Automatic Adaptation to Step-Climbing in Elastically Coupled Dual Legged-Wheels

We develop a mobile platform design for commercial vehicles intended to transport a wide range of weights over paved roads with relatively high steps. We propose a transformable wheel mechanism called the dual legged-wheel (DLW) system, each with a tri-legged structure coaxially connected out-of-phase through a unique elastic mechanism that enables automatic adaptation to step-climbing, eliminating the need for terrain sensing and precise control of both legged-wheels. As a result, only rotating the active legged-wheel at a constant angular velocity allows the passive legged-wheel to automatically adapt to terrain, thus facilitating the DLW's movement in the circular-wheel form on flat terrain and enabling climbing of a high step with both legged-wheels fully overlapped in front of the step, even under varying load conditions. A robot equipped with additional rear standard active wheels successfully ascends and descends stairs, traverses uneven terrain, and climbs steep slopes. Moreover, our proposed elastic mechanism enables the DLWs to passively transform into the legged-wheel form only during necessary time in the fields, i.e., while climbing a high step and stairs.