Stabilizing a quadruped robot locomotion using a two degree of freedom tail

This paper investigates how to improve locomotion stability of a dynamical system composed of four spring-mass subsystems by using a tail-like inertial appendage. The paper presents a Denavit-Hartenberg parameterization based kinematic model combined with a Newton-Euler based dynamic model of a two degree of freedom tail. Impedance based leg control simplifies the leg motion so that it can be modeled as a damped spring-mass system. The tail presented in the paper is used as a counterweight, capable of shifting its center of mass so as to balance the body of the robot. To that end, a recursive algorithm that moves the tail in order to balance the robot is proposed. A realistic robot model is built in the Open Dynamic Engine environment and is used to conduct a series of tests proving the effectiveness of the proposed algorithm.