Actuation

MIC

The fish is actuated using magnet-in-coil (MIC) actuators. By fixing the coil and alternating the direction of current through it, its magnetic field flips. A magnet, placed in the center of the coil, will try to align its permanent magnetic field with that of the coil's, making the magnet rotate. The appeal of the MIC for actuation, as opposed to servos, piezo-electric, or shape-memory alloys, is its cheap cost and simplicity. The MIC configuration can also be immersed in water and you need to only waterproof the connection between the coil (two thin wires) and the controller.

Propulsor

The coil is held fixed inside of a propulsor case. To harness the rotation of the magnet, it is glued inside of a hinge. The hinge can only rotate with the magnet. Two posts inside of the propulsor prevent side to side movement and rotation. Two tiny plugs that are glued to each post stop the hinge from moving up and down.

H-Bridge

To alternate the current passing through the coil, an H-bridge is used (circuit schematic below). If the left high side and right low side switches are the only closed switches, the current will flow from left to right across the coil or motor. If the right high side and the left low side switches are the only closed switches, the current flows in the opposite way, right to left, across the coil. By controlling which pair of switches is closed, you can create an alternating current across the coil and control its magnetic field direction.

We are using the SN754410 Quadruple Half-H Driver, an IC that can independently control two H-bridges (it has 4 half bridges which control current in only one direction). A simple program on an Arduino Pro-Mini board controls the opening and closing of the proper switches and the timing of the alteration. A 3.7V 400mAh Li-Po battery powers the board.

TAKE VIDEO OF JUST THE PROPULSOR MOVING, NO RUBBER BANDS. ADD CIRCUIT DIAGRAM + PHOTO OF FULL CIRCUIT