Re: [CAD_CAM_EDM_DRO] Any old encoder or how to make an inexpensive servo motor

etfrench wrote:

>Will any encoder work for creating a servo motor from a PMDC motor?
>
>or
>
>Will the encoder on this gear motor
>(http://www.surpluscenter.com/item.asp?
>UID=2003120116311635&catname=&qty=1&item=5-1440) work with the motor
>suggested by Mariss Freimanis (http://www.surpluscenter.com/item.asp?
>UID=2003070308293941&item=10-1931&catname=electric)?
>
>

Maybe. Don't be completely sure you can get the encoder off the motor
in such condition that it can be reused. They don't really say that the
encoder can be removed in working condition, just that the brake/encoder
is removable.

Second, they don't say anywhere that the $24.95 motor is a servo motor!
It may well work fine for servo positioning use, but apparently was a
treadmill motor. It could have a lot torque or velocity ripple, or
magnetic cogging, which will interfere somewhat with smooth motion at
low speeds.

>p.s. How do you calculate the oz/in for just the motor from the
>following?
>
>SPECIFICATIONS
>• RPM primary 25
>secondary 4.5
>• Voltage 12 DC
>• Amps 130 mA no load
>• Torque primary 33 in. lbs.
>secondary 125 in. lbs.
>• Ratio 620:1
>• Rotation reversible
>• Duty continuous
>
>
>

Pretty tough. I'm guessing the 620:1 is from the 4.5 RPM rating point, so
the motor RPM is 2790. If you get 125 In-Lb at 4.5 RPM, then the motor is
delivering 125/620 In-Lb = 0.202 In-Lb or 3.23 In-Oz. Not a tremendous
motor,
for sure. Actually, a 620:1 gearbox is pretty lossy, so the motor could be
twice that.