Fast Motion Performance of a Bionic Ray Robot With Serial Pectoral Fins

Rays have shown superior ocean swimming performance, but the underwater robots that use rays as bionic objects still need to be improved in terms of forward speed. In this letter, we observe and investigate the structure and motion characteristics of rays, and design a bionic ray robot driven by two pairs of serial pectoral fins. In Addition, theoretical analysis of the deformation of the pectoral fin motion is conducted, and fluid simulation and experimentation studies are used to examine the forward propulsion capabilities of the anterior and posterior fins under various phase differences. The enhanced propulsion performance of the posterior fin is explained from the perspective of fluid vortices, which are related to the jet direction and position of the front fin vortices. The results show that the phase difference has a significant impact on the forward speed of the robot. The maximum forward speed of the robot fish is up to 1.2 m/s at 30° phase difference, i.e., 2.86 body length per second (BL/s), which is ahead of the existing robots of the same type.