FSAE Chassis Design and Manufacturing

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Formula SAE Senior Design Chassis Team Phase IV: Performance Validation and Path Forward

Customer: Eric Easterby

Advisor: Dr. Steve Timmins

Team: CFO - Bob Iannaccone Logistician - Marcel Okoli Rulesmeister - Matt Schaefer Captain - Tyler Walker

December 14, 2012

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Table of Contents Introduction .................................................................................................................................. 3 Project Sponsor............................................................................................................................. 3 Scope ............................................................................................................................................ 3 Wants and Needs: ......................................................................................................................... 3 Constraints: ................................................................................................................................... 5 Metrics: ......................................................................................................................................... 9 Benchmarking: ........................................................................................................................... 11 Design Aspects: .......................................................................................................................... 11 Concepts: .................................................................................................................................... 13 Design Changes for final design ................................................................................................ 18 Frame Analysis and Validation (FEA) ....................................................................................... 22 Material Choice .......................................................................................................................... 23 Rule Compliance of Final Concept ............................................................................................ 24 Chassis Budget ........................................................................................................................... 25 Fabrication Preparation .............................................................................................................. 25 Fabrication Process..................................................................................................................... 27 Manufacture................................................................................................................................ 31 Testing ........................................................................................................................................ 39 Looking Back and Plan Forward ................................................................................................ 39

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Introduction “Formula SAE is a student design competition organized by the Society of Automotive Engineers, where a fictional manufacturing company has contracted a design team to develop a small Formula-style race car. The prototype racecar is to be evaluated for its potential as a production item. The target marketing group for the race car is the non-professional weekend autocross racer.� (SAE International)

The goal of the chassis team is to develop a successful chassis that meets all of FSAE regulations and complies with other teams’ components. The vehicle as a whole will rely on the chassis for torsional and flexural rigidity. Mounting points for all subsystems will be integrated into the chassis with sufficient strength and clearance. The overall driver ingress and egress will be determined by the profile of the chassis. Through numerous iterations of the design process, an optimal design will be reached.

Project Sponsor Our project sponsor has generously donated his time and expertise in order to guide our group in the right direction and consult us during the design and fabrication process. Eric Easterby is an engineer at RATH industries as well as the owner and master fabricator at Killer Koncepts, a custom car shop that specializes in chassis and metal work. He was an invaluable resource during the fabrication process, sharing his knowledge and providing tips for welding and notching the tubing in order to produce a structurally solid, clean chassis.

Scope Our goal is to design a chassis for a small formula car in cooperation with Ergonomics, Suspension, and Powertrain while conforming to the 2013 FSAE rules.

Wants and Needs: Low Weight Lower weight increases acceleration by increasing the power to weight ratio. Having a lower weight also contributes to less weight transfer which is favorable in maneuverability.

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High Torsional and Flexural Rigidity To ensure perfect chassis rigidity, the car features need to be intelligently designed to include a bracing along the bottom of the chassis to create a rigid and robust platform for the suspension members, as well as handling the high stress from the powertrain. Triangulation throughout the chassis will give the car high torsional and flexural rigidity which is needed to effectively manage the high gravitational forces at peak cornering, acceleration and loading.

Low Cost Because of budget restrictions, low cost is an important factor for feasible production and large profit margin for the customer.

Low Center of Gravity Whenever force is applied to a vehicle, there is some side-to-side or lateral movement as weight is transferred from one part of the chassis to another. Lower center of gravity creates less weight transfer. Less weight transfer gives the vehicle the greatest stability and also allows the suspension to return to its normal state more quickly.

Ease of ingress and egress This will allow drivers of different sizes to be able to enter, exit, and operate the vehicle without being uncomfortable. A comfortable driving position without any interference is critical for safe and accurate control of the vehicle.

Nodes at high stress joints To ensure rigidity and strength of the vehicle, there must be reinforcements at points of high stress such as mounting points of suspension, especially the rockers.

