Shell Eco-Marathon Competition

Submitted to:

Mr. Darek Bruzgo

1500 Illinois Street

Golden, CO 80401

ATTN: Richard Passamaneck

Submitted by:

Team CSMPG

Division of Engineering

Colorado School of Mines

Golden, Colorado 80401

CSM Engineering Senior Design Program:

Final Design Report

Team Members:

Alexander Timberlake, Team Leader (atimberl@mines.edu)

Asher Clinger (aclinger@mines.edu)

Brian Smith (bsmith0@mines.edu)

Chester Gemaehlich (cgemaehl@mines.edu)

Jonas Cafferty (jcaffert@mines.edu)

Lee Mortimer (lmortime@mines.edu)

William Sekulic (wsekulic@mines.edu)

Faculty Adviser: Darek Bruzgo (dbruzgo@mines.edu) Technical Consultant: Jason Porter (jporter@mines.edu) -

April 30, 2013

Acknowledgments

Team CSMPG would like to thank our client, Richard Passamaneck, for

presenting us with the opportunity of working on the Shell Eco-Marathon Competition

car. In addition to the opportunity, we would like to thank Dr. Passamaneck for the

engineering insight he has given us regarding the project.

We give thanks to our technical consultant, Jason Porter, and all the professors

who agreed to be interviewed. Their technical expertise has proven to be very valuable

for our project. We appreciate the time they have taken out of their busy schedules to

assist our team.

Lastly, we would like to thank our Faculty Advisor, Darek Bruzgo, for the

guidance he has given us regarding our project. His assistance has been very beneficial to

our team.

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Table of Contents

List of Figures ................................................................................................................................. 3

List of Tables .................................................................................................................................. 4

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

1. Introduction ............................................................................................................................. 7

2. Design Methodologies ............................................................................................................. 8

3. Body, Frame, and Material ...................................................................................................... 9

4. Steering .................................................................................................................................. 13

5. Wheels and Hubs ................................................................................................................... 14

6. Wheel, Steering and Body Integration .................................................................................. 17

7. Electrical System ................................................................................................................... 19

8. Engine .................................................................................................................................... 24

9. Conclusion ............................................................................................................................. 25

10. Patents and References .......................................................................................................... 27

Appendix A ................................................................................................................................... 29

Appendix B: Electrical ................................................................................................................. 44

1. Schematics ...................................................................................................................... 44

2. Arduino Code for Automatic Start and Throttle System................................................ 47

3. Procedure for Operation Auto Start/Throttle System ..................................................... 61

4. LCD Display Code ......................................................................................................... 61

Appendix C: Mechanical Design .................................................................................................. 62

Appendix D: Steering ................................................................................................................... 65

List of Figures

Figure 1: Mind Map ...................................................................................................................... 30 Figure 2: Black Box Model........................................................................................................... 30 Figure 3: Function Structure ......................................................................................................... 31

Figure 4: BOM Exploded View Callouts - Steering ..................................................................... 31 Figure 5: BOM Exploded View Callouts - Car ............................................................................ 32

Figure 6: Quality Function Deployment ....................................................................................... 33 Figure 7: Force/Energy Analysis Calculation ............................................................................... 33 Figure 8: Starter Circuit - Old Car ................................................................................................ 34 Figure 9: Throttle Circuit - Old Car .............................................................................................. 34

Figure 10: Work Breakdown Structure ......................................................................................... 35 Figure 11: Full Project Gantt Chart .............................................................................................. 43 Figure 12 Car Electrical Schematic ............................................................................................. 44

Figure 13 Arduino Auto Starting and Throttle Control System .................................................. 45 Figure 14 RPM Sense Circuit ...................................................................................................... 46 Figure 15 Arduino Code Flow Diagram ....................................................................................... 47 Figure 16: Carbon Fiber Shell....................................................................................................... 62 Figure 17: Carbon Fiber Shell Cutaway View .............................................................................. 62 Figure 18: Carbon Fiber Shell with Design Intent ........................................................................ 63

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Figure 19: Front Structure Initial Design ...................................................................................... 63

Figure 20: Front Structure Intermediate Design ........................................................................... 64 Figure 21: Front Structure Final Design ....................................................................................... 64 Figure 22: Final Design SolidWorks Simulation .......................................................................... 65

Figure 23: Correct Ackermann Steering Principle........................................................................ 65 Figure 24: Rack and Pinion........................................................................................................... 66

List of Tables

Table 1: Total Budget ................................................................................................................... 29

Table 2: Morphological Matrix ..................................................................................................... 29

Table 3: Bill of Material ............................................................................................................... 32 Table 4:Tensile Testing (Round 1) ............................................................................................... 36 Table 5: Tensile Testing (Round 1) Results ................................................................................. 36 Table 6: Tensile Testing (Round 2) .............................................................................................. 37

Table 7: Tensile Testing (Round 2) Results ................................................................................. 37 Table 8: Steering Purchases .......................................................................................................... 38

Table 9: Wheel Purchases ............................................................................................................. 39 Table 10: Body Purchases Part 1 .................................................................................................. 40 Table 11: Body Purchases Part 2 .................................................................................................. 41

Table 12: Electrical Purchases ...................................................................................................... 42 Table 13: Turn Radius Design Calculation ................................................................................... 66

5

Shell Eco-Marathon Competition

Prepared by: Alexander Timberlake, Asher Clinger, Brian Smith, Chester Gemaehlich,

Jonas Cafferty, Lee Mortimer, William Sekulic

Team CSMPG

Division of Engineering

Colorado School of Mines

Executive Summary

The objective of the Shell Eco-Marathon Competition is to create a car that maximizes fuel economy.

In previous years, Colorado School of Mines teams have achieved reasonable results using off the

shelf components and hardware. The 2013 competition team placed in the top 10 with an average

fuel economy of about 966 mpg. Building a new competition car from the ground up will give Mines

students the opportunity to experiment with novel concepts in fabrication, materials selection and

engine control systems. The processes used to create concept variants for a new design involved

reverse engineering the old car as well as using several design methodologies covered in EGGN 491.

The reverse engineering portion of the class opened up the teams minds to possible solutions for creating a car. It showed the team what has worked and what hasnt worked in the past. The design methodologies utilized were the quality function deployment, morphological matrix, function

structure, brainstorming, and force/energy analysis. These design methodologies helped develop

ideas that could be improved upon as well as uncover the major challenges that will be presented to

the team during the design process. Based on the design methodology, designs for the four distinct

subsections of the car were developed. The body and frame structure was built as a unibody framed

system. Materials were tested in order to make an informed decision as to the proper layup, structural

support and necessary rigidity. Wheels and steering have been designed around a similar sub

structure as the previous CSM competition cars. The main differences in the new design will come in

form of lubricants, more efficient wheels and minor tweaks to the sub-frame alignment to reduce

overall rolling resistance. The electrical system was redesigned from the ground up. Wiring

assemblies, engine controller interface and driver interface were designed in order to reduce driver

variability and improve the safety of the car. The engine being used in the old car was found to be

excessive in size and horsepower. In order to squeeze the most efficiency out of the new design,

software tools were setup in order to determine the required power necessary to move the car and

driver around the course at a 15 mph average speed. When chosen, the new engine should be smaller

and more efficient to operate. The teams end goal was to design a new car to achieve 1500 miles per gallon. We planned on achieving this by making the car lighter and more aerodynamic, having an

improved electrical system, correctly sizing the engine, upgrading the transmission, and tuning the

steering. The car was made lighter by making a unibody shell design out of carbon fiber that requires

little to no internal framework. The team designed a new body in SolidWorks and used the flow

simulation software to reduce the coefficient of drag of the design. Installing a throttle controller for

the acceleration of the vehicle is an example of an improvement to the electrical system. Controlling

the acceleration electronically is beneficial because it removes the driver induced variations that

lower gas mileage. Through calculations it was determined that the current 50 cc engine is too large

for the car and it would be beneficial to switch to a smaller engine. Upgrading to a three speed rear

hub is another example of an improvement made to the vehicle. This will allow for lower RPMs at cruising velocities which will maximize our engine efficiency. Lastly, regarding the steering, the

caster, camber, toe, and Ackerman angle can all be tuned to help the performance of the car. In this

report, we will discuss the concept variants that have been developed for each subsystem of the car,

the process of developing the detailed design for each subsystem, and the process of constructing

several subsystems.

