A novel jellyfish-and butterfly-inspired underwater microrobot with pectoral fins

In this paper, we introduce a new biomimetic underwater microrobot with a shape memory alloy (SMA). It moves like a jellyfish while floating or sinking and has two pectoral fins to implement a swimming motion like that of a butterfly. To achieve a larger volume change, the body was designed as a triangular prism. We then modelled the characteristics of the body and calculated its floating speed. Moreover, we used two pectoral fins to push water horizontally and analysed the resulting swimming motion. We measured the response time of the SMA actuator with different driving voltages and calculated its theoretical swimming speed. Finally, we developed a prototype hybrid biomimetic microrobot and evaluated floating and swimming speeds experimentally. The values obtained from the floating and swimming experiments were in close agreement with the theoretical values. Also, the experimental floating performance of the new microrobot was better than that of the earlier two-ring units. Its floating speed reached a maximum of 10.2 mm/s, and it attained a maximum swimming speed of 57.2 mm/s at 24 V, a frequency of 0.4 Hz, and a duty cycle of 35%. Additionally, it exhibited better flexibility, balance, and load capacity than its predecessors.