Design and Implementation of an Angle-Bisecting Foot Mechanism for a Leg-Wheel Transformable Robot

Abstract

This paper presents the design, modeling, and experimental validation of a novel leg-wheel mechanism featuring an integrated, passive angle-bisecting foot. The core of the design is a two-stage planetary gear system. This system mechanically ensures a consistent foot-ground contact angle, addressing a key limitation in transformable robots with symmetrical leg-wheels. To leverage this innovation, we developed a comprehensive kinematic model. Furthermore, we designed a hierarchical motion planning framework that utilizes the pure rolling motion enabled by the mechanism. The effectiveness of the proposed design was validated through hardware experiments on a 23 kg prototype. The results demonstrated improved energy efficiency based on the Cost of Transport (C.O.T.) metric, achieving up to a 16.2% reduction in C.O.T. alongside a 28.6% reduction in pitch oscillation compared to a baseline design. This study provides a valuable guideline for developing adaptive gait controllers that can optimize for energy efficiency in real time.