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7

Shell Eco-Marathon Competition

Prepared by: Alexander Timberlake, Asher Clinger, Brian Smith, Chester Gemaehlich,

Jonas Cafferty, Lee Mortimer, William Sekulic

Team CSMPG

Division of Engineering

Colorado School of Mines

1. Introduction

The steps that have been followed to develop a new design for the 2014 Shell Eco-Marathon

Competition are the following: identify customer needs for each subsystem of the car, develop

concept variants for each subsystem, choose the best concept variant based on engineering

analysis, create a detailed design for each subsystem, and finally begin construction of the car.

Customer needs were determined through interviews with lead users and other stakeholders,

namely previous years competition team members and experts in different fields of design. Based on seven interviews, several latent and constant needs became apparent for our project.

These needs included making the frame and body lighter, making the car more aerodynamic,

improving the alignment, improving the electrical system, resizing the engine, and increasing the

drivetrain efficiency. All of the customer needs from the interviews were used to create a Mind

Map with three main categories of focus and minor points corresponding to each of the

categories.

The first point is vehicle weight. The current Mines Shell Eco-Marathon car has a weight of

approximately 120 pounds, but there are several cars at the competition which carry a weight of

less than 100 pounds. Based on this fact, one of our goals has been to redesign the frame and the

shell such that our car also weighs less than 100 pounds. We have set a delighted goal of 85

pounds meaning we dont necessarily expect to achieve this result, but we would be delighted if that is the end result.

Secondly, from the interviews we conducted, we determined that there were several components

and imperfections that could use major improvements. The aerodynamic shape of the car was

identified as an area of concern. One noticeable issue with the current Mines car is the lip

between the windshield and the body; the windshield overlaps the body causing a discontinuity

in the airflow resulting in eddies and turbulence. During the interview with Dr. Sullivan, he

explained that this lip could be a significant percentage of the total drag [1]. A proposed solution

was to create notches in the body so the windshield sits flush with the surface and has a smooth

transition to the rear of the vehicle. Another area of concern regarding the aerodynamics was the

bottom of the car and its non-rounded design. During the interview with Dr. Passamaneck, he

pointed out that the shear drag from the bottom of the car would be large. The large drag is due

to the flat shape and close proximity to the ground [2]. A suggested fix was proposed to slightly

round the bottom of the new body design. In addition to this, lifting the car slightly higher off the

ground would reduce this viscous shear on the bottom of the car. The lift would compromise the

cars stability slightly, but that was accounted for with other design choices. Finally, the wheels and axle provide a significant percentage of drag due to their blunt cross section. There were two

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recommended solutions: design a body where the wheels will fit inside the shell or install

aerodynamic covers that deflect the air around the wheels & axle.

Third, from interviews with the old team members, it was determined that the electrical system

was in need of an upgrade and reorganizing. The old team members pointed out that a major

improvement to the gas mileage of the car could be achieved through proper tuning of the

electrical system. They also suggested the improvement of upgrading to MegaSquirt III from

MegaSquirt II. Also, driver induced variations in the acceleration were identified as consuming

extra gas. A useful electrical system that could be implemented is a throttle control that could

automatically manage the acceleration of the car.

Lastly, Dr. Passamaneck emphasized the importance of tuning the alignment of the car [2]. The

variables to consider are the camber, caster, toe, and Ackerman angle. The camber and toe need

to be zero degrees due to the fact that this causes the least drag. Even though there are stability

and control benefits from adjusting these two variables, they will negatively impact the rolling

friction. Ultimately the team is more concerned with reduced friction rather than improved

stability or control. The caster should be about one to two degrees with the steering pivot point in

front of the contact point, as this makes the car more stable. The last variable is the Ackerman

angle; this is the angle between the front axle and the pitman arms when they are in the neutral

position. The basic rule of thumb is that the pitman arms should point straight at the center of the

rear axle.

2. Design Methodologies

Team CSMPG conducted several design methodologies during the post-disassembly analysis of

the old Shell Eco-Marathon competition car in order to develop concept variants. These design

methodologies included creating an exploded view, bill of materials (BOM), quality function

deployment (QFD) matrix, morphological matrix, function structure, force diagram, and

performing a subtract and operate procedure. Out of these methodologies the ones that had the

most insight were developing the function structure, QFD, force diagram, and morphological

matrix.

To start, the final function structure follows the inputs of information, energy, and mass through

the system. The informational input deals with steering the car. While the driver is driving the

car he/she is taking in visual, auditory, and tactile information. Some examples of the types of

information are: the driver can see where the car is going and if the car is on course, the driver

can hear the engine as the car accelerates, and the driver can feel the steering wheel turn with the

road. These sensory inputs are used to make decisions on whether or not to accelerate/decelerate

or turn the car. To perform either of these actions requires a human interface. This is where the

mass input comes into effect. The driver uses their hand to turn the steering wheel or apply the

throttle/brakes. This is human energy being transferred into mechanical energy. This mechanical

energy is then transferred to the wheels where it is converted into rotational energy. This

rotational energy is then transferred to the ground where it is converted into translational energy

and thermal energy caused by friction. The translational energy causes the car to change

direction or accelerate. Thus, the outputs of the functional model are direction, acceleration,

translational energy, thermal energy, and the drivers hand. By creating the function structure,

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energy flows were much easier to identify. Eventually this helped the team members develop

better concept variants for the subsystems of the car.

The QFD helped solidify the stakeholders needs and organize them based on priority. It also helped explore the different ways to meet these needs and the obstacles that will need to be

overcome. For example, the QFD helped identify the engineering metrics that have a positive

and negative correlation for the vehicles performance. A few metrics that have a negative correlation are reducing the weight of the car by 10kg and all of the strength requirements of the

car. It will be a challenge to maintain the strength of the car while also reducing the material.

Depending on the design, the more material used in the frame and on the body, the stronger those

components will be. The options to overcome these obstacles are laid out in the morphological

matrix.

Lastly, a force diagram was evaluated for the car, based on the analysis; the rolling resistance

constitutes most of the drag applied to car at an average velocity of 15 mph. An EES program

was developed to evaluate the forces affecting the cars overall fuel efficiency. From these results, aerodynamic drag accounts for 28% and rolling resistance accounts for 72% of the

influence on fuel efficiency at the average velocity.

3. Body, Frame, and Material

During the reverse engineering portion of this project customer needs were gathered from

research and interviews with knowledgeable professors. As previously mentioned, it was

determined there were two main needs that pertained to the body and frame of the car. These

needs were to make the car lighter and more aerodynamic while still maintaining the strength of

the design [3]. There are many options to achieve these needs such as changing the design or

material of the body and frame. The concept variants were determined through many

brainstorming sessions. Some tools that were used in these sessions were creating a mind map

and playing Brainball.

From the brainstorming sessions, it was determined there are two primary directions that could

be taken for design of the body. The first option is to use the current concept of a structural frame

with an outer shell. The second option is a unibody car that has its structural supports built into

the shell. There are pros and cons for each design; for example, a unibody car will have better

aerodynamics because it will get rid of the lips created by interfacing a frame and shell. In

addition to removing lips, it is possible to design an overall better aerodynamic shape for the

unibody because the structural members are built to fit the shell design [4]. Conversely, with

option one, the body design has to be constrained to fit the frame. If designed properly, a

unibody will also be lighter because it will get rid of the weight of the frame. However, a

unibody design requires more engineering, longer time to construct, and is challenging to build.

