Dr. Ryan Krauss | SIUE School of Engineering

ME 482 SIUE SOLAR CAR CHASSIS DESIGN

Table of Contents

INTRODUCTION

PROBLEM STATEMENT

BACKGROUND

DESIGN STRATEGY

LITERATURE REVIEW

ANALYSIS

TIMELINE

BUDGET

CONTEMPORARY ISSUES

COMPUTERS AND SOFTWARE

CONCLUSION

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Abstract

Designing a competitive solar car requires the team to successfully integrate many different

aspects of engineering into one reliable and high performance package. Each of these aspects is important

and critical in the creation of the final product. The foundation of the vehicle, the chassis, provides the

base for which each of these components are built. The current SIUE solar car has poor handling

characteristics and limited acceleration due to its excessive weight and poorly designed front and rear

suspension assemblies. The biased weight distribution further hinders the car's capabilities. Furthermore,

stress and safety analysis were not performed for the current chassis. To correct these shortcomings, a

new chassis will be cohesively designed with front and rear suspension assemblies. This chassis will be

precisely fabricated and thoroughly tested to ensure the goals of the design were achieved. World Solar

Challenge (WSC) regulations will be strictly followed throughout the process.

Introduction

The environmental and financial impacts of fossil fuels have sparked a furious competition

among proponents of renewable energy. While gasoline and diesel powered vehicles may have dominated

transportation in the past, hybrid and pure-electric vehicles are quickly increasing their presence in the

marketplace. For this reason, many schools worldwide, including SIUE, build high efficiency, pure-

electric solar cars to compete in events such as the World Solar Challenge. To be competitive, teams must

cohesively integrate many complex electrical and mechanical systems.

All vehicles are expected to be reliable, safe, and predictable regardless of their powertrain. The

expectations are no different for a solar powered vehicle. Properly engineered chassis and suspension

assemblies play a significant role in ensuring these expectations are met. The current SIUE solar car

chassis is excessively heavy, distributes component weight poorly, and rides on a stiff, binding

suspension. Furthermore, stress and safety analysis were not performed for the current chassis. These

issues will be corrected with the construction of an all new chassis which cohesively integrates

suspension assemblies. All components will be engineered to operate efficiently and effectively during

long distance travel. Some of the primary objectives of this design will be to avoid unnecessary weight,

ensure the chassis reacts predictably to both driver and road input, reduce frictional losses, maintain

driver safety and comfort, and allow for future maintenance and repairs. The successful execution of these

goals will result in a highly competitive solar car.

Problem Statement

The purpose of this project is to design and build a new solar car chassis for the SIUE Solar Car

Team. This is necessary because the current SIUE Solar Car is not competitive in solar car races nor is it

safe for the driver under all driving conditions. Therefore, there is a lot of room for improvement. The

primary goal of this project is to build a chassis that complies with certain criteria. First, the chassis must

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comply with World Solar Car (WSC) race regulations. Second, the chassis must be able to safely operate

during normal driving conditions of 60 mph on highways. Third, the chassis must be able to protect the

driver in the event of a crash, proven by analysis. Fourth, specific design aspects of the new chassis must

be quantifiably improved compared to the current SIUE Solar Car chassis. Finally, this project must be

completed successfully in accordance with the timeline imposed by the SIUE Solar Car Team.

There are several design aspects of the chassis which will be improved upon. The weight of the

new chassis should be less than the old one. During stress testing, the stress concentrations at nodes on

the roll cage surrounding the driver should be no greater than those on the current chassis. The dynamic

stability of the new chassis must have calculated safety factors for vehicle tipping, slipping, and nose-

diving which are greater than those of the current chassis. This will be accomplished with strategic

calculation and placement of the vehicle components to control weight distribution, wheel placement,

suspension design, and movement of the center of gravity to a desirable location. Additionally, the

frontal area of the new chassis should be less than that of the old one to improve the aerodynamic

potential of the finished car. The new suspension system and wheel placement should allow the vehicle

to handle with improved stability and driver comfort on a basic figure eight and slalom test track. Some

aspects of the new and old chassis suspension to be compared are: roll center, camber, toe angles,

sprung/unsprung suspension ratio, and proper spring rate and damper use. The new chassis braking

system must allow the driver to stop the vehicle in a reliable and timely manner. Finally, the chassis

steering system must be reliable with an improved turning radius.

