The purpose of this study is improvement of a fish robot actuated by four light-weight piezocomposite actuators
(LIPCAs). In the fish robot, we developed a new actuation mechanism working without any gear and thus the actuation
mechanism was simple in fabrication. By using the new actuation mechanism, cross section of the fish robot became 30%
smaller than that of the previous model. Performance tests of the fish robot in water were carried out to measure tail-beat
angle, thrust force, swimming speed and turning radius for tail-beat frequencies from 1Hz to 5Hz. The maximum swimming
speed of the fish robot was 7.7 cm/s at 3.9Hz tail-beat frequency. Turning experiment showed that swimming direction
of the fish robot could be controlled with 0.41 m turning radius by controlling tail-beat angle.