Abstract. Figure 1: Rendered Prototype Model Created By 2015 Baja Bengals

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1 Final Report Team 40: Mini-Baja Project LSU Capstone Mechanical Engineering Written by: Lance Angelle, Clinton Bourgeois, James Burgard, Colby Cheneval, Kevin Hall, Hannah Neitzke, Kevin Sextro, Carey Snell, Drake Strother Faculty Advisor: Dr. Waggenspack Alumnus Advisors: Devin Poirrier, Aaron Mcdonald Figure 1: Rendered Prototype Model Created By 2015 Baja Bengals Abstract The Mini-Baja Project is an off-road design competition in which over 100 Universities design and compete a vehicle. The LSU team consists of eight senior mechanical engineers and one electrical engineer whose ultimate goal is to place first in competition this year at Auburn University. The main objective is to eliminate the failure that last year s team experienced which led to a 72 nd place finish. Reducing the weight of the car is another objective and will also help preventing failure of components, as there will be less stress put on the vehicle during competition. The drivetrain will consist of a single speed gearbox with a continuous variable transmission. A double A-Arm suspension mount in the front with a 3 link-trailing arm set up accompanied by Fox Float 3 EVOL R shocks is what will make up the suspension for the vehicle. Ackermann steering geometry accompanied with correct rack and pinion placement will reduce the tie rod failure that last year s team underwent during the endurance competition. The vehicle in total will cost roughly $12,000, which will save $5,000 for competition and travel costs. Next semesters agenda is to manufacture the vehicle completed by March first for testing, and attending competition on April 9 th.

2 Executive Summary Baja SAE is a design competition in which collegiate students design, manufacture and race an all-terrain vehicle. The competition entails three aspects: Static Events: Design, Cost Report, and a Safety Inspection Dynamic Events: Hill Climb, Acceleration, Suspension, and Maneuverability Tests Endurance Race: two-mile circuit with four hours to complete as many laps as possible This project is in conjuncture with the LSU Mechanical Engineering Senior Design Program and consists of nine senior students. LSU teams have been very successful, with first place finishes in the 1980s and top twenty finishes in the 2000s. Lack of experience has presented to be a major challenge to recent teams. The current team has consulted with alumni Baja members and professors to rectify this issue. The Baja team has existing technology at their disposal in the form of last year s Baja vehicle. This car placed 72 nd which indicates improvements need to be made. Last year s car had many failures which led to this poor placement, one thing this year s team plans to prevent. Weight reduction of the car is another one of the primary objectives of this year s team. Reducing the weight allows the car to be faster, more maneuverable, stop quicker, and lower impact forces. One of the most critical aspects of reducing the weight is minimizing the size of the frame to have the fewest secondary members as possible. The safety of the driver and components is another very important aspect that needs to be designed for in the generation of the frame. The frame also must be able to handle all loads applied. For material of the frame, the team selected AISI 4130 which was chosen based on its acceptable bending strength and stiffness while being the most lightweight option. This option has an OD of one inch and wall thickness of.062 inches for primary members. It was selected based on being the lightest choice with the appropriate bending strength and top teams most commonly use this material. The Drivetrain is an important aspect to the speed of the vehicle as is it responsible for transmitting engine power to the ground and providing mobility to the vehicle. The team decided a Continuous Variable Transmission along with a custom single speed gearbox. This sacrifices the ability for reverse in order to save weight and optimize the vehicle performance. Frame Design Drivetrain Design The decision for this was to greatly reduce the weight Front Suspension Design of the gearbox and the confidence of the driver to be able to maneuver the course without

3 need for reverse. The suspension decreases the amount of stress on the vehicle, and the Baja team improved the suspension while decreasing the weight from last years vehicle. The twelve inches of travel will ensure that the rigours of the track will not damage the vehicle. For the front suspension, a offset double a-arm was selected by the team. This is the design used by all top ten teams. Coupling structural integrity with minimal camber variance upon travel propels the LSU Baja team into a position to drastically enhance the maneuverability of the vehicle compared to the 2013 build. The rear suspension design entails a three-link trailing arm. This configuration gives a high Rear Suspension Design strength-low weight ratio that optimizes the design for the vehicle. The 3-link trailing arm design further reduces weight by combining the hub assembly with the structural members comprising the trailing arm. The shocks chosen by the team are Fox-Float 3 EVOL R shocks. This set of shocks is considerably more expensive but are vastly lighter than coil and spring shocks. Fox Float 3 EVOL R shocks are infinitely adjustable by regulating the pressure maintained in the piggyback canister. Adjusting the pressure in the external piggyback reservoir regulates spring rate when approaching the extremes of shock stroke. The steering sytem of last years design was a weak point as the team broke five tie rods in competition and did not have suffecient manueverability. This was because the tie rods were placed in bending and not axial loading. While bending stress is unavoidable, this years team has reduced the bending moment by relocating the rack and pinion.one of the design decisions the team made was at least one inch of lateral travel in the rack and pinion, so that tire-turning angles of roughly 45 degrees could be met without large sacrifices in drivability. Steering Design Braking is another design component within the Baja vehicle. Hydraulic Disc brakes will be used in the design based on feasibility and their use by all top teams. Another design selection based off of the solid rear-end was to use a single disc and caliper assembly located near the gearbox, as opposed to having a disc and caliper assembly at each rear wheel. This will reduce the overall weight and number of components of the braking system. Overall, the team made key decisions based off a team objective of reducing the weight. The five major subsystems have been meshed together and meet this criteria. This completion of the model will ensure that in the manufacturing process there will be as few issues as possible. The figure to the right contains represents the 2015 Baja Bengals Team Final Design. In the next stage the team will order and manufacture all components and 2015 Baja Vehicle 3

4 prepare for competition in April at Auburn University. 4

5 Table of Contents Abstract... 1 Executive Summary... 2 List of Figures... 9 List of Tables Introduction Team Goals and Objectives Functional Decomposition Baja Assembly Frame Introduction Objective Functional Requirements Qualitative Constraints Concept Generation & Selection Final Design Material Selection Drivetrain Introduction Objective Functional Requirements Concept Generation Concept Evaluation and Selection System Description Materials Selection Engineering Analysis Manufacturing and Assembly Suspension Introduction Objective Functional Requirements Qualitative Constraints Concept Generation and Selection Final Design Material Selection Engineering Analysis Manufacturing and Assembly Steering Introduction Objective Functional Requirements Qualitative Constraints Measurable Engineering Specifications

6 Concept Generation and Selection Final Design Materials Selection Engineering Analysis Brakes Introduction Objective Functional Requirements Constraints Concept Generation and Selection Final Design Engineering Analysis Baja Electrical System Design Requirements Electrical Components Circuit Schematics Component specifications Brake Light Brake Switches Engine Kill Switches Transponder Battery Wire Connectors Cost Estimate Engineering Calculations Assembly Drawings and Parts List Frame Drivetrain Suspension Parts List Miscellaneous Parts List Brakes Safety Frame Drivetrain Brakes Steering and Suspension Electrical Other Anytime in the shop Welding/Cutting/Grinding Heavy Items/Crane Use Driver Protection Proper Vehicle Function Track Crew/Pit Crew Testing Plans

7 Project Management Budget Timeline Milestones Appendices... Error! Bookmark not defined. A. Assembly Drawings... Error! Bookmark not defined. A.1 Baja Vehicle... Error! Bookmark not defined. A.2 Frame... Error! Bookmark not defined. A.3 Drivetrain... Error! Bookmark not defined. A.4 Suspension Assembly Drawing... Error! Bookmark not defined. A.5 Steering... Error! Bookmark not defined.... Error! Bookmark not defined. A.6 Brakes... Error! Bookmark not defined. B. Frame Analysis... Error! Bookmark not defined. B.1 FEA Results... Error! Bookmark not defined. B.2 Progression of Frame Design... Error! Bookmark not defined. C. Drivetrain... Error! Bookmark not defined. C.1 Power Transmitter Options and Final Drive Options... Error! Bookmark not defined. C.2 Gearbox... Error! Bookmark not defined. C.3 Drivetrain Analysis... Error! Bookmark not defined. Suspension... Error! Bookmark not defined. D.1 Flow Force Schematic... Error! Bookmark not defined. D.2 Fox Float Performance... Error! Bookmark not defined. D.3 System Description and Architecture... Error! Bookmark not defined. D.4 Materials for Suspension... Error! Bookmark not defined. D.5 Camber Angles... Error! Bookmark not defined. D.6 4 Bar Linkage... Error! Bookmark not defined. D.7 Materials for Suspension... Error! Bookmark not defined. D.8 Dynamics of Machinery... Error! Bookmark not defined. E. Steering... Error! Bookmark not defined. E Michigan Upright... Error! Bookmark not defined. E Michigan Front Wheel Assembly... Error! Bookmark not defined. E Baja Bengals Front Wheel Assembly... Error! Bookmark not defined. E.5 Cougar Racing Steering System... Error! Bookmark not defined. E.6 DesertKart 14 Rack and Pinion... Error! Bookmark not defined. E Baja Bengals Upright... Error! Bookmark not defined. E.8 Upright Steering Geometry Top View... Error! Bookmark not defined. E.9 True Ackermann Steering Geometry... Error! Bookmark not defined. E.10 More Ackermann Steering Geometry... Error! Bookmark not defined. E.11 Tie Rod and Steering Shaft Calculations... Error! Bookmark not defined. F. Brakes... Error! Bookmark not defined. F.1 Engineering Analysis... Error! Bookmark not defined. F.2 Rear Brake Caliper... Error! Bookmark not defined. F.3 Pedal Assembly... Error! Bookmark not defined. F.4 Master Cylinders... Error! Bookmark not defined. G. Electrical System... Error! Bookmark not defined. G.1 Electronic Figures... Error! Bookmark not defined. 7

