2025 UWFE Brakes

I am the lead for the brake subsystem for the 2025 UW Formula Electric Formula SAE open wheel racecar. I am responsible for the research, design and optimization of our entire braking system downstream of the pedal itself, including:

• Design, structural FEA, and thermal analysis of brake rotors

• Vehicle testing for data acquisition to inform thermal simulations

• Processing raw data using MATLAB to produce a thermal FEA input

• Sizing of off-the-shelf master cylinders based on first-principles vehicle dynamics calculations

• Routing of high-pressure brakelines, including sensor placement and integration

Firstly, master cylinders were sized from first principles, using the maximum deceleration due to tire limitations and dynamic weight transfer and the required braking torque to achieve this deceleration. I chose master cylinders which can provide this torque with a comfortable pedal input, improving drivability. Brake pads were also chosen based on their temperature-friction curve, based on previous year's rotor temperatures.

From there, the structural forces on the brake rotors were determined from the clamping force and the friction of the brake pads. The rotors were analyzed using ANSYS Mechanical. The rotors are designed with a safety factor of 2.0 with regards to yielding under the maximum observed pedal force, with a temperature adjustment factor applied to the yield strength. AISI 1018 mild steel was chosen due to its balance of high strength and strong thermal characteristics. Additionally, fatigue life was defined for the rotors using Marin fatigue factors to define an acceptable lifespan for the rotors.

Testing was done on our 2024 car to gather data to inform our thermal simulations. The raw data gathered was vehicle speed, brake pressure and rear rotor temperature using an IR sensor. They were processed using a script to extract a heat input into the brake rotors (considering front/rear brake bias), neglecting drag, rolling & mechanical friction to preserve the true "worst case".

Then, the thermal performance of the brake rotors was analyzed with a transient thermal study using ANSYS Mechanical. The heat flow into the rotors was taken from testing data previously processed. The convection coefficient was determined by correlating the simulation results with the measured temperature during the same testing session. My temperature target was based on the temperature-friction characteristics of the brake pads.

After thermal simulations, I did a tolerance stackup analysis to define the clearance between the rotor and the bobbins. Based on the simulated temperatures, I also verified that at the peak temperature would not induce seizing or thermal stresses between the rotors and bobbins.

A smaller focus during this time was routing brake lines and defining all fittings, lines, sensors, and procuring these parts. Minor improvements were made, including reducing the total number of fittings to reduce failure points, and changing the routing of flexible lines from the frame to the calipers, along the control arms. This has the twofold benefit of decreasing weight, while improving pedal feel due to less total compliance in the hydraulic system.

Around the same time, once all the rotor design was wrapped up, I coordinated with sponsors for the two-step manufacturing process of the rotors. They were first waterjet out of 1/4" steel, then Blanchard ground to their final thicknesses for superior flatness and parallelism between faces, which improves brake pad lifespan and promotes even pad wear.

This would be the workflow in an ideal world - in reality, I was constantly iterating, discovering issues in previous stages, and redoing work with a slightly improved understanding of the structural, thermal and mechanical considerations in a high-temperature system. The journey was the best part of the process and it was such a rewarding feeling seeing the car brake (and not break) for the first time.