FSAE 2024

The brake rotor design process began with a detailed material selection using a design matrix where thermal conductivity was identified as the most critical factor to ensure effective heat dissipation during operation. A514 steel was chosen for its high thermal conductivity, cost-effectiveness, and proven performance in prior designs. 

To validate the thermal performance, data from the previous year’s endurance runs were analyzed to determine the duration and intensity of brake application. These insights were used to calculate the energy absorbed by the rotors during braking events. The energy data provided the basis for a SOLIDWORKS thermal simulation, where rotor temperatures were modeled under peak braking conditions. The design ensured that rotor temperatures remained  below the brake fluid boiling point of 611°F.

Building on the thermal analysis, material removal was strategically implemented to reduce the rotors' mass while preserving structural integrity and thermal efficiency. Slots were incorporated into the rotor design instead of traditional drilled holes to enhance durability and mitigate potential failure points. This approach minimized stress concentrations and reduced the risk of crack propagation under repeated thermal cycling and high mechanical loads, ensuring long-term reliability and safety.

Through this optimization, the original rotor design, which weighed 1.25 lbs, was reduced to 1.12 lbs for the front rotor and 1.03 lbs for the rear rotor. The total weight savings across all rotors was 0.7 lbs, representing a 15.1% reduction in unsprung mass. 

Brake buttons were incorporated into the rotor assembly to address potential misalignment issues by providing a tolerance of 0.01 inches. These components also served as a critical thermal barrier, minimizing heat transfer from the steel rotors to the aluminum hubs and protecting the hub from thermal distortion or damage. SOLIDWORKS FEA simulations were conducted to verify that the brake button standoffs could withstand the forces applied by the hub during braking. E-clips were selected to retain the brake rotor between the flange and the clip, facilitating easy maintenance. This design allowed the clips to be quickly removed, enabling straightforward removal of the rotor when needed. 

Throughout the design phase, constant communication was maintained with team members responsible for the hub and upright designs. Design changes and specific requirements were continuously discussed to ensure seamless integration between components, accommodating packaging constraints and aligning with the suspension system geometry. 

The design of the brake pedal began with taking driver measurements to ensure a comfortable and ergonomic experience. Feedback was gathered from drivers to understand their preferences regarding pedal positioning, travel, and force application. 

A horizontal master cylinder arrangement was selected to eliminate over-centering issues commonly associated with vertical master cylinder configurations. In this setup, forces applied to the pedal act directly through the master cylinder and into the pedal tabs, minimizing compliance and maximizing force transfer efficiency. 

To ensure smooth and consistent pedal actuation, bronze bushings were incorporated at the pedal pivot points. Additionally, a Tilton 900-Series Balance Bar was integrated into the pedal design, allowing for brake bias adjustments. Off-the-shelf Tilton pedal faces were utilized to streamline manufacturing, reducing fabrication time while ensuring reliability and durability. 

Key performance targets were established, including limiting deflection to 1 mm under a 2000 N load for a stable pedal feel. SOLIDWORKS FEA simulations verified that stresses remained well within acceptable limits, with a maximum stress of 95.3 MPa, significantly below the 150 MPa endurance limit of 7075 aluminum to eliminate fatigue concerns. 

The pedal's adjustability was a significant focus, offering three selectable pedal ratios—4.73, 4.02, and 3.44—through adjustable pushrod mounting points. This provided flexibility to tailor the pedal's force and travel characteristics to specific driver preferences and racing conditions. The pedal face was also adjustable, enabling drivers to fine-tune its position for improved ergonomics and control. 

To protect the master cylinders and provide a resting place for drivers’ feet during operation, a 1.8 mm thick aluminum plate was designed and integrated into the pedal assembly. 

Through iterative design, testing, and continuous collaboration with the chassis subteam, the brake pedal assembly delivered ergonomic precision, mechanical efficiency, and adjustability. 

Validation of the brake system was conducted through a series of rigorous tests to ensure performance, reliability, and compliance with competition requirements. The testing process began with a thorough inspection for any leaks within the hydraulic system, ensuring its integrity before further evaluation. Following this, the system's ability to lock all four wheels was tested, demonstrating compliance with FSAE regulations.

During mock autocross and endurance runs, rotor temperatures were measured using a heat gun to verify that the braking system could dissipate heat effectively under repeated use. This step validated the thermal design of the rotors, confirming that the temperatures remained well below critical thresholds to prevent brake fade or fluid boiling.

Driver feedback played a crucial role in fine-tuning the system. By adjusting the pedal ratio and brake bias, drivers were able to personalize the braking performance to suit their preferences and driving styles.

The ultimate validation occurred at the FSAE Electric Vehicle Michigan 2024 competition, where the car successfully passed the critical brake test on the first attempt. This marked the first time in Texas A&M Electric Racing history that the car passed all of its technical inspections and tests. Furthermore, the braking system demonstrated its robustness and reliability by performing flawlessly throughout the competition without any mechanical issues. 

Throughout the design and development process, several important lessons were learned that will inform future projects. One of the key takeaways was the critical need for open and effective communication between the suspension subteam and other subteams, particularly chassis and electronics. It became evident that maintaining an open dialogue about design considerations was essential, as decisions within the suspension design often had direct implications on the chassis and electronics. This communication required us to provide engineering justifications for any changes made to the current design, ensuring that all stakeholders were aligned on the impact of such modifications.

Another important lesson was the significance of keeping manufacturability and assembly in mind throughout the design process. While the design of the braking system was optimized from a performance standpoint, issues arose with the e-clips and their placement, as well as difficulties in assembling the rotor assembly due to its close proximity to the upright. These challenges could have been mitigated by considering assembly constraints earlier in the design process, ensuring smoother integration of components.

There were also engineering design shortcomings that became apparent during the project. One of these was the design of the pedal tabs, which were not adequately designed to counteract the moment arm forces they would experience. A more robust solution should have been considered to prevent potential issues with pedal flex and durability. Additionally, the design of the rotors was a point of concern; while the decision to reduce the rotor weight by 15% was made, there was insufficient validation to determine whether the trade-off was worth it in terms of the safety margin and temperature performance. In future projects, it would be essential to validate such design choices more thoroughly to ensure that performance gains do not compromise safety.

Finally, proper validation of the brake system was another area where improvements could be made. While pressure sensors and temperature monitoring were incorporated into the system, time constraints prevented comprehensive testing and data collection. Multiple inline pressure sensors and more extensive temperature data collection would have allowed for a more complete understanding of the brake system’s performance under various conditions. Future projects should prioritize sufficient testing time to fully validate systems before final implementation. These lessons learned will guide future improvements, particularly in terms of design integration, manufacturability, and testing to ensure a more robust and reliable braking system.