8 References... Error! Bookmark not defined. 8

9 List of Figures Figure 1: Rendered Prototype Model Created By 2015 Baja Bengals... 1 Figure 2: LSU Baja History Figure 3: Functional Decomposition of Baja Vehicle Figure 4: Baja Assembly Created by 2015 Baja Bengals Figure 5: Functional Requirements of the Frame Figure 6: Initial Frame Design Baja Bengals Figure 7: Front Suspension Mounting Points Created By 2015 Baja Bengals Figure 8: Front View Frame Created By 2015 Baja Bengals: First Frame Design Figure 9: Front View Frame Created By 2015 Baja Bengals: Final Revision Figure 10: Frame Final Design Created By 2015 Baja Bengals Figure 11: Frame Assembly Drawing Created By 2105 Baja Bengals Figure 12: Frame FEA Created By 2015 Baja Bengals Figure 13: Drivetrain Functional Decomposition Figure 14: Operation of CVT Drive Figure 15: Custom Gearbox Created By 2015 Baja Bengals Figure 16: Suspension Functional Decomposition Figure 17: Unequal Length Control Arms Figure 18: 3-Link Trailing Arm Figure 19: Fox Float 3 EVOL R Figure 20: Final Suspension Design Figure 21: Lower Control Arm Figure 22: Initial Lower Control Arm Model Figure 23: Lower Control Arm with added shock mount bracing Figure 24: Functional Decomposition of Steering Figure 25: Steering Modeled with Car Created By 2015 Baja Bengals Figure 26: Steering Model Created By 2015 Baja Bengals Figure 27: Braking Functional Decomposition Figure 28: 2015 Collegiate Design Series Baja SAE Rules for Braking Figure 29: Front End Braking System Figure 30: Brake Schematic Created By 2015 Baja Bengals Figure 31: Floor Mounted and Hanging Pedal Assemblies Figure 32: Forward-Facing and Rear-Facing Master Cylinder Mounting Figure 33: Balance Bar Figure 34: Single Rear Brake Centrally Mounted Near Gearbox Figure 35: Front End and Pedal Assembly Braking Components Figure 36: Wilwood Braking Bias Adjuster Figure 37: BMI Karts Disc and Disc Hub - Rear Brake Figure 38: Wilwood Billet Spot Caliper - Rear Brake Figure 39: Baja Car Assembly Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 40: Frame Assembly Drawing Created By 2015 Baja Bengals Error! Bookmark not defined. Figure 41:.75 Ball Bearing Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 42:.75 Shaft Seal Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 43: 1" Radial Ball Bearing Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure Error! Bookmark not defined. Figure 45: Right Casing Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 46: 1" Shaft Sea Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 47: Engine... Error! Bookmark not defined. Figure 48: Final Gearbox Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 49: Final Shaft-Gear Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 50: Gearbox Tab Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 51: Input Shaft-Gear Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 52: Intermediate Shaft Gears Created By 2015 Baja Bengals Error! Bookmark not defined. Figure 53: Input Shaft Created By 2015 Baja Bengals... Error! Bookmark not defined. 9

10 Figure 54: Left Casing Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 55: 1" Intermediate Shaft Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 56: Oil Fill Plug Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 57: Engine Mount Plate Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 58: Output Shaft Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 59: Spur Gear 18T Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 60: Spur Gear 46T Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 61: Spur Gear 21T Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 62: Wheel Adapter Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 63: Spur Gear 56T Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 64: Suspension Assembly... Error! Bookmark not defined. Figure 65: Ball Joint Rod End... Error! Bookmark not defined. Figure 66: Cap Screw- Grade 8... Error! Bookmark not defined. Figure 67: Hex Nut... Error! Bookmark not defined. Figure 68: Clevis End... Error! Bookmark not defined. Figure 69: Clevis End 2... Error! Bookmark not defined. Figure 70: Desert Kart Rack... Error! Bookmark not defined. Figure 71: Driver side Upright... Error! Bookmark not defined. Figure 72: Passenger Side Upright... Error! Bookmark not defined. Figure 73: Rear Bracket... Error! Bookmark not defined. Figure 74: Steering Shaft... Error! Bookmark not defined. Figure 75: Steering Assembly... Error! Bookmark not defined. Figure 76: Tie Rod... Error! Bookmark not defined. Figure 77: Wilwood Integral Reservoir Compact Master Cylinder... Error! Bookmark not defined. Figure 78: Wilwood Billet Spot Caliper... Error! Bookmark not defined. Figure 79: Wilwood Brake Pedal... Error! Bookmark not defined. Figure 80: Rear Collision Frame FEA... Error! Bookmark not defined. Figure 81: Side Collision Frame FEA... Error! Bookmark not defined. Figure 82: Suspension Forces on Frame FEA... Error! Bookmark not defined. Figure 83: Front Impact Frame FEA... Error! Bookmark not defined. Figure 84: Progression of Frame Design... Error! Bookmark not defined. Figure 86: Closed Gearbox Schematic Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 87: Gear Ratio Schematic Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 88: Gear Ratio Exploded Created by 2015 Baja Bengals... Error! Bookmark not defined. Figure 88: Displacement of Gear Tooth 385 ft-lb Force... Error! Bookmark not defined. Figure 89- Force Flow Schematic... Error! Bookmark not defined. Figure 90: Fox Float Petrformance Curves... Error! Bookmark not defined. Figure 91: Fox Float Position Diagram... Error! Bookmark not defined. Figure 92: Spring Force vs Travel of Suspension... Error! Bookmark not defined. Figure 93: Force vs Velocity in Compression... Error! Bookmark not defined. Figure 94: Force vs Velocity Rebound... Error! Bookmark not defined. Figure 95: Front Suspension... Error! Bookmark not defined. Figure 96: Rear Suspension... Error! Bookmark not defined. Figure 97: static height camber angle... Error! Bookmark not defined. Figure 98: full compression camber angle... Error! Bookmark not defined. Figure 99: full extension camber angle... Error! Bookmark not defined. Figure 100: Four Bar Linkage... Error! Bookmark not defined. Figure 102: Front View Geometry of Suspension Travel... Error! Bookmark not defined. Figure 103: Spring Coefficient of Fox Float EVOL R... Error! Bookmark not defined. Figure 103: Lower Control Arm Force Diagram... Error! Bookmark not defined. Figure 104: Solid Mode Suspension Mount Design Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 106: Michigan Upright... Error! Bookmark not defined. Figure 106: Michigan Front Wheel Assembly... Error! Bookmark not defined. 10

11 Figure 107: Baja Bengals Front Wheel Assembly... Error! Bookmark not defined. Figure 108: Cougar Racing Steering System... Error! Bookmark not defined. Figure 110: Rack and Pinion Setup... Error! Bookmark not defined. Figure 110: Solid Model Steering Mount Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 111: Upright Steering Geometry Created By 2015 Baja Bengals... Error! Bookmark not defined. Figure 112: Ackerman Steering Geometry... Error! Bookmark not defined. Figure 113: Ackermann Steering Geometry... Error! Bookmark not defined. Figure 114: Kill Switch Circuit... Error! Bookmark not defined. Figure 115: Brake Light Circuit... Error! Bookmark not defined. Figure 116: Comparison of Battery Chemistries at 200mA... Error! Bookmark not defined. Figure 117: Connection Configuration... Error! Bookmark not defined. Figure 118: Wire Selection... Error! Bookmark not defined. 11

12 List of Tables Table 1: Frame Parts List Table 2: Frame Material List Table 3: Frame Tubing Geometry List Table 4: Summary of Forces Table 5: Mesh Convergence Table 6: Suspension Co-Requisites Table 7: Camber Variance Table 8: Steering Specifications Table 9: Cost Analysis of Steering Table 10: Cost Analysis for Braking System Table 11: Engineering Specifications of Braking Components Table 12: Cost Analysis of Electronics Table 13: Frame Parts List Table 14: Drivetrain Parts List Table 15: Suspension Parts List Table 16: Miscellaneous Parts List Table 17: Brakes Part List Table 18: Baja Car Budget Table 19: Winter/Spring Timeline Table 20: Assembly Drawing Part Specification... Error! Bookmark not defined. Table 21: Power Transmitter Options... Error! Bookmark not defined. Table 22: Final Drive Options... Error! Bookmark not defined. Table 23: Gear Calculations... Error! Bookmark not defined. Table 24: Gear Lifetime... Error! Bookmark not defined. Table 25: Gear Shift 1 Calculations... Error! Bookmark not defined. Table 26: A-Arm Material... Error! Bookmark not defined. Table 27: 3-Link Trailing Arm Material... Error! Bookmark not defined. Table 28: Front Suspension Dimensions... Error! Bookmark not defined. Table 29: A-Arm Material... Error! Bookmark not defined. Table 30: Parameter Inputs... Error! Bookmark not defined. Table 31: Tie Road Steering Shaft Calculations... Error! Bookmark not defined. 12

13 Placement Introduction Baja SAE is an engineering competition in which collegiate students construct and compete an off road vehicle in various terrain. The competition takes place in Auburn Alabama and will occur April 9-11, The aspects of competition include, safety inspections, hill climb, maneuverability, suspension travel course, acceleration testing, and an endurance race. 100 teams will be able to take place in the competition and the rules of Baja SAE must be followed to the letter or the team will be disqualified from competition. The competition and design process is not only to design but also manufacture an off road vehicle, while raising the funds to make it conceivable. All vehicles in competition contain the same unaltered engine in order to ensure the competition is based on design and not one monetary restriction. LSU has had a long tradition with Baja SAE that dates to the 1980 s, where the team s had many top finishes. In the 2000 s, LSU continued its tradition by placing highly in many of the competitions. In recent years LSU has not enjoyed its success in the past, but the 2015 team is looking to turn that around. Shown below is figure 1, which illustrates LSU Baja Competition history over the past 20 years. LSU Baja Competiton History Competition Year Figure 2: LSU Baja History The vehicle itself is broken into six major subsystems: The frame, drivetrain, suspension, steering, brakes and electronics. The components have different design 13

