I have 2 DC motors with encoders on the back of them. How do I use the
encoders? The motor has 2 wires to make it spin like a normal DC
motor, but
the back end also has 6 additional wires coming out of it. What do I
do
with them? I know that encoders are supposed to be used to watch the
motor
to see how many turns it actually makes, but I don't know how.

Is there a semi-standard way to figure out how to use encoders (much
like there's a standard way to figure out how to use stepper motors
even if you don't have a spec sheet)? Or are encoders special hardware
that's always different on each motor?

I don't have a link to the spec sheet, but they're both labeled as
follows:
  MINERTIA MOTOR
  R SERIES
  P/N  R02MAKUE  UTOPI-200SE
  S/N  7W0125-1

I'm trying to make a robot, but all the stepper motors I have too
little torque to even turn the wheels on my robot. These 2 motors are
the only DC motors I have which also have encoders, so I need to use
these or buy some other ones somewhere.

I am confused that there are 6 wires coming from the encoder.  I've
found a datasheet for the motor, though.  You can try clicking on this
link:
http://www.yaskawa.com/web/download/DLCenter.nsf/7464d0d465a8d70886256bbb0065f480/0deb7409fe4603a186256c48004cd6f4/$FILE/TSE-C253-20G.pdf

If that doesn't work then goto:
http://www.yaskawa.com/website/news/frnews.htm
Click "Download Center"
Choose "Servo Products" from the "Series" listbox.
Choose "DC Servos" from the "Sub-Category" listbox.
Click Search
Click one of the Minertia R Series documents.

The datasheet lists the wires as:
   Red: +5V or +12V
 Black: 0V
  Blue: Channel A output
 Black: Channel A common
Yellow: Channel B output
 Black: Channel B common
 Green: Channel Z output
 Black: Channel Z common

Eight wires!
If the datasheet is correct, then this is a quadrature encoder with
2000 pulses per revolution.  A search should bring up enough
information on how quadrature encoding works.  I have code at work for
decoding the output on a PIC, but I got this either from a Microchip
application note or from the PIClist, so you should be able to find it
online.  If you can't find code, let me know and I'll post a link.

It's possible that this is not the correct pinout (for example, if the
encoder were replaced), so do a sanity check!

Bradley

Thanks! How did you find that page? I did some searching and I
couldn't find anything at all.

It looks like the decoders are indeed different. Besides not matching
the # of wires, the colors also don't match. My motors have wires
green, yellow, blue, red, black, and black. (besides the red and black
wires that power the dc motor).

The decoder on the back of one of them says:
  "Z"-AXIS MOTOR
  FOR ATM ?00/200
  P.N.: 1010-3949 Rev 1

The ? is where part of the label was scratched off, so I don't know
what number it says there.

The other motor doesn't have a label on the back, but it has the same
number of wires and the same wire colors, so I'm assuming they're the
same (although the length of that motor is longer than the other one).

Once I found out that Yaskawa was the manufacturer (which wasn't
immediately obvious), I snooped around the Yaskawa site and found the
datasheets.

The best thing to do (I think) would be to open the encoder up.  It
may have the industry standard HEDS module, which you can look up
online.  Otherwise, get some part numbers of internal components. 
Without seeing the inside, I'm guessing that red/black will be
power/ground and the three outputs share a common ground.  I would
start with 5V on the power/ground and then rotate the shaft and see
what appears on the outputs.  Hopefully you have an oscilloscope.  If
5V doesn't work, then I would guess 12V.

If you break the encoder, get new ones off of eBay.

The other label you describe is probably an OEM stock label.  I don't
think there is much to be gleaned from it unless you can find the name
of the OEM.

Bradley