Clearance of all parts through ranges of motion There will be moving parts that will be moving through the chassis at different points and there must be clearances in these sections so that under all operations nothing will interfere.

Rear Biased weight distribution A goal for the car as a whole is to have rear bias to mimic that of formula based cars found in benchmarking for better handling.

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Room for any size driver to operate without interference FSAE rules mandate accommodation of a 5th percentile female and a 95th percentile male. As a team we must also accommodate wider ranges than that for certain possible drivers.

Constraints: There are certain and specific rules that every part of the vehicle must adhere to in order to enter the FSAE competition. These rules can be found at the FSAE website listed in the benchmarking section below. Our designs are also constrained by the budget that does not have strict limitation but we must use common sense and research to determine what is acceptable.

Some main requirements that we have to consider in the design of the chassis are: The chassis must be capable of supporting a 5 foot wheelbase. The entire frame must be fabricated of the specified materials for each item listed in the chart below.

Table 1: Minimum dimensions of separate parts of chassis The chassis requires having a main (rear) roll hoop, a front roll hoop, and a front bulkhead. From the front roll hoop to the rear roll hoop, there is a safety test that specifies if a straight line is drawn from the tops of both roll hoops, there must be a 2� clearance of the 5th percentile female and 95th percentile male. There also is a requirement for either front bracings or rear bracings for the rear roll hoop. If the rear bracing method is chosen, there is a line drawn from the bottom of the bracing to the top of the rear roll hoop and that line must be at

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least 2� clearance to the back of the driver’s helmet. If the front bracing method is used, the driver’s helmet must not be rearwards of the plane created by the rear roll hoop.

Figure 1: Helmet Clearances.

The required braces for the rear roll hoop must be properly triangulated at a node as to transmit all loads down to the major structure without failing. The braces must also be at 30 degrees minimum from the axis of the rear roll hoop as shown in figure 2. The front roll hoop must also have bracing that goes to the front of the vehicle on both the right and left side of the hoop but connect to the hoop no lower than 2 inches from the top of the hoop.

Figure 2: Roll hoop bracing specifications Page 6

The side impact structure must consist of minimum three members located on each side of the driver. The specifications for these three members are as follows and are shown in Figure 3. The upper Side Impact Structural member must connect the Main Hoop and the Front Hoop. All of the members must be at a height between 300 mm (11.8 inches) and 350 mm (13.8 inches) above the ground. The upper frame rail may be used as this member if it meets the height, diameter and thickness requirements. The lower Side Impact Structural member must connect the bottom of the Main Hoop and the bottom of the Front Hoop. The lower frame rail/frame member may be this member if it meets the diameter and wall thickness requirements. The diagonal Side Impact Structural member must connect the upper and lower Side Impact Structural members forward of the Main Hoop and rearward of the Front Hoop.

Figure 3: Design example of Side Impact Structures For ease of ingress and egress, the opening for the cockpit must meet the required template in figure 4 for minimum size of the entrance. There is also a template that must fit down inside the cockpit shown in figure 5.

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Figure 4: Cockpit entrance template

Figure 5: Inside Cockpit Template

The cockpit must also accommodate all measurements of the 95th percentile template that sits in the seat as shown in figure 6.

Figure 6: 95th percentile driver that is required to fit

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Metrics: From the initial wants and needs, values can be obtained that should be the goal of the overall project. A primary concern for all performance car designers is weight. Every component adds to the weight of the vehicle, and every pound decreases the acceleration and handling characteristics. As noted in the metric table below, we have updated our weight metric for acceptable value based on adding in the front bulkhead plate which weighs about 5 pounds. We simply added 5 pounds to our previous acceptable weight to accommodate this since last years’ car did not account for it. These numbers were originally based on use of a one cylinder engine which was drastically changed when powertrain changed to a four cylinder engine.

Chassis designers must specifically design for a high rigidity chassis. Rigid chassis have better handling and control of the forces present in performance driving. Rigidity is measured two ways: torsionally and flexurally. Both of these can be estimated with computer modeling, but a more reliable method is testing of the actual frame.