If all of these design aspects are completed within the allotted budget and given timeline, the new

chassis will be considered a successful project, as well as an undeniable improvement over the current

chassis.

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Background

There are two primary solar car races which professional solar car teams aspire to compete in: the

ASC (American Solar Challenge), and the WSC (World Solar Challenge). These two organizations

usually alternate years and race locations. The ASC races are held in North America during even years

and the WSC races are in Australia during odd years. The next race is in Australia on October 16th 2011,

with ASC following in 2012. In 2009, the WSC had 38 entered to race, and only 10 actually finished. In

2008, the ASC had 17 teams entered into the race and at least five finished. [1] These races are cross

country style and can span up to 1900 miles. [9]

These races require participants to create a vehicle which runs on one hundred percent solar

power. This is accomplished using photovoltaic (solar) cells to convert sunlight into electricity and store

that electricity in batteries. Energy management and weather conditions play significant roles during

solar car racing. In general, the sunnier the day, the faster and farther the car can travel.

Each team wishing to compete in a solar car race must submit fees and various engineering

reports to meet deadlines before each race. Before race day, teams go through “Scrutineering,” or an

evaluation and scrutinization of the team‟s engineering of the solar car. The primary goals of

Scrutineering are to ensure the safety and reliability of all vehicle equipment and to check for

compatibility with race regulations. Over time, the race organizations change the regulations slightly to

prevent teams from reentering the same exact car in consecutive races.

The SIUE Solar Car Team was started in 2004, when SIUE purchased a completed solar car from

Lincoln Land Community College (LLCC). LLCC had used this car to compete in Sunrayce (the original

name for the ASC) in 1999. The SIUE students gave the car a new paint job and some minor alterations,

but they never raced that car. In 2006 the Solar Car Team made some minor body alterations to the car,

including making a new cockpit with solar panels on the roof. In 2007, the Solar Car Team entered the

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vehicle which weighed nearly 1600 lbs fully loaded into the ASC racing competition. With that much

weight, the batteries were drained by the end of the Scrutineering. Race rules required the batteries to be

charged solely on power from the sun. So, the team could not adequately recharge their batteries before

the race and despite the team‟s best efforts, the charge was not enough to complete the first day of racing

and the team was disqualified.

Figure 1, The Team and Car in 2004

Figure 2, The Team and Car in 2007

The SIUE Solar Car Team has not done a very good job of passing on the techniques learned by

the older students to the younger students. As a result, when students tried to revitalize the team in 2008,

they were basically starting from scratch. The only resource they had was the existing SIUE Solar Car.

From 2008 to early 2010 the Solar Car Team‟s primary goal was to modify the previous chassis to

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remove half the weight, for a race weight of 800 lbs fully loaded. New lightweight solar panels were

purchased and installed. A new Lithium-Ion battery pack replaced the old lead-acid batteries.

Lightweight fiberglass panels were installed to reduce the weight of the body. The team also aspired to

increase the top speed of the car from 65 to 100 KPH (40.39 to 62.14 mph). For this they needed a new

motor and controller. Increasing the top speed of the car made it more competitive for multiple reasons.

The unobvious reason is that race rules required the team to pull over and let pass any formation of 3 cars

driving behind the team. The slowing down and speeding up associated with pulling over is a waste of

both time and electricity. Maintaining a higher speed reduces the frequency of pulling over, therefore

helping to conserve energy and vastly reduce race time. Unfortunately, the team was not able to attain the

necessary funds for the new motor. Due to the poor motor as well as the non-aerodynamic body shape

and low wattage solar panels, it was decided that it was impossible to modify the car anymore to become

race worthy.

In the fall of 2010, the team stepped up recruitment and now is comprised of experienced students

who have participated in years past as well as new students who are excited for the chance to learn and

gain experience. Consisting of mostly juniors and seniors in various fields including Mechanical and

Electrical Engineering as well as Business and Marketing, the current team represents a variety of groups

from multiple disciplines at SIUE.

