Front Hub Design

The front hub is the part that connects the front rims of the car to the shaft coming from the gearbox. As the direct interface between the front wheels of the car and the drivetrain, it sees some of the highest load of any component on the car. Additionally, the brake rotors mount to it, making it very important for the hub to be stiff and sturdy. This year, the team's goal was to decrease the weight of the hub as much as possible in order to decrease our outboard unsprung mass, which would help us greatly with maneuverability.

In order to allow the car to turn without the use of a differential, our front drivetrain uses a sprag clutch to allow wheels to slip if they are spinning faster than the drivetrain. Last year, this sprag clutch was mounted within the front hub itself. This necessitated two bearings to support the sprag clutch as well as signifcant amounts of material to retain the sprag clutch and ensure appropriate stiffness. All these requirements made the front hub quite heavy.

This year, I had the idea to move the sprag clutch inboard to the front gearbox. This removed the sprag and the bearings from the hub, which significantly decreased the weight of the front outboard assembly. Additionally, without the bearings in the hub, we didn't need all of the supporting material, further saving weight. Reducing weight on the outboard is of the highest priority, since decreasing our outboard unsprung mass substantially increases manueverability and ease of handling. The team also switched to lighter wheel rims to further reduce weight. Moving the bearings out of the hub also allowed us to design the outboard such that we could apply pretension to the entire suspension stack, increasing the reliability of the assembly. In total, I designed the hub to be nearly half the weight of last year's hub with no performance penalty.

To validate the performance of the hub, I ran FEA analysis using real load cases the team obtained from a wheel force transducer test. I optimized the design so that we used the least material possible, targeting a factor of safety (FOS) of around 1.5. An FOS of 1.5 strikes a balance between minimum weight and some margin to account for weakening due to cyclic loading fatigue. The team designs components for only 16 hours of total runtime, so it is desirable to have parts operating close to their material limits. I also made sure that the hub performed at least as good or better than last year's hub as part of a comparative analysis. Since we know that last year's hub held up, if the new hub can handle the same loads, it will also hold.