A String of Tethered Drones - System Dynamics and Control

In this paper we present a novel concept of a tethered-drones system. The system includes an arbitrary number of drones connected serially to an active ground station. The considered drones are of quadrotor type. Utilizing a unique pulley-gimbal mechanism, each drone can freely move along the tether and its position is measured with respect to the ground station without the use of standard onboard inertial sensors. The proposed system can be thought of as a robotic arm where each tether section acts as a variable-length link and each drone is a joint actuator. We model the coupled behavior of the ground station and the string, taking into account an arbitrary number of drones. Then, a controller that combines tools from geometric-control and linear-control is suggested. Finally, the concept is demonstrated using numerical simulations, which also illustrate its potential effectiveness.