Figure 3, The 2009-2010 Team and Solar Car

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Design Strategy

To start off the design process of the new chassis, this design team intends to begin by identifying all

of the specifications and constraints imposed on the chassis design by the SIUE Solar Car Team and WSC

regulations. To name a few constraints, the WSC regulates the maximum vehicle dimensions, type of

tires, and design of roll cage. The Solar Car Team requires the chassis to have adequate space for the

solar panel array and its attachment points, the battery box, and the electrical motor control unit. They

have also selected to model the car based on a 1987 design called “Solar Resource”, which is pictured on

the title page.

One of the first design considerations will be that of material selection. Many different metals are

available in various shapes and sizes. The team will decide between the many aluminum and steel alloys

currently available and calculate the appropriate wall thickness required. Strength, stiffness, cost, and

fabrication constraints will be a few of the primary considerations in this selection.

With these constraints in mind, the design process will move forward. The design process will begin

with wheelbase and track width, proceed to the tires, and move inward. With this method, the most

critical components of the car are addressed first and determine the design of the rest of the vehicle.

Moving in from the tire, the hub, bearing, and spindle assembly will be addressed next. If possible,

existing parts will be utilized to reduce design and fabrication time as well as cost. However, if suitable

components do not exist, custom fabrication will be necessary. From the spindle, a suspension setup will

have to be will have to be selected. This will require a thorough cost, performance, and feasibility analysis

of all existing suspension types. The final selection will determine the location of suspension mounting

points at the frame. These mounting points will help the team decide how and where to arrange the

members of the frame.

With the suspension mounting requirements determined, the focus will shift to the driver's cockpit,

the front impact area, and the solar array mounting points. The cockpit will be designed for driver

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comfort during long distance travel and safety in the event of a collision. Furthermore, the Solar Car

Team has specified that a modular, adjustable, and removable solar array will be mounted to the rear of

the chassis. These constraints will play a significant role in the design strategy of the chassis.

Although there is a design plan in place, this will still be an iterative process. As the design

progresses, it will be necessary to redesign certain components to accommodate newly realized issues and

to improve upon the original design. Ideally, these iterations will be performed during the 3D modeling

and FEA processes.

Literature Review

In the book, “The Winning Solar Car” By Douglass R Carroll, every aspect of solar car design is

discussed. Carroll was a professor at the University of Missouri-Rolla, who has spent years working with

their solar car team to perfect many different solar cars over the years. His book will be useful

specifically when choosing the spring rate of the suspension and when designing the front and rear

suspension. It will be a great resource for perfecting the spindle design to achieve Ackerman steering,

finding a desirable toe angle, and reducing tire scrub. [2]

The 1995 text, Race Car Vehicle Dynamics, by William and Douglas Milliken, addresses a

plethora of issues concerning vehicle performance. A total length of 890 pages allows the authors to

provide in-depth explanations of each component and their effect on the dynamics of a vehicle. Although

all of the information contained in the book is useful, there are sections which will be referenced more

frequently than others due to the specific goals and constraints of this project. These sections address

vehicle stability and control, steering and suspension geometry, chassis stiffness, center of gravity

location, brake systems, dampers, and suspension springs. The text also covers the testing, development,

and adjustment of these components. Implementation of this information will increase reliability,

predictability, driver comfort, and efficiency of the vehicle. This is a high quality, valuable reference

published by the Society of Automotive Engineers. [3]

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“How to Make Your Car Handle” covers many topics, including general handling information

and calculations, suspension tuning, and general chassis design. This book will aid when choosing

suspension geometry, spring and shock selection, as well as chassis weight distributions. Many equations

and formulae can be found throughout the book, which will help in the chassis design process by allowing

much of the design to be done on paper prior to software usage, which will in turn require fewer design

iterations and changes during the software stage of development. [4]

“The Automotive Chassis: Engineering Principles” by Reimpell and Helmut discusses vehicle

dynamics issues including braking behavior, body roll center, steering correction, and spring and shock

absorber systems. It also describes an experimental process to determine the center of gravity of the

chassis without a computer program. It will also be a useful resource to refer to when deciding on a

suspension type. [5]

