Tuesday, July 24, 2007

PBR Motor Controller

{PBR = Phidget>Battery>Relay }

I made an enclosure for the Phidgets and the relays. I got the metal box from an old power supply I had lying around. I also added some switches to switch the main battery and the relay circuit on or off. This box allows me to save space on the robot. If you look in the pictures before; the
battery,relays, and phidgets were just spread out everywhere, with wires making a big mess. This box is much nicer and smaller. I can't wait to try out the box with my wheelchair motors( they should arrive in the near future...) The wires for the motors are hidden in this picture, but they come out from the back of the box.

Circuit is as follows: Each motor is connected to two DPDT relays, giving a total of four DPDT relays. The relays are powered by four AA batteries and are switched on by the Phidgets Interface. Each relay is DPDT, meaning there are two poles to be switched. SO whenever a relay is triggered it is switching BOTH positive and negative current to the motor. The reason for this is due to the fact that if a motor were to be wired with two switches meant to turn the motor in two directions( each switch controls a motor movement) instead of four switches to control motor direction, a short circuit will result ,killing the battery and potentially producing an electrical fire.

The battery, Phidgets Interface, and relays are all stored in an aluminum box. The enclosure is from a power supply and is all metal. In order for the relays and Phidgets Interface not to short circuit upon touching the metal, a thin plastic film was glued onto the surface. Two switches were placed in the front of the enclosure. The bottom black switch is responsible for switching the main battery that runs the motors. The red switch above it is responsible for switching the battery that powers the relays.

Here is the schematic of the relay to motor interface.

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