Chassis. Introduction. Design Objectives

Chassis Introduction Purpose and Goals The chassis is the backbone of the Mini-Baja; it must support all the car s subassemblies as well as protect the driver. The chassis design is crucial to the success of the project because if the chassis fails, that puts the Baja and the driver at tremendous risk. The goal of the 28 Mini Baja frame will be to protect the driver, offer sturdy mounting for all subsystems, maintain all SAE rules and regulations, and still be lightweight. Background Chassis design in the SAE Mini Baja competition is critical for a winning car. These cars are all powered by 1 horsepower Briggs and Stratton engines. To extract maximum acceleration from this engine a lightweight chassis is necessary. At the same time the chassis must undergo the rigors of off-road racing. To analyze a structure that will undergo such loads, finite element analysis (FEA) is often a viable solution. FEA breaks the structure into smaller elements and analyzes each element as a body and can calculate the stress, deflection and other reactions of any structure. A Transient FEA will be the main simulation done to optimize the weight and strength of the 28 Mini Baja Chassis. From here forward a few assumptions have been made to aid design and analysis. The total weight of the Mini Baja car, without a driver, is estimated to be 4 lbs, with the lightest car weighing 318lbs. [] This is the average weight of the most competitive school s cars from 27. The driver will be referenced as a 6 foot 3 inch tall male weighing 25lbs, as per the SAE rules. [] Design Objectives To build a chassis to meet all of the previously mentioned goals the frame must: Endure the maximum dynamic load according to SAE Technical paper 26-13626[] with a factor of safety of 1.5 Keep a driver alive during a 7.9g front impact 19

Keep a driver alive during a 7.9g side impact Keep a driver alive during a 7.9g Roll over situation Abide by all SAE rules and Regulations Weigh less than 8lbs Have mounting structures for all subsystems that will withstand the loads produced by those subsystems. SAE Rules and Regulations All SAE rules and regulations can be found in Appendix A. The Frame rules are specifically in SECTION 3 ROLL CAGE, SYSTEMS & DRIVER S EQUIPMENT. [] Some highlights of that section are: The driver s helmet to be 15.24 cm (6 in) away from the straightedge applied to any two points on the cockpit of the car, excluding the driver s seat and the rear driver safety supports. [] The driver s torso, knees, shoulders, elbows, hands, and arms must have a minimum of 7.62 cm (3 in) of clearance from the envelope created by the structure of the car. [] Fit a 95% Male driver, while maintaining all constraints above. The LBD, LFS, SIM, FAB, and FLC must be at minimum.35 wall thickness tubing with a minimum outside diameter (O.D.) of 1 inch. The RRH, RHO, FBM, and LC must be (A) Circular steel tubing with an outside diameter of 2.5 cm (1 inch) and a wall thickness of 3.5 mm (.12 inch) and a carbon content of at least.18%, or (B) Steel members with at least equal bending stiffness and bending strength to 118 steel having a circular cross section with a 2.5 cm (1 inch) outer diameter and a wall thickness of 3.5 mm (.12 inch). [] Figure 2 below displays the location of each frame member referred to above. 2

Figure 2: Frame Members Maximum Dynamic Load The loading conditions used to analyze the Chassis are just as important as the analysis itself. The more accurate the load the smaller the factor of safety can be used. The 28 Mini Baja Chassis team purchased SAE technical paper 26-1-3626[], Structural Considerations of a Baja SAE Frame. In this paper Auburn University students used load cells to measure the amount of force translated into a Mini Baja Frame during two loading conditions. These load cells, shown in Figure 3, gave a load data on a time scale shown in Figure 3 for a single wheel vertical impact in Figure 4. Figure 3: Left - Load Cell [], Right - Vertical Impact Graph [] 21

Figure 4: Vertical Impact Demonstration [] This data can be directly used on the frame during a transient FEA analysis. Because the material that will be used for analysis, chromoly steel, is a well-known material and the loads and stresses that are being used for the shock force analysis are from actual test cases a factor of safety of 1.5 is used for the analysis of the frame. (See Appendix B for factor of safety justification) 7.9G Impact Using data from The Motor Insurance Repair Research Centre [] the estimated maximum g-force that the Mini Baja car will see is 7.9g s. The Motor Insurance Repair Research Centre did rear impact tests for vehicles of different masses. To estimate the maximum g-force on the Mini Baja car the g-force of the closest in weight car will be used. The mass and g-force of each car used in the impact test is shown in Table 1. [] Table 1: Left - Impact Acceleration [], Right - Vehicle Mass [] 22

