Author Topic: Grounding a spinning motor shaft  (Read 2113 times)

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Offline captainscarlet

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Grounding a spinning motor shaft
« on: December 11, 2014, 12:56:07 pm »
Hi all,

I have this motor: http://tinyurl.com/lf85rwq and I need to ground the shaft while the motor is spinning at 6kRPM.
I tried a spring loaded test pin, but there's too much friction and noise at high speeds
I'd imagine there's some sort of brush that can make contact with either the shaft or the cylinder at the rear of the motor but I can't find anything on RS or Farnell that can do this.

Anyone have any ideas on how this can be achieved?

 

Offline fcb

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Re: Grounding a spinning motor shaft
« Reply #1 on: December 11, 2014, 01:13:39 pm »
Have you talked to MAXON (the makers of the motor) - they will have done this before.
 

Offline N2IXK

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Re: Grounding a spinning motor shaft
« Reply #2 on: December 11, 2014, 01:14:20 pm »
Look for a scrapped VCR.

They use a graphite button on a BeCu spring to ground the shaft on the video head motor assembly.
"My favorite programming language is...SOLDER!"--Robert A. Pease
 

Online Zero999

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Re: Grounding a spinning motor shaft
« Reply #3 on: December 11, 2014, 01:16:56 pm »
Just one question: why? It's 24V so it's not required for safety.

The shaft is probably in fairly good electrical contact with the motor frame, although you shouldn't use the bearings to carry any current.
 

Offline SeanB

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Re: Grounding a spinning motor shaft
« Reply #4 on: December 11, 2014, 05:15:13 pm »
You will need the grounding carbon button to make contact with the back of the shaft, or replace the grease in the bearings with a graphite loaded grease, which in this small bearing will be both hard an will reduce bearing life considerably. the thing with a spinning bearing is that the inner and outer race tend to be separated by a thin film of oil from the grease, effectively insulating it, and if the applied voltage is high enough then the breakdown of the grease causes a small arc which eventually erodes the bearing raceway and the balls. When you open one it is full of black deposits and the raceways and balls are badly pitted.
 

Offline WarSim

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Re: Grounding a spinning motor shaft
« Reply #5 on: December 12, 2014, 04:32:30 pm »
Isn't a pin bearing on the shaft end an acceptable method?  I have seen it done in allot of safety gear.  Older stuff, I haven't been into the newer stuff. 
 

Offline SeanB

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Re: Grounding a spinning motor shaft
« Reply #6 on: December 12, 2014, 05:18:35 pm »
Pin does wear eventually and can stick fast with wear or overload, that is why the preferred method is to use the copper loaded graphite button so that it will still conduct and not stick. As well it has low friction.
 

Offline Richard Crowley

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Re: Grounding a spinning motor shaft
« Reply #7 on: December 12, 2014, 05:19:28 pm »
Exactly how (and where) did you "tried a spring loaded test pin"?

Is the shaft exposed on the "back side" of the motor?  That would be the place for a spring-loaded contact.

If you are having a problem with "much friction and noise at high speeds" then you need to properly prepare (polish) the surfaces.
 


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