Design, analysis, and validation of a custom planetary gearbox for a Formula SAE Hub motor

Abstract

This thesis presents the analysis, design, manufacture, and validation of a custom in-hub planetary gearbox for use within a Formula Student electric vehicle powertrain. This work establishes a baseline for the transition from an inboard single power unit into a dual motor rear wheel drive architecture.

Existing commercial transmission solutions were unsuitable for direct integration into a Formula Student platform due to their packaging limitations, excessive mass, and lack of optimisation for the specific operating case. The limited availability of documented Formula SAE specific solutions justify the development and validation of a custom gearbox solution.

The gearbox was developed with consideration for manufacturability, packaging requirements, and future team integration. A stepped planetary configuration is used, achieving a gear ratio of 14:1. The design process focuses on the gear geometry selection, powertrain integration, as well as the stresses experienced through critical components under peak loading conditions.

Experimental testing demonstrated that the gearbox was capable of operating under the predicted torque input of 8 Nm. The custom planetary gearbox was able to complete a full endurance length of 22 km fatigue test without structural failure or significant wear. A post-test inspection of the gearbox identified minor surface wear present on the gear faces with no evidence of any other damage to supporting components throughout the system.

The developed prototype serves as an early stage foundation for future in-hub powertrain development within the Formula Student platform. With the gearbox validated, opportunities remain for improvement, particularly in the area of mass reduction, optimisation and long term durability validation.