The mass of the Mini Baja car is 2.2 slugs, therefore the g-force that will be used for analysis is 7.9g s(the car with the closest mass(ow3718)). These values are highlighted in Table 2 below. Delta V MPH pulse(ms) g-force Mass of Car(slugg) 6.337986158 92 3 81.549154 6.83583112 68 4.4 99.356567 8.77825496 84 4.4 134.645272 8.264236854 8 4.9 99.1395187 8.947745165 72 5.7 92.2988188 9.25843761 129 3.3 12.329966 1.31476179 13 3.6 12.329966 1.62544738 65 7.9 69.2698366 1.62544738 13 4.9 94.83412414 1.6875845 89 5.5 96.2738123 1.6875845 74 6.6 91.7564467 1.6875845 116 4.1 99.356567 11.24681858 65 7.9 123.3391788 11.43322993 82 6.4 119.91395 11.43322993 93 5.6 98.6282127 12.546112 93 5.6 1.1131 Table 2: Vehicle Mass and Acceleration [] Frame Weight To calculate the maximum frame weight, the estimated values of each subsystem were added up and subtracted from an estimated total vehicle weight of 4lbs. This resulted in a frame weight of 8lbs as shown in Table 3. Co m pon ent W ei gh t(lb) Tir es 5 Suspe nsi on 5 Stee ri ng 15 Engin e 6 Transm i ssio n 6 Re ar Housi ng 4 Bo dy Panel s 1 Ski d Plate 1 Ele ctro ni cs 5 Br akes 2 Total 32 Tar ge t 4 Fram e w e ight 8 Table 3: Estimated Vehicle Weight Design and Analysis Material Selection To build the Mini Baja frame steel must be used according to the rules. There are many different types of steel available to the public. The frame of the Mini Baja will be 23

made from tubular sections. Tubular sections offer superior loading capabilities per pound when compared to solid sections or square sections. The material selection criteria are very similar, so the suspension material selection chart will be used to choice a material for the chassis. According to that material selection chart (Table 16 on page 69) 413 steel is the preferred material for use in the Mini Baja frame. Roll Cage Tubing According to Roll Cage Material Specifications 31.5 in the SAE Rules [Appendix A] the roll cage must (A) Circular steel tubing with an outside diameter of 2.5 cm (1 inch) and a wall thickness of 3.5 mm (.12 inch) and a carbon content of at least.18%, or (B) Steel members with at least equal bending stiffness and bending strength to 118 steel having a circular cross section with a 2.5 cm (1 inch) outer diameter and a wall thickness of 3.5 mm (.12 inch). [] From the material selection chart 413 alloy steel was chosen as the material to be used for the entire frame. There is a note in the rules about the use of alloy steel: NOTE: The use of alloy steel does not allow the wall thickness to be thinner than 1.57 mm (.62 inch). To allow the use of this alloy steel an equivalency calculation must be made to that of 118 steel. This calculation is demonstrated below in Equation 1. E = The modulus of elasticity [] I = The second moment of area for the cross section about the axis giving the lowest value [] Sy = The yield strength of material in units of force per unit area [] c = The distance from the neutral axis to the extreme fiber [] ID = Inside Diameter Bstiff = Bending Stiffness Bstrength = Bending Strength For 118 Steel: E =297ksi π π 4 4 4 4 4 ( c ID ) = (1.75 ) =.3355583in I = 64 64 Sy =53.7ksi 24

