Re: [CAD_CAM_EDM_DRO] Servo issue

Jason Cox wrote:

>Jon and all,
>
>Heres what I did. First swapped other motors on the same g320's which worked
>fine, so Im assuming that it is the motor only.
>
>It spins freely with nothig connected but when I connected the terminals as
>you said it felt smooth and consistent for whole rotations clockwise, but
>when anti clockwise I can feel a very light cogging, it does not however get
>easy in one part or the rotation.
>
>

The ONLY thing that it could possibly be is bad brush contact. After a
burn-up,
that is quite possible. I'd just hook it to a moderate DC voltage, or the
servo driver, and set it up to spin at 1000 RPM for half an hour, and
try the
same test.

>I did this same test on another motor and it was smooth both ways.
>
>I also tested the motor at 90deg intervals with no change in its anti
>clockwise weakness!
>
>If this motor has a high number of windings could this cogging when turning
>be an open winding? But would I feel this in only one direction?
>
>

No, I can't imagine any reasonable scenario for a PM brush motor to act
like that.
Oops, except now I can! If a commutator segment got loose (melted plastic
commutator hub) and was shorting to the next segment, that could easily be
a one way phenomenon. You might want to pull off the end cap on the
brush end and inspect the commutator, brushes and brush holders for any
obvious damage, looseness, etc. Hmmm, actually, if the brush holder has
melted, it could be allowing the brush to shift to a position where it makes
poor contact going one way. I think you really should pop the cap off and
take a look. Some motors can lose strength in the field magnets if you
pull the armature out, so you probably should leave it in place, and just
remove one end cap. (You probably can't hurt this motor more than it
already has been!)

>The main thing is could this be the cause of my x axis going crazy? Or could
>it have been my crazy x axis that drove itself into the stops and overheated
>the motor?
>
>

I have a strong feeling the overheating is somehow the cause of the problem.
If you are able to actually figure out the cause, though, you may be able to
determine the sequence of events.

>Could I be getting noise or something from the computer, this worries me
>cause all has worked fine for six months and nothing has changed except that
>I overheated the motor but still which came first the chicken or the egg?
>
>

Well, now I'm trying to remember the original event. It ran into the
stop and
was not discovered for a while? I'm guessing that the encoder may have
gotten
unhooked, ot a bad connection, or something like that?

Does this motor still move correctly in both directions until it goes crazy?
Is there any rattling or jerkiness in the movement? I'm getting a strong
feeling that there may be just some tarnished commutator segments from
the overheating, but the REAL problem is still a bad encoder!

Have you tried the same encoder cable and Gecko drive on a different motor?
If the cable proves to be completely reliable, then it really points to the
encoder.

Jon