Design and implementation of a robotic fish based on revolute wingtips

Pectoral fin motion discipline of the cownose ray as a nature prototype is analyzed. According to the analysis results, a bionic pectoral fin with multiple fin rays and one revolute wingtip is designed. The angle of attack distribution principle of the bionic pectoral fin is also analyzed. The analysis results show that the angle of attack of pectoral fin reaches its maximum at the wingtip. In order to improve the deformation ability of the tip of rigid fin ray, a novel revolute joint is designed and applied to the bionic pectoral fin. The simulation results show that the maximum angle of attack of the revolute wingtip can reach about 35°. The relationship between the pitching angle of fin tip and the average thrust/lift generated by pectoral fins is analyzed. In the thrust/lift experiments, with the help of the revolute joint, the maximal average thrust of 3.3N is achieved and the maximal absolute value of average lift is less than 2N. In the swimming experiments, a maximum forward speed of 0.7BL/s (body length/s) is reached. Under the same motion parameters, the maximum speed decreases to 0.35BL/s when the revolute joint is locked.