Leader-follower formation control of two quadrotor UAVs

This paper reports the design and implementation of a leader-follower (L-F) formation control of two Parrot AR Drone 2.0 quadrotor UAVs (drones). In order to implement such control, three control elements were developed. These were the flight-dynamic characteristics, the position tracking and L-F formation control, and the data communication system between drones and ground-control station. The dynamic characteristics were identified as the first-order process with time delay models, which were asymmetrical to x(-), x(+), x(-) and x(+) directions. Accordingly, dedicated Proportional-Derivative (PD) controllers were designed for the respective models. A Pole-Placement strategy was applied to design the PD controllers in order to achieve a non-oscillatory position tracking. These controllers were combined with five operating modes to form an F-L formation control. The controls were implemented on two-drones and one-ground-control station. The ground-control station dictated a prescribed path for the leader drone. Subsequently, the leader position became follower set-point. During the implementation test, these drones completed their L-F formation. The follower drone tracked the y-axis coordinate of the leader's drone and maintained a safe distance to the respective x-axis coordinate. The accuracy of the controls was measured in terms of the root mean squares errors, and these were within 50-115 cm.