Wheel Assemblies & Brakes
for Formula SAE
As Dynamics Lead, the design, manufacturing and assembly of wheel assemblies and brakes was my responsibility. Starting from scratch, our concept for this subsystem involved utilizing 10" wheels in place of the 13" wheels that had been used in years prior. These significantly reduced un-sprung mass and the vehicle’s total mass, but they presented the difficulty of packaging the assembly within a smaller space. Each wheel had a disc brake, with the rears being mounted inboard on the differential to reduce un-sprung mass. The overall goals for this subsystem were:
- Withstand the forces experienced from driving
- Have camber and Ackermann adjustability
- Have low un-sprung mass
- Be able to lock up all four wheels during braking
Front Wheel Assembly
This assembly consists of an aluminum upright that houses a wheel bearing and a stainless steel center-lock wheel hub within the bearing. The components were designed to fit the geometry I specified when selecting suspension hardpoints and to fit within the confines of a 10" wheel. I selected the wheel bearing based on calculations of the dynamic equivalent load, which came from expected wheel loads and bearing life. Each of the components were validated with FEA, where the load cases were braking, turning and a combination of both.
This design was very robust and durable during testing and never posed any issues, especially not with the wheel nut backing off, which was a concern. The only issue with this design was the weight. The hub and nuts being made of aluminum (instead of steel) would have helped reduce weight significantly. I opted not to go that route, as I thought the wear on the threads would be substantial with aluminum.
Exploded view showing front rotating assembly.
Back of assembled front wheel assembly.
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All of the CNC machining here was done by the team's brilliant machinists, Jonathan Parra, James Garcia, and Mihir Pai. I merely assisted by overseeing the manufacturing, specifying fits and tolerances, cutting stock, manual machining, drilling, tapping and post-processing.
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Front of assembled front wheel assembly.
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All of the CNC machining here was done by the team's brilliant machinists, Jonathan Parra, James Garcia, and Mihir Pai. I merely assisted by overseeing the manufacturing, specifying fits and tolerances, cutting stock, manual machining, drilling, tapping and post-processing.
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Center-lock hub CNC machined out of 17-4 stainless steel.
________________________________________________________________
All of the CNC machining here was done by the team's brilliant machinists, Jonathan Parra, James Garcia, and Mihir Pai. I merely assisted by overseeing the manufacturing, specifying fits and tolerances, cutting stock, manual machining, drilling, tapping and post-processing.
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Topology study used as guidance for weight reduction of the brake rotor carrier feature on the hubs.
Rear Wheel Assembly
This assembly consists of an aluminum upright that houses a wheel bearing and an aluminum 4-stud wheel hub bolted to a 4130 steel tripod bearing holder within the bearing. The components were designed to fit the geometry I specified when selecting suspension hardpoints and to fit within the confines of a 10" wheel. I used the same wheel bearing as the front wheel assembly to keep the overall system's design simple, while still making sure that the bearing could withstand the distinct loading in the rear of the car. Each of the components were validated with FEA, where the load cases were braking, turning, accelerating and combinations of each.
This design gave us a bit of trouble. During the first test drive around the parking lot adjacent to the garage, the three bolts holding the tripod holder to the hub sheared. After some calculations of the stress within the bolts, it was obvious why the failure occurred, and I decided the best way to mend it would be to re-drill the holes and use 3/8-24 bolts instead of 10-32. The calculations gave a safety factor of about 2 and the bolts have since held up through many rounds of hard driving. The other issue we faced with this design was that the bearings wore out fairly quickly. They developed some play after competition and testing, and I think the cause of this was the preload on the bearing being too high. Unfortunately though, I had to move back home before being able to establish the root cause.
Exploded view showing rear rotating assembly.
Assembled rear wheel assemblies and inboard rear brake rotor mounted to stub shaft.
________________________________________________________________
All of the CNC machining here was done by the team's brilliant machinists, Jonathan Parra, James Garcia, and Mihir Pai. I merely assisted by overseeing the manufacturing, specifying fits and tolerances, cutting stock, manual machining, drilling, tapping and post-processing.
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The rear hubs bolts were an oversight during design and ended up being far too small. They sheared during the first test the night before competition.
The rear hub to tripod holder connection after being mended. I decided to re-drill the holes and use the largest bolts (3/8-24) that could fit in the area.
FEA of the rear wheel assembly to simulate the effect of accelerating longitudinally during a turn.