Controller Design, Analysis, and Experimental Validation of a Robotic Serpentine Tail to Maneuver and Stabilize a Quadrupedal Robot

This paper analyzes how a multisegment, articulated serpentine tail can enhance the maneuvering and stability of a quadrupedal robot. A persistent challenge in legged robots is the need to account for propulsion, maneuvering, and stabilization considerations when generating control inputs for multidegree-of-freedom spatial legs. Looking to nature, many animals offset some of this required functionality to their tails to reduce the required action by their legs. By including a robotic tail on-board a legged robot, the gravitational and inertial loading of the tail can be utilized to provide for the robot's maneuverability and stability, while the legs primarily provide the robot's propulsion. System designs for the articulated serpentine tail and quadrupedal platform are presented, along with the dynamic models used to represent these systems. Outer-loop controllers that implement the desired maneuvering and stabilizing behaviors are discussed, along with an inner-loop controller that maps the desired tail trajectory into motor torque commands for the tail. Case studies showing the tail's ability to modify yaw-angle heading during locomotion (maneuvering) and to reject a destabilizing external disturbance in the roll direction (stabilization) are considered. Simulation results utilizing the tail's dynamic model and experimental results utilizing the tail prototype, in conjunction with the simulated quadrupedal platform, are generated. Successful maneuvering and stabilization are demonstrated by the simulated results and validated through experimentation.