Servo motor noise

[Northmount]

On 10/12/2023 at 6:16 PM, Dwight said:

OK . . . go out into the shop . . . get the longest . . . skinniest screw driver you can find . . . 

Rudimentary stethoscope, works very well.  Have used it in many cases, machinery in power and process plants, automotives, etc.  Works so well I bought a stethoscope (mechanical, not medical) and have used it a few times.  Screw driver is usually closer at hand so I often use it instead of going back to get the stethoscope.  A stethoscope helped me find a cracked/broken wrist pin in a old style Dodge 318 V-8.  Top side of the engine, noise was on front cylinder on right bank, on the bottom it was on the 3rd cylinder.  Cracked wrist pin was on the 2nd cylinder directly between the two measurement locations.  Replaced piston, wrist pin, rings, rod and gaskets, and was back on the road for about $80 in parts.

[Northmount]

2 hours ago, GerryR said:

Check the bearings while the rotor is out of the housing; they should be smooth as butter while applying some pressure on them as you rotate them.  If they feel "gritty" or there seems to be a "bump" while rotating, then it is a bearing problem, otherwise they are good to go. 

This bearing was cleaned and spun by the shop maintenance man/machinist.  Pronounced as good, no need to replace it.  I had done vibration sampling and found it to be 'noisy'.  Had the print out to show it.  Took the bearing away from him and cut it with an angle grinder.  This is what it looked like.

I had run vibration tests on the machine because it was literally screaming at 5000 RPM.  So don't trust that cleaning and spinning a bearing is an adequate measure of its health. 

Bearing on the opposite end of the shaft was the main culprit, but once you have the machine apart, replace the $10 bearing and save another 18 hours work in tear down and repair.

 

Bearing in the 2nd photo was causing the shaft to jamb during attempted startup, so he put a pipe wrench on the shaft to loosen it up.  A real no-no!  Half deaf so he didn't notice the machine screaming.  This was in a steam turbine lab in a technical school.  I could hear it from out in the hallway with the door closed.

 

[GerryR]

9 hours ago, fibersport said:

I agree that the circled part isn't the issue, that is what the bore of the bearing sits on, if the bearing is turning on that there's a big problem. Also, I don't think the flash on that end cap or end bell is causing it, look at the distance from the bearing to the armature.

I wasn't suggesting that the flash was causing the problem, but seeing that you had it apart, you might as well clean it up.  Also,  you might want to just replace the bearings as they are not very expensive and are probably stock items at McMaster-Carr Supply.  Another issue is that the rotor itself may be out of balance; from the rough machining that was done, it is a distinct possibility.  (I guess we know why a lot of the cheaper import stuff is less expensive; hit-and-miss on quality.)

[Hidden]

Been in contact with the store I bought the motor from (vevor.de), and look at this:

I replied I wanted a new motor or a full refund twice, looks like Pedro REALLY doesn't want me to return this thing (if Pedro is not a bot!). I found it quite amusing.

[AlZilla]

It doesn't make it with the belt off but does with the belt on. It's got to be a bearing. Take their 70 euros, replace the bearings and never buy another vevor product.

[dikman]

That sort of reply is pretty typical when dealing with Chinese companies, they generally try to avoid refunds/returns as much as possible. I have had issues in the past and have tried to get help from ebay/paypal and they usually insist that I have to return the goods first at my expense (which can be an expensive proposition). 

I'm a bit surprised, I thought Vevor were better than that, I guess not.

[Hidden]

  

10 hours ago, AlZilla said:

It doesn't make it with the belt off but does with the belt on. It's got to be a bearing. Take their 70 euros, replace the bearings and never buy another vevor product.

That's what I'll do. Just ordered some bearings and accepted Pedro's third offer :') thanks for the advice, @AlZilla and everyone else.

Edited October 20, 2023 by Hidden

[dikman]

I think you made the right decision, you've probably avoided a lot of stress/messing around/anguish! I was in a similar situation once over a $450 mini-lathe, dealing with the chinese company was frustrating and Paypal were unhelpful, refusing to acknowledge my consumer rights under Australian Consumer Laws. It took me three months and then only after I got the Australian financial authorities involved did Paypal relent and give me a refund (grudgingly, I must add).

I should have taken the company's best offer!

[Agarbers]

I am late to the party but it sounds like the rotor is rubbing against the stator. Look for wear marks on both.

Rotor:

Stator:

 

Or the bearing housing may not be true/out of round and allowing the bearing to move. Look for wear marks there.

Lastly, like Northmount shows, the bearing may have been damaged during assembly. If it was driven on with a hammer, brinelling may have occurred. Installing a bearing takes special tools to prevent this. If the installer used hammer blows on the outer race to push it down the shaft, damage could have occured. 

[GerryR]

There would be definite and obvious scrape marks on those components, but it does bring up a point about the bearing slipping in the bore.  Loctite makes a product that you can put on the bearing OD so when put into the housing bore, it will prevent it from slipping in the bore.  The same can be used on the shaft-to-inner-bore interface, but you should be able to tell by the fit, when assembling, whether it is needed or not.  Just something to keep in mind.