Stable, quiet, and efficient propulsion methods are essential for underwater robots to complete their tasks in a complex marine environment. However, with a single propulsion method, such as propeller propulsion and bionic propulsion, it is difficult to achieve high efficiency and high mobility at the same time. Based on the advantages of the high-efficiency propulsion of a bionic undulating fin and the stable control of the propeller, an underwater robot based on the hybrid propulsion of a quadrotor and undulating fin is proposed in this paper. This paper first introduces the mechanical implementation of the underwater robot. Then, based on kinematic modeling and theoretical derivation, the underwater motion and attitude of the robot are analyzed and the 6-DOF dynamic equation of the robot is established. Finally, the underwater motion performance of the robot is verified through field experiments. The experimental results show that the robot can realize the heave motion, surge motion, and in-situ steering motion independently and can hover stably. When the undulating frequency is 6 Hz, the maximum propulsion speed of the robot can reach up to 1.2 m/s (1.5 BL/s).

In this paper, an amphibious robot with flexible undulating fins and self-adaptive climbing wheels are proposed for satisfying the needs of industrial applications. The structure of the climbing mechanism and undulating fin are firstly designed. Then, the adaptive obstacle climbing and the hydrodynamic characteristics are investigated through numerical simulations by using the Adams and Fluent, respectively. Finally, the experimental measurements of the land walking and underwater propulsion are studied. The numerical results illustrate that the amphibious robot could climb the vertical obstacle adaptively. In the underwater marching pattern, the underwater velocity could reach 1 m/s. In the rotating and yawing patterns, the angular velocity increases to the certain value while the rotating angle keeps increasing. The robot moves forward and turns around with the difference frequency of the undulating fins. The underwater propulsion and land-walking experiments show good swimming performance and the obstacle crossing ability of the amphibious robot, respectively, which verify the numerical simulation.

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The tilting trirotal UAV is a new type of aircraft that combines the characteristics of fixed-wing UAVS and multi-rotor UAVS. To study and solve the control problems of tilting rotor UAVs, This paper focuses on the mechanical analysis of the rotor mode, and establishes the mathematical model. Simulation of rotor flight mode in MATLAB/SIMULINK environment, provides strategies for the design of tilting rotor UAV control systems.