MECH 460 Final Design Report

2006 Formula SAE Chassis Design

Queen's University

Department of Mechanical Engineering

Advisor:

Dr. Diak

Design Team:

Michael Hynes

Asle Olsen

Pravin Advani

Rami Laitila

Submitted:

December 5 2005

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For the 2006 season the Formula S.A.E. team is looking to change some components of the car to better its performance. A redesign of the chassis will be done to better suit an ergonomic driving position and to better the suspension. Also, the safety during side impact will be investigated. To determine the most comfortable driving position fort the 95

th percentile male, a mock-up chassis was built in which various parameters such as steering column height, angle of backrest, position of pedals, and dash distance could be adjusted. With the personal preferences from each team member, averages were found that would suit everybody, and adjustable pedals were used to accommodate the differences in height of the team members. Also a computer model of the 95

th percentile male was used during the 3D modeling of the car, to make sure anyone up to that size would fit properly. It was found that every driver would fit in a cockpit with a length of 54 inches, while the shortest drivers needed a cockpit with a length of 50 inches. By allowing adjustments of the backrest by up to 2.75 inches and the pedals by up to 2 inches, all drivers will fit comfortably in the cockpit. The cockpit was also made wider, by 6.3 inches in the front and 2.126 inches in the back, to accommodate for wider drivers and to make it more spacious for everyone in general. To further improve the chassis, its overall shape was adjusted to improve the integration with the suspension. The chassis profile was changed to allow for longer lower A-arms, which improves cornering. In order to allow for longer lower A-arms, the walls of the chassis are now at a 40-degree angle for some distance, before going vertical at the desired width, while the old design had the walls going up at an 81-degree angle. This design allows for the lower A-arms to be much longer than the upper A-arms, as specified by the suspension team. After some research an appropriate method of testing the monocoque for side impact was found. The selected test is based on the ASTM D 3763-02 (see Appendix C), which has been modified for thicker sample sizes than that of the original test. This test will be performed at the local Novelis site as soon as a date is agreed upon. It will be performed at 20m/s, at least five times, to assure that the results are correct. With high-rate impact research and testing, improvements in an ergonomic driving position, and improvements in the integration of the suspension, the overall result will be an increase in reliability and drivability of the car.

Abstract

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ABSTRACT........................................................................................................................... 2

TABLE OF CONTENTS ......................................................................................................... 3

1. INTRODUCTION ......................................................................................................... 4 1.1 Background ........................................................................................................... 4 1.2 Objectives.............................................................................................................. 4

2. PERFORMANCE CRITERIA ........................................................................................ 6 2.1 Ergonomics .............................................................................................................. 6 2.2 Suspension Integration ............................................................................................. 6 2.3 Impact Equivalency.................................................................................................. 6

3. ANALYSIS .................................................................................................................. 8 3.1 QFD Analysis........................................................................................................... 8

3.1.1 Design............................................................................................................... 8 3.1.2 Test Methods .................................................................................................... 8

3.2 Methods.................................................................................................................. 10 3.2.1 Ergonomic Influence ...................................................................................... 10 3.2.2 Suspension Influence...................................................................................... 11

4. FINAL DESIGN ......................................................................................................... 13

5. FUTURE WORK ....................................................................................................... 15

6. CONCLUSIONS ......................................................................................................... 16

7. REFERENCES ........................................................................................................... 17

8. APPENDICES ............................................................................................................ 18

Appendix A: Ergonomic mockup rig........................................................................... 18 Appendix B: Ergonomic Data...................................................................................... 19 Appendix C: ASTM D 3763-02................................................................................... 20 Appendix D: Test rig for ASTM D 3763-02 test ......................................................... 30 Appendix E: Comparison of old and new chassis........................................................ 31

Table of Contents

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1.1 Background

Since 1993, Queen’s University has participated in the Formula SAE competition. This is a competition for students to use their knowledge to design, build and race a small formula style racecar. Each year teams from all around the world assemble in Pontiac, Michigan, bringing their cars to be evaluated in many areas important to the success of a car. Judges evaluate the cars based on design, cost, manufacturability, dependability, safety and performance. Over the years in which Queen’s has participated there has been a steady improvement in the design of the chassis. Material selection in particular has had a great impact on the cars’ performance. Originally a steel tube space frame was built with aluminum body panels, weighing 85 lbs. This was reduced to 47 lbs with the use of an aluminum-balsa wood composite monocoque, and even further reduced to 35 lbs last year using the current carbon-aluminum honeycomb monocoque.

