Body Rolling Analysis and Attitude Control of a Quadruped Robot during Trotting

To solve the problem that the body of quadruped robot always rotates about the body diagonal line during trotting, a simple and effective attitude control method is proposed through theoretically analyzing the essential cause of the body rolling. Firstly, the kinematic model of the quadruped leg is established to run the numerical analysis, hence the underlying reason for body rolling is obtained. That is, the reaction torques of the forward joints at the hips of standing legs cause the rolling motion about the body diagonal line. Based on the analysis, an attitude control method, which uses the torques of the sideward joints at the hips of the standing legs to resist the body rolling, is proposed, and then the potential lateral movement of the robot is discussed. At the end, dynamical simulations are conducted. The results show that the robot is easy to lose balance without attitude control. However, with the proposed attitude control method, it can achieve stable trotting and keep the roll angle changing within a small range. The dynamical simulations verify that the proposed approach can effectively control the body rolling motion and maintain dynamic balance of the robot.