WheeLeR: Wheel-Leg Reconfigurable Mechanism with Passive Gears for Mobile Robot Applications

This paper presents a new passive wheel-leg transformation mechanism and its embodiment in a small mobile robot. The mechanism is based on a unique geared structure, allowing the wheel to transform between two modes, i.e., wheel or leg, potentially adapting to varying ground conditions. It consists of a central gear and legs with partial gears that rotate around the central gear to open or close the legs. When fully closed, the mechanism forms a seamless circular wheel; when opened, it operates in the leg mode. The central gear actuated by the driving motor generates opening and closing motions of the legs without using an additional actuator. The number of legs, their physical size, and the gear ratio between the central gear and the partial gears on the legs are adjustable. This design is mechanically simple, customizable, and easy to fabricate. For physical demonstration and experiments, a mobile robotic platform was built and its terrainability was tested using five different sets of the transformable wheels with varying sizes and gear ratios. For each design, the performance with successful wheel-leg transformation, obstacle climbing, and locomotion capabilities was tested in different ground conditions.