Towards Safe Landing of Falling Quadruped Robots Using a 3-DoF Morphable Inertial Tail

TL;DR

This paper introduces a 3-DoF morphable inertial tail for quadruped robots to achieve safe landing by effective aerial reorientation, demonstrated through simulation and initial robot experiments.

Contribution

It proposes a novel tail design and control architecture enabling quadruped robots to reorient mid-air and land safely, addressing a gap in existing fall mitigation methods.

Findings

The tail effectively reorients the robot in 3D during flight.

Retractable tail length improves landing stability.

Experimental robot successfully lands from non-zero initial angles.

Abstract

Falling cat problem is well-known where cats show their super aerial reorientation capability and can land safely. For their robotic counterparts, a similar falling quadruped robot problem, has not been fully addressed, although achieving safe landing as the cats has been increasingly investigated. Unlike imposing the burden on landing control, we approach to safe landing of falling quadruped robots by effective flight phase control. Different from existing work like swinging legs and attaching reaction wheels or simple tails, we propose to deploy a 3-DoF morphable inertial tail on a medium-size quadruped robot. In the flight phase, the tail with its maximum length can self-right the body orientation in 3D effectively; before touch-down, the tail length can be retracted to about 1/4 of its maximum for impressing the tail's side-effect on landing. To enable aerial reorientation for safe landing in the quadruped robots, we design a control architecture, which has been verified in a high-fidelity physics simulation environment with different initial conditions. Experimental results on a customized flight-phase test platform with comparable inertial properties are provided and show the tail's effectiveness on 3D body reorientation and its fast retractability before touch-down. An initial falling quadruped robot experiment is shown, where the robot Unitree A1 with the 3-DoF tail can land safely subject to non-negligible initial body angles.