Model-based dynamic gait in a quadruped robot with waist actuation

Abstract

We report on the development of a dynamic gait in a robot based on a sagittal-plane and reduced-order model that fits the natural dynamics of the robot. The proposed model, referred to as the two-rolling-legs model with waist actuation (TRLW), consists of two rolling and compliant legs and two rigid bodies connected by an active waist joint. The numerical fixed-point analyses of the model suggest that with adequate touchdown conditions and waist motion, dynamic and periodic bounding and pronking behaviors of the model are achievable. Several identified fixed points of the model, or passive dynamics of the model, serve as the control guidance to initiate bounding and pronking on a newly-developed quadruped robot. The experimental results show that though several un-modeled factors cause behavioral discrepancies between the TRLW model and the robot, the robot can still initiate its dynamic behaviors by directly mapping the leg trajectories of the model onto those of the robot and via a simple pre-set joint position control strategy, without any other state feedback. This work confirms that the dynamic behavior of the robot can be initiated by using the passive dynamics of the reduced-order model.