A passive planar model with rolling contact and its application for bounding and pronking on a quadruped robot

Abstract

The development and investigation of a quadruped robot's dynamic bounding and pronking gaits using a sagittal planar model that captures the robot's natural dynamics are presented. The proposed reduced-order model, termed the Two-rolling-leg (TRL) model, is a 3-DOF planar rigid-body model consisting of two half-circular compliant legs with pure rolling contact. Throughout the non-dimensional steps-to-fall and fixed-point analysis, the model with feasible intrinsic parameters can passively perform the periodic dynamic behavior of bounding and pronking, revealing a relationship between the body parameters and the preferred dynamic behaviors. Dynamic bounding and pronking on a quadruped robot were initiated by developing a model-based control strategy based on the searched periodic dynamic behaviors of the TRL model. The experimental results showed that the robot can initiate its dynamic bounding and pronking behaviors at various forward speeds merely by causing the motor to track a preset trajectory derived from the fixed-point motion of the TRL model using position control. The higher success rate of the robot in stable bounding than in pronking is in line with the results from the analysis of the model. This paper confirms that the dynamic multi-gait locomotion of a quadrupedal robot can be initiated by utilizing a reduced-order model for control guidance and that the body configuration plays an important role in determining the characteristics of the dynamic behaviors.