Background

The Cooper Union FSAE team, known as Cooper Motorsports, is composed of approximately 20 dedicated to designing, manufacturing, and testing a racecar for the annual Formula SAE competition. Each year, team leaders subdivided the team into groups focused on specific vehicle subsystem.

2018 Cooper Motorsports racecar, presented during design reveal (left) and tested with driver (right).

From 2016 through 2019, I led the frame subsystem. My responsibilities included designing a frame to meet structural rigidity, ergonomic, subsystem packaging, manufacturability, and time constraints each year. I designed and manufactured frame welding jigs and suspension mounting tabs, and notched pre-purchased tubes in preparation for welding in Cooper Union’s machine shop. I managed a team of junior engineers throughout the design process to ensure timely completion of all design objectives.

Design Concept and Objectives

We consistently used a 4130 chromoly steel space frame as our design concept. This steel alloy was chosen for its high strength-to-weight ratio, toughness, weldability, and heat treatability. A space frame was chosen for its efficient strength-to-weight ratio, modular design, and ability to distribute weight by strategically placing more steel tubing closer to the desired center of gravity location.

Cooper Motorsports 2019 frame.

Each year, the frame needed to hold all vehicle components in their desired locations while resisting loads applied by the suspension, engine, and aerodynamic systems. Previous frame designs proved to be overly stiff, used too many tubes in areas that did not transmit enough force, did not allow for easy ingress/egress, and did not fully utilize the aerodynamics package. Our frame design plan balanced 7 priorities:

• Knowledge of how tube forces were distributed throughout the frame when braking, accelerating, and cornering.
• Maintenance of a low center of gravity with a slight rear-heavy weight distribution.
• Maintenance of a high torsional rigidity (at least a full order of magnitude above the designed difference in roll rates).
• Minimization of vehicle weight.
• Easy driver accessibility (ensuring drivers could easily enter/exit the vehicle, reach pedals, see over the front roll hoop, and have sufficient room to turn the steering wheel).
• Manufacturability (ease of welding, ensuring no difficult-to-access locations on the vehicle for maintenance).
• Packaging (ensuring each subsystem has ample room to allow for design modifications).

Design Implementation

To meet our design objectives, we held weekly meetings with drivers and other subsystem leaders to preliminarily gauge how much space each subsystem needed. We constructed a rough simulacrum of the frame front bulkhead and cockpit using PVC tubing to gauge driver ergonomics. We simulated the frame behavior under braking, accelerating, and cornering conditions using ANSYS Mechanical APDL, recording the resulting frame deflection and forces through each frame member. Tubes were placed to maximize torsional rigidity while minimizing overall frame weight.

Frame with interior subsystems installed.

Results

Left: 2017 frame subsystem photoshoot. Center: Gelcoat application on a 2018 bodywork mold. Right: 2019 overall team photoshoot.

The FSAE competition ranks approximately 120 student teams based on design, cost, and racing performance. Our dedication to consistent communication and good engineering design practices consistently placed us in the top 20 teams. Our highest-ever chassis design score was 22/25 in 2019, helping our team to tie for 8th place in overall design.