Control of Multiple Quad-Copters With a Cable-Suspended Payload Subject to Disturbances

In this article, a new control scheme is proposed to enable multiple quad-copters to cooperatively carry a cable-suspended payload. This cascaded controller takes into account the quad-copters underactuation and exploits the energetic passivity of the payload-cables-drones multibody system to achieve stable control. The controller is simple and requires no information about the cables tensions. A storage function inspired by the mechanical energy of the system is introduced and used to derive the control laws that achieve semiglobal exponential stability. The stability is shown to be robust with respect to bounded disturbance forces acting on the quad-copters and the payload. Additionally, a time-domain observer estimates the energy that perturbations may inject to the system and dissipates it through variable damping. This helps suppress disturbance-induced oscillations. The effectiveness of the control strategy is demonstrated in several experiments.