14 challenges and aspects but all must come together to form the Baja car. The frame is the main structure that encases all components, and is also the most important component in keeping the driver safe. The frame must also sustain all loads of the components. The drivetrain, suspension and steering are all mounted onto the frame and need to mesh properly. In the sections following, each subsystem is analyzed through the design process. Team Goals and Objectives The 2015 Baja Teams Ultimate Goal is to place first in Competition at Auburn University in April. However with lack of experience, and a late starting date in reference to other universities this may be a little unrealistic. A set of realistic goals the Baja team has set is a top 30 finish in competition and to leave a legacy at LSU. This year s team would like to begin to set up an organization in order for the teams in coming years to build off one car design, not reinventing a new design each year. This will help LSU to get to the power program it used to be. The Objectives of the Baja Team are to prevent failure of components on the vehicle. Last year s vehicle broke 5 tie rods in the endurance competition, which led them to not completing a single lap. Another objective is to overall make the car more lightweight in reference to last year s car. The vehicle from last year for LSU weighed 540 lbs. Top ten teams from last year s competition all weighed less than 340 lbs. so it is the mission of the team to reach this benchmark. Another objective is to enhance the maneuverability of the car to increase the performance in the hill climb, maneuverability and endurance events at competition. This will be accomplished by reducing the overall car length, shortening components of the vehicle. If we meet these main objectives the team believes it will be able to meet their goals for competition. 14

15 Functional Decomposition Mini Baja Frame Drivetrain Steering Suspension Electronics Protect Driver Top Speed Control Vehicle Direction Dampen Vibrations Applied Brake Light Protect Components Acceleration Maintain Tire Connection Kill Engine when needed Withstand Applied Forces Control Stability Figure 3: Functional Decomposition of Baja Vehicle The functional decomposition shown above is a brief overview of what the team design goals are. There are four main sub-systems that need to be redesigned from the previous year s vehicle. The sub-systems consist of the frame, drivetrain, steering, and suspension. One of the design criterion is to reduce the weight of the vehicle and respectively each component. The frame of the vehicle has a main purpose of protecting the driver and keeping the car structurally sound. Last year s vehicle frame weighed over 100 pounds due to unnecessary secondary members. The teams plan is to eliminate those members and will result in a weight reduction of about 25 pounds. For the drivetrain the team decided to go with a custom gearbox to reach a design goal of 40 mph top speed. Last year s car used a four-wheeler gearbox, which was overweight by Baja standards. The next sub-system is steering, which was a main problem in last year s car, which resulted in poor performance at competition. The placement of the 2014 teams rack and pinion was incorrect and caused the vehicle to have two degrees of freedom. This resulted in their car breaking five tie rods during competition. The suspension system is important in the car s ability to overcome obstacles throughout the competition, such as logs, rocks, etc. Another objective for the suspension is to make sure the driver is comfortable and not being thrown around inside the cab. This year the 2015 Baja team 15

16 decided to use air shocks which have an increase in damping from coil over shocks, the choice of last year s team. This decision also resulted in an 18 lb weight reduction. This will make the driver s ride smoother when he or she has to complete the four long hour endurance course. Baja Assembly Figure 4: Baja Assembly Created by 2015 Baja Bengals The figure above illustrates the compiled Baja vehicle in an assembly drawing. This figure is an exploded view of each major subsystem. The vehicle design had a final weight of 360 lbs reducing the weight from last year s car by 180 lbs or 30%. Also the steering system is placed in primary axial loading with as little bending force as possible to avoid tie rod failure. This design met all of the team s objectives and set the team up to meet their goals. 16

17 Frame Introduction The frame is the backbone of the Baja vehicle. It provides support and mounting for all of the components of the vehicle, and most importantly, has the structural integrity to withstand the applied forces in order to protect the driver. In addition, the frame plays a critical role in determining the overall success of the final design. For example, it is a major contributor to the overall weight of the vehicle. The most competitive vehicles during competition are also the most lightweight. A lightweight vehicle is beneficial because it allows for higher accelerations, lower impact forces, and improved maneuverability. In addition, the frame is inspected thoroughly during competition. If any team s frame does not abide by the Baja SAE Rulebook (Reference 1), they will not be able to compete in competition. Therefore, the frame must be carefully designed in order to abide by the outlined rules to compete. Overall, the success of the frame design is dependent on adequate structural integrity to protect the driver, low weight in order to optimize performance, and the ability to carefully follow the competition rules in order to compete. Objective The objective of this year s frame is to decrease the overall weight from 100 lbs. to 75 lbs. This will significantly reduce the weight of the overall vehicle. In addition, the frame needs to be designed to abide by all the rules outlined in the Baja SAE Rulebook (Reference 1). If any rule is broken, the design will not pass tech inspection at competition and the team will not be able to compete. Another goal of this year s frame is to provide proper mounting supports for the suspension. The suspension is designed in a certain geometrical orientation to minimize camber angle. The frame must agree to the geometry of the suspension in order for the suspension design to be properly implemented. Lastly, the frame must have the structural integrity to withstand the forces during competition. Even the weight will be greatly reduced, the structural integrity must still be considered so the driver will be safe and protected. Functional Requirements 17

18 System Integration Safety Comfort Brakes Strucutral Integrity Adequate Driver Space Suspension Includes Required MembersComf ort Mounting Point Location Steering Easy Driver Entrance and Exit Drivetrain Dimensions Miscellaneous Figure 5: Functional Requirements of the Frame The frame s primary functions are to integrate all the components of the system together, protect the safety of the driver, and lastly, provide comfort to the driver. Qualitative Constraints The constraints for the frame are listed in the Baja SAE Rulebook (Reference 1). The frame has four different types of constraints 1. The frame must consist of primary members or secondary members. The specifications for these members are described in the material selection portion of the frame 2. Geometrical constraints: The frame needs to abide to certain length and angle specifications. For a detailed description of these geometries, refer to the Baja SAE Rulebook (Reference 1). 3. Material: The frame must be made of steel with a carbon content of at least.18%. 4. Size: The frame must fit the 95 th percentile male, 5 th percentile female, and the largest driver 18

19 Concept Generation & Selection The first step in the concept generation phase is to thoroughly understand all the rules outlined in the Baja SAE Rulebook (Reference 1). The next step is research. The Figure 6: Initial Frame Design Baja Bengals 2015 team researched LSU s frames from previous years and frame s from other universities, which were successful in competition. The main conclusion that was taken from this research is that all successful frames have one thing in common: they are light (under 400 lbs.) and compact. Therefore, the team decided to focus on reducing the frame from 550 lbs. to 375 lbs. The third step in the concept generation phase for the frame is to create an initial model. This model was based off research and the overall engineering constraints. The initial frame design is shown in the picture below. The driver was modeled in Solidworks in order check fit and clearances. In addition to this, the 95 th percentile male and 5 th percentile female were also placed in the car with CAD to test for fit. After the initial frame design is complete, the frame is revised multiple times to meet the proper specifications from the other sub-systems of the vehicle. For example, in Figure 7: Front Suspension Mounting Points Created By 2015 Baja Bengals order to properly reduce the camber angle of the vehicle, the suspension must be mounted at a specific orientation on the frame. Zooming in to the desired front suspension mounts (denoted number 1 in Figure 1 shown in Figure 5), it can be seen that the suspension system requires the mounting members to be parallel and 6 inches apart. Many changes related to this one were completed during the design process. To see the entire transformation of the frame, refer to Appendix B.2. After the requirements from the sub-systems were met, removing unnecessary members and decreasing specific dimensions reduced the weight of the frame. For example, as seen from the images 19

20 below, the initial width of the front end of the frame was selected to be 20 inches. However, the team decided that 11 inches would be sufficient by measuring the distance across the driver s feet spaced 2 inches apart. Figure 8: Front View Frame Created By 2015 Baja Bengals: First Frame Design Figure 9: Front View Frame Created By 2015 Baja Bengals: Final Revision In conclusion, the frame is originally designed based off research and extensive consideration of the Baja SAE Rules (Reference 1). However, it s modified several times in order to fulfill its critical function: to provide proper support for the sub-systems of the vehicle. 20

21 Final Design a. Key Aspects Figure 10: Frame Final Design Created By 2015 Baja Bengals The final design for the frame is shown above. The overall weight calculated in SolidWorks came out to be lbs. This is a lb. reduction from last year s frame. The overall height is 48 inches, length 80 inches, and width 32 inches. b. Parts List Table 1: Frame Parts List Part Number Part Manufacturer Material Quantity Price inch OD/.062 inch thickness tubing 2 1 inch OD/035 inch thickness tubing Cartesian Tubing Cartesian Tubing AISI 4130 AISI $1, $1,000 21

22 The parts list for the frame is shown above. The tubing for the frame will be supplied and bent by Cartesian Tubing Company. The bent tubes will be shipped to LSU and the team will TIG weld the frame together. c. Assembly Drawing Figure 11: Frame Assembly Drawing Created By 2105 Baja Bengals Material Selection According to the Baja SAE Rulebook (Reference 1), both primary and secondary members must be made of steel. For secondary members, this is the only material constraint. However, for primary members, there are additional constraints. Primary members must be made of steel with a carbon content of.18%. In addition, there are two options on the dimensions of the primary members that dictate the type of steel used: 1. Circular steel tubing, outside diameter of 1 inch, and wall thickness of.120 inches. 22

