Underwater rotorcraft vehicle with a passively adjustable configuration based on a U-joint

This paper proposes a novel underwater rotorcraft vehicle with a passively adjustable configuration based on a universal joint (URV-PAU), which addresses the issue of increased propeller load and control stability caused by the rigid structure of existing vehicles when tilted. Compared with designs that do not incorporate a U-joint structure, this vehicle can reduce energy consumption and enhance system manoeuvrability. First, a kinematic and dynamic model of the URV-PAU is established based on its configuration. Considering the nonlinearity of the system, the modelling errors of the dynamic model, and external disturbances, an adaptive backstepping sliding mode controller(ABSSMC) is designed to achieve motion control in proximity to the seabed. A prototype of the underwater rotorcraft vehicle was constructed according to the principles of modular design. Subsequently, underwater trajectory experiments were carried out within a water tank. The experiments demonstrated that the URV-PAU results in a reduction of approximately 10 % in system energy consumption and an improvement in system manoeuvrability compared with designs without a U-joint structure during motion at a constant depth.