Quadrotors suspended water containers may be used for fire-fighting services. Unfortunately, the complicated dynamics in this type of system degrade the flight safety because of coupling effects among the quadrotor attitude, container swing, and liquid sloshing. However, few effects have been directed at the attitude-pendulum-sloshing dynamics in this type of aerial cranes. A novel planar model of a quadrotor carrying a liquid tank under dual-hoist mechanisms is presented. The model includes vehicle-attitude dynamics, load-swing dynamics, and fluid-sloshing dynamics. Resulting from the model, a new method is proposed to control coupled oscillations among the vehicle attitude, load swing, and fluid sloshing. Numerous simulations on the nonlinear model demonstrate that the control method can reduce the undesirable oscillations, stabilize the quadrotor’s attitude, and reject the external disturbances. The theoretical findings may also extend to the three-dimensional dynamics of quadrotors slung liquid tanks, and other types of aerial vehicles transporting liquid containers including helicopters or tiltrotors.
The dual-quadrotors slung system may be utilized in the handling service of heavy and bulky loads. However, the coupled oscillations between the quadrotor attitudes and suspended load exhibit complicated dynamic behaviors, which degrade the safety and efficiency of the transport system. Although many works have been focused on the multiple quadrotors suspending a load, those prior studies did not consider the coupling effects between the quadrotor attitudes and the cable pendulum. This paper established a nonlinear dynamic model of dual-quadrotors carrying a slender beam undergoing planar motions, which described the coupled attitude-pendulum oscillations. Then a frequency estimator was resulted from the system parameters for investigating the dynamics. In addition, a novel combined modified model-following control and discontinuous piecewise smoother was proposed to suppress oscillations. The technical results in the simulations not only describe the dynamic behavior of the analytical model but also validate the effectiveness of the control method.
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