c =1inch ( ) Bstiff = EI = 297 13.3355583 = 99668.14 Bstrength = ( ) SyI 53.7 13.3355583 = = 181.94857 c 1 Equation 1: Bending Stiffness and Strength In Table 4 below the bending stiffness and strength were calculated for available sections of 413 steel tubing. The available sections were found using a popular metal vendor. [] OD(in) ID(in) Moment of Inertia(in^4) bending stiffness(lb*in^2) bending strength(lb*in) 1.75.3355583 99668.14 2117.372856 1.125.959.3719744 112159.4 281.444313 1.25 1.134.38667283 1148418.3 1951.924434 1.25 1.12.4262298 1265288.25 215.5648 1.25 1.84.5264518 1546316.18 2628.216858 1.25 1.6.5787556 1718755.52 2921.35677 1.25 1.1.68761719 242223.6 3471.91583 1.5 1.37.75582124 2244789.9 3179.48824 1.5 1.31.13942577 38794.54 4372.517738 1.5 1.26.124781421 3768.21 5249.138454 1.625 1.59.8775855 266428.95 347.73222 1.625 1.459.119852623 3559622.91 4653.969554 1.625 1.435.13413926 3983688.51 528.4741 1.625 1.385.16166136 48136.3 6277.387421 1.5 1.43.4324292 1284236.66 1818.974939 1.5 1.42.5885911 1747872.6 2475.661658 1.5 1.37.75582124 2244789.9 3179.48824 Weight(lb/ft) 1.17128662.92596649.7427886.824671841 1.3746923 1.174775953 1.45187877.998653243 1.42956463 1.773431.973753 1.37288222 1.556196717 1.93362526.548978237.761224839.998653243 Table 4: Bending Stiffness and Strength of Available Tubing The lightest section is in bold. This is the 1.25 O.D. tubing with a.65 thickness wall. This is the lightest usable tubing that is still within all of the SAE restrictions. The other members of the roll cage(frame) will use at a minimum 1. inch O.D. tubing with a.35 wall thickness as per the minimum requirements in section 31.2.1[]. Design The design of the chassis has to incorporate two major things, driver comfort and safety and subsystem mounting. The driver safety for the design section is simply satisfying all of the SAE frame rules. Driver Comfort and safety To verify that a driver of 6 foot 3 inch, 25lbs would fit comfortably into the frame, a model of that person was drawn. The driver was then placed in the frame in the 25

driving position as in Figure 5. While this driver was in the frame measurements were made to make certain all of the SAE safety rules were satisfied. Figure 5: 95% Male in Mini Baja Frame Subsystem Mounting To mount the subsystems that subsystem was first placed in space in relation to the frame with mounting tabs at the mounting location. Finally piping was routed to the mounting tabs of that subsystem. This two step process is demonstrated with the engine/gearbox assembly in Figure 6. Figure 6: Two step subassembly mounting process step 1 on the left and step 2 on the right Initial Design Using the rules, subsystem dimensions, and a 95% male as the driving factors a frame was designed using the minimum frame tubing specified in the Roll Cage tubing 26

section above. The total weight of the initial frame design is 49.875lbs. This frame is displayed below in the left of Figure 7 without subsystems, and the right of Figure 7 with subsystems. Figure 7: Initial Frame without subsystems (left) and with subsystems (right) Analysis Shock Load As stated before, a transient FEA analysis is preformed on the frame using the force vs. time chart shown previously in Figure 3 on page 21. This force is broken up into X and Y values because the shock is not mounted vertically. The maximum and minimum angle of the shock (theta) in relation to the frame is 2.71 and 23.7 degrees respectively. The calculation of the X and Y forces are shown in Equation 2, and the resulting forces are listed in Table 5. This force will be applied to the front and rear shock mount points individually. 27

Figure 8: Shock angle in relation to the frame FX = F sin(θ ) FY = F cos(θ ) Equation 2: Calculation of X and Y components of the Shock Force Total Force X Force Y Force TIME(s)Load(lb)TIME(s)Load(lb) TIME(s)Load(lb).5 112.5.5 44.836875.5 15.23475.75 112.5.75 44.836875.75 15.23475.1 4.1 156.742.1 374.1528.125 128.125 51.5744.125 1197.28896.15 8.15 313.484.15 748.356.175 146.175 572.183.175 1365.65772.2 39.2 152.82345.2 364.79898.225-45.225-176.33475.225-42.9219.25 15.25 58.77825.25 14.373 Table 5: Shock Force X and Y Components For the FEA analysis the mass of the driver and engine/transmission are also modeled in the FEA program. To satisfy the SAE rules section 2.2 vehicle configurations the driver is assumed to weigh 25lb. [] The engine and transmission was weighed and found to be approximately 1lbs. The density of the frame tubing (.284lb/in^3) is also modeled with acceleration due to gravity taken into account. 28

