brushed dc servo axis motor, needs cleaning?

[tom.jelly]

Preparing for a retrofit that has DC brushed servo axis drives. Resistance for motor chassis ground to motor power leads for one motor is 4.0 megohms, 0.63 M for the second and infinite for 3rd axis. All axes were tested for function and working fine prior to the test, but I'm pretty sure these readings should all be infinite. Is it possible there is some carbon dust inside from wear to brushes causing this? is it an issue that needs to be dealt with or can I ignore it? It is a used machine with some mileage on it but in good shape. I've never taken apart a servo motor; one of the motors with the issue also has a brake. I'm not too keen on taking the motor apart as I've heard rumors of that being a one way ticket to failure but I don't know if that's true or based on someone who is not very careful . I do not want to screw anything up, would the best course of action be to remove the brushes and try to vacuum out any carbon dust then use a blowgun with all the brushes out, or what? These will be used with an expensive 3 axis integrated servo drive/controller that I need to protect over all....

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[BBMNet]

Preparing for a retrofit that has DC brushed servo axis drives. Resistance for motor chassis ground to motor power leads for one motor is 4.0 megohms, 0.63 M for the second and infinite for 3rd axis. All axes were tested for function and working fine prior to the test, but I'm pretty sure these readings should all be infinite. Is it possible there is some carbon dust inside from wear to brushes causing this? is it an issue that needs to be dealt with or can I ignore it? It is a used machine with some mileage on it but in good shape. I've never taken apart a servo motor; one of the motors with the issue also has a brake. I'm not too keen on taking the motor apart as I've heard rumors of that being a one way ticket to failure but I don't know if that's true or based on someone who is not very careful . I do not want to screw anything up, would the best course of action be to remove the brushes and try to vacuum out any carbon dust then use a blowgun with all the brushes out, or what? These will be used with an expensive 3 axis integrated servo drive/controller that I need to protect over all....

Hello.

If you are still thinking on opening them PLEASE DO NOT! The rumors you have been hearing of are correct. Even under controlled conditions it is very difficult to service them. At the factory we had quite a good workshop to repair all kinds of motors. So we thougnt. We knew we had to keep the working area nearly as clean as an operating room or perhaps even cleaner.Also we had to be very careful on how to disassemble it. To make a long story short we ended up with a working motor WITH ONLY ABOUT HALF of it rated power. After many years I still don´t know what we made wrong or what changed.

I don´t know how they do it but there are workshops that specialize in servicing this type of motors. In case of doubt you may find some after some googling.

In reference to the readings you are right. The reading from leads to frame should be infinite. Carbon dust could be an issue if there is too much at the commutator rings. I´d suggest you use an air bottle to clean it. That might help.

By the way check how scratched are the commutator rings as copper particles can also be causing this.

On the other hand I´d suggest you wait until those motors are 100% ok.

In remembering a broken carbon cap might also be causing those faulty readings.

I hope these ideas may help.

Best regards.

[Al_The_Man]

One of the reasons some say you should not dismantle a PM field motor is that you will get demagnetization of the field, unless a metal 'keeper' is slid in to replace the armature.
I have only seen this happen on steppers, with the PM DC servo's I have taken apart and cleaned, I have not found any problem along these lines.
You have to be very careful when removing the armature not to fracture the PM, due to sudden attraction of the armature when free of the bearings.
For some time now, Rare Earth magnets have been used that do not seem to suffer from this phenomenon as easily.
At the very least, blow the motors out and check brush length.
Al.