Hybrid Motion Control for a Novel Wheeled Quadruped Robot

We present a modeling and hybrid locomotion control method for a novel wheeled quadruped robot, Pegasus, featuring a unique lightweight linear-actuator-driven ankle structure that enables four-wheel independent steering. A quadruped model, which only activates 12 joints(hip, thigh, and knee), and a vehicle model are implemented on Pegasus simultaneously, with a hybrid velocity allocation strategy aiming to combine both legged and wheeled movements, distributing desired linear and angular velocity to both locomotion modes. Moreover, a model predictive control (MPC) controller is designed to generate optimal torque for the quadruped model in real-time, and a "telescopic vehicle model" is derived to calculate the commands for ankles and wheels. Our experimental results demonstrate that the proposed modeling method and velocity allocation strategy with our controller can enable Pegasus to track the desired commands and adapt to various terrains, such as ramps, curves, and gravel roads. Furthermore, the utilization of ankle joints has led to a considerable reduction in the cost of transport (CoT) by surpassing 20% compared to scenarios lacking ankle joints.