The order of frame tubing used is listed below in Table 6. These are all readily available sections according to our online retailer. [] They are listed in order of increasing weight pre foot. If a section of tube needs to be larger to reduce stress the next size up from Table 6 is used. This will insure that the lowest weight frame is created. Cross Section THICKNESS Wieght/FT Reference Number 1.35.359 1 1.49.542 2 1.58.5912 3 1.125.58.6579 4 1.25.58.748 5 OD Table 6: Frame tubing sections and reference numbers Front Shock Load The Initial frame was analyzed using the shock force at the front shock mount as shown in Figure 9. Figure 9: Front Shock Force The results are shown in Table 7, with the graph of maximum von-mises stress shown in Figure 1. 29

Initial CASE Initial Test with Minimum Tubing Thicknesses MAX Stress = 4266.66667 Time Maximum Von Misses Stress Location Location Reference # FAIL? 2337 Cross Bar 1 PASS.5 4614 SIM Triangle Support 2 PASS.75 489 Cross Bar 1 PASS.1 9635 Cross Bar 1 PASS.125 28694 SIM Triangle Support 2 PASS.15 4462 SIM Triangle Support 2 FAIL.175 5493 Cross Bar 1 FAIL.2 5272 Cross Bar 1 FAIL.225 49861 SIM at RRH 3 FAIL.25 38674 SIM at RRH 3 PASS Table 7: Maximum Von-Mises Stress for Front Shock Force Figure 1: Time vs. Stress for Front Shock Force To change the stress at the times that the frame fails the tubing sections were modified or braces were added. The first time optimized was at.15s. At time =.15sec the maximum von mises stress was 4462psi and is located at the SIM Triangle Support as shown in the left of Figure 11. To decrease the stress value in the SIM the SIM tubing size was moved up to tubing cross-section 2 from cross-section 1. This reduced the maximum stress to 354psi as shown in the right of Figure 11. 3

Figure 11: Left - Initial Von-Mises Stress at time.15sec, Right - Stress after increased SIM size At time =.175sec the maximum von mises stress was 5493psi and is located at the cross bar that connects the left and right front shock mounts as shown in the left of Figure 12. To decrease the stress value in the cross bar the tubing section was moved up to cross-section 2 from cross-section 1. This reduced the maximum von mises stress to 42321psi as shown in the left of Figure 12. This is still above the maximum stress of 4266psi, so to further reduce the stress the cross bar section was increased to crosssection 3, which reduced the maximum von mises stress to 38372psi as shown in Figure 13. Figure 12: Left - Initial Von-mises Stress at time.175sec, Right - first revision at time.175 sec 31

Figure 13: Final revision at time.175 At time =.2sec the maximum von mises stress was 5272psi at Cross Bar as shown in the left of Figure 14. Due to previous changes in the Cross bar and SIM section size the maximum von mises stress was reduced to 42852psi and moved to the SIM at the RRH as shown in Figure 14. This is still above the maximum 4266psi, so a small support of cross-section 1 tubing was added between the RRH and SIM. This reduced the maximum von mises stress to 39818psi as shown in Figure 15. Figure 14: Left - Initial Von-mises stress at time.2sec, Right - first revision at time.2sec 32

Figure 15: Final revision at time.2sec At time =.225sec the maximum von mises stress was 49861psi and is located at the SIM and RRH as shown in the left of Figure 16. Due to previous changes in the frame s tubing sections the maximum stress reduced to 4656psi as shown in the right of Figure 16. Figure 16: Left - Initial Von-mises stress at time.225 sec, Right - Final revision at time.225sec The changes to the frame to withstand the front shock load resulted in a gain of 8.381 lbs giving a total weight of 58.256lbs. The new stress vs. time graph is shown below in Figure 17 and the data in Table 8. 33

Second Test with Changes at Maximum Values MAX Stress = 4266.66667 Maximum Von Misses Stress Location Location Reference # FAIL? 2184 Cross Bar 1 PASS.5 3744 SIM Triangle Support 2 PASS.75 3912 SIM Triangle Support 2 PASS.1 794 Cross Bar 1 PASS.125 25744 Cross Bar 1 PASS.15 35217 SIM Triangle Support 2 PASS.175 38275 Cross Bar 1 PASS.2 39818 Bottom Spot 4 PASS.225 4656 Bottom Spot 4 PASS.25 33462 Front Triangle 5 PASS Time Table 8: Maximum Von-mises stress, time, and location after front shock force optimization Figure 17: Time vs. stress of Frame after front shock force optimization Rear Shock Load The frame was analyzed using the shock force at the rear shock mount as shown in Figure 18. 34

