A Swinging, Variable-Length Soft Tail from 3D Printed Origami: Steps Toward Bioinspired Robot Walking

Tails are flexible appendages that many vertebrates use for balance, gait stabilization, thrust generation, and more. While robots rarely have them, soft walking robots may benefit from a tail that stabilizes locomotion in unstructured terrains. We present a tendon-driven, soft robotic tail capable of swinging and shortening to change the momentum and center of mass of a robot body. The tail comprises three origami bellows fully 3D printed from thermoplastic polyurethane. The bellows are highly compressible, allowing motorized tendon actuators to shorten the tail by 110 mm, or 30% of the tail’s initial length. The tail’s flexibility also enables large swinging motions, which are achieved by alternatively pulling and releasing two tendons routing at the sides of the bellows structures. Since the tail’s servo motors are at its end, the tail can generate up to 0.5 N•m torque while swinging. In this paper, we characterize the tail’s range of adjustable lengths, the swinging motions it can produce, and the torque it generates. Swinging and torque generation are evaluated at several different initial tail lengths. Finally, we demonstrate the tail’s controllability through a closed proportional-integral-derivative (PID) feedback controller. This work sets in motion future investigations of how vertebrate-inspired tails can enhance the mobility and stability of (soft) robot walking.