing Analysis

64

Figure 4: Broken Side

Testing Analysis

65

Firstly, one major improvement we’ve decided to implement is the inclusion of a gear train, with a

compound gear. We’ve already ran the calculations again, and have come up with a 3.11:1 gear ratio,

with respective teeth of 28,20,15, and 12, where the 12 teeth gear will be directly connected to the

back axle wheel. This also ensures that the torque on the wheel does not exceed the friction force on

the wheels, preventing any slip that would hinder the distance our car could travel, this is something

we did not do properly in our previous design.

Secondly, we avoided 90 degree sharp turns for our new design so that there is a less chance of it

failing, because now there are no critical points with high stress, protecting the acrylic from any

potential

cracks. We are still finalizing the design for our new side panel, but as of now we are making it such

that the entire side is free of any discontinuities.

Thirdly, we added in supports for our gear so that the gears do not wobble from side to side and

only have rotational motion. Since there is a large force being applied to our gears this causes the

gears to wobble and we did not consider this in our previous design, so now we have brackets and

washers to prevent this unwanted movement. Along with this, we added side supports for our gear

rack so that it travels in a straight line, maximizing the force transferred to the gears.

One more thing we have to improve is our locking mechanisms. Right now it essentially consists of a

pin and hole system, where we lock our components by putting a pin (piece of the aluminum rod)

through multiple parts. The cons of this method is that once the car is loaded, there is a large amount

of force on components such as the rack and the force multiplier, so it isn’t easy to pull the rod out

safely. We need to come up with a way to solve this problem efficiently.

It was definitely disheartening for our car to break after having spent many man-hours into our

project, but we are treating it as a learning experience, and we are hoping our next revision ends up

working.

We have learned to think outside the box and consider all possible mishaps that can occur in any project

we have. Overall, we have definitely learned a lot from this project.