Cooperative-transportation dynamics and oscillation control of two helicopters transporting a rigid load

The twin helicopter slung system can be effectively utilized for handling rigid loads. Nevertheless, the intense oscillations caused by the coupling dynamics of two helicopters, cables, and slung loads complicate the transportation system, reduce transportation efficiency, and bring pilot challenges. While considerable research has been conducted on twin or multiple helicopters suspending a load, fewer studies have addressed the coupling characteristics among multi-helicopter attitudes, multi-cable swing, and cable-suspended loads pitch. This paper established an analytical dynamic model of twin helicopters carrying a rigid load in the horizontal position undergoing planar motions. The model accurately describes the effects of load size on the dynamics of horizontal lifting motions and the differences in the coupled oscillations between the two helicopters and two cables. Additionally, a hybrid control architecture, integrating a dual-feedback model-tracking controller with two cascaded discontinuous piecewise smoothers, was designed to simultaneously reject external disturbances and minimize oscillations. The simulation results verified the dynamics of transportation system, and quantitatively prove the effectiveness of the proposed controller in comparison to a prior controller.