Baja SAE — Drivetrain
For the 2024–2025 GW Baja SAE season — my year as team captain, competing at Maryland — I designed and machined the car's reduction gearbox from scratch. The previous car had struggled with torque output, and shortening the rear subframe was a standing structural goal, so the gearbox was the right place to address both at once.
The two main goals were shortening the rear subframe and increasing available torque. The previous car couldn't produce enough torque for hill climb events, and the rear end was longer than it needed to be. Changing the gearbox input angle let me shorten the subframe without relocating the differential — everything else bolted up as before.
The housing is 6061-T6 aluminum and the gears are 4340 steel. Shafts are COTS. I designed the bearing and mounting access so the unit could be pulled and serviced at competition without touching the rest of the drivetrain — a real priority when you have a short turnaround between dynamic events.
Gear ratio selection started with a target acceleration time that would put us in the top 30. From that target I worked backwards through the drivetrain — accounting for CVT characteristics and making assumptions about its output at various engine speeds — to land on a ratio that hit both the acceleration target and a realistic top speed.
The ratio also had to meaningfully improve torque over the previous car, especially for hill climb. Once the ratio was set, I ran hand calculations on torque transfer, gear contact stresses, and bearing life. FEA on the shafts, gears, and housing confirmed adequate margins — FOS exceeded 1.1 across all critical features under peak load, with deflection within tolerance.
Gears were wire EDM cut from 4340 steel (outsourced); shafts are COTS. The housing was CNC machined from 6061-T6 in-house — and this is where it got interesting.
My first attempt at the casing failed because I was holding the fixturing block in two vises, which introduced enough flex that one face came out out of tolerance — had to scrap that side. On the next attempt I had tool pullout partway through, which took out the other half. That meant machining a third casing, this time with better fixturing, which came out clean. Bearing bores and mating surfaces were held to tight tolerances throughout. One half of the casing has an O-ring groove to seal the assembly. Press-fit bearings, standard fasteners.
Explore the CAD model in 3D — rotate, pan, and zoom.