This paper presents an experiment and parametric study of a biomimetic fish robot actuated by the Lightweight Piezocomposite
Actuator (LIPCA). The biomimetic aspects in this work are the oscillating tail beat motion and shape of
caudal fin. Caudal fins that resemble fins of BCF (Body and Caudal Fin) mode fish were made in order to perform
parametric study concerning the effect of caudal fin characteristics on thrust production at an operating frequency range.
The observed caudal fin characteristics are the shape, stiffness, area, and aspect ratio. It is found that a high aspect ratio
caudal fin contributes to high swimming speed. The robotic fish propelled by artificial caudal fins shaped after
thunniform-fish and mackerel caudal fins, which have relatively high aspect ratio, produced swimming speed as high as
2.364 cm/s and 2.519 cm/s, respectively, for a 300 V<sub>p-p</sub> input voltage excited at 0.9 Hz. Thrust performance of the
biomimetic fish robot is examined by calculating Strouhal number, Froude number, Reynolds number, and power
This paper presents a mechanical design, fabrication and test of biomimetic fish robot using the Lightweight Piezocomposite Curved Actuator (LIPCA). We have designed a mechanism for converting actuation of the LIPCA into caudal fin movement. This linkage mechanism consists of rack-pinion system and four-bar linkage. We also have tested four types of caudal fin in order to examine effect of different shape of caudal fin on thrust generation by tail beat.
Subsequently, based on the caudal fin test, four caudal fins which resemble fish caudal fin shapes of ostraciiform, subcarangiform, carangiform and thunniform, respectively, are attached to the posterior part of the robotic fish. The swimming test using 300 V<sub>pp</sub> input with 1 Hz to 1.5 Hz frequency was conducted to investigate effect of changing tail beat frequency and shape of caudal fin on the swimming speed of the robotic fish. The maximum swimming speed was reached when the device was operated at its natural swimming frequency. At the natural swimming frequency 1 Hz,
maximum swimming speeds of 1.632 cm/s, 1.776 cm/s, 1.612 cm/s and 1.51 cm/s were reached for ostraciiform-, subcarangiform-, carangiform- and thunniform-like caudal fins, respectively. Strouhal numbers, which are a measure of thrust efficiency, were calculated in order to examine thrust performance of the present biomimetic fish robot. We also approximated the net forward force of the robotic fish using momentum conservation principle.