As part of the Penn Electric Racing FSAE Powertrain design team I worked with Mechanical Lead Foster Collins to develop this alternative transmission configuration. Due to the incorporation of a higher power motor than last year, this year we aimed for a 5:1 reduction. This higher reduction exceeds the reasonable limits of the single stage chain reduction design we used last year, thus we needed to explore other options.
In this two-stage chain reduction system, the tensioner was designed to have two degrees of freedom so that it could tension both chains, and be adjusted as the different chains expanded at different rates during use.This was achieved by putting the output shaft in two nested offset circular parts, one offset of center from the other. Thus, by rotating the axle around the two centers, 2 DOF were achieved. A hole configuration around each part was designed to give a 1/16th inch axle placement resolution. The output shaft itself clamped the assembly together, along with 6 #6 placement screws set in helicoils.
However, as the design process went on, the assembly needed to become more and more complex. We developed concerns about the manufacturing difficulty and the untested nature of this design, and in the end decided to go with a heavier, yet surprisingly inexpensive secondhand GM planetary gearbox.
Rendering by Foster Collins