Hybrid Dynamics Modeling and Trajectory Planning for a Cable-Trailer System with a Quadruped Robot

Introduction

Inspired by the utilization of dogs in sled-pulling for transportation, we introduce a cable-trailer system with a quadruped robot. The motion planning of the proposed robot system presents challenges arising from the nonholonomic constraints of the trailer, system underactuation, and hybrid interaction through the cable. To tackle these challenges, we develop a hybrid dynamics model that accounts for the cable’s taut/slack status. Since it is computationally intense to directly optimize the trajectory, we first propose a search algorithm to compute a sub-optimal trajectory as the initial solution. Then, a novel collision avoidance constraint based on the geometric shapes of objects is proposed to formulate the trajectory optimization problem for the hybrid system. The proposed trajectory planning method is implemented on a Unitree A1 quadruped robot with a customized cable-trailer and validated through experiments.

A preprint of the paper is available at arXiv

Motivation

Method

Experiment

We validate our planning method through numerical simulation and conduct real-world experiments in various scenarios to demonstrate its effectiveness. The trajectory optimization problem is formulated using CasADi, with IPOPT serving as the solver.

Experiment result: tractor average speed ≈1m/s, trailer position error <10cm, and trailer yaw angle error <5.25° (calculated by motion capture system)