Effects of a Biomimicked Flapping Path on Propulsion Efficiency of Twosegmental Fish Robots Having an appropriate flapping path to yield efficient propulsion is an interesting issue in fish robotics. In most works, especially twosegmental structures, the flapping motion is limited to sinusoidal functions. In this paper, to cope with the aforementioned limitation, a conceptual nonsinusoidal path is proposed. The proposed flapping path and the conventional one, both are optimized for a sample fish robot. According to some simulation results, it is shown that if a proper actuator is employed to generate both optimized paths, the proposed approach yields more propulsion efficiency. Furthermore, it is discussed that our method can better imitate fish muscle output power. Finally, through experiments, some practical issues are considered.

Design of a Robotic Fish Based on a Passive Flexible Mechanism In recent years, along with the rapid development of manufacturing, control, sensing and other technologies, biomimetic robotic fish has played an increasingly important role in marine exploration, underwater rescue, water quality monitoring and other fields. This paper designed a robotic fish based on a passive flexible mechanism to realize the fishlike propulsion function. The motion simulation of the designed transmission mechanism was carried out to get the actual curve of the structure. Through the analysis of the force of the fishtail, the preliminary selection scheme of the elastic joints based on the passive flexible mechanism was obtained. Finally, this paper built a robotic fish based on a passive flexible mechanism, which could achieve the motion frequency adjustable from 0.5 to 9 Hz, and the maximum swimming speed reaching 1.05 BLs (BL, body length). This design scheme provided a new reference for the design of the biomimetic robotic fish and had certain practical significance.