Figure 18: Rear Shock Force The results are shown in Table 9, with the graph of maximum von-mises stress shown in Figure 19. CASE 1 Initial Test with Minimum Tubing Thicknesses Time Maximum Von Misses Stress Location 142 FAB at RRH.5 18831 FAB at RRH.75 12685 FAB at RRH.1 37894 FAB at RRH.125 143664 FAB at RRH.15 14962 FAB at RRH.175 12479 FAB at RRH.2 97511 FAB at RRH.225 67675 FAB at RRH.25 61185 Middle of FAB MAX Stress = 4266.66667 Location Reference # FAIL? 1 PASS 1 PASS 1 PASS 1 PASS 1 FAIL 1 FAIL 1 FAIL 1 FAIL 1 FAIL 2 FAIL Table 9: Initial Von-mises stress of rear shock load Figure 19: Time vs. Stress Graph of Initial rear shock load 35

The maximum von mises stress at.125sec is 143664psi, and is located on the FAB at the RRH as shown in the left of Figure 2. The FAB is in need of a bracing bar to transmit the force from the shock. A bracing bar of cross-section 1 was added at shock point to the RRH, this lowered stress to 69736psi and moved maximum stress point to the FAB at the shock point. This is shown in the right of Figure 2. The tubing section of the FAB was increased until the maximum stress went down to 38282psi with crosssection 4. This is shown in Figure 21. Figure 2: Left - Initial Von-mises stress at time.125sec, Right - first revision at time.125sec 36

Figure 21: Final revision at time.125sec At time =.15sec the maximum von mises stress was 14962psi and was located at the RRH on the FAB as shown in the left of Figure 22. Due to previous changes in the frame s tubing sections the maximum stress reduced to 39854psi as shown in the right of Figure 22. Figure 22: Left - Initial Von-mises stress at time.15sec, Right - Final revision at time.15sec At time =.175sec the maximum von mises stress was 12479psi and was located at the RRH on the FAB as shown in the left of Figure 23. Due to previous changes in the 37

frame s tubing sections the maximum stress reduced to 52332psi as shown in the right of Figure 23. The FAB tubing was increased to cross-section 5 to reduce the stress to 41165 as shown in Figure 24. Figure 23: Left - Initial Von-mises stress at time.175sec, Right first revision at time.175sec Figure 24: Final revision at time.175sec At times.2,.225,.25sec the maximum stresses were reduced to 27442, 2153, and 3276psi respectively due to previous changes. These results are displayed in Figure 25 and Figure 26 respectively. 38

Figure 25: Left - Final Revisions at time.2sec, Right - Final revision at time.225sec Figure 26: Final revision at time.25sec The changes to the frame to withstand the rear shock load resulted in a gain of 6.158 lbs giving a total weight of 64.414lbs. The new stress vs. time graph is shown below in Figure 27 and the data in Table 1. 39

CASE 2 Second Test with Changes at Maximum Values MAX Stress = 4266.66667 Time Maximum Von Misses Stress Location Location Reference # FAIL? 2614 Shock mount on FAB 3 PASS.5 4458 Shock mount on FAB 3 PASS.75 4175 Shock mount on FAB 3 PASS.1 1392 Shock mount on FAB 3 PASS.125 3566 Shock mount on FAB 3 PASS.15 37495 Shock mount on FAB 3 PASS.175 41165 Shock mount on FAB 3 PASS.2 27442 Shock mount on FAB 3 PASS.225 2153 FAB at LC 4 PASS.25 3276 FAB at LC 4 PASS Table 1: Maximum Von-mises stress after rear shock optimization Figure 27: Time vs. Stress after rear shock load optimization SubsystemSupport The frame is analyzed at the mounting points of the suspension. The suspension sub system translates the greatest reaction forces of all the mounted systems. The reaction forces gathered from the suspension sub team s FEA will be applied at the mounting points. Table 11 summarizes those reaction forces and Figure 29 and Figure 3 displays the stress results. The rear suspension forces are added together and applied at the same time because both the upper and lower arms are connected to the same mount as shown in Figure 28. The forces and moments were applied dynamically to the frame. 4