1.2 Objectives

The objective of this project is to design the chassis for Queen’s 2006 Formula SAE car. Last years carbon-aluminum honeycomb monocoque will be used as a baseline for this years design, focusing on making adjustments to driver comfort, sub-system integration, performance, and driver safety with respect to crashworthiness. .

1.2.1 Ergonomics In order to achieve the ergonomic goals of this project, chassis

dimensional changes will be investigated in order to adjust the driving position, and provide more space in tight areas pointed out by drivers last year. Furthermore, it will now be easier for larger drivers to comply with FSAE evacuation regulations, which state that a driver should be able to exit the car, from a fully strapped in driving condition, in under five seconds.

1.2.2 Suspension Geometry Significant changes to the suspension geometry have called for

corresponding changes to the shape of the chassis. Working closely with the suspension team has allowed the chassis to be designed such that it optimizes the integration of the new suspension system.

1.2.3 Impact Equivalency To achieve the desired level of driver safety, the crashworthiness of the

carbon-aluminum honeycomb composite must be fully explored. A relevant testing procedure, and corresponding apparatus, must show that the carbon composite used in the chassis is fully equivalent to the FSAE baseline design of a steel tube frame. Another goal is to implement the testing procedure as standard

1. Introduction

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protocol for the team in future years, as SAE regulations require equivalency test results each time a chassis differs from the steel tubing design.

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2.1 Ergonomics Ergonomic concerns are based upon drivers’ observations from previous years.

From these concerns it was determined that the chassis width, length, and the driver position are to be modified. FSAE safety regulations require that a driver should be able to exit the car, from a fully strapped in driving condition, in under five seconds. The car should be able to accommodate the team’s largest member in this regard. Because of the tight confines of last year’s cockpit, it has been decided that the chassis will be made slightly wider. This will create more space for driver’s shoulders, which have been concerns for some of the larger drivers to date. Furthermore it was felt the driver’s position was too reclined. It is believed that addressing this concern will make it easier for drivers to evacuate the vehicle. In addition, driver’s response will also be improved by bringing the driving position closer to the steering wheel, which was also a concern with the previous chassis. This change will also necessitate making a taller roll hoop to meet FSAE regulations, and refining the position of the driving pedals.

2.2 Suspension Integration

In an effort to increase the turning performance of the car, the suspension team has lowered the vehicle’s roll point. This is the longitudinal axis about which the car leans in a turn. By lowering this axis, the suspension team is confident in their capabilities to improve camber gain in static cornering, thus increasing the grip achieved in turns. In order for the chassis to facilitate the suspension integration, it must be built such that the lower control arms are significantly longer than the upper control arms. By designing the chassis to fit the desired suspension geometry a better overall performance is achieved. 2.3 Impact Equivalency

The baseline FSAE regulations call for three tubes to be used as side impact beams for each side of the car: One upper bar which is to be 300-350 mm above the ground, one lower bar, and one diagonal bar which connects the two previous. These bars are required to be at least as strong as 1% carbon tubing having an outer dimension of 25.4 mm and a wall thickness of 1.60 mm. A schematic is shown in Figure 1 below.

2. Performance Criteria

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3.1 QFD Analysis

Considering the SAE judging criteria - design, cost, manufacturability, dependability, safety and performance- two different designs, and five different tests were ranked in a Quality Function Deployment (QFD) chart. This allows the design parameters to be ranked as an analytical process, and effectively outlines the most appropriate design solution. Each factor was weighted and assigned a ranking out of nine for each design solution, and then the sum of the products was normalized to produce a score out of nine.

