Observer-based Distributed MPC for Collaborative Quadrotor-Quadruped Manipulation of a Cable-Towed Load

This paper presents a collaborative quadrotor-quadruped robot system for the manipulation of a cable-towed payload. In particular, we aim to solve the challenge from the unknown dynamics of the cable-towed payload. To this end, we first propose novel dynamic models for both the quadrotor and the quadruped robot, taking into account the nonlinear robot dynamics and the uncertainties associated with the cable-towed load. Moreover, we design observers for the hybrid interaction between the robots and the payload. Theoretically, the convergence of these observers is analyzed using Lyapunov functions under mild technical assumptions. Finally, we seamlessly integrate the dynamics models and the observers into a distributed Model Predictive Control (MPC) framework with kinematics limitations and collision avoidance constraints. The proposed system is validated through challenging field experiments in indoor and outdoor environments, involving push disturbances, varying and unknown payloads, uneven terrains, etc.