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

hi... I have a bit of experience playing with these Globe
Gearmotors. You can remove the gearhead held by the three pins by
punching the pins INWARD enough to remove the head. Then, once
removed, you can force the pins back out for reassembly/use.

The brake and Hall-effect sensor CAN be removed in fine condition and
reused. You need to shim under the rear-end assembly pieces with the
armature hanging free (say in a lose vise) and hammer (I use an old
centerpunch) on the end of the shaft. A few hard taps and it comes
off undamaged. Be careful to support the armature so it doesn't fall
from the vise when the "backend" stuff comes free. Be careful not to
damage the brushes or rotor pieces in the process.

These parts are pressed on TIGHT, but can be removed successfully if
you are careful but not afraid to use some force!

Russ

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@y...>
wrote:

> 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.