Hobbies

2017 Racecar Pedalbox

How do you make pedals adjustable without compromising performance?

Formula SAE is a collegiate competition where teams conceptualize, design and manufacture a 1/3rd scale Formula 1 vehicle in a year. As the lead designer, I overhauled the previous design and made improvements to the pedal system's adjustability, manufacturability, and robustness to failure. This design was proven successful at the 2017 FSAE Michigan competition (success criteria = brake pedal can withstand 2000N force without failure), and used for the following year in 2018.

Research and Design

To start designing, I used last year's design as a benchmark and started asking questions. Was the adjustment method usable? How did the driver feel about last year's "pedal block" design in practice? After gathering this information, I started to research F1 and top ranking teams' designs to look for inspiration for a new adjustment system. After brainstorming several ideas, I created conceptual mockups for each subsystem (rails, pedals, baseplate) and used an alternatives matrix as well as consulting other members to help decide the most practical design.

Manufacturing

I wanted to focus on a design that was simple to machine on a 3-axis CNC, so I designed the baseplate, throttle and gas pedals to fit on the same 5/8 inch aluminum blank. As a result, I machined the pedals, baseplate, and rails in a total of 11 hours, cutting down the manufacturing time from the 2016 year around 55%.

Improvements from Previous Year

This year’s design was optimized for standard FSAE design factors – weight, manufacturability, serviceability, packaging, adjustability and cost. Emphasis was placed on increasing the overall adjustment length for a wider range of users, and increasing the speed of adjustment between different positions. This required a complete redesign of the adjustment system from the previous year. As a result of a this redesign, the pedals were able to be adjusted in an average of 15 seconds, compared with an average of 151 seconds in the 2016 design. Emphasis was also placed on designing for high stiffness, rather than material yield strength. Designing for high stiffness, and consequently small deflection, reduces compliance in the system, which ensures accurate and consistent control over the brake and throttle pedal response.

One area my partner and I improved upon was in the throttle cable assembly, which translates pedal movement at the driver's foot to movement at the engine intake. In the past, we used a bolt fastened to the pedal that added a significant moment to the throttle pedal. This year, we kept the throttle components in line with the pedals to minimize this moment and allow adjustment of the throttle pedal gain (see video above).

Key Takeaways

This project was illuminating because I was able to iterate on the same system over two years. This year in particular, I learned the importance of having data behind each design decision. For example, the adjustment interval of 1.8 inches was based on data from a ergonomic mockup of the cockpit. In fast-paced design competitions, the rationale behind each decision sometimes ends up being "we don't have enough time, let's just do this". This leads to poor engineering analysis and a lot of fires to be put out in testing, or at competition. It was refreshing to be able to step back, look at where the previous decision needed some love, and build a pedal box robust enough to serve as a framework for future teams.

The finished product! The result of many, many hours spent in Ford. Thank you to all who helped along the way.