A-Arm Front Upper Front Lower Rear Upper Rear Lower Rear Total Mounting Area Front Rear Front Rear Single Mount Front Rear Front Rear X -568-48 -116.715-116.715-616 -48.5895-48.5895-48.5895-664.5895 Reaction Forces(lb) Y 93.95 93.95 338.515 338.515 338.515 1242.465 Z 78.38 78.38 32.115 32.115 32.115 11.495 Reaction Moments(lb*in) MY 156 156 Table 11: Suspension Reaction Forces Figure 28: Rear Suspension Mount Figure 29: (Left) Front Upper A-arm Stress, (Right) Front Lower A-arm Stress with support 41

Figure 3: (Left) Initial Rear Suspension Stress, (Right) Final Rear Suspension Stress The stress values were initially above the max allowable 42,67psi for the front lower analysis, so a bar of cross-section 1 was added as shown in right of Figure 29. The rear suspension section was changed from section 1 to section 2 to stay below the allowable stress. Impact Loading To calculate the forces used to analyze the 7.9g impact and newton s second law is used. The force calculation is shown below in Equation 3. f = ma m = 2.2slugs ft ft = 254.38 sec sec f = ( 2.2 ) ( 254.38) = 5138.476lb a = 7.9 32.2 Equation 3: Newton s Second law for Impact Force The 5113.38lb force will be used in a transient FEA. The force will be ramped over a pulse of.65sec. [] The impact analysis is done to verify that no frame member will fail during the impact and the driver will therefore remain safe. The ultimate tensile strength of the chromoly steel being used is 92,7psi. As long as the stress remains below this value the frame will be considered safe enough. The displacement of the pipes will be also be monitored to verify that the driver will not be harmed by any protruding bars during the impact. SAE rules [] state that the driver s arms etc must be at minimum three inches from all structural members of the frame. Therefore any displacement values over three inches will be deemed harmful to the driver. 42

Front & Side Impact Only one modification was made to the frame during Front and Side impact analysis. During the side impact force the part of the LFS that meets the RRH needed extra bracing of 1 inch O.D. and.35 wall thickness to keep the stress below the ultimate tensile of 92,7psi. The front and side impacted are summarized below in Table 12. Front Impact Side Impact Side Impact after Gussett Revision Maximum Vonmises Stress (psi) Time (sec) Maximum Displacement (in) Setup Figure 9717.345.41166 Figure 28 1577.69.55313 Figure 29 79985.69.51962 Figure 3 Table 12: Side and Front Impact Summary Figure 31: Left - Front Impact Force, Right Front Impact Stress Figure 32: Left - Side Impact Force, Right - Side Impact Stress 43 Stress Figure Figure 28 Figure 29 Figure 3

Figure 33: Left - Supporting Member added to LFS at RRH, Right - Revised Side Impact Stress Roll Over The force used for the roll over analysis is dependent on the height of the drop. The purpose of the roll over analysis is simply to rate the frame for a certain drop height. The starting point will be a ten for drop. The force used to anlyze the frame at that height is gathered using data from The Motor Insurance Repair Research Centre. [] A impact velocity can be calculated using Equation 4. That impact velocity is then used to interpolate a impact acceleration and pulse using data from The Motor Insurance Repair Research Centre. [] PE = Potential Energy KE =Kinetic Energy h =drop height v =impact velocity PE = KE PE = mgh 1 KE = mv 2 2 1 2 mv = mgh 2 Equation 4: Impact Velocity For a ten foot drop the impact velocity is calculated to be 25.4 ft/s and impact acceleration and pulse is interpolated as 6.8g s and 7 miliseconds respectively. Using 44

