Experimental Evaluation of Obstacle Clearance by a Hybrid Wheel-Legged Robot

This paper deals with the problem of frontal obstacle crossing by a poly-articulated wheeled robot. We focus on the particular architecture of hybrid wheel-legged robots that are redundantly actuated systems. In this paper, experimental results that show the climbing capabilities of such system when crossing large obstacle are presented. We focus on the case of a step like obstacle whose height is superior to the diameter of the wheels. In this case, the adhesion properties have a large impact on the crossing capabilities. First, we introduce our control methodology which is based on the optimization of both the robot posture and the distribution of internal forces. The optimization criterion represents the maximum allowable force disturbance that the system can support before violating the frictional contact constraint. Then, our experimental prototype, the robot Hylos2 and the experimental setup are presented. As our approach is based on the control of the contact forces, experiments used to quantify the level of friction in the mechanical transmissions are first reported. Then a step-crossing trial on the real system is presented.