Flexural rigidity is easily measured by loading the front suspension mounts of the chassis and measuring deflection as the load increases. The units of this measurement are force/displacement. Torsional rigidity can be measured by fixing the rear frame to rigid supports and then adding weight will be applied to a lever arm mounted to the suspension points of the chassis. The units of this measurement are torque/degree.

The cost has been updated from previous to accommodate the purchase and fabrication of materials that made up the welding jig and all mounting components as is expanded upon in the welding jig section further below. This cost includes 50% excess in chassis material.

Another important metric for vehicle handling is the vertical center of gravity. This is defined as the vertical distance between the ground and the center of mass of the entire car.

This can be determined by supporting the car on scales at either end, while inclining one end.

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By recording and analyzing the change in weight distribution as one end is inclined, the center of mass can be found.

Time of egress is very important and is based on ergonomic constraints as well as roll hoop placement and cockpit opening size. This time is constrained by 5 seconds per regulation. Our design ensures that we beat this constraint.

Weight distribution has been researched and found to be more tending to rear bias. It is important for the accelerating, braking and handling characteristics. Under acceleration, more weight is being shifted to the rear enabling more traction. Under braking, more usage of the rear brakes is possible. In handling the close to 45-55 the distribution is, the better traction can be obtained.

Metric

Target Value

Acceptable Value

2013 Projected Value

Weight

75 lb

90 lb

87 lb

Torsional Rigidity

1600 ft-lb/deg

1400 ft-lb/deg

1730 ft-lb/deg

Flexural Rigidity

4000 lbs/in

3000 lbs/in

3900 lbs/in

Chassis Material Cost

$1000

$1500

$1385

Vertical Center of Gravity

10”

13.25”

12.5”

Time of Egress

3 Seconds

5 seconds

2 seconds

Weight Distribution (Front-Rear)

45-55

50-50

45-55

Table 2: Metric Table

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Benchmarking: Previous year designs were taken into consideration for target values and quickly seeing what has already been done in order to make our design better. Additionally technical reports from other teams were examined for more information. Specifically reports from Florida Institute of Technology, and University of Missouri were analyzed.

Design Aspects: Removable Main Roll Hoop Bracing Removable Bracing is an alternative that is preferred in order to remove the engine from lifting it vertically out of the vehicle. To achieve this, we will have to make the mechanical attachment for the bracing a sleeve joint which is illustrated in figure 7. This method is allowable by the rules and will make for easy disassembling by just taking out a few bolts. Taking off the bracing will allow for easy access to the engine from above and easily extracting it after disconnecting a few engine supports.

Figure 7: Example of a Sleeve joint

Angled Roll Hoops By slanting the roll hoops the vehicle can be made aesthetically pleasing while improving the ease of ingress and egress, and allowing for the dash to be mounted further forward. Last year’s design had roll loops that were essentially perpendicular to the ground, Page 11

creating an unnatural, visually displeasing profile. By slanting the top of the roll hoop toward the rear of the car, a slick profile is achieved that will not only improve ingress and egress, but allow for the possibility of a seat integrated into the firewall. The seat can follow the shape of the roll hoop, creating a rigid connection on the seat upright, where shoulder support is critical for stabilization of the driver in competition situations. Slanting the top of the front roll hoop toward the front of the car will improve ingress and egress and will create a more visible dash assembly. One of the major complications of ingress and egress in the 2012 vehicle was caused by interference of a tall driver’s knees with the front roll hoop. Increasing the distance from the top bar to seat will allow the driver to slip his/her legs in and out of the car without binding into an unnatural and unsafe position. It will allow for more knee room and better pedal control by eliminating interference of the drivers legs with the roll hoop. Last year’s dash display was very difficult to view, limiting the amount of information the driver could obtain at a quick glance. By slanting the top of the front roll hoop toward the front of the vehicle, the mounting position of the dash will be shifted away from the driver’s eyes. This creates a perceptively smaller display that can be viewed through the window of the top cut-out in the steering wheel. The dash will be moved closer to the driver’s line of sight of the race track and will allow for more data acquisition while keeping the driver’s sight from deviating far from the approaching road.