An advantage of option one is that it has been done by previous teams. This would provide a

foundation for a new design, again, making option one an easier route. Option one is clearly

simpler but it has certain limitations that go with the design.

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Through much brainstorming and the use of a decision matrix, the team decided a unibody

design would be the best alternative. The primary reasons for this are the team believes a

unibody design is more advanced and has a higher potential for performance. If engineered

correctly, a unibody will be lighter, more aerodynamic, and have greater strength due to the

structure being implemented directly into the body.

A decision that was made in parallel with choosing a unibody was what material to make the car

out of. Since a unibody was chosen, the practical materials to choose from were carbon fiber and

fiberglass. It was not immediately clear which option was best because they are similar in nature.

Carbon fiber has a greater strength to weight ratio, but it is more expensive. To make an

informed engineering decision, our team performed tensile tests on many different samples of

carbon fiber, fiberglass, and combinations of the two. Results from the testing can be seen in

Tables 4 through 7. From this testing and analysis of our budget, we decided carbon fiber was

the better option. We had more than enough money to purchase all the carbon fiber we needed

and the results from the tension testing conclusively proved carbon fiber was superior in

strength. We also determined the number of layers of carbon fiber we should use for the car

through the results of our testing. We determined that six or more layers should be used in areas

of high stress and four to six layers should be used in areas of low stress.

Before we could begin the design of the car, there were a few other decisions that needed to be

made that affected the geometry of the shell. These decisions were: three wheels or four wheels,

wheels inside or outside the body, engine in front or behind rear tire, and front or rear wheel

steering.

The first of these decisions that needed to be made was whether to have a three wheel design or

a four wheel design. The three wheel design won by a landslide in our decision matrix. A three

wheel design would weigh less, be simpler to design, cost less, give the car better aerodynamics,

and be easier to build. There is basically no reason to have four wheels for this competition, as

history shows that virtually all of the top performing cars are three wheel designs.

The next decision to be made was whether to have the wheels on the inside or outside of the car.

This decision was not as easy as some of the others because there were uncertainties in the

criteria. For example, it was not clear which decision would actually result in a better

aerodynamic shape. Having the wheels on the inside of the car would reduce the viscous drag

from the wheels and axle, though having a larger frontal area for covered wheels would increase

overall drag. To determine which design would be best, the team performed SolidWorks Flow

Simulations on several different designs. From the results, it was evident that having a smaller

frontal area was more important to aerodynamics than having the wheels on the inside of the

body. Some other benefits of having the wheels on the outside of the body are greater stability

(from a wider wheel track) and less weight (from a smaller body). Thus, the team decided to go

with the wheels on the outside of the body.

Next, we had to decide whether to have front wheel or rear wheel steering. The primary criteria

for this decision were the stability, the rules, and ease of interfacing the engine. Having front

wheel steering is more stable than rear wheel steering due to weight distribution throughout the

car, especially during a turn. The rules make it difficult to incorporate rear wheel steering. Also,

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if you have rear wheel steering it makes it harder to interface the engine. Thus, the teams decision was front wheel steering.

Once the team decided on front wheel steering, the next decision was where to place the engine

in the car (in front of or behind the rear tire). One benefit of having the engine in front of the rear

tire is it helps shift more weight to the front tires. Since we have front wheel steering, this is

beneficial. However, having the engine behind the rear wheel greatly reduces our wheelbase

which improves the turning radius of the car. Also, if the engine is in the back, the exhaust can

be released into the pressure void behind the car which improves the aerodynamics. After

performing the decision matrix, it was determined that having the engine behind the rear tire

would be most beneficial.

Now that these four decisions were made, it was possible to begin the detailed design of the

shell. The design method of choice was SolidWorks due to its immense computational abilities

and ease of use. To determine dimensions of the car, measurements were made for the foot

space, head room and length required to fit a 5 6 driver. The dimensions were rounded up slightly to ensure the inside of the design would not be so small that the next team could not find

a suitable driver. Based on these dimensions, three cross sections were made on offset planes

representing the foot space, head area, and back taper of the car. These three cross sections were

connected by four guide curves; one on top, one on bottom, one on the left, and one on the right

of each cross section. Using these guides curves, the three cross sections were lofted together to

give the car a smooth and gradual transition between the three cross sections. Once this major

part of the body was completed, the nose and fin were created using several other SolidWorks

features. The goal of the design was to minimize the drag. Therefore, flow simulations were

performed in SolidWorks to optimize the guide curves. The guide curves could be slightly

adjusted to tweak the shape of the design. Many iterations were made between adjusting these

curves and testing the results in the flow simulations. After about a week of these iterations, the

team came up with the final design for the shell which you can see in the Appendix. The final

design came out being 136 in length and 18 wide by 21 tall at the largest cross section with 9 radius fillet. Also the rear cross section has a height of 8.6 and width of 5.6 while the front cross section is a 5.5 radius circle with a flattened bottom.

Once the final design was set in stone, the construction of the mold could begin. This process

took several months to complete. Other than being a time consuming process, we experienced

delays in shipping of vital materials. The process begins with making the basic shape of the mold

out of styrofoam. Two of the team members developed a clever method of projecting cross

sections of the design in Solidworks onto flat sheets of styrofoam to accurately cut out the 72

cross sections necessary to build the molds shape. These styrofoam cross sections were then glued together and smoothed out using a cheese grater. Grating ensured there were smooth

transitions between each individual cross section of foam. Once this basic shape was created, the

next step was to apply bondo on top of the styrofoam to create a smooth outer layer on which we

could apply carbon fiber. Unfortunately, the team learned that when bondo is mixed with its

hardener, an exothermic reaction is created which shrinks the styrofoam. To mitigate this, the

team began to place drywall tape over the styrofoam to create a layer between the foam and the

bondo. Applying the bondo was not a simple task. It took many applications to cover the entire

surface and required many iterations of applying bondo and sanding to get the right shape. Once

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we reached an acceptable shape, several layers of primer were added on top of the bondo. These

layers of primer were then wet sanded to make the outer surface silky smooth. We needed the

outer surface of the mold to be as smooth as possible because if there were any imperfections,

resin would get trapped and make it difficult to pull the carbon fiber off the mold.

After many Tuesday and Thursday mornings of alerting the senior design lab to our presence

with the deafening noise of power sanders and the pungent smell of bondo, we were finally ready

to construct the shell. This process does not take nearly as long as making the mold. In fact, it

had to be done all at once over the course of a few hours. Despite being a much faster process,

the difficulty is substantially greater. One mistake from laying up the carbon fiber could cost the

entire semester of work. Realizing this, we did a practice run before doing the final lay up.

For the practice run the team laid carbon fiber on the top half of the mold to get an idea of what

to expect. Just doing the top allowed us to pull off the carbon fiber without damaging the mold.

The basic process involved first applying wax and PVA to the entire mold. These two both help

the carbon fiber from sticking to the mold so that we can pull the shell off the mold after it has

hardened. Next, we applied one base layer of resin over the car and begin laying carbon fiber

pieces over the car. After each layer of carbon fiber, we applied more resin and use flat paddles

to squeegee the resin into the carbon fiber.

The resin is an epoxy based resin that we mixed with a hardener before applying. To ensure a

constant ratio of resin to hardener, we had the same person do all the mixing and pouring of the

resin. Before starting this process, we precut different pieces of carbon fiber, ranging in size from

about 2 x 4 to 2 x 11. This was required as we needed to lay up the carbon fiber quickly or else the resin would harden prematurely and prevent the different layers from bonding together.

From our test run, we determined we should have pieces that go lengthwise down the car, pieces

at a 45 degree angle, and pieces at a 90 degree angle to the lengthwise pieces.