23 2. A steel shape with bending stiffness and bending strength exceeding that of circular steel tubing with an outside diameter of 1 inch and a wall thickness of.120 inches. The bending stiffness and strength must be calculated about a neutral axis that gives minimum values. A modulus of elasticity of 205 GPa is used. In order to determine the most ideal type of steel to use for the frame, three common types of steels were compared, as shown in the chart below. After analyzing these materials, AISI 4130 was selected. It has higher strength, higher stiffness, lower density, and is used by essentially all teams at competition. Table 2: Frame Material List Material Young s Tensile Strength Yield Strength Density (g/cc) Modulus (GPa) (MPa) (MPa) AISI AISI AISI II. Engineering Analysis a. Cross-Sectional Geometry In order to determine the most optimum geometry to use for the primary members of the frame, a comparison of various geometries of AISI 4130 was conducted. As stated by the rulebook, AISI 1020 must be used as a reference material; the bending stiffness and strength of the cross-sectional geometry used must be greater for AISI 1020 with Bending stiffness and strength principles are used: Bending Stiffness = EI E= Modulus of Elasticity I=Second Moment of Area for the structural cross-section Bending Strength = S yi c Sy= Yield Strength c= Distance from Neutral Axis to Extreme Fiber The below table represent a comparison of various cross-sectional geometries to AISI

24 Table 3: Frame Tubing Geometry List MATERIAL AISI 1018 (Option A) AISI 4130 (Option B1) AISI 4130 (Option B2) AISI 4130 (Option B3) Modulus of 29,732 29,732 29,732 29,732 Elasticity (kip) Yield Strength (kip) Outside Diameter (in) Wall Thickness (in) Bending 3,463 6,215 6,221 3,575 Strength (lb in) Bending 972, ,581 1,217, ,987 Stiffness (lb in 2 ) Unit Weight (lb/ft) After comparison, AISI 4130 (B2) was determined to be the best option. This option has an OD of 1.25 inches and wall thickness of.062 inches. It was selected because it has the lowest unit weigh of.789 lb/ft while still exceeding the bending stiffness and strength of option a. In addition to this, many successful teams use this configuration for primary members. b. Failure Analysis i. Generating Forces When generating the forces that act on the Baja vehicle, the following scenarios are considered: 1. Impact from Drop (Roll-Over): Forces acting on upper corners of frame (initial height=3.5 m) 2. Impact from Drop: Vehicle landing on wheels (initial height=3.5 m) 24

25 3. Impact from Vehicle collision: Front collision crash, Side collision crash, Rear collision crash The force from scenario 2 is calculated by using the governing equation below: v=velocity at impact m=mass of system k=spring coefficient F = v mk At a starting height of 3.5 meters, the final velocity is calculated by using the conservation of energy principle. The equation is shown below: v = 2gh The calculated velocity came out to be 8.3 m/s. With an estimated overall mass of kg and a spring coefficient of 35 kn/m using the figure in Appendix C.3, a best fit line, and converting to metric units for consistency, the overall force came out as 26, N or 5926 lbs. For scenario 1 and 3, experimental forces are used. After studying Structural Considerations of Baja Frame (Jones 2006), and discussing with Dr. Jones himself at Auburn University, it was concluded that the maximum force a Baja vehicle will see during competition can be calculated by multiplying 2.6 by the overall weight of the vehicle and driver. The calculated force by using this approach comes out to be 1690 lbs. In summary, the following forces are used for the preliminary FEA: Table 4: Summary of Forces Scenario Force lbs lbs lbs. 25

26 ii. Preliminary FEA SolidWorks was the chosen software for FEA. Initially, ANSYS was used, but the analysis could not be completed in ANSYS due to its inability to properly mesh. It was unable to mesh due to its incapability to accept the imported trim extend features in SolidWorks. In order to properly mesh the frame, the frame would have to be drawn by manually re-importing every single point and length of tubing in the frame. This was not feasible given the time constraints of the project. The tubing members of the frame are treated as beam elements with a mesh size of.25 inches (point of convergence). A table of the mesh convergence at a test point is shown in Table 5. The experimental force of 1690 lbs. is applied to the upper bends of the frame as shown in Figure 8. In addition, the frame is fixed at the lower supports. With these boundary conditions, the maximum stress seen in the frame is 91.7 ksi. Therefore, the frame will not fail given that the ultimate strength of AISI 4130 is ksi. However, the frame in this situation would be expected to yield (Sy=66.7 ksi). This is expected given that this is a worst case scenario. Overall, the FEA proves that the frame will not fail in this scenario and therefore provides confidence to the team that the frame will not fail in similar situations during competition. The remainder of the FEA results can be found in Appendix B.1. Table 5: Mesh Convergence Stress (ksi) Mesh Size (inches) Percent Change in Stress N/A % % 26

27 Figure 12: Frame FEA Created By 2015 Baja Bengals iii. Future Improvements for Failure Analysis Below is a list of improvements that can be made for the failure analysis on the frame. These changes will be implemented during winter break. Improvements: o Theoretically determine impact forces on frame for scenario 1 and 3. Use the following equation: o o o o F = v mk When calculating the impact force for scenario 1 and 3, compute the k value for the earth experimentally. This would be done by applying a certain weight to the similar soil seen at auburn and physically measuring the indentation. In calculating k for your suspension force, include the k of the tire as well and add it to the k of the suspension in series. The k of the tire can be experimentally calculated by sitting on the tire and measuring the distance of compression. For the suspension force FEA, change the fixture points: Apply the load directly at the mounting point on the frame. Apply the fixture at the opposite end. Apply a moment that would to compensate for this applied fixture. 27

28 Drivetrain Introduction The Drivetrain is the life force of the Baja vehicle. It powers the shafts and is the source of movement for the car. The drivetrain consists of an Engine connected to a transmission which is the main source of design. Baja SAE rules stipulate no modifications to the Engine, to keep it a design competition and not a matter of funding. This section delves into the design objectives and decisions of the Baja drivetrain. Objective The primary objective of the drivetrain is to power the vehicle the most efficient way possible. To succeed with our goal of making the vehicle as light as possible, the drivetrain needs to remove significant weight in comparison to last year s car. Functional Requirements Structural Performance Maintainability Easy to Operate Transfer Power with Minimal Loss Durable Simplistic Design Operate at Peak RPM Readily Available Replacement Parts Rigid Easy to Service Weight saving Figure 13: Drivetrain Functional Decomposition 28

29 Concept Generation 29

30 There is a wide variety of drivetrains that exist in the Mini-Baja competition, each having their own unique qualities and success. Most Baja vehicles consist of a manual or automatic transmission but due to the design complexity and weight constraints of an automatic transmissions, only manual transmission are considered when more than one gear is necessary. The option of the Continuous Variable Transmission (CVT), which is the most popular among the SAE Baja competition due to its ability to have variable gear ratios through the power range of the motor and having relatively low weight, was decided along with a custom single speed gearbox. The team decided this would be the most efficient design option for the drivetrain. This design allows for a relatively easy flow of energy and is supplied by the engine, which creates a rotational torque. From there, this torque is transferred to the CVT, which leads to gearbox. The gearbox will be a single speed, dual reduction gear set with no neutral or reverse, which allows the flow of energy to go directly to the final CV joints. From the CV joints the energy is transmitted to the driveshaft, which flows directly to the wheels and then to the ground to give the car its forward motion. The CVT has a wide range of gear ratios and usually has a limit set by the manufacture for both the high gear and low gear. Varying two pulleys, a drive pulley and a driven pulley controls these ratios. These pulleys have the capability to collapse and expand depending on the torque applied. The basic operation of the CVT can be seen in figure 14 below. The drive pulley of the CVT is connected directly to the engine, which provides the rotational torque needed to transmit the power to the driven pulley, by the means of a belt. The pulleys are indirectly proportional meaning as one pulley contracts the other expands and vice versa depending on the torque applied and once the torque is applied to the driven pulley it then transmits power into the gearbox. 30

31 As the power flows through the CVT, it is transmitted to the final gearbox. To achieve both high torque and high speeds a two-speed transmission can be used. From the transmission, the energy flows through the CV joints and driveshaft before transmitting to the wheels. The CV joints and the driveshaft are components for the vehicle to perform efficiently with an independent rear suspension (IRS). Constant velocity joints (CV joints) are used to allow the driveshaft to articulate in various directions with power being maintained at all times. Another component to a Figure 14: Operation of CVT Drive transmission is the use of a differential or a spool. The team chose a solid spool due to it being more suitable to the teams design because of its lightweight design as well as limiting failure of components. Concept Evaluation and Selection When selecting a drivetrain concept, previous designs were evaluated. The 2014 car drivetrain uses a CVT drive, multi-gear transmission featuring two forward, neutral, and reverse gearing, and a chain and sprocket system to connect to the final drive solid axle. The downside of this design was the overall weight of the components as well as no shift linkage to operate the transmission. The solid axle rear consisted of a large diameter chromoly pipe and the team was unable to take advantage of two separate forward gears or reverse during any event due to not being able to operate the shift fork. This added excessive weight and hurt performance during some of the competition events. Research was also conducted on what top performing competitors used in their designs, which found all teams used a CVT coupled to some form of gearbox. 31