In the book, “Tune to win”, by Douglas Carroll, the focus is based on suspension and braking. It

discusses the different types of suspension systems. To name a few there are: the four bar linkage

independent system, solid axle, and Macpherson strut. This book also explains how suspension travel,

chassis roll, and different lengths and angles for control arms affect the camber and tire movement with

respect to the road. Besides suspension details, it also goes into great detail showing how to set up a

brake system that will stop the vehicle in a safe manner while also allowing the pedal for the brake is not

too stiff or too soft for the driver. This book will help when designing the suspension to minimize camber

and wheel shift when entering a turn or hitting a bump. Also, it will help when designing a reliable

braking system for the chassis. [6]

The working paper by Starr, Patrick J. entitled “Designing Stable Three Wheeled

Vehicles, With Application to Solar Powered Racing Cars”, is a resource created by a mechanical

engineering professor at the University of Minnesota. It was created for the sole purpose of giving solar

car teams a resource to refer to when designing the wheelbase, track width, and desired center of gravity

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of solar car chassis. This resource will more than likely be the primary resource when designing the

above listed aspects of the chassis. [8]

Analysis

Material selection for the chassis will be an important decision to be made. An analysis of yield

strength to weight ratio for selected materials will be compared. The strongest material for a given weight

will be the ideal candidate for chassis materials. A secondary objective of the material selection is a cost

analysis, although the price of the material should be second to yield strength per weight ratio.

There will also be an extensive analysis of the chassis design prior to the actual fabrication of the

chassis. The analysis will be done using Finite Element Analysis (FEA), utilizing Autodesk Inventor,

Abaqus, or another similar program capable of performing the FEA. In an impact, the primary concern is

driver safety. Even if a chassis member does not fail, deflection could still cause safety issues for the

driver. Using the computer analysis, driver safety can be optimized. Tubing sizes may also be optimized

by using thinner walled members where the strength is not needed, resulting in additional weight savings

for the car.

In order to do an extensive analysis of the car, it must be complete, running and driving under its

own power. For this to happen, the solar car team will be required to finish the remainder of the car once

the senior design team completes the chassis components. Without a complete car, testing and analysis

will be very limited. One thing that can be tested is chassis rigidity. Both torsional and flexural tests can

be performed on the chassis. The goal will be to have a chassis with minimal flex, with the suspension

taking care of any necessary vehicle articulation.

Should the solar car be complete, other tests will need to be performed. Analysis of body roll,

turning radius, and possibly even lap times may be performed.

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Timeline

Milestone September-10 October-10 November-10 December-10

Week 1

Week 2

Week 3

Week 4

Week 1

Week 2

Week 3

Week 4

Week 1

Week 2

Week 3

Week 4

Week 1

Week 2 Chassis Design

Tires/ Hubs Design

Fin

al E

xam

We

ek

Suspension Design

Frame Design

Steering Design

Brake Design

Order Steel

Fabrication

Tire, Wheel and Hub Assemblies

Build Frame

Build Front and Rear Suspension

Assemble and Mount Steering System

Assemble and Attach Brake System

Final Assembly and Testing

Milestone December-10 January-11 February-11 March-11

Week 3

Week 4

Week 1

Week 2

Week 3

Week 4

Week 1

Week 2

Week 3

Week 4

Week 1

Week 2

Week 3

Week 4 Chassis Design

Tires/ Hubs Design

Co

mp

lete

Ch

assi

s

Suspension Design

Frame Design

Steering Design

Brake Design

order steel

Fabrication

Tire, Wheel and Hub Assemblies

Build Frame

Build Front and Rear Suspension

Assemble and Mount Steering System

Assemble and Attach Brake System

Final Assembly and Testing

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Budget

Item Number

used

Price per

unit ($) Total Price ($)

Hardware (Nuts, Bolts, Screws, etc.) 200 0.75 150.00

4130 Steel Sheet 30 20.00 600.00

4130 Steel Tube 230 5.88 1352.40

Tires and Wheels 3 1000.00 3000.00

Spindle 2 300.00 600.00

Hub 3 300.00 900.00

Swing Arm 1 500.00 500.00

Rod Ends with Bungs 20 20.00 400.00

Shocks 3 200.00 600.00

Steering System 1 250.00 250.00

Brake System 2 500.00 1000.00

Miscellaneous 1 281.51 281.51

Total

Price 9483.91

Contemporary issues

The design and construction of a solar powered car is quite an event and can potentially attract

media attention. Part of this is due to the current attitude of the general population on the subject of

renewable energy and green technology in general. These days companies are effectively capitalizing on

the „green movement‟ and for good reason. Competition between car manufacturers attempting to

produce the most fuel efficient vehicle is becoming fierce. Toyota came out with the „Solar Prius‟ in

