A novel butterfly-inspired underwater microrobot with pectoral fins

This paper proposed a new biomimetic underwater microrobot using shape memory actuator (SMA). It moved like a jellyfish while floating and sinking, and had two pectoral fins to implement the swimming motion like a butterfly. To achieve a larger volume change, we designed the body as a triangular prism. Then we modelled the characteristics of the body and calculated its floating speed. Also, we used two pectoral fins to push water in horizontal direction and analysed its swimming motion. We measured the response time of shape memory alloy (SMA) actuator with different driving voltages and calculated its theoretical swimming speed. Finally, we developed a prototype hybrid biomimetic microrobot and evaluated the floating and swimming speeds experimentally. In the floating and swimming experiments, the experimental values fitted the theoretical values very well. And, the experimental results showed that the microrobot had better performance in floating than the previous two-ring ones. Its maximal floating speed reached 10.2 mm/s, and its maximal swimming speed achieved 57.2 mm/s at 24 V, frequency of 0.4 Hz, a duty of 65%. In addition, it had better flexibility, balance and load ability than its predecessors.