Energy-Efficient and Stride-Level Hybrid Locomotion of a Leg-Wheel Transformable Robot

Abstract It is desirable to operate the robot with all its possible driving mechanisms for energy-efficient locomotion. In this work, using a leg-wheel transformable robot as an example, we proposed a methodology to thoroughly explore the stride-level leg-wheel hybrid locomotion to fill the gap between pure legged mode that uses point contact and pure wheeled mode that rolls on the ground. The developed wheel-like walking motion/gait can be operated at a wide range of body heights and forward speeds while maintaining energy efficiency. A comprehensive kinematics analysis of the leg-wheel transformable mechanism was conducted, which explores all possible contact conditions of the mechanism. A generalized revolute-prismatic and reduced-order dynamic model that captures the inertia effect of the leg-wheel mechanism was proposed to model the torque required to drive the mechanism. In addition, leg-wheel's two repositioning methods in the aerial phase were developed. Combining all three, the constrained optimization was conducted for the energy-efficient motion/gait of the robot. To validate the proposed methodology, various experiments of the robot were conducted, and the results confirm that the proposed method is beneficial and fills the gap between the pure wheeled mode and the pure legged mode of the leg-wheel transformable robot.