Widened Driver Pod Last year's chassis was not ergonomically pleasing due to the narrow midsection. The distance between the edge of the steering wheel and the side of the chassis was made so small that the shifter had to be placed against the chassis, not allowing for finger room on the shifter.

Widening this section will allow a comfortable driving position with all of the driver’s body and extremities contained within the driver pod. This will create a safe seating position with greater resistance to intrusion in a side impact situation. Since the midsection will be lengthened, it will need to be reinforced for both torsional and flexural rigidity. Increased width in this section will increase the lever-arm of the reaction forces created by the chassis to combat torsion. A widened chassis will allow for more triangulation in the mid-section to increase flexural rigidity.

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Strengthen Rear Section Taking into consideration the bigger engine this year, the rear section will have to accommodate the larger assembly. Increasing the size of this section will increase the forces created by the engine. This increase in force will be multiplied by the projected increase in power and torque produced by the new engine.

Lighten Front Section Last year’s front section was over complicated, adding unnecessary weight to the chassis. The front end needs to support the forces generated through the suspension, steering and breaks. This can be accomplished with simple nodes up front that will be specially designated by the suspension team. The front end will have to be large enough to clear the “Htemplate” and the three pedal box that will be integrated into this year’s vehicle and provide a boxed front section for the impact attenuator to be mounted to.

Concepts: Many iterations have been done and many more will have to be done in order to have a successful chassis that will comply with all needs and metrics. A design log has been kept of chassis iterations to note what main changes were made and why they were made.

Figure 8: Iteration 0

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In iteration 0, the main goal was to reduce weight in the front due to supposed over engineering in reference to last year’s car. Also a thought on making the rear section removable prompted the use of the main roll hoop bracing being in front of the roll hoop instead of rear of it. Another idea implemented in this design was the slanted roll hoops as discussed in the above section of design aspects. This design was not acceptable because of numerous points such as no mounting points for some needs of suspension. Also, the frontward facing braces for the main roll hoop were not preferable and were seen as a problem for the ergonomics of the vehicle.

Figure 9: Iteration 4 There were some in between iterations done that were not fully complete due to noticeable flaws in the designs with respect to certain mounting points needed. Iteration 4 in Figure 9 includes reverting to the rear mounted roll hoop bracings. After recognizing more from constraints, side impact was altered to follow rules. The width of the driver pod was also increased by this point. This design was not acceptable because suspension points did not want to be located directly on the bottom of the main chassis structure so the assumed mount points were not successful.

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Figure 10: Iteration 6 Iteration 6 includes major alterations due to the discovery of using a new 4 cylinder engine opposed to the presumed single cylinder engine. This iteration also included new mounting nodes for both front and rear suspension points as well as incorporation of head rest mounts and elongating the driver pod even further due to angling the front roll hoop. The problem with this iteration is that the suspension mount points were still not completely accurate so slight modification will be necessary when that is determined. Also, the front roll hoop will need to move back towards the driver slightly to accommodate the mounts for the steering column so they will not be under too much stress.

Figure 11: Iteration 7 Iteration 7 introduces new suspension geometry. Also the front bulkhead was increased to 14"x14". The front roll hoop was moved backwards 1� as well as widened by 1.5� for Page 15

ergonomics. The side impact structure had to be altered to adhere to rules. We also had to add members to the front box to properly triangulate mounting nodes.

Figure 12: Iteration 8

Iteration 8 was made to accommodate the updated Rear suspension points. Also, at this point we altered weldments where it was seen fit and allowable from the FEA done in SolidWorks.

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Figure 13: Iteration 10 Iteration 10 was made to bring the front roll hoop towards the driver to better suit ergonomics. Also changes were made to the front and rear box geometry to enable rocker placement per suspension wants.

