Hyperredundant Dynamic Robotic Tails for Stabilizing and Maneuvering Control of Legged Robots

Abstract

High-performing legged robots require complex spatial leg designs and controllers to simultaneously implement propulsion, maneuvering and stabilization behaviors. Looking to nature, tails assist a variety of animals with these functionalities separate from the animals' legs. However, prior research into robotic tails primarily focuses on single-mass pendulums driven in a single plane of motion and designed to perform a specific task. In order to justify including a robotic tail on-board a legged robot, the tail should be capable of performing multiple functionalities in the robot's yaw, pitch and roll directions. The aim of this research is to study bioinspired articulated spatial robotic tails capable of implementing maneuvering and stabilization behaviors in quadrupedal and bipedal legged robots. To this end, two novel serpentine tails designs are presented and integrated into prototypes to test their maneuvering and stabilizing capabilities. Dynamic models for these two tail designs are formulated, along with the dynamic model of a previously considered continuum robot, to predict the tails' motion and the loading they will apply on their legged robots. To implement the desired behaviors, outer- and inner-loop controllers are formulated for the serpentine tails: the outer-loop controllers generate the desired tail trajectory to maneuver or stabilize the legged robot, and the inner-loop controllers calculate control inputs for the tail that implement the desired tail trajectory using feedback linearization. Maneuvering and stabilizing case studies are generated to demonstrate the tails' ability to: (1) generate yaw angle turning in both a quadruped and a biped, (2) improve the quadruped's ability to reject an externally applied roll moment disturbance that would otherwise destabilize it, and (3) counteract the biped's roll angle instability when it lifts one of its legs (for example, during its gait cycle). Tail simulations and experimental results are used to implement these case studies in conjunction with multi-body dynamic simulations of the quadrupedal and bipedal legged platforms. Results successfully demonstrate the tails' ability to maneuver and stabilize legged robots, and provide a firm foundation for future work implementing a tailed-legged robot.