Modeling and In-flight Torso Attitude Stabilization of a Jumping Quadruped

TL;DR

This paper presents a hierarchical NMPC-based control framework for in-flight torso attitude stabilization of jumping quadrupeds in low-gravity environments, combining collision-aware modeling and online trajectory planning.

Contribution

It introduces a convex decomposition for collision geometry, a hierarchical NMPC control architecture, and a torque allocation strategy leveraging system symmetries for jumping quadrupeds.

Findings

Achieved rapid stabilization of 90-degree rotations in simulation.

Successfully demonstrated experimental stabilization of constant and changing orientations.

Provided a comprehensive framework for model-based attitude control in jumping legged robots.

Abstract

This paper addresses the modeling and attitude control of jumping quadrupeds in low-gravity environments. First, a convex decomposition procedure is presented to generate high-accuracy and low-cost collision geometries for quadrupeds performing agile maneuvers. A hierarchical control architecture is then investigated, separating torso orientation tracking from the generation of suitable, collision-free, corresponding leg motions. Nonlinear Model Predictive Controllers (NMPCs) are utilized in both layers of the controller. To compute the necessary leg motions, a torque allocation strategy is employed that leverages the symmetries of the system to avoid self-collisions and simplify the respective NMPC. To plan periodic trajectories online, a Finite State Machine (FSM)-based weight switching strategy is also used. The proposed controller is first evaluated in simulation, where 90 degree rotations in roll, pitch, and yaw are stabilized in 6.3, 2.4, and 5.5 seconds, respectively. The performance of the controller is further experimentally demonstrated by stabilizing constant and changing orientation references. Overall, this work provides a framework for the development of advanced model-based attitude controllers for jumping legged systems.