Cooperative Transportation of a Cable-Suspended Load: Dynamics and Control

The cooperative transportation of a cable-suspended load by two rotorcraft is analyzed. First, the equations describing a system made of three point masses and two rigid cables are obtained. Then, the model is linearized about the hovering condition and analytical expressions are derived to describe the eigenstructure of the open-loop system. Based on the particular problem parametrization, the different dynamic modes are discussed with special focus on payload swing. A controller is proposed that allows the agents in the formation to simultaneously perform trajectory-tracking, formation geometry keeping, and payload swing stabilization. Although closed-loop stability is preliminary investigated in a linear framework, validation of the approach is performed in a realistic simulation scenario where two multirotors are modeled as rigid bodies under the effect of external disturbances and rotor-generated forces and moments, as obtained by Blade Element Theory. The proposed method has the merit of relative simplicity and is shown to significantly improve vehicle flying qualities of future delivery operations, while minimizing hazardous payload oscillations and reducing energy demand.