The primary difference between the test run and the actual lay up was the final lay up required

wrapping the carbon fiber pieces completely around the mold. Thus, we needed a system to

suspend the car in the air. The solution was to use adjustable straps to hold the mold in the air.

We attached these straps to the I-beam in the ceiling in the senior design lab. This added a

significant degree of difficulty to the process because every time we needed to apply another

layer in the area of one of the straps we had to remove it and reattach it somewhere else. Thus,

for each layer of carbon fiber this had to be done three times while squeegeeing resin into the

shell. The straps presented another problem besides just creating an awkward working

environment. They put pressure points on the carbon fiber and caused the layers to move and

fold. This unexpected circumstance made it even more difficult for the pieces to lie flat and

without wrinkles. Needless to say, there were many areas during the lay-up process which could

have proven to be disastrous. The team was prepared and efficient in their work so luckily any

major setbacks or problems were avoided.

The final lay-up has three layers of lengthwise pieces, four layers of alternating 45 degree pieces,

and two layers of 90 degree pieces. From the tensile testing it was determined we needed a

minimum of six layers; however, we decided a few extra layers would be beneficial with regards

to strength and safety of the shells integrity. After all the layers of carbon fiber were squeegeed

13

full of resin, the next step was to cover the entire car in peel-ply and place it in the vacuum bag.

To add more resin on top of the car we also inserted a green mesh sheet. The mesh stores resin in

the weave, so we poured a very generous amount on the car at the end. Once this was done, the

final step was to connect the vacuum bag to the vacuum pump and pump out all the air and

excess resin. Once the carbon fiber and resin had hardened, we cut out three sections from the

shell. There was one cut-out for the engine placement, one for the windshield, and one more for

the driver to enter the car. The entirety of the foam and bondo mold was removed from the

interior through these three sections.

The completed shell weighs 56 pounds and is very strong; it can easily support the weight of an

average sized human and it withstood being hit by a sledgehammer many times (we hit the

outside of the shell many times to loosen the mold from the carbon fiber). Since the shell came

out so strong, it was determined that we will not need to add any additional carbon fiber support

structures. The only thing left to do with regards to the body is fit a windshield to the shell and

make minor changes to the shell to interface the other subsystems into it. This will be left for the

next team to complete.

4. Steering

One of the main decisions made at the nascent of the project was whether to use front or rear

wheel steering. There were clear advantages and disadvantages for each option. Front wheel

steering is widely in use in automobiles and other vehicles. Since most existing automobiles use

front wheel steering, there is a plethora of good information that already exists. It would also be

easier and more affordable to get parts if we went with front wheel steering. An advantage of

using rear wheel steering is that it would allow a lower cross sectional area in the front of the car

to allow it to be more aerodynamic [4]. From group discussions, we determined that it would be

difficult to make one end of the vehicle responsible for both steering and the drivetrain

connection. One of the main reasons we found this to be a challenging configuration is that the

wheel(s) would be introduced to torque-steering, causing unpredictable feedback for the driver.

An easy way we avoided this interference was by making the front wheels become the mode for

our steering and the rear wheel to transfer the power from the engine.

An important concept we considered and future teams will have to take into account is the

Ackermann steering principle. This principle is the relationship between the front wheels and

how they relate to each other during a turn. While in the middle of a turn, the front inside wheel

will be traveling at a smaller circle and a greater angle than the outside wheel [6]. With our goal

to achieve the most efficient vehicle, we designed to achieve the correct relationships and

geometry of the wheel alignment. If there is an incorrect alignment, then the vehicle would be

compromising fuel economy and could have other problems arise. Camber, caster, and toe were

also alignment criteria we considered when designing. Optimizing these three values leads to

minimal friction between the tires and the road.

Through brainstorming and research we discovered several ways that we can incorporate steering

into our car. They included: lever-arm actuated steering, rack and pinion, and electrical steering.

The lever arm steering was the most basic design, and there are several different types that could

have been incorporated into a car [7]. This type of steering can be seen on equipment from

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companies such as Toro, Walker, Bob Cat, and John Deere. Some of these applications are

controlled by hydraulics, brake, clutch or lever mechanisms and allow the vehicles to turn in a

very small radius. We could have taken the basic principle and used connecting rods to interface

the wheels and steering apparatus. With the Shell Eco-Marathon Rules, we were restricted to

using a steering wheel type of device where both hands are able to obtain full control of the

vehicle at all times. One advantage of this is that is it a fairly inexpensive method to apply to our

vehicle. One of the disadvantages of this steering is that it will have metal rods and more pivot

points, which could cause the car to weigh more and become less aerodynamic due to a large

frontal area.

Another steering method we considered was using a rack and pinion. This is widely used in

almost all automobiles today. After conducting research on the topic, we found a few external

rack and pinions in which there was a two gear connection that was exposed to the outside. One

gear is a round gear connection from the steering device, and the other is a flat gear that connects

to the wheels and turns them to the desired direction. While this device is compact and has few

components, it still has external moving parts that pose a potential for other problems. With a

more modern rack and pinion, everything is housed internally except for the tie rod end

connections. The advantages with this type of system include: reduced moving parts, fewer

connections and a very adaptable platform that will allow us to incorporate the Ackermann

Steering Principle.

The final option we looked into was an electronic steering system. This method is allowed in the

competition, but the rules emphasize to ensure the safety of the driver. This means a backup

mechanism would have been required in the case of a failure in the system. Overall this system

had some great advantages. One of these was that it would allow us to place the steering device

at almost any location. Another would have been the small footprint in the cockpit of the vehicle,

as the components involved in an electronic steering system are typically spread throughout a

car. There were also some disadvantages that came about from the systems need for electric power. This would have added weight to the vehicle through the requirement of a larger battery.

A bigger battery would be needed to ensure the system had sufficient power to operate for the

duration of the competition. It would have also made the steering components more complex and

required more effort to ensure it followed all of the rules set forth by Shell.

Based upon several design criteria, the team decided to select a rack and pinion steering method.

This decision came down to a desire to keep the steering simple and remain well within all rules

specified by Shell. The rack and pinion method poses the least risk to the driver. It also is very

widely used, so finding spare or replacements parts would be rather easy. We were able to order

parts for the rack and pinion, but we ran into a familiar problem of not receiving the parts in time

to complete the project. The components were ordered about 2 months prior to the date of Trade

Fair, but they failed to reach our hands in time. Upon completion of this report, we have still not

yet received the needed parts.

5. Wheels and Hubs

When considering ideas for the wheels and hubs of a new car design, the rules presented by Shell

for the competition allow for freedom of choice for both matters. The wheel size and tire type is

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not restricted, but, in accordance to Article 41 of the 2013 Shell Eco-Marathon Rules, The wheel axles must be designed for cantilever loads (like in wheel chairs) rather than for load

distributed equally on both sides (like in bicycles). This note by the race organizers promotes the engineering of a more complex hub and axle system, for which many concepts have been

brought about in our brainstorming process.

When conceptualizing different designs for the CSMPG vehicle, the wheels, hubs, hub/axle

mounts, and braking methods were all considered as a subsystem due to the dependence on each

other for their integration into the car body/frame subsystem, as well as the steering subsystem.

The main design concepts that were approached for this subsystem were wheel size, wheel and

hub strength parameters and requirements, hub/axle mounting mechanism, hub/axle mount

integration, rear hub capabilities, and brake design compliance with the foregoing parts of this

subsystem.

The design constraints for the wheels and hubs of the car were to be determined by the overall

design of the body and drivetrain, as front or rear steering and weight distribution for the car play

a large role in determining wheel size and strength, and, therefore hub mounting configurations.

