Transfer Case (In Progress)

July 2025 - March 2026 (Projected) | Baja SAE

Currently designing internals for the transfer case gearbox for the 2025-2026 Northwestern Baja SAE car. The transfer case is a 1:1, 90 degree gearbox used to transmit power from the main gearbox to the prop shaft, enabling the car to use 4WD.

Gear Selection

The transfer case for the 2024-25 car, the only one our team has made thus far, was very overdesigned. With this design, one of my main goals was to reduce the weight and size of the gearbox to only what is necessary.

Since our team doesn’t have the ability to custom-manufacture gears, I chose two commercially-available spiral bevel gears with a calculated factor of safety of 1.20. This maintains a good margin of safety while not forcing us to use larger, heavier gears.

Shaft, Bearing, and Keyway Analysis

CAD of the input and output shaft assemblies.

To conduct stress analysis on the shafts and bearings, I created a spreadsheet to automatically calculate factors of safety for the shafts and bearings as parameters like shaft material, components, distances, and key dimensions change in further design iterations. This spreadsheet allowed me to rapidly iterate through designs while maintaining a high degree of confidence in the success of the part.

Manufacturing

To manufacture this gearbox, I mostly used CNC and manual lathes, as well as conversational mills. I began by turning down the major dimensions of each shaft on a CNC lathe, then grooving and threading on a manual lathe. All gear modifications (turning down the hubs and adding counterbores) were also done on the CNC lathe. As of the beginning of February, 2026, I have finished all gear modifications. My shafts are almost completely manufactured, only needing keyways and one hex to be milled.

Next Steps

Finish manufacturing the shafts
Assemble all components and shim
Test efficiency
Install on car and test drive!

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