Servo - March 2016

insert the electronics. In the past, I have tried using a six inch coupling with one end threaded and then using a six inch threaded plug. Even with the use of Teflon tape around the threads, there was still some leakage. These large threads were made to have pipe-joint compound for a tight seal, which does not work well for ease of removal. Instead, I used a six inch black rubber cap sealed with a metal hose clamp; this has worked very well. The entire six inch tube is held in place underneath two 1/2 inch PVC cross pieces at the top by two eight inch band clamps.

The top of the main tube has a 1/2 piece of Plexiglas vertically glued with marine epoxy for attachment of the up/down motor, and two 1/2 inch PVC threaded couplings also glued in with marine epoxy to receive the PVC plugs containing the wires feeding into the tube.

A Hall-effect switch was added with a third 1/2 inch PVC threaded coupling glued into the main tube. A Hall-effect switch and LED are potted into the coupling with marine epoxy. A 1/2 inch PVC plug with a Neodymium disk magnet cemented into it acts as the switch. When the plug is screwed into the coupling, it triggers a 12 volt 20 amp relay inside the main tube, activating the 12 volt circuitry. The relay contacts are wired in parallel with the main power switch. This allows power to be turned on and off without having to open the main tube. This circuit continuously draws about eight milliamps of current from the battery, which is not a problem for a 15 amp-hour battery.

That’s all for this installment. In the next issue, we will cover the electronics package that reads the joystick and linear potentiometer, and then controls our motors. SV

SERVO 03.2016 41

Item Description A1 Adafruit 9-DOF (Optional)

B1 12V 15AH B2 9V Battery BTS7960B Motor Driver ( 3)

C1 1,000 µF, 16V C2 2,700 µF, 6.3V D1 Blue LED F1 18A Mini Circuit Breaker or Fuse FL Flood Lamp (Optional)

H1 Hall-effect Switch 3144

J1 Three-pin Header J2 Three-pin Header J3 Three-pin Header J4 Four-pin Header M1 Left Motor, Johnson Pump 500 GPH M2 Right Motor, Johnson Pump 500 GPH M3 Up/Down Motor, Johnson Pump 500 GPH P1 Header Socket P2 Header Socket Q1 TIP127 PNP Darlington Transistor R1 8.2K 1/4W Resistor R2 4.7K 1/4W Resistor R3 1K 1/4W Resistor R4 1K 1/4W Resistor R5 5K 1/4W Resistor R6 5K 1/4W Resistor R7 20K 1/4W Linear Potentiometer R8 4.7K 1/4W Resistor R9 8.2K 1/4W Resistor R10 4.7K 1/4W Resistor Relay 12V 20A Contacts Switch 20A Contacts Switch Mini Toggle U1 Arduino Nano U2 Arduino Nano U3 LM7805 5V Regulator Video Camera, NTSC Miscellaneous

1/2 inch PVC Pipe

1/2 inch PVC Elbows

1/2 inch PVC Tees

1/2 inch PVC Threaded Couplings

1/2 inch PVC Threaded Plugs Six inch PVC Pipe Six inch PVC Pipe Cap Six inch Rubber End Cap, with Band Clamp 1/4 and 1/2 inch Plexiglas PVC Cement Marine Epoxy Silicon Cement Eight inch Band Clamps Nylon Cable Ties Various Screws, Nuts Hookup Wire Cat5 Cable, 50 feet Petcock Valves ( 2) Ceramic Tile

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