  In this work, we propose a centralized control method based on nonlinear
model predictive control to let multiple UAVs manipulate the full pose of an
object via cables. At the best of the authors knowledge this is the first
method that takes into account the full nonlinear model of the load-UAV system,
and ensures all the feasibility constraints concerning the UAV maximumum and
minimum thrusts, the collision avoidance between the UAVs, cables and load, and
the tautness and maximum tension of the cables. By taking into account the
above factors, the proposed control algorithm can fully exploit the performance
of UAVs and facilitate the speed of operation. Simulations are conducted to
validate the algorithm to achieve fast and safe manipulation of the pose of a
rigid-body payload using multiple UAVs. We demonstrate that the computational
time of the proposed method is sufficiently small (<100 ms) for UAV teams
composed by up to 10 units, which makes it suitable for a huge variety of
future industrial applications, such as autonomous building construction and
heavy-load transportation.
