Adjustable Pedalbox Design
For the 2024-2025 season, I redesigned our EV's pedalbox completely from the previous season, incorporating design judge and driver feedback about slop and compliance as well as ergonomics to optimize the design.
Brake Locking Force Analysis
To start, I needed to determine the maximum brake locking force to choose a brake pedal ratio, which would inform how I mounted the brake master cylinders. As per FSAE rules, all four wheels must be able to be locked by the driver during the brake test. Using human dynamometer data obtained from a biomechanics lab on campus, we determined the peak moment able to be exerted by the driver's ankle to be 103 lb-ft, meaning that for a size 10.5 foot of approximate length 11 inches, the force exerted at the pedal would be approx. 112 lbf. Using a Python script that backsolves from maximum tyre friction to brake locking force, a pedal ratio of 4:1 was chosen.
The brake bracket was then designed with this specification in mind. To make the parts more easily machinable, each mount was mounted to a base plate with four #10 bolts. FEA of the entire pedalbox assembly, including rails, was conducted with a target minimum safety factor of 2.0 at a 450lbf load applied at the inside of the pedal face, which is a rules-required loadcase. The previous year's pedalbox had a large amount of deflection at the base plate, so plate thickness was varied until a target maximum displacement of 0.1 inches was reached (hence the high safety factor other than stress concentrations at the mounting pin and master cylinder bolt locations). The double shear mounting pins are Jergens stainless steel push-button quick release pins for ease of removal and adjustability.
Accelerator and Drive-By-Wire
Per rules, the accelerator pedal must include two redundant position sensors (a single OEM housing with redundant sensors in the same body is permissible, and is what we chose to use). A system of two pivoting linkages attached to the pedal with a cotter pin to mate a keyed shaft to the sensor was chosen so that the entire range of the sensor could be used with limited pedal mechanical travel. The positive stop at the front of the accelerator pedal is simply a flat machined into the pedal body, which is 6061-T6 aluminum. A set of spacers of varying outer diameters was machined for the connection between the torsion springs and pedal body, limiting rearward pedal travel to varying degrees.
