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

1. National Technical University of Athens, Greece
2. Norwegian University of Science and Technology, Norway

The code of this work will be available in the future.

Code

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.

Research Highlights

Simulation results from tracking 90 degree turns in roll, pitch and yaw.

Mass ablation study results. The influence of increasing the paw or torso mass is investigated. The controller managed to stabilize the orientation in all cases, showcasing its robustness.

The experimental setup. The quadruped is placed on a testbed that allows rotation on a single axis, which is parallel to gravity to minimize its effect on the torso's rotation.

Roll experimental results.

Yaw experimental results.

Collision geometry convexification process

Convexification process of collision geometry to achieve accurate and efficient collision handling.

Experiments

In the first set of experiments, the controller is tasked to track 90 degree rotations in roll and yaw.

In this set of experiments, the controller is tasked to track changing orientation references. In the final maneuver, it continues to turn in the positive direction to minimize the distance metric. The plot references for these maneuvers are shifted (+360 degrees) to showcase the controller convergence.