Motion mechanism and thrust characteristics of amphibious robots with long fin fluctuation for propulsion on hard level ground

This paper presents the principle of motion, mechanical modeling and key characteristics of the propulsive force of a new flexible-fin traveling wave propulsion mechanism used in an amphibious robot. Firstly, the form of motion and the basic propulsion principle of traveling wave propulsion of flexible fins on the ground are described. During fluctuation of the flexible fins, the relative motion between the outermost contact line on the fin surface and the ground generates the propulsive force of forward motion and the lateral force along the fin surface. Based on the laws of flexible-fin fluctuation kinematics and the basic principles of friction mechanics, the propulsion mechanics model of flexible fins during traveling wave propulsion on the ground is established. By numerically solving the propulsive force equation, the relationship between the propulsive force of the flexible fin and the motion parameters of the fin surface can be obtained. Numerical calculations combined with the results of experimental tests reveal that the flexible-fin propulsive force shows periodic variations within one fluctuation period of the fin surface, and the variation period is related to the number of waves present on the fin surface. The wavenumber on the fin surface has a large impact on the fluctuation amplitude of the propulsive force. In the range of 1.6-1.9 waves on the fin surface, the average propulsive force is the most ideal, while in the range of fin-surface inclinations less than 50° and fluctuation amplitudes greater than 30°, the propulsive force of the flexible fin is the ideal parameter range. This research provides theoretical support for the design of a flexible-fin traveling wave propulsion mechanism.