For example, a stronger wheel construction will be required for a heavier weight distribution on a

single wheel, and a lighter wheel construction will be allowed for a lower weight distribution

between two wheels. Hub choice is also dependent on the hub/axle mount configurations that

will be determined by the overall vehicle layout and steering. Once the body and frame

subsystem ideas have been determined for the vehicle, the following concepts presented for the

wheels, hubs, and brakes can be used for determining the best configuration.

The ideas we have presented for the overall layout of the vehicle include three or four wheeled

configurations. Some advantages of a three-wheeled design would be lower rolling resistance,

fewer components and better aerodynamics as a result of the more compact design. Some

disadvantages would be the high weight concentration on the single wheel and the independent

braking system required for the single wheel. A four-wheeled design would provide design

benefits due to symmetry, such as more even weight distributions across the four wheels and

front and rear axles compatible with integrated braking. The disadvantages associated with a

four-wheeled design are the increased rolling resistance and addition of more components, which

would increase weight and reduce aerodynamics.

The hub/axle mounting techniques present the greatest challenge for designing the vehicle. Some

ideas surrounding the axle mounting method for a three-wheeled vehicle are, For the two-wheel

end of vehicle: a single axle with one brake for both wheels, a single axle with brakes on each

wheel, independent axle-less hubs for both wheels with brakes for each wheel, and the use of an A-Arm rigid suspension. For the one-wheel end of vehicle, some design concepts are a

symmetric hub/axle mount in the body/frame and disc or rim brake compatibility. Some ideas

surrounding the axle mounting method for a four-wheeled vehicle are: single axles with one

brake for both wheels, single axles with brakes for both wheels, and independent axle-less hubs for both wheels with brakes for each wheel. These concepts all present viable concept

variants, but the final selection will be dependent on the vehicle layout and body/frame design.

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Our team found four different types of hub mounting concepts that would be compatible with an

axle-less hub design. These include: a Cannondale Lefty spindle axle arm, a TerraTrike 20mm thru-axle hub mount, a Surly trailer stub axle, and a custom 15- or 20mm thru-axle hub mount.

For a single-axle design, a threaded end is the main hub mount concept, as a single-axle would

already have its body/frame integration included through housings with bearings.

The key design influences for these types of hub mounts are steering incorporation, hub selection

and body/frame integration. Axle-less hub mounts would be easier to utilize for our steering

concepts presented above, and a single-axle design would be easier to incorporate into our

body/frame concepts. The axle-less hub mounts would allow for fewer and lighter components to

be used when integrating with the steering components and their design could be optimized for

the connections between the steering components and body/frame.

For the varying wheel strengths required by the different vehicle layouts and hub configurations

presented thus far, wheel size and spoke count are the most important factors that come into

consideration, as well as hub flange width and hub design. The bicycle wheel promotes many

key features that are beneficial to our overall goal: lightweight, aerodynamic, and easily

implementable. While the excerpt from the rules mentioned previously note that bicycle wheels

are not designed to handle substantial lateral forces such as the ones our vehicle will be subjected

to on the race course, certain methods in the wheel building process can be used to provide the

strength required for our purposes. Wheel stiffness is determined mostly from the hub flange

width - or the distance between the edges of the thru-holed plates on each side of a bicycle hub -

and the size of the rim being laced to. General relations for these two factors are: wider hub

flanges provide greater stiffness because of the lateral tension being created by the spokes that

are laced to the rim, and smaller rims provide greater stiffness because of the increased angle of

the wheel spokes between the hub flange and the vertical plane of an upright wheel- therefore

also increasing the lateral tension created by the spokes. [8] These concepts will be taken into

consideration when determining the types of hubs and size of wheels that will be used for the

final vehicle layout. Spoke count on the wheel is a large determining factor for the overall

strength of the wheel, as in how much weight it can support under radial loading. The spoke

counts will also be determined by the layout of the car, as we will be looking to have the best

balance between wheel weight and wheel strength for the appropriate corners of the vehicle. If a

three-wheeled layout is chosen, a high spoke count and small rim will be required for the one-

wheel end of the car, as that particular wheel will be introduced to both a heavier weight

distribution and more concentrated lateral forces in turns. If a four-wheeled vehicle is chosen, the

spoke count will be determined by the weight distribution from front-to-back, with the heavier

end requiring a higher spoke count. General wheel building theory is covered more in depth by

The Bicycle Wheel by Jobst Brandt.

Common bicycle freehubs come with hole-counts of 24, 28, 32, 36, 40, 42, and 48, and common

bicycle rims come in sizes of 16-, 20-, 24-, 26-, 27-, 29-inch, 650b (583mm), and 700c (622mm).

Hubs with fewer holes will be lighter, just as rims with smaller diameters will also be lighter.

Compatible hubs for the hub-mount designs presented above are: Cannondale Lefty Hub (24 or

32 hole) for the Cannondale Lefty spindle axle arm, Surly Bill and Ted trailer wheel hub for the

Surly stub axle, or any mountain or road bike 15- or 20-mm thru-axle hub for the TerraTrike

assembly or a custom mount. Hubs can also be determined based on our braking needs; the Surly

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hubs and some 15mm thru-axle hubs are not disc brake compatible, but the Cannondale Lefty

hub, most 15mm thru-axle, and all 20mm thru-axle hubs are disc brake compatible only. The

Cannondale Lefty hub is a very attractive option because it has already been designed to manage

greater lateral loading than a symmetrical hub.

Another design concept that came about through team discussion was concerning a multi-speed

hub for a three-wheeled vehicle layout with a single powertrain wheel. This would have the

benefit of matching the vehicle engine speed to the actual vehicle speed to improve efficiency,

but an internally-geared hub weighs substantially more than a freewheel hub. [9] The

effectiveness of an internally-geared hub will be determined by the logistics of the race plan

regarding vehicle speed and acceleration, as well as with a cost/benefit analysis for the added

weight in comparison to the added efficiency.

With the consideration of all of the previous design decisions, the team ultimately chose a three-

wheeled, front wheel steering, rear-wheel drive configuration for the car. This prompted the use

of a stub-axle design for the front wheels, implemented with Cannondale Lefty spindle hub

mounts with Cannondale Lefty 32-hole mountain bike hubs. The spindle hub mounts were

donated by a local bike shop, Pedal Pushers Cyclery, so this in addition to the previous cars design also utilizing this setup resulted in the decision to move forward using them. The 32-hole

Left hubs were chosen because of their high spoke-count, but they still needed to be paired with

appropriate rims in order to provide the necessary strength for the cornering forces the car would

be subjected to on the course. In order to achieve this wheel strength, 20 Velocity Aeroheat 32-hole rims were chosen, with DT Swiss Champion spokes (183mm length for rear spokes, 185mm

length for front spokes) to complete the wheel build. The wheels were assembled by Pedal

Pushers Cyclery. In addition to choosing the Cannondale Lefty setup for the front wheels, the

team opted to use a three-speed hub for the driven wheel. The hub selected was a Shimano

Nexus-3 hub, and was also laced to the 20 Velocity Aeroheat rims.

6. Wheel, Steering and Body Integration

With the wheels, hubs, steering, and body configurations and designs all completed, the team had

to develop a design to integrate all of the subsystems in order to create a rolling chassis. The

carbon fiber shell design resulted in the need for separate structures to mount the front and rear

wheels, as well as the integration for a steering mechanism.

The front structure was of the most concern because of its combination of mounting the front

wheels and including the steering mechanism for the car. In order to design a lightweight

structure, the materials the team considered were aluminum and titanium due to their high

strength-to-weight ratios as compared to steel. Upon researching methods for integrate aluminum

and titanium into a carbon fiber based platform, it was realized the aluminum would not be a

satisfactory choice since it causes Galvanic corrosion when interfaced with carbon fiber. This

could be addressed by anodizing the aluminum with a sulfuric acid, but this solution only lasts

for one to two years. In order to remove the possibility of corrosion and to have the best strength-

to-weight ratio possible, the team chose to use titanium for the structure. At the time the design

for the front structure began, the carbon fiber lay-up process had not yet begun, and therefore all

of the designs for the structure were based off of the SolidWorks model for the vehicle mold.

