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

Hello,

I can tell you that that specific "encoder" will not work as a servo
feedback type. It is a hall effect single pulse per rev; more of a
tach actually. FWIW, The brake is easily removable. The gearbox on
the end of the motor itself is held on by three spiral pins, which
sould need to be drilled out to remove the gearbox. The gearbox has
excessive backlash for use with CNC.

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
>
> 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.