How to test an AC servo motor

I have been doing a fair amount of scrapping CNC equipment, lately.

It works out great, typically just the ironplus copper wires pays me back 2x what I pay for the machine, and then I am left with servo motors, boards, hydraulic pumps, coolant pumps, etc to sell.

But, at the same time I feel that listing and saying things like "this motor comes from an obsolete piece of CNC equipment that belonged to a bankrupt company" does not let me get the highest value for the item.

Whiel I have no hope of being able to test boards, I do feel that I could adequately test the motors.

So, what would constitute a good test of an AC servo motor like a red cap Fanuc motor?

I see a few things.

  1. Run it from a VFD and measure vibration
  2. Somehow test the encoder.

Anything else?

I know that there are companies that buy those motors for $200 each, refurbish and test them professionally (this involves change of bearings, rebalancing etc) and sell for 2,000 each. I would like to be able to do the same and can invest a few grand into scavenging proper test setups.

Any comments?

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You should already have most of the parts for the test setup if you scrapped the machine, i.e. the servo drives and power supply. AC servos aren't very likely to go bad, they're just three phase motors, nor are their bearings likely to go bad since in use they don't see a lot of loading. Encoders are the usual failures and just being able to power the encoder and check the outputs on a scope should provide good indication if they are ok.

Reply to
Pete C.

Short the power leads, and turn the motor. If it turns with a "lump" then one of the magnets is demagnetized. Smooth, but high torque resistance, is good. Not likely if it was being ran in a machine up until the end.

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Google it, you dumb ass.

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IF you have the electronics back-ground, get a good servo drive (like Granite Devices VSD-E) that is configurable for differents kinds of motors. Then just hook up the motor and encoder to servodrive, tune the servo to the motor, and run it. You can put the curves from the Granite devices tuning software as part of your ebay ad. The tuning is done completely from PC software and is rather easy. It works with DC brushless, DC brush and AC servo motors..

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I have no connection to the company except I used that servo amp for my CNC upgrade, and was very happy with it.

But, I do wonder if it really pays for itself in your application. The hardware setup is rather easy and cheap, but you need a person with electronics knowledge testing the motors.. A couple of hours per motor (figuring out pinouts and making connections to wierd connectors) will cost quite a lot for an electronics technician..

Also, the motor is still the unknown runtime motor without warranty.. It may work at the moment, but might fail next week. It does not have the same value as a tested and refurbished motor which is mechanically and electronically quite close to a new motor.

IMHO not worth it.

Kristian Ukkonen.

Reply to
Kristian Ukkonen

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