Figure 14: Iteration 11 Page 17

Iteration 11 included another increase in the front bulkhead to 15"x15". Also from rules testing on the previous iteration, it was found that the front roll hoop and front box was too narrow to accommodate the H insert template. Two additional members were added into the rear in order to triangulate the rocker nodes, and prevent bending loads from being applied to the chassis. Finally the seatbelt support bar was lowered to accommodate a request from ergonomics to better fit their seat.

Design Changes for final design Moved nodes forward

Figure 15: Old

Figure 16: New

The reason for this change was due to altered suspension geometry and simplification of the chassis while still ensuring strength.

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Front roll hoop moved forward

Figure 18: New Figure 17: Old The front roll hoop was moved forward mainly to accommodate a more rear biased weight distribution. Moving the front roll hoop forward moved the front suspension forward and allowed more weight to be on the rear tires.

Added Members

Figure 19: Old

Figure 20: New

There were alterations made to the design in order to add triangulation and nodes at the spring mounts

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Unnecessary Supports Removed

Figure 21: Old

Figure 22: New

The elimination of the shoulder harness bracing was done because it was found to not have to be as strong as we initially saw in the rules. Also, this alteration was made in order to ease the decision of using removable roll hoop bracing by having less attachment points on the bracing.

Roll Hoop Shape

Figure 23: Old

Figure 24: New

The roll hoop shapes had to be slightly varied due to manufacturability with the obtainable resources. The tubing bender that we had access to could only do 3 inch radii bends which was not how the final design was to be made. The shape change did not change the design drastically.

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Removable Roll Hoop Bracing

Figure 25: Old

Figure 26: New

There was much back and forth with the removable roll hoop bracing. The initial plan was to use double lug joints as shown in figure 25 above; however, this was decided not a viable option due to difficulty of manufacturing and repeatability. Another option was brought to our attention of doing sleeve joints which was also a legal method of attachment. Research was done on this method and it was agreed on as a group and entire team to do this.

Figure 25: SolidWorks image of final concept

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Frame Analysis and Validation (FEA) Force analysis was done on the design using the analysis software in Solidworks.

Suspension mounting nodes in the rear were set as fixtures while the front suspension mounting nodes were loaded in both flexural and torsional ways. In order to load the chassis in a flexural nature, the front nodes were loaded to simulate going over a large bump so the force on all front suspension nodes was in an upward position as shown in figure 26.

Figure 26: Flexural Rigidity testing scenario The results of this analysis test gave a flexural rigidity of 3800 lbs/in.

Next, an analysis was done on the torsion of the chassis. In order to do this, still the rear mounts were fixed but this time the front suspension was loaded upward on one side while being loaded downward on the other side as shown in figure 27.

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Figure 27: Torsional Rigidity testing scenario The flexural rigidity test resulted in a rigidity of 1375 ft-lbs/deg. Both of these values were stated in the initial projected values in the metrics section in table 1. When tested in the same way to compare this design to the previous year design it was found that both flexural and torsional values were improved from last year.

Material Choice The chassis must be constructed of steel tubing with at least 0.1% carbon content, eliminating the use of exotic alloys. The chassis has been designed with 1inch outer diameter steel tubing with various wall sizes: 0.095”, 0.065”, and 0.049”. There was much debate on choice of steel type, especially between 4130 chromoly and 1020 carbon steel. The main advantage of 4130 chromoly was the exceptionally higher strength characteristics without sacrifice in weight. Since the chassis is composed of relatively small and thin wall tubing, strength per weight is extremely important. The downside to 4130 is its price and difficulty of welding as compared to 1020 carbon steel. 4130 is more difficult to weld and must be preheated and post heated in the welding process in order to avoid cold cracking; however with wall thickness below 0.120” it is generally agreed that this process is not as critical. 1020 DOM carbon steel is about 20% less expensive but nearly 30% weaker, making it much harder or impossible to meet the rigidity metric while staying close to the target weight. Taking all Page 23

into consideration, 4130 chromoly tubing was chosen. This was concluded on because we realized that 20% in material savings was not worth trading for extra weight and weaker material.

