Fansler, David [DFANSLER@AUTOCYTE.COM] wrote:

After reviewing the circuit mounted to the motor, I did find an error - so
here is the revised schematic.

                      Red
                       |
            27 ohm     |     .3 ohm power resistor
Yel -----/\/\/\/\/\----|----/\/\/\/\/\/--|
      |                                  |
      |      220 ohm                     |
      |----/\/\/\/\/\/----|---Motor------|
                          |              |
                          |              |
                          |              |
                        Blue           Green

Just in case the ASCII art gets distorted,  there is a yellow wire that
feeds a 27 ohm and a 220 ohm resistor.
The other end of the 27 ohm goes to a red wire and a .3 ohm power resistor.
The other end of the 220 resistor goes
to one terminal of the motor, and to a Blue wire.  The
other end of the .3 ohm power resistor goes to the 2nd terminal of the
motor and a Green wire.

This is more than likely a protection scheme to limit the current to the motor.  The 27R and 220R resistor provide a reference to the control circuitry.  By placing these devices in close proximity to the motor, any voltage drops in supply cables are ignored.  The current limit will probably become active when the voltage drop across the 0.3R resistor exceeds that accross the 27R resistor.

I=(V*(27/247))/0.3  where V is the supply voltage.

Your original post asked if this was some kind of feedback circuit.  Well it is in a sense, but it dosen't feedback positional information, only current draw

Cheers

Mike.