3.1.1 Design Design 1: Steel Tube This design uses steel tubing to reinforce the sides of the carbon composite monocoque in the event of impact. QFD Score: 4.3 This design ended up scoring lowest of the two considered, mainly due to its high weight, and the difficulties integrating it with the current carbon composite monocoque. Design 2: Carbon Composite This design either just use the monocoque as is, or adds an extra layer of carbon composite to the sides to increase safety. This is dependant on the test results that are going to be performed on the existing monocoque material. QFD Score: 8.1 The carbon composite design was by far the better of the two, as it is lighter, stronger, and easier to integrate with the monocoque and is aesthetically pleasing. Based on the result in the QFD this is the design that was chosen. Whether or not the sides will need reinforcing will be evident after testing the properties of the material.

3.1.2 Test Methods Test 1: Static Test This tests the strength of the material, through bending the material until it breaks. QFD Score: 6.6 The static test ended up scoring second highest, due to its low cost and low time consumption. However, due to its low relevancy to high velocity impacts it is not the ideal test to perform.

3. Analysis

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Test 2: Drop Test In this test an object of known mass is dropped from a known height, on to the test specimens. The results are measured and compared to decide if the carbon composite is strong enough, or if it needs to be reinforced. QFD Score: 6.9 This test scored highest of all the tests, due to its ease of construction, high velocity impact relevance, and its low cost. Test 3: Impact Sled In this test an impact sled is driven into the side of the car. This means that a whole car has to be made and tested, instead of just a small sample of the material. QFD Score: 4.6 Although this test is a very good way to see how the car actually performs in a side impact, it ended up scoring fairly low. This is due to the fact that a whole car would have to be constructed, which would be both expensive, time consuming and hard to do. Test 4: Theoretical This involves constructing the car in a computer program, including the material properties, and then simulating a side impact. QFD Score: 5.7 Due to its low cost and its high relevancy to high velocity impacts, this test scored fairly high. However, due to its significant time consumption and the difficulty involved in making a virtual model of the car, it is not the preferred test. Test 5: TMAC (Test Machine for Automotive Crashworthiness) The TMAC crushes the test specimen at a predetermined velocity and force, similar to a drop test. However, in this case the velocity and force is constant throughout the test. QFD Score: 4.6 Although this is a very good test, it is not feasible to perform, due to its high cost and low availability. After deciding on the drop test, a way of performing it was needed. Novelis was contacted and agreed to the use of one of their machines for this test. In principle it is the

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same as a drop test, but instead of simply dropping an object onto the test specimen, a piston is driven into the specimen at a known velocity. The piston also has sensors attached to it that will record data, such as the velocity and force. 3.2 Methods

3.2.1 Ergonomic Influence To find the best ergonomic seating position a mock up rig was

constructed. This rig was made to be fully adjustable so that members of the team could find their comfortable seating position. The measurement data from each driver was compiled and is shown in appendix B!. The most important dimensions for modeling the car can be seen below in Table 1 and Figure 2.

Table 1: Pertinent Ergonomic Data

Axis 1: centered at rear roll hoop

Axis 2: centered at front roll hoop

Driver A B C D Chris 32.50 54.00 -32.50 21.50Dallas 29.75 51.00 -29.75 21.25Mike 31.50 51.00 -31.50 19.50Ereth 30.00 50.00 -30.00 20.00Christie 30.50 51.00 -30.50 20.50Ethan 31.00 51.00 -31.00 20.00John 30.50 50.00 -30.50 19.50Bruce 31.00 51.00 -31.00 20.00Max 32.50 54.00 -29.75 21.50Min 29.75 50.00 -32.50 19.50S.D. 0.88 1.25 0.88 0.75Range 2.75 4.00 2.75 2.00Mean 30.84 51.13 -30.84 20.28

As can be seen, dimension D for all drivers is very close with a standard deviation of 0.75 inches and a range of 2.0 inches. The range of values of D can be compensated by an adjustable pedal system, which will be incorporated into the final assembly of the car. The distances A and C will be compensated by different seat foam thickness for various driver heights. The car was then modeled for the largest driver’s seating position and can still be adjusted for smaller drivers.

