Servo motor rebuilding

[metalcaster4jc]

Has anyone had a servo motor rebuilt? I think that I have a tach going out of one as I get a "run away" intermittantly. The motor has all the torque necessary, and I hate to trash something that can be fixed. BTW it's a powertron 60 in-lb, 113 v servo. Is it too small to bother rebuilding?

[Al_The_Man]

If indeed it is the Tach, you could try checking the brushes and the tach commutator, there is not a lot that can go wrong with a tach, it does not operate at any appreciative current.
Tach's are seldom used now, even on DC servo's, as they tend to operate in the torque mode rather than the velocity mode as yours probabaly does.
Depending on the controller, you could upgrade to a torque mode drive such as A-M-C type .
Al.

[metalcaster4jc]

It is a 1981 Sharnoa controller and the run away is on the z axis both directions to the limits. Could it be a failed encoder not giving position back to the controller? Then the controller would keep increasing voltage to get the motor to move wouldn't it? Or if the driver is not proportioning the voltage?

I've had run away conditions before on the x&y axis that was casused by a faulty feed override switch ( bad contacts in the #3 position). When that happened the drivers would kick out and give me a PF error. But the drivers don't kick out with this z run away which leads me to think that it is a feed back failure.

I've been watching the postings here flro others with this controller and wanting to do an upgrade to either Ajax or Mach. Seems no one here has done it yet, or if so hasn't posted.