Bidirectional Manipulation of a Buoy With a Tethered Quadrotor UAV

Offshore Unmanned aerial vehicles (UAVs) are finding new applications. In this work, we upgrade the control system of an original robotic system consisting of a marine locomotive quadrotor UAV that manipulates the velocity of a floating buoy by means of a cable. The proposed upgrade is a step toward a real-life implementation of the robotic system and allows it to maintain stability when the tether is slack. The contribution of this work includes defining the full spectrum of the UAV-buoy system's operational modes, design a polar UAV-buoy relative position controller, and a state-machine that allows the smooth manipulation of the buoy in different directions and even to stop the manipulation of the buoy. This results in a full controller of the system in all of its operating modes, as demonstrated via numerical simulations in wave-free and wavy seas.