2010, which they claim can get “30 miles per day in electric mode … improving fuel economy by up to

34-60%” [7]

The creation of solar cars is also such a big event because they aren‟t built very often. This is due

to their inherently high costs in manpower and capital. Their design requires the participation of many

people from multiple disciplines. As shown in the budgeting section, this is project is clearly going to

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require a lot of money. Much of the high cost of the new solar car chassis is funded by SIUE, through the

Solar Car Team. Additionally, the final product of this senior design project is going to represent SIUE

for many years to come. For these reasons, it will be important for the students involved in this project to

ensure the adequate and timely completion of this vehicle chassis. If this project is done correctly, it will

be a very prestigious accomplishment for SIUE.

Computers and Software

3D modeling software will be used extensively throughout the design process to reduce time, aid

with visualization, and provide exact dimensions. Although there are many modeling software packages

available, Autodesk Inventor will likely be used due to the team's familiarity with its functions and layout.

This software will be especially helpful in animating the various suspension geometries and types because

the combined component assemblies can be analyzed throughout their full range of motion. Furthermore,

this software provides exact dimensions for frame members, machining tolerances, and linkage angles.

Using a program capable of Finite Element Analysis, the chassis will be given a series of loads on

various members, after which the program will show the amount of stress present in each member and

joint. With given material specifications, the program will be able to show which members or joints fail,

as well as the deflection of each member. The program will also produce a total weight of the chassis.

This will aid in reducing weight by varying member size and placement to achieve a design with the

lightest weight and greatest strength without sacrificing safety.

In addition to the powerful mathematical programs already discussed, Microsoft Excel

will certainly play a key role in the calculation of the chassis wheelbase, track width, and center of

gravity. Only Excel offers the capability to make multiple parallel calculations, which can be varied by

simply changing a single cell.

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Conclusion

If all of the design criteria presented in this proposal are followed during the design and

fabrication stages of the new SIUE Solar Car chassis, then it is certain to be a great improvement over the

current car. The new chassis will comply with the WSC regulations, allowing the SIUE Solar Car Team

to race the new car in upcoming WSC races. At the same time, the new chassis will be safer, more stable,

and more competitive in cross-country solar car races than the current one. It will be able to protect the

driver in the event of an accident, as proven by stress and/or impact analysis on the chassis in CAD

programs. A plan of action has been prepared which encompasses all general aspects of the chassis

design. Ideally, this chassis project will help the SIUE Solar Car Team produce a vehicle which will be

an asset for the school and will last for years of use for solar car teams in the future.

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Bibliography

1. "American Solar Challenge." American Solar Challenge - Home Page. Web. 02 Oct. 2010.

<http://americansolarchallenge.org/events/asc2010/>.

2. Carroll, Douglas R. The Winning Solar Car: a Design Guide for Solar Race Car Teams.

Warrendale, PA: SAE International, 2003. Print.

3. Milliken, William F., and Douglas L. Milliken. Race Car Vehicle Dynamics. Warrendale,

PA: Society of Automotive Engineers, 1995. Print.

4. Puhn, Fred. How to Make Your Car Handle. Tucson, AZ: H.P., 1981. Print.

5. Reimpell, Jornsen, and Helmut Stoll. The Automotive Chassis: Engineering Principles.

Warrendale, PA: Society of Automotive Engineers, 1996. Print.

6. Smith, Carroll. Tune to Win. Fallbrook, CA: Aero, 1978. Print.

7. Solar Electrical Vehicles. Web. 03 Oct. 2010. <http://www.solarelectricalvehicles.com/>.

8. Starr, Patrick J. Designing Stable Three Wheeled Vehicles, With Application to Solar Powered Racing

Cars. Working paper. Minneapolis, MN 55455: University of Minnesota Solar Vehicle Project,

November 8, 2006 Revision. Print.

9. 2011 World Solar Challenge. Web. 02 Oct. 2010. <http://www.worldsolarchallenge.org/>.