Variable-speed quadrupedal bounding using impulse planning: Untethered high-speed 3D Running of MIT Cheetah 2

This paper introduces a bounding gait control algorithm that allows a variable-speed running in the MIT Cheetah 2. A simple impulse planning algorithm is proposed to design vertical and horizontal force profiles which make net impulse on the system during one cycle zero. This design of force profiles leads to the conservation of linear momentum over a complete step, providing periodicity in horizontal and vertical velocity. When designed profiles are applied to the system, periodic orbits with an ability to change running speed are obtained. A virtual compliance control in the horizontal and vertical direction has been added onto the designed force profiles to stabilize the periodic orbits. The experimental results show that the algorithm successfully achieved untethered 3D running of the MIT Cheetah 2, with speeds ranging from 0 m/sec to 4.5 m/sec on treadmills as well as on grassy fields.

I. Introduction

Quadrupedal animals exhibit a remarkable capability to achieve high-speed, agile, and robust locomotion. Recent advances in the study of quadrupedal robots have shown a potential to realize this great locomotion capability in robotic systems. BigDog [1], LS3 and WildCat [2] developed by Boston Dynamics have demonstrated dynamic walking and fast running in outdoor environments with great robustness. Trotting gaits shown by StarlETH [3] and HyQ [4] are other exemplary results of advances in quadrupedal robotic systems. Recently, MIT Cheetah 1 and 2, research platforms with a unique electric actuation system for the study of high-speed quadrupedal locomotion [5], [6], have achieved a fast and high-energy-efficiency trotting gait [7] and a dynamic quadrupedal bounding gait [8].