On designing an active tail for legged robots: simplifying control via decoupling of control objectives

Abstract

Abstract-This work explores the possible roles of active tails for steady-state legged-locomotion. A series of simple models are proposed which capture the dynamics of an idealized running system with an active tail. The models suggest that the control objectives of injecting energy into the system and stabilizing body-pitch can be effectively decoupled via proper tail design: a long, light tail. Thus the overall control problem can be simplified, using the tail exclusively to stabilize body-pitch: this effectively relaxes the constraints on the leg-actuators, allowing them to be recruited specifically for adding energy into the system. We show in simulation that models with long-light tails are better able to reject perturbations to body-pitch than short-heavy tails with the same moment of inertia. Further, we present the results of a one degree-of-freedom tail mounted on the open-loop controlled quadruped robot Cheetah-Cub. Our results show that an active tail can greatly improve both forward velocity and reduce body-pitch per stride, while adding minimal complexity. Further, the results validate the long-light tail design: shorter, heavier tails are much more sensitive to configuration and control parameter changes than longer and lighter tails with the same moment of inertia.

Design and Experimental Validation of Reorientation Manoeuvres for a Free Falling Robot Inspired From the Cat Righting Reflex

“…While reproducing weightlessness conditions in 3D space on Earth remains a challenge, several research initiatives have resulted in interesting experimental work. For instance, the results in [24], [25], [26] show that a tailed robot can effectively accomplish inertial reorientation in at least one plane. The in-depth analysis of [27] and the simulations in [28] concluded that the use of a tail or appendages is particularly interesting for terrestrial robots and also explored the use of flailing limbs.…”

Towards Jumping Locomotion for Quadruped Robots on the Moon

“…The updated version of Salto, Salto-1p makes use of a reaction wheel and fans to stabilize and steer the robot [13]. The use of a tail was explored with the 2.5 kg Jeorba hopper [14] and the 1.25 kg Cheetah-Cub [15]. A reaction wheel was proposed during a simulation study to stabilize the pronking motion of a 10 kg quadruped on compliant terrain [16].…”

The effect of head movement on the bounding gait of a quadruped robot with an active spine

“…They proved that an active tail can both greatly improve forward velocity and reduce body pitch per stride. 8 In addition, the tail plays an important role in free-falling robots 9 and bionic lizards running on the water. 10 In most studies, the tail is made of a rigid rod, but there are exceptions.…”