32 The key governing factors in concept selection contained, performance, weight, cost, durability, and gear ratio. Decision matrices were completed; one matrix for the power transmission component of the concept and a second matrix to determine the final drive and the decision matrices for this can be seen in Appendix C.1. After completion, it was found that the CVT with a custom gearbox would be the best option. Creating custom gearing scored low in cost, but the overall weight reduction and performance capabilities outweighed this drawback. Figure 15: Custom Gearbox Created By 2015 Baja Bengals System Description The drivetrain of the vehicle is responsible for transmitting engine power to the ground and providing mobility to the vehicle. This subsystem of the car is composed of several parts. The vital elements of the drivetrain are the engine, CVT, gearbox, CV axles, and wheels. A Briggs and Stratton 10hp engine is specifically constrained by the competition rules. In addition to this, the engine must also remain completely unmodified. The CVT, as previously explained, is the device that allows for variable gear ratios by the use of pulleys that can either expand or contract. This allows the engine to operate at peak RPM while further multiplying output power. The gearbox provides the drivetrain with the final gear reduction required, as the CVT does not fully create the 32

33 required power by itself. The gearbox will consist of a dual reduction gear set. A single reduction will not be used because the gear diameters would be far too large to reach the same gear ratio of a dual reduction set. CV axles are used in independent suspension setups to transfer the engine power from the final drive to the wheels. Proper optimization as well as tuning of these components will allow the vehicle to perform exceptionally at competition. Materials Selection Materials used in certain drivetrain components are constrained by SAE rules. Gearbox construction is limited to two options. It must either be made of 6061-T6 Al having a minimum wall thickness of 3mm or ANSI 1010 steel with wall thickness of 1.5mm. Aluminum was chosen due to its high machinability and lightweight nature. The material selected for the gears and shafts will be made from 4340 steel. This is an industry standard material and can also be hardened after machining. The CVT, CV axles, and wheels will be purchased. Engineering Analysis After CVT selection, the final drive optimal gear ratio needed to be determined. In order to do so, the team needed to find the minimum torque required to push the vehicle forward. This was approached through the use of dynamic equations to calculate the amount of force needed to provide the vehicle with positive motion up an incline. Knowing that torque is the cross product of the wheel radius and the force on the ground, the force on an incline was calculated because the force due to friction and the weight of the vehicle parallel to the plane would oppose forward motion. A 35 degree incline was used in calculations because this is the steepest hill present across all Baja competition locations. The repelling force came out to be lbf from using a 600lbf vehicle, which includes a driver that weighs 200 pounds. Next, we took into account all necessary performance criteria that affected the total reduction. Because a 10hp engine limits us, the main focuses will be on optimizing speed and torque. Using top performing Baja teams as a baseline, a top speed of 40 mph is considered competitive. To calculate top speed, we must consider torque at the 33

34 governed engine rpm of 3800, total reduction, wheel diameter, and final CVT ratio. The wheels to be used are 21.5 inches in diameter, engine max torque is 14.5 ft-lbs., and the final CVT ratio is 0.9:1. We calculated a total reduction of 6.76:1. With this reduction, max torque available at the axle is ft-lbs. When compared to the dynamics design test incline required torque at 35 degrees, a torque design factor of 1.11 is achieved. Formulas used with the American Gear Manufacturer Association (AGMA) were placed into an excel spreadsheet to further optimize the gearbox with respect to weight and size. Using the most optimized gear train design, a gear ratio of 6.8:1 is achieved, which changes the output goals minimally. Calculations and excel spreadsheet can be seen in Appendix C.3. Manufacturing and Assembly Due to the complexity of design, a CVT and CV axles will be ordered from manufacturers. Wheels and the engine will also be ordered, as they are standard parts. The gearbox housing will be made with a CNC machine from aluminum billet. Gear manufacturing requires knowledge of the process as well as access to the tooling required, so the custom specified gears will be outsourced. Research shows that many teams continue weight reduction by removing gear material, which can be done with a water jet cutter. The shafts can be machined by lathe and then keyed with a mill, but splining the output shaft will also be an outsourced process. 34

35 Suspension Introduction The overall task of the suspension system in relatively simple. In order for various subsystems to remain coupled and functioning, the system as a whole must retain structural integrity, absorb forces encountered off road, and maximize tire contact. Achieving the stated tasks will promote an environment suitable for subsystem integration. Objective Enhancing steering response is directly proportional to success in the SAE Baja competition. Maximizing the steering response via steering subsystem is redundant without the appropriate means of positioning the wheels in an effective manner. Minimizing camber variance throughout wheel travel provides the appropriate medium to achieve this objective. Singularly, minimal camber variance fails to perform to the standards set by SAE Baja Competition. The following co-requisites, in conjunction with minimizing camber variance, propel the Baja car into a position able to maximize the steering response. Table 6: Suspension Co-Requisites Requirement Target Acceptable Range Static Ride Height 10" 8-12" Full Compression Travel 7" 6-8" Full Extension Travel 5" 4-6" Camber Variance 3 ±5 CV Plunge.25".5" Maximum Width 60" < 64" Front Track Width 55" 50-55" Rear Track Width 50" 45-55" Wheelbase 75" 70-80" 35

36 Functional Requirements Dampen Vibrations Maintain Tire Contact System Integration Dissipate vertical forces acting on frame Dissipate horizontal forces acting on frame Minimize camber upon front suspension travel Recovery from lost contact Maintain minimal ground clearance Couple steering and front suspension Quick recovery from impacts Limit CV angles Distribute weight evenly Reduce bump deflection Reduce deflection from front tire impacts Optimal ground contact through turns Protection against full droop Protect tie rods at maximum turning angle Maintain CV Plunge tollerances Figure 16: Suspension Functional Decomposition Qualitative Constraints Due to a relatively high degree of uncertainty regarding geometries postmanufacture, adjustability plays a vital role in a successful suspension design. Incorporating a design with easily adjustable parameters including: static camber static caster static toe static ride height thoroughly lead to faster manufacture of prescribed objectives relative to fixed design. Concept Generation and Selection Off-road suspension design is a broad field dependent on constraints as well as vehicle application. Discussing critical failures associated with past LSU Baja Alumni gave insight on where to begin narrowing the scope of suspension design. Researching top placing SAE Baja teams further narrowed the concept generation phase of the project. Selecting unequal length control arms for the design of the front suspension was a quick realization due to the near unanimous application in SAE Baja as well as off-road 36

37 communities. Popularity associated with this particular design is due to the correlation between large wheel travel and minimal camber variance. A labeled pictorial reference of a preliminary design is located in Appendix D.5. With the fundamental design selected, realizing geometries associated with the various components is of order. An extreme relationship between optimal parameters such as camber, caster, toe, and roll center, exists depending on the radial lengths and angles associated with the upper and lower control arms. Simple four-bar linkage equations were used to recognize geometries that display favorable characteristics. Upon realization, iteration proved many concepts unobtainable due to physical constraints. To eliminate impractical design at an early stage, a dimensionally accurate three-dimensional four bar linkage was modeled as shown in Appendix D.6. With camber variance limited favorably, roll center of the Baja vehicle was analyzed. It was concluded that minimizing camber variance and optimizing roll center was an impractical task due to the drastic variance of camber variation relative to roll center and vice versa. Camber variance was selected as the primary parameter to optimize due to the large expected wheel travel. Restricting the roll center to the inside of the vehicle was then made a priority and ultimately achieved by ensuring that the angle between the upper and lower control arms is converging from the mounting points at the upright to the brackets anchored to the frame, as plotted in Appendix D.5. LSU Baja alumnus Aaron Figure 17: Unequal Length Control Arms McDonald and Devin Poirrier conveyed the importance of an independent rear suspension design which is more capable of traversing extreme terrain relative to a dependent solid axle rear setup. An independent rear suspension can transfer more power to the ground while positioned on uneven terrain due to the absence of a solid body connecting both wheels. Therefore either rear wheel can be articulated independently of 37

38 the other while retaining the ability to transfer power to the ground via two continuous velocity, CV, shafts connected to the gearbox. Researching rear suspension design of top-tier SAE Baja competitors yielded conclusive results, in that either unequal length control arms or a three-link trailing arm was selected. Both designs exhibit the ability to achieve the selected wheel travel while remaining structurally stable, yet the three-link trailing arm demonstrated higher strength and simplicity. This stems from the ability to transfer forces encountered at the wheel to that of parallel orientation at mounting points on the frame. This is achieved with the application of a spherical bearing positioned at A, allowing two degrees of freedom. The second degree of freedom upon travel at A keeps the tire, shock absorber, and mounting forces, parallel which is pictured in Appendix D.1. Because of low bending forces as a result of the ability of the trailing arm to rotate to a parallel plane with forces encountered, thin walled tubing may be exploited for the Figure 18: 3-Link Trailing Arm radial arms due to the high axial strength of such tubing, thus lowering weight. The 3-link trailing arm design further reduces weight by combining the rear hub assembly with the structural members comprising the trailing arm, as pictured in Appendix D.1. This feature reduces areas of high stress typically found at threaded mounting locations. 38

39 After a considerable amount of fundraising, pneumatic shocks were selected as the spring-damper system of choice. With the budget constraint eased, it was decided by the team to be impractical not to shed the excessive weight associated with less expensive coil-over shocks. Taking advantage of Fox Racing s SAE Baja University discount, Fox Float 3 EVOL R shock absorbers, depicted in Figure 19, were selected to be incorporated into all four corners of the vehicle. These particular shocks have a variety of features that will enhance the performance of the entire vehicle throughout the separate events at competition. The Fox Float 3 EVOL R Figure 19: Fox Float 3 EVOL R shocks are infinitely adjustable by regulating the pressure maintained in either of the two reservoirs. Varying the pressure supplied in the main chamber steadily increases the force vs. displacement curve whereas adjusting the pressure of the external piggyback reservoir regulates spring rate when approaching the extremes of shock stroke. Decreasing the piggyback reservoir pressure provides a semi-linear force versus displacement plot whereas increasing pressure exponentially increases the force required to fully compress the shock absorber, or bottom out the shock, as shown in Appendix D.2. The rebound damping of this shock absorber has dual speed compression, which varies, relative to position throughout stroke, ensuring quick delivery of the tire to ground after considerable displacement while also having low speed compression for that of small bumps encountered on track. This optimizes tire contact throughout all scenarios applicable to SAE Baja. As a precautionary measure, the shock includes an internal chamber which is sealed within 25% of extreme shock stroke to provide up to 3000 pounds of additional damping force before bottoming out, as shown in Appendix D.2. This feature drastically reduces the scenario of extreme force acting upon the frame throughout suspension travel. 39