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This ultimately resulted in the SolidWorks designs of the structure being guidelines for the actual

fabrication process, but they did provide reasonable accuracy for loading simulations.

The design of the front structure was based on a classic A-Arm configuration commonly seen in

cars and other vehicles with independent suspensions. The initial goals for the design were: to

have as little impact on the carbon fiber structure in order to maintain the vehicles rigidity, include multiple points of contact on the carbon fiber structure in order to provide adequate

connection strength between the shell and the wheels, incorporate an appropriate amount of room

for the driver to fit through the structure, provide an adjustable kingpin alignment, and allow for

a steering mechanism to be installed alongside the structure. The SolidWorks designs were

simplified by removing the requirement of adjustable alignment angles because it was assumed

that separate lower support arms would provide the adjustability required.

The first series of designs were based on mounting the A-Arms to built-up platforms in the car.

This design can be seen in Figure 19 in Appendix C. This design was not used because of the

complicated manner in which it would be mounted to the car, would be difficult to ensure proper

alignment, and would be over-dependent on the structural rigidity of the unproven carbon fiber

structure.

The next series of design were based on connecting the A-Arms for both sides together across

the middle of the car. This design removed any over-dependence on the structural integrity of the

carbon fiber, and would provide a more symmetric result in the fabrication process. This design

can be seen in Appendix C Figure 20. This basic design was chosen for the front structure, but

was simplified again in order to allow to more consolidated loading simulations. The final design

used as the guideline for the fabrication process and final structural simulation can be seen in

Appendix C Figure 21, with the SolidWorks simulation results found in Appendix C Figures 22.

When it came time for the fabrication of the front structure, the final SolidWorks design was

only used as a guideline, and was simplified even further by replacing the separate pieces for the

A-Arms with single pieces of the titanium tubing bent to form the A-Arms. This was done with a

three-die tubing bender, with the shape of the pieces dictated by the actual carbon fiber shell

measurements. The lower support hoops were also made using this method. The downfall to

fabricating the structure this way was that none of the parts were precisely symmetric and that

some of the tighter bends in the tubing resulted in crimping of the titanium. These problems were

unavoidable though, as the shape of the carbon fiber shell was not symmetric and included

tighter bends than what we were able to achieve with the tubing bender.

The lower support arm from the final SolidWorks design was also changed in order to

accommodate for adjustment of the front wheel alignment. Instead of a single piece of tubing

spanning the distance between the two kingpins for the spindle hub mounts, two pieces were

used with a three inch gap between their ends in order to allow for a range of motion for each of

the kingpin angles.

In order to mount the hub spindles and kingpins, larger tubing was cut into short sections and

welded to the ends of both the top A-Arms and the lower support arms. A kingpin tube was cut

to length to fit from the top of the A-Arm ends to the bottom of the lower support arms, with

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excess room on each end to insert cotter pins. The hub spindle mount, A-Arm connection, lower

support connection and kingpin were all mated with steel bushings to allow for rotation and

efficient steering. Two bushings were press fit into the hub spindle mount and one bushing was

press fit into the top and bottom structure connections. The hub spindle mounts needed their

inner diameters machined in order to allow for the press fit of the bushing. The bushings were

also machined on both the inner and outer diameters in order to fit into the hub spindle mounts,

top and bottom structure connections and kingpin.

All of the bent tubes that comprised the bent tubes of front structure were 0.75 OD x 0.049 WT Grade 2 titanium. The larger tubing used for the end connections of the structure were 1.5 OD x 0.07 WT Grade 5 titanium. The kingpin tubing was 1 OD x 0.07 WT Grade 5 titanium. The steel bushings for the top and bottom structure connections were 1-3/8 OD x 1 ID x L and the steel bushings for the hub spindle mount were 1-1/4 OD x 0.9062 ID x 1-1/2 L.

The tubing structure was welded together using a TIG welder and titanium filler rods. The use of

single tubes for the top A-Arms resulted in fewer total welds than were shown in the final

SolidWorks design. This increased the structures overall strength by limiting the possibility of weak welds, and also made it less complicated for the welder.

At the time that this report was written the final assembly of the front structure was not complete.

This was due to the careful attention that was required to ensure proper alignment of the kingpin

angles. Also, the asymmetry of the carbon fiber shell and bent tubing resulted in unequal kingpin

lengths for each side of the car. This was being addressed and the fabrication was ongoing at the

time of this report submission.

7. Electrical System

The electrical systems on the existing Shell Eco-Marathon car are fairly simple with the

exception of the engine controller. Discussions and interviews were held with former Colorado

School of Mines Shell Eco-Marathon Team members, Dr. Passamaneck and Darek Bruzgo to

determine where the electrical systems could be improved or enhanced on the new car being

designed. Key electrical items to be addressed for the new build are wiring, better tuning for the

engine controller and a method to automatically control engine starting and throttle control.

The electrical needs were defined as follows; safe wiring, properly sized circuits, an accurate and

clean wiring diagram, use of terminal blocks, proper wire sizing, combining all ground points of

the car to one centralized location, and the addition of an automated starting and throttle control

system. The list of needs was pared down to three main areas of focus; electrical wiring, engine

controller and automated starting and throttle control system. Each area requires a different

approach when searching for suitable solutions.

Building a functional, safe electrical wiring system should be one of the top engineering

priorities of any project. In AC power systems, there are standards that dictate installation and

design practices for electrical wiring in residential and industrial systems. Some of these

standards can be adapted to the low voltage engine control systems found on this project. These

safety standards are found in the NEC (National Electric Code) Handbook for residential systems

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[10] . Following NEC codes will help resolve almost all of the wiring issues found in the existing

cars electrical system. Other issues can be resolved by using standardized fuse blocks, relay blocks, screw terminals, proper grounding lugs and stranded wire for all subsystems. Parts and

components used in automotive electrical applications should be sized and rated to handle

designed voltage and currents. The NEC is written for residential AC circuits, but there are

articles that can be applied to low voltage systems and most electrical equipment in the interest

of best grounding practices. Grounding issues can be found in NEC article 250, wire sizing can

be found in article 316, termination and wiring practices can be found in article 110.

Engine controller tuning was determined to be a major issue that directly affects the overall fuel

efficiency of the car. Past teams have not spent enough time ensuring that the tuning profile for

the engine was sufficiently understood and properly performed. Many former team members, our

client and faculty advisor have mentioned the need to fully understand the tuner software and

engine performance parameters. While this will be a challenge that the team taking their car to

competition will need to address, the new car may not need this expertise.

Research into suitable engine controllers resulted in the following list of possible candidates;

Megasquirt 2 [11], Megasquirt 3, Ecotrons SE-EFI, National Instruments cRIO, MSD small

engine controller and Delphi Multec. Since the main focus of this build is to get a rolling chassis,

the list was reduced to the Megasquirt 2 and 3, and the Ecotrons controller. National Instruments

was not a suitable choice due to the cost and the lack of code available for tuning. The MSD

controller was found not to be a suitable choice due to lack of sensor inputs and flexibility. The

Delphi Multec engine controller is similar to the Megasquirt units, with less online support.

Since the main focus of the build is not tuning or competition, the needs analysis determined that

the current Megasquirt 2 or upgraded Megasquirt 3 engine controller may be adequate for the

new build car. The choice in engine controller will hinge largely on sensors used in the new

engine, bells and whistles necessary to operate the car, and potential options in starter and

throttle control system needs.

