To convert driver leg force into brake line pressure and throttle position, accurately and repeatably, for every driver in the pool, with adjustment that does not require tools.
A pedal box on a shared rail. Each pedal is a waterjet 6061-T6 arm pivoting on a pin in a tray, with a CFRP face over a balsa wood core. The brake pedal drives a balance bar between two Tilton master cylinders; the bar's position sets front-to-rear brake bias and is trimmed from the cockpit through the bias knob. The accelerator pedal drives a Bosch RPS-F rotary hall-effect accelerator pedal position sensor with fully redundant power, ground and signal, which is what makes electronic throttle control rules-legal. Pedal position is adjusted by sliding the tray on the rail and locking it with a clamping handle.
Adjustability is worth structure. The pedal rail added 1.61 lb of tubing to the CR26I frame, and it was accepted because per-driver pedal position is an ergonomics requirement. Driver force targets come from the NASA Anthropometry, Biomechanics and Strength handbook rather than from what the current drivers can push. 1. Take brake and throttle pedal position ranges from the ergonomics study (brake optimum 38.22 in, throttle optimum 38.48 in; CR26I sits at 38.7 in and 38.5 in). 2. Select the pedal ratio from the master cylinder sizing and the required pedal force, then set the geometry that achieves it. 3. Analyse the arm. CR26I brake arm: 225 lbf applied, fixed at the hinge, minimum FoS 1.23, with a mesh convergence study. 4. Waterjet the arms, lay up the faces, assemble on the rail. 5. Validate pedal force and travel against the brake calculation on the car.
- Reduce adjustment time. CR26I cut it 60%, from 3:00 to 1:45, and eliminated the need for tools. - Hold the required pedal force inside driver capability. CR26I requires 137 lbf for maximum deceleration, with a brake sensitivity of 77 lb/g. - Keep the assembly light while carrying full braking load. - Give consistent pedal feel so drivers can brake to the same point every lap.
- Pedal position adjustment historically needing tools and taking too long between drivers. Solved with the clamping handle and rail. - Master cylinder sizing driving pedal force. CR26I swept front/rear combinations before settling on 5/8 in front and 13/16 in rear.
SolidWorks FEA for arm analysis with convergence study. Brake system MATLAB calculation for master cylinder sizing, pedal ratio and required force. NASA strength handbook data for driver force limits. The ergonomics jig for position ranges.