Steel Type

Tensile

Yield Strength

Density

Strength

Modulus of Elasticity

4130 CRMO

85,000 Psi

70,000 Psi

0.283 lb./in^2

205 GPA

1020 Carbon

61,000 Psi

51,000 Psi

0.284 lb./in^2

200 GPA

Source: Substances and Technologies SAE steel information

Rule Compliance of Final Concept From the research done on the 2013 FSAE rules, the designed chassis is following all rules and regulations. Minimum material requirements are being met as mentioned above.

There are brief tests that will be done for competition such as the template tests as shown in figure 26, the broomstick tests as shown in figure 27, and other helmet clearances are easily met. The side impact structure is also within the range it must be for rule compliance.

Figure 26: Image with templates inside

Figure 27: Broomstick test

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Chassis Budget Overall our expenditures put us about $110 over our original budget. The higher material cost for the Welding Jig was the primary cause of this. Fortunately we were able to recoup some of this money by getting an educational discount for the chromoly tubing.

Table 3: 2013 Chassis Team Budget

Fabrication Preparation Welding Table In order to fabricate and maintain quality with the chassis, a welding jig table was made. The jig table is all steel and rolls on four swivel castors with leveling feet at each corner to anchor the jig during work as well as make sure it is a level surface to reference in the fabrication. The welding jig consists of a 4 foot by 8 foot sheet of steel that creates a flat plane surface for an accurate reference. This surface will be large enough to accommodate the length and width of the chassis while still providing a comfortable work surface. This table will be re-used by teams in the future as a valuable chassis fabrication tool.

\

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Figure 28: Welding table

Figure 28: Completed Welding Table Much was considered in order to accurately assemble the chassis. There were options to drill holes in the welding table; however, when thought more about the reusability of the welding table, this decision was dismissed to save it for future use. Multi-adjustable clamps as shown in figure 29 were thought of to help aid in the assembly and accurately hold chassis tubing until a tack could be placed to fully mate the chassis tubes. These clamps were to be adjustable in 4 directions. The clamp can slide up and down the rod for height setting. It can rotate around the rod to give accurate adjustment while clamping the base plate down to ensure no movement once all clamps are held in place. The clamp can be rotated against the vertical direction also. This is a very useful feature and is used to set many angles for the chassis design.

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Figure 29: Custom Clamps

Fabrication Process Notching Eric Easterby, our customer, allowed us to borrow his tubing notcher to help provide clean mates in the chassis. The notcher could be used to achieve notch angles ranging from 065 degrees in relation to creating a perpendicular mate as being a 0 degree mate. The tubing notcher can be seen in figure 30 below creating a notch that created a clean mate.

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Figure 30: Tubing notcher

Notching (Lathe) The tubing notcher can only create clean joints for mates up to 65 degrees. The final design consists of many steep notched angles. The attachment holder for lathes holds 1 inch diameter tubing while a hole saw can be held in the lathe chuck and the tube can be notched at any angle which is set by the user by handing of a angle finder. This process can be seen in figure 31 below.

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Figure 31: Lathe being used for notching

Bending FSAE requires that the front and rear roll hoops be continuous members. These members were bent from 1� outer diameter, 0.095� wall thickness 4130 chromoly tubing.

Tools were limited in this process so a 3� radius was used for all bends. The finished product did not follow the same shape as the model, however critical dimensions such as suspension points and driver pod width were maintained. At this point, the model was changed and other groups were notified of the dimensional change in order to prevent complications in the fabrication process of components such as the dash and steering column.

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Figure 32: Metal Bender

TIG Welding The entirety of the chassis was welded using the TIG method with ER70s-2 filler rod.