The final portion of the electrical system to be designed came from discussions with Darek

Bruzgo, Dr. Passamaneck, and old team members. Through these discussions, a significant

performance change was identified when different people drove the car. Discussions and

brainstorming sessions identified several inconsistencies that could be attributed to the driver and

a lack of stable driving technique. Sources of error identified were driver steering, throttle

control, starter on/off time, hot throttle or multiple throttle cycles in a lap, the engine not starting

first time and driver error in starting or throttle control. Driver weight, car tire pressure, engine

performance and aerodynamics were not part of this discussion as they were addressed

separately. Since inconsistencies in starting, throttle ramping and throttle position could reduce

fuel economy, an automated method for controlling the engine cycle was chosen as a possible

method to reduce that variability and improve performance.

Through brainstorming, the following needs were identified for the system: simple operation,

able to be changed quickly from manual to automatic mode, possibly allow for variable starter

time, variable throttle and ramp times, have a method to reset, allow for manual operation if the

system fails. These parameters and controls should help maintain a more stable and consistent

throttle ramp and hold. Through these discussions, several possible solution schemes were

21

developed: microprocessor controlled start circuit, manual controlled starter, mechanical timer

circuits, foot controlled starter and spring starter mechanism. Schemes to accomplish this task

include: manual start with manual throttle, automatic starter and manual throttle, manual start

with automatic throttle, throttle by wire, kick start from car momentum, manual kick start with

hand or spring assist, throttle lock - motorcycle style.

Viable solutions include a microprocessor controlled starter with automated throttle controller,

electro-mechanical based starter with mechanical throttle lock and electro-mechanical based

starter with automated throttle controller. Brainstorming sessions and decision matrices helped

the team choose a manual based starter and throttle with an automated system installed in

parallel. The system was designed with the intent that either system could be engaged with the

flip of a switch.

Design and Prototype of Automated Throttle Controller

The primary goal for all systems incorporated into the car is to improve and gain efficiency and

overall miles per gallon. Electrical systems in automobiles can help improve and enhance fuel

economy but most of this improvement comes from the engine control system. The design of the

automatic throttle control subsystem has the potential to improve fuel economy by reducing

throttle hold and ramp error. Variability in driver performance is one of the contributing factors

in engine efficiency. Preliminary designs for this system incorporated a microcontroller, RC type

servo and associated relays and switches in order to provide driver controls. The system

operation would be comparable to a cruise control on a standard automobile.

Cheap microcontrollers have helped streamline the design and implementation of these type of

systems in the automotive industry. Since a simple, cheap solution was preferable to a

complicated system, the Arduino family of microcontrollers was found to be more than adequate

and cheap. The design incorporates an Arduino UNO microcontroller, chosen for the number of

digital inputs and familiar C style programming. Code can be developed using a widely used and

supported freeware format. The C programing is easy to implement and programming techniques

taught in the beginning programming class at Mines can be utilized and implemented. This

design requires numerous digital inputs and outputs for the controlling relays and reading

switches. Another key feature of the Arduino platform is the ability to define inputs and outputs

on each digital or analog pin using a pin_mode statement in the code.

For simplicity it was determined that the starting and throttle system should be installed using the

same controls the driver would use for manual control. Using a double pole, double throw

switch, the driver is able to choose between automatic and manual mode and can utilize the same

controls. The rest of the control system was developed to operate through software and not

interfere with any of the manually operated controls.

Throttle control was installed in parallel with the manual control cable through the use of a

second pulley connected to an RC servo motor. This design allows for either system to be

engaged and not interfere with the other. The RC servo was sized initially for about 60 oz-inch of

torque, using a force scale. When purchasing the RC servo from Servo City, the technical

representative suggested that the servo be sized by a factor of 2 in order to provide a margin of

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safety and provide enough power to overcome the no load torque required to move the throttle.

This servo proved to be provide more than enough torque to ramp and hold the throttle at any

location specified.

The initial design incorporated an RPM sense line fed directly from the negative line off the

spark plug ignition coil. This design was later replaced by using an IR reflective beam sensor

from Vishay, part number TCLT5000. The sensor was installed adjacent to the magneto cover

and used three pieces of reflective and non-reflective tape mounted on the cover. Arduino C has

a pulse_read timing command that reads the microsecond time for a high or low pulse, then

through some custom coding we wrote, the timing pulse was converted to an RPM signal. This

value is displayed for the driver as part of the status LCD screen.

The structure of the Arduino code contains three distinct states or modes of operation. First is the

wait for button press state. In this state, the Arduino UNO waits for a High signal from a digital

input labeled Start Enable, digital input 10. This button is configured with a pullup resistor of

about 5 kohms. The code cycles through the button loop every 150ms, allowing for quick

response to the button press and not overwhelming the LCD display with status information.

Displayed information on the LCD includes Start Timer Time and Throttle Timer time. These

timers are hooked to the analog potentiometers installed on the outside of the Arduino controller

box.

The second program state is the starting state. This state is only valid after the Start Enable

button has been pressed and acknowledged. Once this state is active, the StartLED is turned on

and when engaged, the Start Solenoid LED is also turned on. Code checks to ensure the RPM

input is below 1000 RPM and starting is high. When these two conditions are met, the Arduino

attempts to start the engine by pulsing the starting solenoid for the Start Timer time. The code

can be set with any number of attempts, but it has been found that only 2-3 attempts are

necessary to start the engine. Immediately after the solenoid is disengaged, the RPMValue is

read using the pulsein counter. If the engine is started, RPMs should be over 1000, otherwise the

algorithm will count down number of tries until it reaches 0 and exit the routine and wait for the

next Start Enable button press. If RPMs are over 1000, the state is changed to 3, Start Solenoid

LED is turned off and the program moves on to the Throttle ramp and hold state.

The third and final state for the Arduino code is the Throttle Ramp and Hold state. This state is

valid when the Start Enable button has been acknowledged and the engine RPMs are over 1000.

Code is written to take the Throttle Timer input, set it equal to a variable, Time, and use this in

conjunction with the Throttle Set variable to ramp and hold the throttle to a predetermined,

Throttle Max and Throttle Timer hold time. The delay time is set to about 50-100 ms, depending

on desired response time. This short delay time is necessary to incorporate a quick and reliable

abort scheme. Throttle Set should be greater than Throttle Max and Time should be greater than

0 in order for the Throttle hold circuit to keep running. When time equals 0 or the Abort switches

are active, the code will exit and move back to the wait for button press state.

Abort functionality is accomplished by placing a digital read command to look at the abort pin

every cycle through the throttle hold algorithm. This time, about 50ms provides more than

enough resolution and response to adequately abort the throttle sequence and ramp to idle. When

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abort is active, Abort will be printed to the LCD and the Arduino will reenter the wait for button

press state. Variables will be reset to ensure the system is ready for the next start sequence.

Final design schematics are located in the lab notebooks and the appendix of this report. The

Arduino code is also included in the appendix of this report and on the CDROM. Sizing of

relays, resistors and other components were calculated using measured coil current for the

starting solenoid (3 amps), LED requirements (20 mA), and resistors sized using Ohms law. Construction and testing were all performed on the old Shell Car with the help of the Revenge of

the Enginerds team.

Prototype and Implementation of Automated Start and Throttle System on Old Shell Car

Building and implementing the design wouldnt have been possible without a working engine and car. Code blocks were developed for testing and final implementation for each of three

subsystems. These three subsystems were the wait state, starting routine and throttle ramp and

hold routine. Once these code blocks were fairly well tested, the hardware was designed and

built to provide the necessary hardware interface between the driver and engine.

Code blocks to test throttle, starting, abort and lcd are located on the CDROM as well as in the

appendix of this report. Each test code is designed to exercise only a piece of the overall system.

Running this code should only be used under a carefully controlled environment.

Starting hardware involved a solid state relay (SSR) and start enable switch. The system was

built on a protoboard and interfaced with the Arduino using a digital input and two digital

outputs. The Arduno digital outputs control the starting solenoid and System Running LED. A

single Arduino digital input is needed for the Start Enable control. The test code also uses the

RPM sense digital input.

