Avoiding obstacles in cooperative load transportation.

This work deals with load transportation by quadrotors, when the load is attached to the vehicles through flexible cables. More specifically, two quadrotors are used to carry a single load, which is attached to both vehicles, through such kind of cables. The idea of using two quadrotors working cooperatively to carry the load is adopted to suppress any load oscillation in the direction of movement, what would happen if just one UAV were used. As a consequence of using two UAVs (or more than two) it can happen collisions between the vehicles when carrying the load, caused by the forces the load exert on the two vehicles, whose tendency is to bring the vehicles closer one to the other when they accelerate forward. The paper proposes a strategy to avoid such collisions and any collision with obstacles eventually present in the working space as well. Simulated results are shown and discussed, using two AR.Drone® 2.0 quadrotor to carry the load, which validate the proposed strategy.