Development of the Formula SAE upright
Suspension, FSAE, CAD, FEA, Topology optimization, BS8888
In 2015, I was appointed as an NCM Polytech (FSAE) chief engineer. I was responsible for developing and testing race cars. Because there were so few mechanical engineers, I also served as the suspension design lead. During two years in this role, I analyzed tons of tire data, developed various CAD models, and launched two Formula cars. On this page, you will find the key stages of the Formula car suspension upright development.
If you found this page interesting, you might also like my other racing/motorsport related publications.
Project summary
• Suspension packaging
• CAD development
• Finite element analysis (FEA)
• Drawing release
Responsibilities
1. Initial assembly development
2. FEA and topology optimization
3. Drawing development
Project objectives
A suspension upright is a vital element of the suspension assembly. The upright's main functions are to withstand all forces and moments at the tire contact patch and transmit them to the chassis via the suspension wishbones. At the same time, it is a core element of the wheel assembly that holds together the following components and systems:
• Outboard wishbone joints or brackets
• Tie rod or steering rod
• Wheel hub and bearings
• Brake rotor and caliper
• Cables and hydraulic lines fixings
• Sensors and auxiliary components
The biggest challenge in the FSAE upright development is the limited space, especially when the team runs 10” wheel rims. The part must fit within the wheel and provide enough clearance and stiffness to prevent the brake caliper and wishbone brackets from scrubbing the rim under load.
To begin the upright design, the team must freeze the suspension kinematics (pick-up points) and have at least the first iteration of the wheel packaging components (or validated geometry for off-the-shelf parts). In my team, we developed the suspension kinematics using MSC Adams Car. I selected the geometry and pick-up points based on the behavior of the Pacejka 5.2 tire model, which was based on TTC tire data. Using this data, I began the initial assembly packaging in Siemens NX. As shown in the picture below, all required components were placed and positioned inside the wheel rim. I designed component clearance considering wheel-rim deformation under heavy braking at the curb and pure cornering loads. However, I positioned the brake caliper not only to provide the required braking torque but also to optimize the "jacking" force (by lowering the wheel assembly CoG) and minimize the vehicle's yaw inertia.
1. Initial assembly development
The 10-inch wheels shown in the picture above present numerous challenges, necessitating a balance among suspension kinematics, brake caliper positioning, and brake rotor size.
Additionally, another project in my portfolio posed even greater challenges for component packaging because of stringent aerodynamic requirements and limited frontal area: a solar-powered race car designed for the World Solar Challenge competition in Australia.
After releasing the component positions, I created a simplified upright representation—the "block"—with bearing bores, a caliper mounting surface, and wishbone mount faces. The picture below shows the simplified initial geometry of the upright that will be fed to the topological optimization algorithm.
2. FEA and topology optimization
To provide the required strength and stiffness of the upright, the optimization was performed using the combination of the following critical cases:
• Outer wheel at apex
• Braking on the curb
To conduct the optimization, I used the SOL 200 Nastran solution. I divided the upright “block” into “Frozen Features” that remained untouched and an “Optimization Area” that was processed. Threads, fastener bosses, and wishbone brackets served as “Frozen Features” while the rest of the body was the optimization target.
The main objective was to minimize mass while keeping stiffness within 90% of the initial geometry. During the optimization, I used the “Compliance” variable as the main input to control the overall stiffness and natural frequency of the upright. The raw optimized geometry is shown in the pictures below.
Because of limited access to metal SLS technology, the freeform geometry was converted into a geometry feasible for a 5-axis CNC milling machine. The adapted geometry was designed to provide a safety factor above 1,5 (for 7075-T6 alloy) and to be compatible with the two-stage manufacturing process (one flip of the part during the machining). To ensure manufacturability, the CNC operator approved the following auxiliary datum features:
• Frontal flat surface
• Rear flat surface
• Top horizontal surface
• Steering arm surface
However, based on the upright's function, the center bore of the outer bearing was used as the main datum feature (A) on the drawing. This was also convenient for the CNC machinist because most upright features were machined using the expansion clamp (by clamping the bore's center surface). The pictures below show the final upright geometry, including the features mentioned above and the released wheel assembly.
3. Drawing development
The main result of this project is an upright design that provides the necessary stiffness while ensuring pilot safety and suspension reliability. The final geometry was created based on the results of topological optimization and recommendations from the CNC machine operator. Finally, the three-dimensional CAD geometry was supplemented with an advanced drawing to ensure high accuracy and minimize the chance of error. The final drawing revision followed the BS8888 standard and is shown in the picture below.
Key results
Godspeed!