Tailbot – Robot with Inertial Assisted Control by an Active Tail Inspired by Lizards
Lizards, discovered to pitch correct in mid-air with their tail when subjected to slippery take-off surfaces, have inspired a novel approach to stabilizing rapid locomotion in mobile terrestrial robots. To demonstrate the benefit of this behavior we built a 177g wheeled robot, Tailbot, with inertial sensors, a microprocessor, and a single degree-of-freedom active tail. Since the tails effective inertia scaled quadratically with length, its mass was designed to be less than 20% of the body mass while still allowing for a one to one ratio of angular stroke. By estimating the body angle from the inertial sensors and utilizing both contact forces and zero net angular momentum maneuvering, Tailbot could take advantage of closed loop feedback control. Feedback produced rapid reorientation during a fall, smooth transitions between surfaces of differing slopes, and stability when faced with perturbations that would overturn a tailless robot. Specifically, Tailbot could perform a 90o self-righting maneuver during free fall in 138ms corresponding to a drop distance of approximately one body length. A nominally catastrophic perturbation, produced a 60o rotation in a passive tailed robot, but resulted in only a 30o rotation in our feedback controlled tailed robot. Landing transitions that were not possible with a tailless robot were made feasible by properly adjusting the reference angle to the tail controller. Capabilities of Tailbot demonstrate how active tails can improve the stability and maneuverability of terrestrial and aerial search-and-rescue vehicles and serve as a physical model to generate new hypotheses of inertial appendage control in animals.