40 Final Design Figure 20: Final Suspension Design Notable Suspension Parameters Camber Variance 3.59 Front Roll Center 5.5" Rear Roll Center 25" Weight 34 lbs excluding hardware Material AISI 4130 Material Selection With reliability as a primary parameter followed closely by low weight, AISI 4130 was selected as the material of choice regarding structural members of the suspension system. AISI 4130 has proven its effectiveness in aerospace, extreme motorsports, as well as SAE Baja, due to its high strength and stiffness coupled with ease of welding and machining. The average bending strength of AISI 4130 proved to be roughly 40% greater than AISI 1018 and 55% larger than Al 6061-T6. All bolts incorporated into the SAE Baja vehicle are required by SAE rules and regulations to be 40

41 of grade eight, marked with six radial lines on the head of the bolt or stronger. Tables showing the material selection can be seen in Appendix D.4. Engineering Analysis Referencing Appendix D.2, the resultant force from full compression of a Fox Float 3 EVOL R can be approximated as 1200 lb when the main chamber is pressurized to 30 psi. For simplicity, the lower control arm is modeled as a simply supported beam as shown in Figure 21. The control arm is F shock =1200 lb F t,x F t,y F c,y Figure 21: Lower Control Arm mounted to the frame on the right side of Figure 21 denoted by subscript c, while the tire is located on the extreme left, denoted by subscript t. Summing the moments relative to the node where Ft,x and Ft,y meet while also the summing forces in both the X and Y directions, Force, shear, and moment diagrams are all pictured in Appendix D.1. F c,x τ = Mc I = psi > Yield Strength = psi τ = bending stress M = moment about neutral axis c = distance from neutral axis to extreme fiber I = second moment of area about the neutral axis Reiterating, the analysis above is modeling the entire lower control arm as a single tube. This is not the case in reality, and FEA must be utilized to determine the equivalent 41 Figure 22: Initial Lower Control Arm Model

42 stresses. The resultant vertical loading, F shock,y will be applied in the Y direction to the two bolt holes extruding from the thin plate shock absorber bracket in the FEA analysis of both Figure 22 and 23 for simplicity. Fixed supports were applied at both tubes extruding in the Z direction as well as the threaded region in the extreme +X direction. During this analysis, the maximum stress in both Figures 22 and 23 has been disregarded, due to being set as a fixed support. This FEA is intended only for analysis of the relationship between the thin plate mounting bracket extending in the Z direction and the structural members extruding from support-to-support. As can be seen from Figure 22 above, the initial lower control arm design produced large stress concentrations on the shock absorber mounting surface. While still under the yield stress, a 1.13 factor of safety was not acceptable due to the uncertainty of loading conditions throughout competition. Adding two.5 x.25 cross sectional supports as shown in Appendix D.3. Drastically reduces stress concentrations as can be seen in Figure 6 below. The improved factor of safety relative to the shock mounting bracket was increased to 3.08 which is a much safer design with uncertain loading conditions. Figure 23: Lower Control Arm with added shock mount bracing Impact force with Spring Damper System 42

43 F = k ( 2Wh k )0.5 = kx and F avg = E y Referencing the Fox force versus displacement curve in Appendix D.2. and assuming h=10 ft, W=500 lb, the impact velocity = ft/s. The average force distributed between all four tires of the vehicle landing flat was found to be 4920 lb and assuming that the car has a front to rear weight ratio of 0.35 : 0.65, the average force exerted on each rear tire is 1600 lb and the average force impacting each front tires is 860. If the entire weight of the vehicle were to land only on one tire from the initial height of 10 ft, the average force equated to 9720 lb. Expanding, this theoretical scenario models the vehicle falling from 10 ft and landing on one tire throughout the entire suspension travel. This scenario is implausible because the vehicle will articulate in three dimensions upon landing on one tire, therefore redistributing the force to other areas of the vehicle. F = impact force x =Δy= shock displacement W = weight h = initial height ΔE=change in energy The nonlinear spring Coefficient, k, of Fox Float 3 EVOL R shock-absorbers, shown in Appendix D.8, was approximated using an exponential trend line on the force versus displacement chart plotted in the appendix. k = e x Shear D pin,min = 2F πτ ult The pins experiencing the highest shear stress are anchoring the shock absorber to the frame or suspension members. Assuming the theoretical force F=9720 lb found above, 43

44 the factor of safety was calculated to be 2.25 for 1.142x10mm grade 8 bolt was found to be 2.25 which exceeded the teams expectation. 4-bar Linkage z 2 = r r 2 2 2r 1 r 2 cosθ 2 = r r 2 4 2r 3 r 4 cosλ λ = cos 1 z2 r 3 2 r 4 2 2r 3 r 4 α = cos 1 z2 + r 4 2 r 3 2 2zr 4 β = cos 1 z2 + r 1 2 r 2 2 2zr 1 Variables regarding 4-bar linkage equations are defined and schematic is provided in Appendix D.6. Camber variance was found to be 3.59 throughout the 12 total suspension travel. Table 6 below shows camber values of intermediate and extreme wheel travel positions. Table 7: Camber Variance Camber Properties Camber Angle (degrees) Δy (in) Δx (in) Maximum Compression Static Height Maximum Extension Manufacturing and Assembly Manufacture of structural members will be performed in house at LSU. The degree of accuracy in pipefitting is relatively high, yet feasible with such few members to be fit. TIG welding will then be utilized to join the structural members of the suspension. Shock absorbers, ball-joints, rod ends, bolts, and nuts, will all be ordered from third party vendors. 44

45 Steering Introduction The steering subsystem s task is to allow the vehicle to be easily and efficiently turned. To design the steering system research was conducted, concepts were developed, and then selections were made. The final design of the subsystem includes the use of a Desert Kart 14 rack and pinion, a custom upright, and 4130 steel tie rods. Objective The steering system is a critical component of the Baja vehicle. It provides the vehicle with the ability to maneuver around obstacles by allowing the vehicle to turn. The ability to efficiently maneuver the vehicle is weighted heavily in many events both dynamic and static. For the dynamic events, the team is steering contributes significantly in the maneuverability, hill climb, suspension, and endurance events. The objective of the steering system is to influence the direction of the vehicle in an efficient and durable manner. Functional Requirements Control Vehicle Direction System Integration Safety Rotate Wheels Compatible With Suspension Removable Steering Wheel User Input Lightweight Unobstructed Egress Tight Turn Radius Durable Enclosed Mechanisms Maintain Direction Driver Comfort Figure 24: Functional Decomposition of Steering In order to identify the critical functional requirements of the steering system, an encompassing functional decomposition was completed on the subsystem. Next, the 45

46 functions that the team felt were critical to the successful design were given more specific focus in order to simplify the concept generation and selection design phases. The functions deemed critical included: I. Rotating Wheels and Tires II. III. IV. Tight Turn Radius Durable Lightweight V. Enclosed Mechanisms Each of the above specified functions contribute significantly to the success of the steering system. The most important aspect of the steering system is that it must influence direction of the vehicle. It is crucial that the vehicle has predictable performance with a given driver input. In addition, the vehicle needs a tight turning radius in order to perform well in the various competition events. Through a site visit to Auburn and research, a 10 feet turning diameter is the goal of the team. The dynamic events are extremely brutal on the components of the Baja vehicle making them susceptible to failure. Therefore, the components must be made to last the duration of the completion, the steering components are no exception. Due to the limited attempts on dynamic events, and the limited time on the endurance race, the team placed high value in designing the vehicle for durability to limit crippling downtime. While the durability is very important, the team must also design with a balance in respect to weight. Because one of the team objectives for this year s Baja car is to reduce the overall weight, opportunities to reduce weight should be taken advantage of if they do not reduce durability drastically. It is important that the steering system contribute to the weight goal in any form possible, but not at the unnecessary sacrifice of performance. 46

47 Finally, as in any part of life, safety must be practiced to the extreme. The entire participation in the competition revolves around the vehicle being safe to both operators and spectators. Therefore, each steering component must be designed with safety in mind. Therefore, the team identified that ensuring moving mechanisms and components of the steering system should be unexposed to the driver. It will be necessary to have covers to eliminate pinch points on all moving parts. Qualitative Constraints The SAE Baja rulebook does not constrain the steering system directly, however the system should not obstruct the five-second egress and fasteners should meet the grade specifications. Therefore, the team is free to design to fit the specifications. However, the design of the system is constrained by several of vehicle characteristics. For instance, the design of the frame dictates where the steering system is mountable. The suspension takes a role in the overall wheelbase and track width, which influences the turning diameter and steering principles such as Ackermann steering geometry. Other things constraining the system are brake components, or frame members that obstruct the motion of either the rack and pinion or the tie rods. Measurable Engineering Specifications Table 8: Steering Specifications Steering Specifications Turning Diameter Rack Travel 10 Feet 4.25 in lock-to-lock Steering Ratio 12:1 Number of Steering Wheel turns lock-tolock 1.5 turns Average Tire Turning Angle 50.5 System Weight 47

