Implementation and demonstration of coordinated transport of a slung load by a team of rotorcraft

A scalable, hierarchical approach to coordinated transport of a slung load by a team of small autonomous rotorcraft is described, implemented and demonstrated. A payload trajectory-following controller computes the net force and moment that must be exerted on the payload center of gravity; a cable force calculator computes the force and direction of each cable to satisfy both the net force/moment requirement and formation constraints; a controller onboard each rotorcraft ensures that the required cable tension and direction are flown. All components of this algorithm are hosted on single board computers carried on the payload and individual rotorcraft. Flight demonstrations conducted in an indoor motion capture studio for both straight line path and octagon path mission. Flight tests showed stable hover, vertical and lateral translation, and rotational motion of the payload. Disturbance rejection test showed system can recover quickly under external disturbance. A human can be brought into the loop at several level. Flight demonstration showed the human operator can fly the payload like flying a normal quadrotor. The whole multi-lift system has the ability to fly both at continuously changing cone angle and under different fixed cone angles. Flight tests demonstrated the payload becomes more controllable as the cable force spreading outward.