4SWLR: A Switched System and Skid Steer Integrated Whole-Body Control Framework for Wheeled-Legged Robots

Inspired by mammalian locomotion and vehicle skid-steering principles, this paper proposes a real-time motion planning and tracking control framework for wheeled-legged robots, integrating the obstacle-crossing capability of legged robots with the skid-steering mechanism of wheeled platforms. Unlike conventional wheeled-legged robot control methods that rely on external swing joints, the proposed framework leverages differential wheel actuation while comprehensively accounting for the robot-environment coupling effects under high-speed conditions, enabling efficient and stable high-speed steering. First, a hierarchical wheel-terrain contact dynamics model and a skid-steering kinematics model are established for wheeled-legged robots with skid-steering. By combining switched-system skid-steering kinematics with refined wheel–environment interaction dynamics, the framework effectively addresses active wheel torque control during high-speed steering. Second, a skid-steering-based motion paradigm is introduced, which co-optimizes legged dynamics and wheeled skid-steering kinematics, eliminating the need for continuous leg-lifting maneuvers to generate lateral forces and ensuring smooth high-speed steering. Finally, extensive experiments conducted in challenging environments—including staircases, trenches, ramps, single-side bridges, and unpaved terrains—validate the robustness and efficacy of the proposed approach. Comparative studies with state-of-the-art wheeled-legged control methods further demonstrate the superior mobility performance and enhanced wheel–terrain interaction dynamics achieved by our framework.