The Design of Formula SAE Half Shafts for Optimum Vehicle Acceleration

Many Formula SAE teams choose to design half shafts instead of purchase them. Commercial half shafts are usually over-designed, so teams make custom shafts to reduce the mass and rotational inertia. Half shafts are commonly designed by predicting the applied torsional loads and selecting inner and outer diameters to not exceed the material's yield strength. Various combinations of inner and outer diameters will support the loads, and the final dimensions may be chosen arbitrarily based on the designer's attempt to minimize both mass and rotational inertia. However, the mass and rotational inertia of a hollow shaft are inversely related and both quantities cannot be minimized simultaneously. Designers must therefore compromise between mass and rotational inertia reductions to maximize vehicle performance.

This paper will present the derivation of an equation which calculates the optimum inner and outer half shaft diameter to maximize vehicle acceleration. Graphical explanations and predictions of vehicle acceleration improvements will be provided. The design, manufacturing, and testing procedure of Cal Poly Pomona's Formula SAE half shafts will be explained as an example for other teams.