ER70S-2 was chosen for its high tensile strength that nearly matches that of the 4130 tubing (only 2.5% lower tensile strength than 4130), its general ease of workability and compatibility with 4130, and its low cost. TIG welding produces a clean weld with very limited oxidation and porosity relative to other welding methods. In the material decision process, there was concern of preheat and post heat treating the chromoly to retain uniform material composition and strength. After consultation with several roll cage builders and research of 4130 chromoly characteristics, it was found that with wall thicknesses less that 0.100�, the effect of heattreating was negligible. This is due to the heat easily travelling an adequate distance from the welded area as compared to the concentration of heat with thicker wall thicknesses. When

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cooling, the hot joints were shielded from moving air in order to slow down the cooling process. This reduced the chance of cold cracking due to rapid contraction of the metal. Since the tube chassis has many tight joints, there was some difficulty in getting the torch end close enough to the weld for the argon to properly shield from oxidation and contamination. In order to reduce the chance of an unshielded weld, aluminum foil was placed around the backside of the joint, “trapping� the argon in this area and effectively shielding the weld in this area. In the rare case that porosity was found in the weld, the porous area was ground down until there was a uniform surface. There was no case of the porosity travelling deep into the weld, so no weld needed to be repaired.

Figure 33: TIG Welding

Manufacture

Base The first section of the chassis to be fabricated was the base and front bulkhead. Both of these sections were built in a flat plane using the welding table. The sections were notched and placed to accurate dimensions, then secured to the table. Having the members secured for the entire welding process ensures that their placement relative to other members remains as Page 31

wanted, without any warping. The bulkhead was secured at this point since it was designated to be at a right angle to the base of the chassis.

Figure 34: Chassis Base

Rear Angle This section of the chassis was the first of the members to be attached in 3-D plane at an angle that could not be set with a square. Simple trigonometry was used to achieve the correct angle and high of the bottom bar of the rear differential box. This was a critical dimension since the rear most bar incorporates the differential and suspension mounting.

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Figure 35: Rear Angle

Roll Hoop Placement After the roll hoops were bent to accommodate the critical dimensions of the suspension mount points and driver pod, they were placed into their correct position and set at their designated angle using the welding fixtures. The bottom of the roll hoops required only mitered ends to the correct angle since their attachment point consisted of many already welded tubes at the base of the chassis.

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Figure 36: Roll Hoops

Side Impact The positioning of the side impact bars was critical due to strict rules designating the positioning and number of members, as well as the wall thickness of at least 0.065�. The first use of the lathe for notches occurred at this point since the bottom angle was only 10 degrees (or set to 80 degrees on the lathe).

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Figure 37: Driver Pod (Side Impact)

Front Box The complexity of the front box required a lot of planning and cooperation between the group. The welding fixtures proved to be very useful in setting critical dimensions of the aarm pick up points. The mounting bar for the steering box was able to be placed inside the chassis between the node for the front, bottom a-arm pick up point.

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Figure 38: Front End

Rear Box The fabrication of the rear box was complicated as well, and required much precision in the high angle notches of the short members. It was important to accurately represent the model during fabrication because of the tight clearance that was designated between other systems, especially the differential sprocket and axles through their full range of motion.

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Figure 39: Rear End

Removable Roll Hoop Bracing (Sleeve Joint) The removable roll hoop bracing fabrication began by tacking in the braces and marking the position of the sleeve joints. The continuous members were then cut at the correct position in to three pieces. The sleeves were turned down on the lathe in order to save weight while retaining the tight clearance between the internal diameter of the sleeves and the outer diameter of the roll hoop braces. The holes of the sleeve sections were then drilled on the mill with the braces placed inside of them in order to ensure correct fitment. Each side of the bracing was fully assembled and placed into the correct position on the chassis. The braces were finally welded at each end completely. Tight clearances and accurate fit were retained after the welding process. Easy access to the engine compartment was achieved with this design.