48 Concept Generation and Selection The concept generation for the steering system is driven primarily by researching existing technology within previous LSU Baja teams and other consistently well performing universities. After studying available information for the systems used by each of the successful teams, it is found that all teams use a rack and pinion steering system. In house, the two previous LSU teams both used rack and pinions as well. The 2013 Baja team made a custom rack and pinion, but did not have success with making it compact, light, or completely enclosed. The 2014 team used one of the popular commercial options and was happy with its performance. Furthermore, majority of the consistently competitive teams design and manufacture custom upright assemblies in order to have more flexibility in turning radii, suspension setup, and to reduce overall vehicle weight. For example, Appendix E.1 and E.2 display the Michigan Baja team s custom uprights that allow them to create a tight turning radius by mounting the tie rods close to the kingpin axis. In contrast, the recent LSU teams have used the same Polaris Outlaw ATV upright assembly, see E.3 in Appendix. The assembly has significantly hindered any customization within both steering and suspension parameters. Additional research yielded that tie rods of the researched teams varied by both material and geometry. Teams take differing approaches for striking a balance between durability and weight savings through the use of materials such as steel, aluminum, and carbon fiber. The previously mentioned material options present different challenges, which will be examined more thoroughly in the material selection section. To make initial decisions for the steering components, the team evaluated the research, carefully evaluated critical functional requirements, and revisited team goals of the steering system. The team identified several key functional requirements of the system including: tight turning radius, system durability, lightweight, and safety. The first decision for the team was to select the steering method. Due to the popularity of the rack and pinion and the lack of other feasible options, the decision to use this system was easy. Next, the team discussed the pros and cons between purchasing a commercial rack and 48

49 pinion or by making a custom design. The driving factors in this decision included: cost, performance, and time required to design and manufacture. Research of the available rack and pinions produced few options, however, an offering by DesertKarts.com, Appendix E.5, was found to be popular among the Baja community. The DesertKart system features a 4.25 travel, a 12:1 ratio, and weighed 3.2 pounds. For the goals of the team, these specifications met the criteria at a cost of approximately $98.00 in a readily available package. However, the team was fortunately able to secure a DesertKart rack and pinion for free by generosity of the LSU SAE Formula team. To thoroughly examine options; the team evaluated the alternative of a custom rack and pinion by examining the raw material cost. Initial estimates for the material were $92.27, which included material for the rack, pinion gear, bearings, and bushings. Examining the additional monetary cost and the effort put into designing and manufacturing a custom system led the team to believe it would be more beneficial to place the effort in other vehicle components. Also, it was determined that designing a system that would function as well as the DesertKart option would likely weigh more and utilize more valuable space in the front of the vehicle. The benefits of using the commercial offering outweighed the customization potential of the rack travel and steering ratio. Much of the effort saved on the custom rack and pinion went into the selection of an upright in order to connect the tie rods to the wheel assembly. After considering the goal of a ten feet turning diameter and determining the design parameters for the suspension mounts, research for existing off-road vehicle uprights was conducted. The search resulted in no uprights that allowed the steering and suspension to have ideal characteristics. Therefore, concept ideas for the upright were modeled in Solidworks. The iterations can be found in Appendix E.6 and E.7. The final design can be seen in figure 26. It features an offset of 1.5 for the suspension to design around the car roll center and camber, both covered in detail in the suspension section. For the steering, the upright places the tie round mount 1.75 vertically and 0.75 laterally from the kingpin axis, see E.8. This configuration should allow the vehicle to have an approximate 10 turning diameter with a slight toe in on turns. The toe in on turns stems from the design 49

50 incorporating a slight More Ackerman steering geometry, E.8, in comparison to True Ackermann, E.9. The higher Ackermann Angle will allow the vehicle to have some over steer in corners which will make it easier to throw the vehicle into a controlled slide around turns and obstacles. Also considered while designing the upright was the location of the steering mount in relation to the center axis of the spindle. The tie rod mount center was located at the midpoint of the spindle in order to reduce bump steer by allowing the upright mount to be at the axis of rotation for the upright assembly. The custom upright was designed to use the existing Polaris Outlaw spindle. The upright is designed so that the spindle can be pressed into the upright, and the existing bearings and hubs can be used. Final Design 50

51 Figure 25: Steering Modeled with Car Created By 2015 Baja Bengals Figure 26: Steering Model Created By 2015 Baja Bengals Table 9: Cost Analysis of Steering Part Number Part Manufacturer Material Quantity Total Price Rack & Pinion 1 DesertKarts N/A 1 $0.00 Tie Rod 2 Baja Bengals 4130 Steel 2 $36.37 Upright 3 Baja Bengals 6061 Alum. 2 $ Steering Shaft 4 Baja Bengals 4130 Steel 1 $36.37 U-Joint 5 DesertKarts N/A 1 $0.00 Steering Wheel 6 N/A N/A 1 $0.00 3/8 Rod End 7 McMaster Steel 4 $15.12 Clevis End 8 McMaster Steel 2 $ /8-24 Bolt 9 McMaster Gr. 8 Steel 4 $9.09 per 25 3/8-24 Nut 10 McMaster Gr. 8 Steel 4 $13.86 per 100 Shaft Bearing 11 McMaster Steel 1 $9.59 Materials Selection Total Cost $ The steering system has multiple components that are not part of the rack and pinion system that contain materials to be selected. For instance, the tie rods and steering shafts both need geometrical and material selection while the material for the upright needs to be decided. Further components necessary to connect all of the steering 51

52 components include the u-joint for the steering shaft, the rod and clevis ends to connect the tie rods to the upright and rack, respectively. The driving material characteristics for the tie rods are that they be durable, light, easy to manufacture, and relatively low cost. Research was done to find the commonly used materials for tie rods. It was found that steel, aluminum, and carbon fiber are frequently used. Due to the team's lack of experience with manufacturing and the higher cost, the use of carbon fiber was ruled out. Therefore, tensile, buckling, and bending calculations were made to determine how suitable the remaining options were. It was found that with reasonable assumptions, 4130 steel was capable of performing to expectations. Multiple geometries were evaluated, found in the engineering analysis, to come to the conclusion of an outer diameter of and an inner diameter of This geometry will allow the team to machine the inner diameter to the necessary diameter and thread it for the rod ends. Comparisons of the various sizes for the tie rods and be found in the Appendix E.10. The team placed more emphasis on the steering system s durability rather than weight leading to the geometry selection to favor the larger outer diameter and thicker walled steel. However, the team believes it is best to purchase both steel rod sizes in order to validate the best option through further live testing in the next semester. It is important to evaluate the compromise between high durability versus lighter weight in the testing phase. For the steering shaft, material and geometry options were kept to those readily available and cost effective. Due the splined shafts on the pinion gear and the U-joint, an adapter is necessary to offset the outsourcing of external splines on the selected shaft. Therefore, material selection was limited to 4130 steel for its ability to be welded to the adapter. The u-joint limits the outer diameter of the shaft to 5/8, therefore torsional calculations were made to select an inner diameter for the 4130 steel shaft. The results indicated that a maximum inner diameter was To provide a factor of safety, the shaft will have a inner diameter. 52

53 The steering system has additional components that are used to make various connections. Each of the components were limited to readily available components from McMasterCarr in order to be able to quickly obtain replacement parts should they be necessary. For the rod ends, the team selected generic steel ball joint with a size of 3/8 and 24 threads per inch with left hand threads. The left hand threads were chosen so that the tie rod length could be finely adjusted to manipulate straight ahead toe characteristics. The selected rod ends have a static radial load capacity of 6,323 pounds, which will be more than sufficient for the application. The team selected forged steel clevis ends for the tie round end that attaches to the rack. Due to the rack using 3/8 rod ends with a 1/2 thickness, the clevis needed to have an opening at least this wide. Therefore, a clevis end with a blank end with the proper opening width was selected. The blank end will be threaded with the appropriate threads. Grade 8 bolts will be used to attach these components to the vehicle as they are specified in the SAE Baja rulebook. Engineering Analysis The steering system design process required several basic engineering and geometric calculations to properly locate and size components. The equations used in the process are shown below. Sample values for III and IV are located in E.10 of the Appendix. I. Average Tire Angle Approximations Rearranging to find the angle, θ: Where W Vehicle Track Width L Vehicle Wheel Base Turning Diameter = W 2 + θ = sin 1 L ( D W ) 2 L sin (θ) The average tire angle was determined in order to properly design the upright. The distance between the tie rod mount and the kingpin axis influences how much the wheels will turn given a known amount of rack and pinion travel. As the distance 53

54 decreases, the tires are able to turn at higher angles. However, this additional angle comes at the price of making the steering harder to control due to the reduced moment arm. Therefore, the driver may find it harder to maintain control when going over obstacles or hitting bumps and ruts. There is no perfect method or ratio to determining the drivability because of its subjectivity by driver. Further experience and testing may lead to changes in the distance. The simple geometry to find the distance is shown below. II. Tie Rod Mounting Distance X = 2.125" tan (θ) III. Tie Rod Analysis The selection of the tie rod geometry was determined by both the constraints mentioned in the material selection, and by completing the analysis in the below sections. For tie rods, the most likely mode of failure stems from bending, whether it be due to improperly placed components or by impact. Therefore, the team selected several potential tie rod geometries and then calculated the bending moment, which caused the rod to yield. After the geometry, which met satisfactory bending loads, additional analysis was performed for both Tensile and Compressive stress. It was found that neither of these loading conditions would be of concern for failure. a. Bending Stress σ = Mc I b. Tie Rod Tensile Stress σ = F A c. Tie Rod Buckling Stress 54

