Path and trajectory planning of a tethered UAV-UGV marsupial robotic system

TL;DR

This paper introduces a novel trajectory planning method for a marsupial robotic system comprising a UAV and UGV connected by a non-taut tether, ensuring collision-free, smooth, and feasible paths in complex environments.

Contribution

It presents the first trajectory planning approach for a non-taut tethered UAV-UGV system, combining optimal RRT* path planning with non-linear least squares trajectory optimization.

Findings

Successfully generates collision-free paths considering 3D environment and tether constraints.

Produces obstacle-free, smooth, and feasible trajectories validated through simulations and field tests.

Enhances planning speed with novel sampling and steering techniques in RRT*.

Abstract

This letter addresses the problem of trajectory planning in a marsupial robotic system consisting of an unmanned aerial vehicle (UAV) linked to an unmanned ground vehicle (UGV) through a non-taut tether with controllable length. To the best of our knowledge, this is the first method that addresses the trajectory planning of a marsupial UGV-UAV with a non-taut tether. The objective is to determine a synchronized collision-free trajectory for the three marsupial system agents: UAV, UGV, and tether. First, we present a path planning solution based on optimal Rapidly-exploring Random Trees (RRT*) with novel sampling and steering techniques to speed-up the computation. This algorithm is able to obtain collision-free paths for the UAV and the UGV, taking into account the 3D environment and the tether. Then, the letter presents a trajectory planner based on non-linear least squares. The optimizer takes into account aspects not considered in the path planning, like temporal constraints of the motion imposed by limits on the velocities and accelerations of the robots, or raising the tether's clearance. Simulated and field test results demonstrate that the approach generates obstacle-free, smooth, and feasible trajectories for the marsupial system.