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Figure 2: Ergonomic dimensioning with 95th percentile male

The 3D model was assembled with a 95th percentile male to ensure that any parts added to a given point could be moved to avoid interfering with the driver.

3.2.2 Suspension Influence Until recently, Queen’s chassis and suspension designs existed separately.

Suspension mounting points were based primarily on available room on the chassis. However, this year the two teams approached this problem by working closely with each other to determine what needed to change in order to attain a favorable suspension system.

One of the main concerns was optimizing the outside front tire’s surface contact during turning. Lengthening the lower A-arm solved this problem. In doing so the system becomes less symmetrical and the overall result is shown in Figure 3 below.

Figure 3: Desired suspension set up under 0o and 10o body roll respectively

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Also the Roll center of the front suspension was placed lower than the rear to assure more force is transferred to the front outside tire during turning. The chassis shape was iterated many times until the mounting points could be placed in both reinforced and plausible positions.

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After all design influences were taken into account, a final chassis design was decided upon. This resulted in a whole new profile for the Queen’s formula car shown in Figure 4 below.

Figure 4: Transformation of Queen’s formula car profile

With the chassis and suspension design working together, the overall output was a much more suitable integration between the two. The chassis was designed around the suspension and not the other way around. Progress was also made to improve the overall ergonomics of the car. The seating position was adjusted to be most comfortable. This new seating position resulted in a shorter, wider chassis, which is shown with a model 95th percentile male in Figure 5 below.

Figure 5: 2006 car assembly with 95th percentile male

4. Final Design

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Early next semester the material testing will be performed at Novelis. The rig to be used has already been constructed, and all that is needed is for Novelis to come up with a date to perform the test. The test data will be analyzed as soon as the test is completed, and any modifications the chassis may require will be dealt with at as such. The chassis will be constructed in early January. The carbon fiber and the aluminum honeycomb have not been delivered to date, but they are expected to arrive within two weeks. As soon as they are delivered the construction of the chassis itself can start. After the chassis has been constructed the other components will be added. If the other parts do not fit, minor modifications may be needed at this point. However, this is not very likely, as everything has been modeled accurately in Solid Edge to make sure a good fit is accomplished on the first try.

5. Future Work

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The 2006 chassis was designed to fit the suspension and ergonomics and not the other way around. The two designs being done together made it easy to assemble the car in Solid Edge and verify all the relevant parts.

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The final design of the chassis has successfully addressed the following concerns. Driver ergonomics and drivability were improved through an ergonomic survey of the team. Also, the integration of the suspension was improved by working closely with the suspension team such that the chassis profile accommodates the new suspension design. Through the ergonomic survey of the team a comfortable driving position was determined which would suit all of the drivers. Different sized drivers, up to a 95th percentile male, were accommodated by incorporating some adjustability in the backrest and foot pedals. This provided everybody with the ideal driving position, improving the comfort and drivability of the car. This also allowed for the chassis to be shortened by 4 inches. Suspension mounting points, which improve cornering, were determined by working alongside the suspension team. The profile of the chassis was then adjusted in order to accommodate the new suspension design. As a result the new suspension integration will improve the car’s handling and drivability. The design of the test procedure, and apparatus were finalized to investigate crashworthiness. The testing, yet to be performed, will hope to confirm the carbon composite crashworthiness as compared to the standard regulation steel framed chassis. In conclusion, the design revisions incorporated into the 2006 chassis successfully improve the ergonomics and cornering ability of the car. In addition, testing methods to prove the crashworthiness of the Carbon Aluminum composite were successfully designed.

6. Conclusions

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1. ASTM D 3763-02, "Standard Test Method for High Speed Puncture Properties of Plastics Using Load and Displacement Sensors" ASTM International

2 SAE International, “2006 Formula SAE Rules” http://www.sae.org/students/fsaerules.pdf

7. References

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Appendix A: Ergonomic mockup rig

8. Appendices