Re: Slight Servo Problem

Mark,

You need to swap drives to see if the problem follows the drive or
stay with the motor. If it stays with the motor, then:

A possibility is the motor may have a shorted commutator segment or
the motor is different from the other ones.

Check the brushes to see if they aren't worn down. When you do, use a
penlight to look down the brushholder hole to see if the commutator
isn't scored or burned. It should look burnished and smooth.

If you can, remove the motor and measure its no-load current while
running it connected to your supply. Compare that against a known
good motor. Both should sound the same. A high no-load current means
the motor has winding problems or a shorted commutator.

Mariss



Make sure you note the orientation of the brush before you remove it;
you will have to put it back exactly the same way you took it out.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "mmurray701" <gmurray@n...>
wrote:

>
> > No. He has the standard 500 cycle encoders, which provide 2000
> counts
> > in quadrature. So, that would be 360/2000 = .18 degree per count.
> > Very interesting that you see such a difference. What motors are
> > you using?
> The Ametek motors have high resistance, and that makes
> > me think they may have very high inductance, too! It may be that
> the
> > motor inductance is so high that it kills the control laws built
> into the
> > gecko drive, and the rapidly oscillating motor current acts to
> defeat
> > the integral windup that is supposed to happen.
> >
> > Do you have external capacitors connected right at the Gecko power
> > input terminals? I put one on my client's system, and it seemed

to

> > improve the stability and stiffness, but I didn't have much time

to

> > investigate before the cap blew up (I had it wired backwards).
> >
> > Jon
>
>
> I'm using Electrocraft E543 motors. They have a resistance of about
> 1.6 ohms which is much lower than the ametek if I remember correct.
> I'm sure the ameteks do have a very high inductance, but I dont

know

> enough about electronics to know if that would cause a problem. My
> encoders are 250cpr or 1000 pulses. Maybe a little to me is alot to
> you, but they do seem very stiff. I guess the resistance/inductance
> could cause it.
>
> I'm not using a cap across the terminals, but the drives are very
> close (maybe 12-14") to the supply which has 8, 100v 4700uf caps in
> parallel.
>
> Mark