Equation 3 the impact force is calculated as 4423lb. The resulting stress is shown in Figure 34. Figure 34: (Left) Roll Over Force, (Right) Roll Over Stress for Ten Foot Drop The stress values for the ten foot drop is 12,84psi which is above the UTS of 92,7psi. The frame is next analyzed at a eight foot drop. For a eight foot drop the impact velocity is calculated to be 22.7 ft/s and impact acceleration and pulse is interpolated as 6.3g s and 72.5 miliseconds respectively. Using Equation 3 the impact force is calculated as 412lb. The resulting stress is shown in Figure 35. Figure 35: Eight Foot Drop Stress The stress value for the eight foot drop is 8,54psi which is below the UTS of 92,7psi. So our frame will be rated for a maximum roll over drop of eight feet. During the Mini Baja race the car should not have to undergo a roll over drop over five feet. [] Design for Manufacturing During initial design, design for manufacturing was considered. The Florida Tech Machine shop has all of the necessary tools to cut, bend, cope, and weld chromoly tubing. The shop only has a limited size of dies for the tube bender. Therefore tubing bend 45

radius is limited by the tubing outside diameter as per Table 13. The initial frame design contained these constraints. There are no necessary revisions to the frame due to manufacturing. Tubing O.D. Bend Radius.5 2.5 1 3 1.25 3.5 Table 13: Available Bend Radii Fabrication Process To build the chassis chromoly tubing was purchased in eight foot sections then, cut, bent, coped and welded in the appropriate spot on the car. To cut and bend the tubing a chop saw and tube bender were provided in the Florida Tech Machine shop. The tubes were then coped to fit a mating tube using a tube notcher as shown in Figure 36 below. Figure 36: Left to Right - Tube Bender, Chop Saw, and Tube Notcher Detailed Drawings Detail Drawings for the frame can be found in Appendix H. 46

Budget Description Price TUBING Chromoly tubing (1.25x.65) Chromoly tubing (1.x.35) Chromoly tubing (.5x.35) Chromoly tubing (1.x.58) Chromoly tubing (1.x.49) Chromoly square tubing (.5x.35) $197.4 48ft $197.4 onlinemetals.com $91.68 32ft $91.68 onlinemetals.com $26.95 8ft $26.95 onlinemetals.com $9.99 2ft $9.99 onlinemetals.com $43.6 1ft $43.6 onlinemetals.com $1.61 2ft $1.61 onlinemetals.com TABS Front suspension -11 Guage Radious tabs -PN2514 Rear suspension - Alloy Steel Sheet 413 ANNEALED.1 thickness (12''x12'' Section) Transmission/Engine -11 Guage Radious tabs -PN2514 Body Panels -Alloy Steel Sheet 413 ANNEALED.5 thickness (12''x12'' Section) Various -Alloy Steel Sheet 413 ANNEALED.5 thickness (12''x12'' Section) TOTAL $2. $2.85 $2. $9.29 $9.29 QT Total Vendor 2 $4. Tabzon Chassis Components 2 $41.7 onlinemetals.com 5 $1. onlinemetals.com 1 $9.29 onlinemetals.com 1 $9.29 onlinemetals.com $481.51 Table 14: Chassis Budget Manufacturing and assembly of the frame will be done by the students using Florida Tech resources (welder, welding rod, coping tool, and mill). The school does not require payment for these resources; therefore they are not listed above in the budget. The complete budget with manufacturing, assembly and retail part cost can be found in Appendix I. Design Changes During the spring 28 Spring semester minimal design changes were done to the chassis. Due to changes in the transmission type the rear end of the car had to be redesigned. The dame FEA analysis was performed on the chassis to verify the changes did not modify the results. The old and new rear end is shown Figure 37. 47

Figure 37: Chassis Rear End Before (left) and after (right) transmission reselection Scheduling Plan for Completion As of now the car is in racing condition, and has passed initial testing. Further testing will be done to prove the chassis has satisfied all nondestructive design constraints. Gantt Chart The Gantt Chart for the chassis section can be found in Appendix D. Conclusions After shock load, and impact analysis on the frame it is ready to endure a Mini Baja race and fulfill all of its goals. Weighing in at a manufactured total of 8lbs (extra weight added due to welding) the frame will help the overall performance of the car during competition. The chassis is completed and has gone through initial testing. This includes low and high speed testing over rough terrain and small (1 foot) jumps. There are plans for high speed extremely rough terrain and larger (4 foot) jumps testing. As of now the chassis is ready for the SAE competitions. The final frame is displayed in Figure 38. 48

Figure 38: Final Frame after Complete Analysis 49