Wolfrom gearbox concept for enhanced load capacity in compact aeronautical actuation systems

• High Load Wolfrom based reducer is proposed. • Practical design and assembly guidelines are provided. • The design enables high number of planets while preserving ratio and efficiency. • Synchronous and asynchronous behaviours are validated through experiments. • Asynchrony improves instantaneous efficiency and backdrive stability. This work presents the High-Load Wolfrom (HLW), a new compact planetary gearbox concept, developed to overcome the trade-off between load capacity and efficiency that limits conventional Wolfrom architectures. In standard Wolfrom designs, increasing the number of planets improves torque sharing but simultaneously reduces the first-stage reduction ratio, forcing higher reductions in the second stage where most efficiency losses occur. The proposed HLW introduces intermediate parasitic planets between the sun and each pair of main planets, enabling a greater number of load-sharing meshes within the same diameter while maintaining favourable reduction ratios and compactness. Analytical formulations for kinematics, reduction ratio, and efficiency are developed and compared with those of the conventional design. Two different HLW reducers are manufactured and tested: a synchronous version validating the concept feasibility, and an asynchronous version improving instantaneous efficiency and backdrivability. The experimental results confirm that the HLW architecture enables the design of lightweight, high-load, and compact gear reducers well suited for aerospace electromechanical actuation.