Automated starting is enabled by the driver by switching the Auto/Manual switch to automatic

and then pressing the Start Button for at least 250 ms. This switch is polled by the Arduino code

and when active, starts the routine. Once started, the test code tries to start the engine by

engaging the starter solenoid for a set amount of time. This time, called Start Timer, is set using

a potentiometer on the outside of the Arduino box, wired to analog input 2, A2. The starting

solenoid is engaged for the Start Timer interval and then the RPM sense code is run to determine

if the engine is running. The engine is determined to be running if RPMs are over 1000. The

engine for the old Shell car routinely idles at 1500 to 2000 RPM. Future additions or

modifications to this code might change this threshold or come up with a different method to

verify that the engine has started.

The throttle control system is engaged only after the engine has been verified as started. In order

to properly ramp and hold the throttle for a predetermined time, the throttle servo must be

ramped at a consistent rate and held at the final position for the duration of the hold time. Timing

for this operation is done by reading a potentiometer, labeled Throttle timer, wired to analog

input 3, A3 and equating this to a variable called Time. Test code written for the throttle ramp

and hold exercises the routine by ramping, holding and delaying the routine and endlessly

repeating this routine. Abort functionality was added later to incorporate abort testing on the

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same platform. Ramp time is set independently and will vary depending on the load on the back

tire of the car. For this reason, the throttle ramp and hold testing and tuning should be done using

the dyno or with a driver on a test track. Overall consistency was not determined at the time of

this report due to time constraints.

Abort functionality was tested with the throttle subsystem mainly because of the manner in

which the abort is to function. Aborting functionally sets the throttle to idle, shuts down the

automated system, all with the intent that the driver will kill the engine or restart the throttle

control system. Abort wiring was installed on the brake levers, one microswitch on each lever.

The switches are installed using the normally open contacts, in series and connect to a digital

input on the Arduino UNO. The microcontroller polls these switches every 50-100 ms in order to

quickly recognize and implement the abort code. In testing, the abort function worked correctly

and ramped the throttle to idle within 250 ms.

There were a few minor issues with the abort functionality on the car, mainly due to time

constraints and the part used in implementation. The microswitches used were mounted to the

brake levers. Unfortunately, these switches and their attached wires were not adequately

protected from damage. The wires were mounted near the brake actuating cables and near the

windshield. When turning the car, the wires were stressed which may have led to them breaking.

Persons moving the car or adjusting brake cables could have inadvertently pulled or stressed the

wires as well. This issue causes the system to start the engine, but terminate before the throttle

ramp and hold state. The solution is to problem is to replace the cheap microswitches with more

robust, enclosed switches with wiring that comes out the end, such as this part from Mouser

Electronics: 653-D2FW-G283M.

The automated starting and throttle control system was installed on the old Shell car in time for

the April 5-7, 2013 competition in Houston, Tx. Unfortunately, proper testing and tuning had not

been completed in order to determine the optimal ramp and hold times for the throttle system.

The system has been tested for proper function and to verify code, but without a running the

system on a test track or over the course of many engine burn simulations, the system will need

more tuning. The system will be tested, code verified and complete functional testing before the

FDR is turned in. Abort switches need to be reworked as specified in previous sections.

Final implementation testing was performed the week of April 22-26, 2013. Final tuning and

track runs were not able to be completed due to weather and time constraints. Overall, the

throttle system has been implemented according to the design specifications. Initial goals for the

automated system included more consistent throttle ramp and consistent throttle hold times and

more repeatable car performance regardless of driver. Given more time to test and tune, all of

these goals should be realized. The hopes for this portion of the project is that future teams will

see the value and potential efficiency gains that might be realized using this control system.

8. Engine

During the Reverse Engineering part of this project it was discovered that the current car is

powered by a 50cc Yamaha scooter engine. Using our calculations for the coefficient of drag and

the rolling resistance, we determined that this motor produces much more power than is needed

for weight of the existing car. Therefore, it is in our best interest to reduce the size of the engine

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to improve fuel efficiency, but also provide sufficient power for our new vehicle design. Using

the minimum values for the engine specifications, we searched for smaller engines and found

two additional options for the car.

In searching for smaller engines, it was found that most are two-stroke engines which are less

efficient and not allowed in this competition. There are some small displacement four-stroke

engines that are produced by power sport vehicle manufacturers, such as Honda or Yamaha.

There are two sizes of engines made by Honda that were found that would be appropriate for our

range of horsepower and torque requirements based on our calculations. They are 35cc and 25cc

in displacement, which are the two common engine sizes smaller than 50cc. The determination

of which engine size to use will be dependent on the final design for the vehicle, with major

influence from the final weight of the car.

There are benefits to each engine size for different desired performance and design aspects. With

the 50cc engine we would have an easier time finding parts and this would make the upgrade and

repair of the engine much easier. The major drawback with the 50cc engine, as mentioned

previously, is its weight and size. The primary benefit of the 35cc and 25cc engine is they are

lighter, smaller and will operate at a higher efficiency level. The major problem with the 35cc

and 25cc engine is that the parts for the engines can be harder to find. These three engines are all

pull or kick start and are carbureted. With the 35cc and 25cc engine there is also the problem that

they are not originally made to run with a chain drive. There would need to be an adapter made

to go from the clutch system to a gear that could be used to drive the wheel of the car.

Using a decision matrix and our team members experience at the competition we recommend using a 35cc engine. The size and weight of the engine will help us maintain our goal for a

lighter vehicle while still providing enough power to propel our car down the track. With the

final goal for this project being an unpowered rolling chassis we will not be installing the engine

into the car. The next team to take over this project will need to design and make mounts for the

engine and to design a way to interface the clutch to the drivetrain of the vehicle. Currently this

engine has a diaphragm carburetor in it and for the megasquirt to work with the fuel injection

system the engine would also need to be converted to have a port injection system. An example

of this port injection system can be found on http://www.ecotrons.com/. This system would

provide a port injection and provide the various sensors to get readings from the engine. These

additions will need to be implemented by the next team that takes over the project.

9. Conclusion

In conclusion, customer needs were collected from a variety of different sources. Interviews with

the previous years team members, Dr. Passamaneck, and Dr. Sullivan proved most useful. Design methodologies such as a function structure, QFD, morphological matrix, and

force/energy flow analysis were performed to get a better understanding of the customer needs as

well as prioritize the importance of each. The function structure and force/energy analysis helped

identify how force, mass, and information were transferred through the systems of the car. The

QFD helped identify possible obstacles based on positive or negative contribution between

customer needs. Lastly, the morphological matrix helped organize and develop possible solutions

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to the customer needs. After performing these design methodologies, many brainstorming

sessions were performed to develop a full spectrum of concept variants that could be pursued in

the design. The next step in the process of building the car was determining which of the concept

variants should be chosen in the final design. A lot of the minor details were determined from

team discussions and using tables to rate the importance of the advantages and disadvantages of

each subsystem.

The first major decision we made was selecting the body/frame type. This was determined from

performing flow simulations and finite element analysis in SolidWorks for several different

possible designs. Once this decision was made, the final design was optimized in SolidWorks

based on the constraints of the type of design and rules of the competition. The team designed to

be within all requirements while maintaining a very aerodynamic shape. Based upon team

discussions, SolidWorks simulations and ultimately a decision matrix, the team chose to pursue a

unibody design for the car. Several more decisions were subsequently made including: three vs.

four wheels, front vs. rear wheel steering, material for the unibody, wheels inside vs. outside the

unibody, placement of engine, steering methods, types of wheels/hubs, design of suspension,

electronic driving, and engine size.

The goal for our team was to have a rolling chassis by the end of the spring semester. We felt as

though this was a reasonable goal given time and budget constraints. Team CSMPG came very

close to achieving this goal, but