An improved multimodal robotic fish modelled after Esox lucíus

This paper focuses on a further exploration of multimodal locomotion governed by bio-inspired central pattern generators (CPGs). To pursue a better swimming performance, an updated robotic fish is constructed. Besides the improved hardware devices involving higher torque servomotors and powerful processors, some innovative mechanical designs are taken into consideration. Specifically, a well-streamlined shape like Esox lucius and a yawing head joint contribute to reduce hydrodynamic drag and strengthen turning ability. A pair of flexible pectoral fins with four degrees of freedom is to enhance the capability of three-dimensional locomotion and to enrich multiple swimming motions. Further discussion on how characteristic parameters in CPGs including frequency, amplitude, and phase relationship impact the swimming performance is also presented. Finally, the robotic fish successfully gains more powerful capability of multimodal locomotion containing forward swimming, backward swimming, turning, diving, and ascending. The experimental results validate the effectiveness of mechanism design and adaptability of multimodal locomotion governed by CPGs.