fish

 

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Micro Fish -- A semi-autonomous robotic catfish

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Front view of Micro Fish showing the drive motor assembly and whiskers

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Rear view  showing the tail flapper assembly

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Bottom view  of Micro Fish

Meet Micro Fish. This was another one of our animal automatons. Micro Fish was designed to emulate the appearance and behavior of a catfish. This model uses parts from the Lego Robotic Inventions set and one touch sensor from another kit.

Two motors were used in the assembly of this robot. One motor provided drive to the propulsion assembly and the other was used in conjunction with a cam to flap the tail of the fish in a back and forth motion. The front wheels are jointly driven by the front motor while the rear wheels are mounted on a straight axle and serve only to balance the model properly.

The body of the model consisted of structural members joined together and attached to the RCX brick. The fin assemblies consisted of flat triangular pieces attached to the structural members and reinforced with smaller flat pieces.

The sensor assembly had two touch sensors sandwiched in between small flat pieces. The two touch sensors are attached to the same input port at the RCX brick. A third touch sensor is located on the top fin. This sensor is used to signal the RCX brick to start the program. Once the program starts, this sensor becomes a "survival sensor" -- when touched, the fish thinks it is about to be eaten and quickly attempts to swim away.

Various pieces of flexible tubing were used to fabricate the head portion of the fish. These tubing pieces also provided support for the eye assemblies and were attached at each end directly to the structural members.

Programming was a little more difficult than some other designs we have tried. We determined that the power for the tail flapper motor needed to be reduced due to vibration caused by the large radius of the tail motion. A routine was added to have the fish start and stop swimming at random intervals to emulate the actions of a real fish. Another routine causes the fish to reverse when it encounters and obstacle with the whiskers. We also added a survival routine that caused the fish to charge forward for a random period when it "felt" a touch on the rear fin.

The only limitation for this robot was that it could not be fully autonomous since it was not able to turn, but merely move in straight lines. In a future model, we may give a similar design more freedom of motion but for this design we tried to use parts only from one set. We also considered adding the light sensor and have the fish search the bottom for food, but we liked the way it looked as shown, so we left it this way.

We did not test this model in water, and recommend that you don't either!