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Figure 40: Sleeve Joints

Figure 41: Complete Chassis Page 38

Testing Chassis torsional rigidity is measured with respect to the suspension mount points. In order to test this, the area below the rear suspension points was mounted to the extra-large welding table from the Spencer machine shop. First torsional rigidity was tested by placing a lever arm through the front suspension mount points. A digital angle finder was placed on the front bulkhead, where angular deflection was expected to be the greatest. 652.5 ft-lbs of torque was applied to the front mount points, and 0.5 degrees of deflection was measured, meaning a torsional 1305 ft-lbs/deg.

Next the lever arm was used to load the chassis in bending, rather than torsion. 115 lbs of force was applied to the front suspension mount points, leading to 1/16� of deflection. This comes to only 2560 lbs/in of deflection, far below our projected value of 3800 lbs/in. However, a significant amount of deflection in the clamps anchoring the chassis was noted. Future testing of rigidity is required, with a better clamping system in the rear.

Scales from the senior design studio were placed between the front and rear wheels to measure the front-rear weight distribution. Because the powertrain lacked fluids (oil, coolant, etc.), spare bags of hardware were used to approximate that weight. The measurements indicated a 45-55 weight distribution.

In our next iteration of testing, we will use the smaller ž� welding table with a large angle bracket on it to more rigidly secure the rear of the chassis. We will then repeat our testing process to get better data for torsional and flexural rigidity.

Once all of the components and fluids are in the car, we will measure the vertical center of gravity by using the lift in the machine shop to elevate the front end of the chassis. Once the center of gravity is above the rear wheels, the chassis will be at equilibrium. From this we may measure how far the vertical CoG is above the bottom of the chassis. Currently not all components, the engine its self in particular, are not fully attached to the chassis, preventing immediate testing.

Looking Back and Plan Forward Although our fabrication went relatively smoothly and was completed on schedule, future years may wish to alter their design process. Since the preliminary chassis was designed

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well ahead of other team’s conceivable designs, many (completely new from scratch) chassis iterations were developed. The chassis groups in the future may want to spend their time helping other teams finish their designs (dimensionally) before spending too much time developing the chassis. Although high angles and complex designs look nice on paper, they are very difficult and time consuming to develop during the fabrication process. In the future, teams may want to simplify their designs and possibly develop less triangulation at less stressed joints (backed by stress analysis). In previous years, some suspension points were not mounted on nodes; this greatly reduced the number of members in the chassis and lightened the chassis. We would advise the future teams to take inventory of tubing bending equipment before designing the roll hoops. The change in the roll hoop design due to limitations of equipment caused some stress for other teams since a few components needed to be altered.

One design aspect we would suggest be carried though into future years is the removable roll hoops. This helped powertrain greatly by allowing them to have easy access to the rear box.

Once the sleeve joints were chosen, the implementation became very easy and was very aesthetically pleasing.

Before competition in June 2013, there are a few tasks that must be completed. The FSAE rules require a chain guard to be placed over the sprocket to avoid injury from moving parts or potential broken chains. The impact attenuator will need to be fabricated from the same foam material as the 2012 car but will be attached to the chassis by tabs that are welded on (no JB Weld). A rear jack point will be added to the lower member of the rear box in order to easy lift the rear wheels with one person operating the jack. After all welding is complete, the chassis will be painted using either POR 15 or Rustoleum brush on paint. Bodywork will be completed over Winter and Spring semester and will most likely be aircraft fabric due to the tight clearance between the rockers and the front box.

Overall, the experience of FSAE senior design was character building and a large dose of reality. Bi-weekly meetings throughout the semester forced us to stand up in front of our peers and higher-ups to present our ideas and progress. This process reinforced good practices of presenting and acceptance of constructive criticism. After the end of the semester our team felt comfortable presenting and will prosper in future endeavors. The immense time commitment to design and fabrication exceeded that of other senior design programs, and built

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our team’s time management skills. The fabrication of a steel tube chassis is not an easy task and takes skill and motivation for good work. Our team gained experience with welding and machining that can be used throughout the rest of our lives, either for hobby or professional employment. At the end of the process, our team was able to take a step back and admire the result of our hard work.

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