Objective
After 3 years of limited success designing and manufacturing the differential sprocket adapter, we got to take a shot at the fourth iteration since the Northwestern’s FSAE team went electric.
Our goal was to adapt the previous design for bidirectional torques, a 4 spoked design, and improved machinability.
Old Design
CAD Iterations
Version 1
Version 7 (Final)
The final iteration of our design features a four spoked design that can interface with the new drive sprocket. Comparing 4 and 8 spoke designs (corresponding to the 8 bore holes in the drive sprocket) validated with FEA, we deemed the 4 spoke design structurally sufficient. It includes symmetrical spokes that are more well equipped to deal with bidirectional torques from the regenerative breaking.
Version 5
FoS Simulation: Factor of Safety 2.9
FEA
We optimized the part through multiple FEA iterations under peak drivetrain torque to ensure a Factor of Safety ≥ 1.25 and durability beyond 450,000 peak torque cycles, while minimizing mass. The von Mises stress results remained below the yield strength of 7075-T6 aluminum, confirming that the design would not yield under operating loads and validating both the analysis and final geometry.
Fatigue Simulation: can withstand >995,000 drivetrain cycles
Fusion 360 CAM
Manufacturing
The DSA was machined using 7075-T6 Aluminum on a 3-axis CNC mill. The spline was pre-cut so to center the stock we used a dial indicator to find the exact center of the spline to avoid tolerance stacking. We added fillets and chamfers to reduce stress concentrations. We used Fusion 360 CAM in two operations.
Operations 1 and 2
After successfully manufacturing the DSA for the first time since the car went electric, it went on to contribute to the first driving car at the 24/25 FSAE competition.
The FoS and Fatigue simulation requirements were comfortable met and the weight was reduced by 12%.
Results
DSA with differential and drive sprocket (seen on the left without spokes)