Design and hydrodynamic experiments on robotic fish with oscillation pectoral fins

A robotic fish propelled by a pair of pectoral fin with oscillation motion was proposed, and experiments were carried out to study the hydrodynamic characteristic. Based on the analysis of motion feature and skeletal structure of pectoral fin of cownose ray, a kind of robotic cownose ray actuated by two DC servo-motors is implemented. A measurement device is designed to test the thrust force and efficiency in the low-speed water tunnel, and the relationship of thrust coefficient and efficiency varying with Sr(Strouhal number) was obtained. Both the maximum thrust coefficient and the maximum efficiency are achieved at the same Sr of 0.4, which is in good agreement with the Sr range of swimming or flying animals' propulsion at high efficiency. Finally, an experiment of free swimming was conducted in a swimming pool, and it demonstrated that the maximum speed of 0.64 m/s (1.5 times body-length) was achieved, which was faster than that of other ray-like' robotic fishes. The results indicate that the design method is effective for building a robotic fish propelled by pectoral fins with fast speed, which is meaningful to implement a kind of UUV(unmanned underwater vehicle) by employing the propulsion mode of cownose ray.