Design of fishtail structure based on oscillating mechanisms using PVC gel actuators

Bionic robot fish, as a kind of underwater robots, has already demonstrated great potential in the ocean. Developing soft actuators for the bionic robot fish has become a key issue. This paper proposed a novel robot fishtail consisting of oscillating mechanisms and the stacked soft polyvinyl chloride (PVC) gel actuators. Based on the fish body wave curve used to control the kinematics of fish swimming, a bionic fishtail skeleton with six joints was developed. A stacked PVC gel actuator was fabricated and its mechanical properties and frequency response characteristics were analyzed. On this basis, a fishtail prototype was fabricated, assembled and tested, which showed good agreement with the theoretical prediction. In addition, mechanical properties and frequency response characteristics of the prototype were also studied. The results showed that the swing amplitude of the fishtail could generate a peak value at about 1.5 Hz (2 Hz on land) due to the resonance effect, which was conducive to the swing of the bionic robot fish. And the underwater tests have demonstrated that the fishtail structure can still generate propulsion and move in the water. The conclusion can provide guidance for the design of bionic robot fish in practical application.