In this paper, we show dynamic locomotion strategies for wheeled quadrupedal robots which combine the advantages of walking and driving. The developed optimization framework tightly integrates the additional degrees of freedom introduced by the wheels. Our approach relies on a Zero-Moment Point based motion optimization which continuously updates reference trajectories. The reference motions are tracked by a hierarchical whole-body controller which optimizes the generalized accelerations and contact forces by solving a sequence of prioritized tasks including the nonholonomic rolling constraints. Our approach has been tested on the torque-controllable robot ANYmal equipped with nonsteerable, torque-controlled wheels. We conducted experiments on flat, inclined and rough terrain, whereby we show that integrating the wheels into the motion control and planning framework results in intuitive motion trajectories, which enable more robust and dynamic locomotion compared to other wheeled-legged robots.
Agile motions over steps and stairs are demonstrated for the first time in our previous work REF , where a hierarchical whole-body controller (WBC) tracks the motion trajectories that include the rolling conditions associated with the wheels.
Keep Rollin' - Whole-Body Motion Control and Planning for Wheeled Quadrupedal Robots
IEEE Robotics and Automation Letters 2019
Engineering Computer Science