55 σ = π2 EI (KL) 2 IV. Steering Shaft Torsional Stress Next, the geometry for the steering shaft was selected. With the aforementioned constraints, the inner diameter of the shaft was determined using a 600 inch-pound load applied to the shaft. The shaft will not see other methods of loading, therefore, this analysis was deemed complete. τ = Tc J 55

56 Brakes Introduction Properly functioning braking systems are a key component in making any motorized vehicle safe. The braking system on this year s Baja vehicle will have to meet certain functional requirements, performance requirements, and also withstand the conditions seen at competition. Thus the design of the braking system focused around items such as safety, performance, weight, and cost. One of the first events at competition is a dynamic braking test that is scored as a pass/fail. The car will not be able to continue with the competition events until this dynamic braking test is successfully completed. That being said, analysis of the braking system capabilities was of the utmost importance. The following sections aim to explain the design and selection processes, as well as the engineering analysis, that led to the final product selection for the braking system on this year s Baja vehicle. Objective The main objective for the braking system is to meet the requirements set out by the competition rulebook. As mentioned earlier, the vehicle will not be able to participate in the majority of the competition unless the dynamic braking test is passed. Another goal for the braking system is to keep the overall weight to a minimum, which is also an objective for the Baja vehicle as a whole. However, performance and durability must not be sacrificed when working towards this goal. Last year s LSU Baja car struggled with locking all four wheels for the dynamic braking test due to the lack of brake bias adjustability. With that, another objective for this year s braking system is to allow for adjustable braking distribution. Part of the competition technical inspection involves all drivers being able to exit the vehicle in under five seconds. This leads to the last objective, which is keeping the foot box area free of hang-ups and pinch points as much as possible. 56

57 Functional Requirements The main functional requirement of the braking system is to effectively slow down and stop the Baja vehicle from speed. The competition rulebook also sets out a few functional requirements: the vehicle must be able to lock all four wheels after accelerating a certain distance (dynamic braking test) and the brake light must be illuminated anytime the brakes are applied (regardless of engine being on or off). The following figure shows a basic functional decomposition of the braking system. Figure 27: Braking Functional Decomposition 57

58 Constraints The 2015 Baja SAE Rules and Regulations provide numerous constraints for the design of the braking system. Braking must be achieved through a hydraulic system with at least two independent fluid circuits. All brakes must be operated through a single foot pedal, which must be rigidly linked to the master cylinders. Lastly, braking on the rear end must act through the final drive. ARTICLE 11: BRAKING SYSTEM B11.1 Foot Brake The vehicle must have hydraulic braking system that acts on all wheels and is operated by a single foot pedal. The pedal must directly actuate the master cylinder through a rigid link (i.e., cables are not allowed). The brake system must be capable of locking ALL FOUR wheels, both in a static condition as well as from speed on pavement AND on unpaved surfaces. B11.2 Independent Brake Circuits The braking system must be segregated into at least two (2) independent hydraulic circuits such that in case of a leak or failure at any point in the system, effective braking power shall be maintained on at least two wheels. Each hydraulic circuit must have its own fluid reserve either through separate reservoirs or by the use of a dammed, OEM-style reservoir. B11.3 Brake(s) Location The brake(s) on the driven axle must operate through the final drive. Inboard braking through universal joints is permitted. Figure 28: 2015 Collegiate Design Series Baja SAE Rules for Braking Other constraints came about through design parameters of the other subsystems. The wheel size is ten inches, which limits the maximum brake disc diameter to about seven and a half inches (in order to fit the disc and caliper inside the wheel diameter). The solid rear-end design of the drivetrain allows for the use of a single brake for the rear end. Due to the frame geometry and drivetrain mounting, the diameter of the brake disc in the rear will have to be seven inches or smaller. 58

59 Concept Generation and Selection To begin generating concepts for the braking system, extensive research on cars from previous competitions was conducted to see what has and has not worked in the past. From this research, it was found that virtually all teams use hydraulic disc brakes on their cars. One of the only other hydraulic braking technologies is drum brakes. Drum brakes are known for poor heat dissipation and large decreases in performance when wet. In addition, drum brakes are much heavier than a disc brake system with the same braking force capabilities. With this information it was decided that hydraulic disc brakes will be used on this year s Baja vehicle. With the hydraulic disc brake system selected, the design options of the various subcomponents were then evaluated. These include pedal type, master cylinder type/mounting, and the rear end braking. The design of the front end braking came down to just sizing the components since the only option was having a disc tucked inside each wheel with calipers mounted on the uprights. Figure 29: Front End Braking System 59

60 Having two independent fluid circuits for the brakes meant having two master cylinders or a single with two reservoirs and a proportioning valve. In order to keep the system complexity down and reduce the risk of entire system failure, it was decided that two master cylinders would be used. The following schematic shows the independent circuits for the front and rear brakes. These two master cylinders had to be linked to the pedal rigidly, which meant the pedal assembly would have to accommodate for master cylinder mounting. With the rack and pinion mounted in place, it was determined that a hanging pedal would have to be used to achieve proper seat-to-pedal distance. A floor-mounted pedal in the correct location would have interfered with the rack and pinion. Figure 30: Brake Schematic Created By 2015 Baja Bengals 60

61 Figure 31: Floor Mounted and Hanging Pedal Assemblies There were two options for master cylinder mounting with the hanging pedal design: forward-facing and rear-facing master cylinders. Figure 32: Forward-Facing and Rear-Facing Master Cylinder Mounting 61

62 The rear-facing design was also chosen due to physical interferences. The proper pedal location makes the brake mounting near the very front of the vehicle, where the bodywork and number plates will be mounted. The forward-facing design would have caused the master cylinders to stick out past the roll bars of the frame, which would have prevented proper mounting of the bodywork. With plenty of room towards the rear of the brake mount, the rear-facing master cylinders are safe from debris and high enough to allow for easy driver exit without hang-ups. Another feature of the selected pedal type is the balance bar, which allows for brake bias distribution for the two fluid circuits. Figure 33: Balance Bar Last year s LSU car had this balance bar, but part of the competition rules state that there can be no tools used on the vehicles in between events. This rendered the adjustability useless since they could not change the balance bar bias without tools. An on-the-fly adjustment knob is available for most of these balance bars, and can be routed to within the driver s reach since it is easily turned by hand. This was selected for use in this year s braking design since it will allow for braking distribution changes in between events as well as when operating the car. 62

63 Lastly, a design for the rear end braking had to be chosen. With open differential vehicles, there must be a brake at both rear wheels. With the solid rear end design like the one chosen for this year s car, it is unnecessary to have a brake at each rear wheel. In order to save weight and better protect the braking components, it was decided that only one disc and caliper would be used in the rear. It will be mounted near the gearbox at the center of the vehicle. This will keep the weight centered and provide consistent braking for both rear wheels. In addition, this location is much less prone to getting wet or hit by debris than if it were mounted near the wheel. Figure 34: Single Rear Brake Centrally Mounted Near Gearbox 63

64 Final Design The following is a parts list and cost estimate for the braking system final design. Table 10: Cost Analysis for Braking System Part No. Title Custom/Commercial/Other Quantity Spares Cost 1 Front Disc Commercial - Last year's car 2 0 Free 2 Front Disc Hub Commercial - Last year's car 2 0 Free 3 Front Caliper Commercial - Last year's car 2 2 sets of brake pads $ Pedal Assembly Commercial - Last year's car 1 0 Free 5 Master Cylinder Commercial - Last year's car 2 0 Free 6 Balance Bar Commercial - Last year's car 1 0 Free 7 Bias Adjuster Commercial - New 1 0 $ Rear Disc Commercial - New 1 0 $ Rear Disc Hub Commercial - New 1 0 $ Rear Caliper Commercial - New 1 1 set of brake pads $ Brake Line Commercial - New 1 set 0 $ $ Total Budget $ Total Cost $99.54 Remaining Through engineering analysis (covered in detail later on), it was determined that the front brakes, pedal assembly, and master cylinders from last year s car would meet the requirements of this year s braking system. Thorough physical inspection and testing of these components was done to be sure they were in the same condition as when new. 64

65 The large cost savings was the driving factor behind the selecting of these components. The Wilwood Bias Adjuster was chosen in order to function properly with the Wilwood Balance Bar included in the pedal assembly from last year s car. Figure 35: Front End and Pedal Assembly Braking Components Figure 36: Wilwood Braking Bias Adjuster The other items to be selected were the rear disc, rear disc hub, and rear caliper. The brake disc and disc hub are products from BMI Karts & Supplies (Product numbers and , respectively). Figure 37: BMI Karts Disc and Disc Hub - Rear Brake 65

66 The rear caliper is a Wilwood Billet Spot Caliper. This caliper was chosen because it is one of the lightest calipers on the market that met the performance requirements, and also for Wilwood s reputation as a leader in the high-performance braking industry. Figure 38: Wilwood Billet Spot Caliper - Rear Brake The rear disc will be mounted to the output shaft via the keyed disc hub, and the caliper will be set in place using a mounting bracket connected to the frame. This mounting bracket will be a piece of 4130 flat plate welded to the frame at one end and drilled with two holes on the other to mount the caliper. Alignment of the brake disc and caliper is crucial for proper braking performance and component longevity. With that being said, the caliper mounting bracket will not be designed until the manufacturing stage for multiple reasons: the frame and gearbox may not line up as planned in design (just a few millimeters of distance change will cause for improper alignment of the caliper and disc); and the rear disc hub does not have detailed drawings available from the manufacturer. The brake light and hydraulic pressure switches will be covered in the electrical section of this report. 66