Cooperative Transportation of UAVs Without Inter-UAV Communication

In this article, a leader–follower system is developed for cooperative transportation. To the best of our knowledge, this is the first work in which interunmanned aerial vehicle communication is not required and the reference trajectory of the payload can be modified in real time, so that it can be applied to a dynamically changing environment. To track the modified reference trajectory in real time under the communication-free condition, the leader–follower system is considered as a nonholonomic system in which a controller is developed for the leader to achieve an asymptotic tracking of the payload. To eliminate the need to install force sensors, unscented Kalman filters (UKFs) are developed to estimate the forces applied by the leader and the follower. Stability analysis is conducted to prove that the tracking error of the closed-loop system is asymptotically stable; however, the dynamics of the UKF estimators is not considered in the closed-loop system, which is assumed to be a deterministic system for the controller. The experiments show that the controllers of the leader and the follower can work in the real world, but the tracking errors are affected by the disturbance of airflow in a restricted space.