Re: What makes a motor a servo? treadmill

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

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me" <cnc4me@g...>

wrote:

> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> > >
> > > a DC motor may have a noticable cog, this is where you can feel

the

> > > steps as you spin the motor. I have a treadmill motor that is a
> > > really hard cog that needs some force to spin it. Bad.
> > >
> >
> >
> > Was this a treadmill motor from surpluscenter or someplace else.
> > What are the specs on the motor. Did you check its smoothness
> > running at 1.5 to 3volts.
> >
> > Wally
> >
>
> This was a pull from a tradmill.
>
> I have been luck to have found 3 treadmills in the last 3 months. I
> have one motor on my lathe right now, but it was a short and very
> large dia motor. nice fot for a 3/4hp 110 VAC motor.
>
> The other two were the long skinny ones. the one with the very
> noticable cog was 2hp, 5,600 rpm.
>
> 1.5V are you talking D cell battery ? I would have thought it would
> have just shorted the battery.
>
> Any specifics on how to do a 1.5 volt test ?
>
> Dave

Here is the post i got the information from. I found i had to use 2
volts to make mine spin. And a warning here i used a simple 3
terminal adjustable supply to perform this test. It is very easy to
burn these chips out on inductive loads. Start on lowest voltage and
increase voltage slowly.

Wally


From: Les Newell <lesnewell@...>
Date: Wed Apr 6, 2005 11:03 am
Subject: Re: [CAD_CAM_EDM_DRO] Re: Has anyone made their own servos
from DC Motors? les_locost
Hi Glen,

When used as a servo, the positioning is dependent on the resolution
of
the encoder not the number of magnets in the motor. Drives are capable
of holding the motor in any position. Ideally the motor should have
little 'cogging' or lumpiness when you turn it. True servos have
virtually none. The drive has to work to counteract this lumpiness
which
translates into a slight unevenness when moving slowly. A good test is
to connect the motor to a 1.5V battery. If it turns smoothly in both
directions it is likely to work quite well as a servo.

One way to improve the situation is to increase the number of lines on
the encoder. The more lines on the encoder, the more quickly and
accurately the drive can compensate for unevenness. You may have to
use
a drive with pulse multiplying with higher resolution encoders.

Most scooter motors tend to be short and fat. The ideal shape for a
servo is long and thin as this reduces inertia.

Les