Stair Climbing of a Transformable Robot Using Varying Leg-Wheel Contact Points

Abstract

Staircases are a challenging terrain frequently encountered in urban environments. While leg-wheel robots take advantage of having both legged and wheeled modes, their ability to negotiate stairs still requires careful planning. This paper presents a novel approach to developing a stair-climbing behavior for leg-wheel transformable robots. A comprehensive stair-climbing strategy is constructed by analyzing the workspace of the leg-wheel mechanism, considering the position of the robot's center of mass, and accounting for foothold displacement owing to the possible leg-wheel forward rolling motion. This strategy enables the robot to safely navigate stairs using its leg-wheel's appropriate parts. Stability during transitions between steps is ensured, and a well-designed swing trajectory is proposed to minimize slippage and impact. The approach is validated through simulations and further tested experimentally on staircases with treads of 27 cm and risers of 12 cm, as well as staircases with treads of 24 cm and risers of 14 cm. The experimental results demonstrate the effectiveness and robustness of the proposed method.