Koichi Hirata and Syusuke Kawai, November 9, 2001

We try to develop a high-performance and multi-purpose-used fish robot. The high-performance fish robot means a good swimmer like a real fish. To get the high-performance, we adopt the simple and unique mechanism for tail movement. The multi-purpose-used fish robot means that it can do various missions in the sea. So, we try to develop the unit-type fish robot, which consists of several components like a power unit and a control system unit.

Merits of the Unit-type Fish Robot (1) The fish robot can do various missions by changing of units. (2) We can select a power source, a control system and others regarding to some applications. (3) The optimum design of each unit may be easy. (4) Because each unit is small size, it is easy to stop water leakage. (5) It is very easy to build every parts. Then, a large-size fish robot can be developed in a general work shop.

The fish robot named UPF-2001 aims to get high-performance and multi-purpose-used. It has about 1 m of body length. The belows figure shows the basic structure of the UPF-2001. It consits of a power unit including a D/C motor, gears and reciprocating motion mechanism, a battery unit, a R/C unit including a receiver and an amplifier for the motor, a control unit for turning and up-down motion, and a tail unit with the unique mechanism.

Power Unit
The figure to the right shows a structure of the power unit. The rotating motion of the D/C motor is reduced to about 1/40 by six gears. The motion is changed to reciprocating motion by a Scotch-yoke mechanism. A slide-bearing is used as the seal device of the reciprocating rod. Linear guides are set to the both sides of the seal, so surplus force is not worked to the seal.

Drive Unit
The unique mechanism shown in the figure to the right realizes smooth motion of the tail fin from one reciprocating shaft of the power unit. As the characteristics of the mechanism, it has a clearance at Joint 1 and a special rod between Joint 1 and 2.

Control Unit
Two R/C servomotors are located in the cintrol unit. One moves the fins for up-down motion. Another moves a rudder for turning motion.

The figure to the right shows the measured result of the swiming speed. When the UPF-2001 swims on the water surface, the body exposes about 20 mm from the water surface, the swiming speed increases with increasing of the frequency.

When the UPF-2001 swims in water, the maximam speed is 0.97 m/s. It is very higher than that of previous our fish robots. We think that the UPF-2001 can get more higher speed after adjustment of the size and shape of the tail fin.