Design and CPG-Based Locomotion Control of a Multi-Flexible Robotic Fish with Hybrid Propulsion

The paper presents a novel design and implementation of a multi-flexible robotic fish and its locomotion controller. Inspired by the swimming patterns of fish pectoral fin and tail, the robotic fish is designed with two symmetrical pectoral fins and a fishtail, each driven by a single servo motor and featuring two passive flexible joints. The mechatronic design of the robotic fish is first provided. Secondly, a central pattern generator (CPG) based locomotion controller is deployed on the robotic fish to mimic fish median and/or paired fin (MPF) propulsion and body and/or caudal fin (BCF) propulsion and a hybrid propulsion is proposed. Furthermore, compared to traditional rigid pectoral fins and sine-based controllers, the CPG-based pectoral fins show better motion continuity and net thrust generation. In the end, swimming tests demonstrate that the robotic fish exhibits good compliant motion in all three modes. More importantly, compared to the traditional robotic fish with BCF propulsion, through the coordinated control of the pectoral fins and fishtail, the proposed hybrid propulsion shows the best speed performance in forward swimming and turning, and MPF provides better heading stability in turning.