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-   -   Gritty motor question (http://www.Wattflyer.com/forums/showthread.php?t=72812)

cbreeze 12-16-2013 01:10 AM

Gritty motor question
 
Greetings,

I am new to electrics. I just bought a new small electric brushless motor from Hobby King to use in a foamie I am building. I got the motor and in the process of inspecting it, I noticed that when I turn the motor by hand, if feels "gritty" like something is rubbing inside. I have several larger brushless motors that to not do this. I was wondering if this is normal for a cheapie motor from China?

Thanks,

cbreeze

kyleservicetech 12-16-2013 01:34 AM

Quote:

Originally Posted by cbreeze (Post 934537)
Greetings,

I am new to electrics. I just bought a new small electric brushless motor from Hobby King to use in a foamie I am building. I got the motor and in the process of inspecting it, I noticed that when I turn the motor by hand, if feels "gritty" like something is rubbing inside. I have several larger brushless motors that to not do this. I was wondering if this is normal for a cheapie motor from China?

Thanks,

cbreeze

H'mmm
If something is rubbing inside the motor, like the "bell" magnets hitting the stator, that motor won't last long when running under power.

hillbille 12-16-2013 01:50 AM

If you've had this motor OUT of it's box or out of the plastic bag it came in and on your bench it is possible that something small, say a washer or almost anything has been sucked into the magnets of the motor by the magnetic field of the motor. STOP turning it by hand.

Disassemble the motor over a clean area of your workspace and inspect it carefully. The object inside my be hidden between the magnets and may not be noticeable at first.

I would not "run" the motor as is without a disassemble and inspection. Might be something in there that was picked up from the factory too. Doesn't matter - except to you as you need to clear the motor of what ever it is that is causing the problem BEFORE it does any damage.

Hillbille

hayofstacks 12-16-2013 02:12 AM

x2 to previous posts.

actually, the only motor I ever ordered from hobby king, the bearing was pressed in wrong and smashed. I ended up replacing the bearing from one at headsuprc. I started using headsuprc since and haven't looked back.

cbreeze 12-16-2013 03:10 AM

Greetings,

Thanks to everyone that responded so far. Looks like I might call Hobby King and ask for a new one. I noticed the problem right out of the box. Pulled it out of the plastic bag it came in and turned the motor noticing the problem. There is no possible way that something could have fallen in the motor at that time. Depending on what HK tells me, might try taking it apart to see what the problem is myself.

cbreeze

hayofstacks 12-16-2013 03:39 AM

also check to see if the shaft or bell is bent.

DHC Beaver 12-16-2013 03:55 AM

Are you sure you're not confusing the "stuttery" feel of a brushless motor with "grit"?They do not spin freely like a brushed motor.
I have bought 20+ motors from HK,and have never had a problem with any of them.A lot of problems are caused by poor handling,e.g.,wrong prop size,too high voltage,etc.
Maybe I've just been lucky,but I do study the specs carefully,and test the motor on a stand, to make sure the motor suits the model it's going in.
On the other hand,lots of people think a concrete or sealed runway is "clean".Don't you believe it.Those surfaces pick up loose dust and sand like mad.That not only kills electrics,IC motors too.
I've been spoiled by always having had grass to fly off.

cbreeze 12-16-2013 04:06 AM

DHC,

Your post got me thinking. I am going to take another look at it. Perhaps you are right. I admit that I have only recently gotten into electrics so I am still learning. The motor was real cheap and probably not worth trouble of a return.

I sure appreciate all the help I have gotten so far. This web site is great.

cbreeze

Wildflyer 12-16-2013 05:16 AM

The jumpy motion caused by the magnetic fields is called gogging.

Some of my motors have LOT of gogging, almost hard to turn, and some motors have a little, and some have no noticeable gogging at all, yet all motors run fine.

I have not figured a pattern to it, not size, not kv, not pole count. Some better people may know why, but not me.

Try to put the motor close to your ear, slowly rotate, goging will just pull the shaft to the next point, gritty bearings will have a tiny sharp sound you would hear or feel through the metal parts. Gogging will be consistent, grit will not.

If it is grit in the motor, the only way I have been able to get it off the magnets is to use clay or chewing gum to absorb the parts and pull them off the magnets.

kyleservicetech 12-16-2013 05:24 AM

1 Attachment(s)
Quote:

Originally Posted by Wildflyer (Post 934553)
The jumpy motion caused by the magnetic fields is called gogging.

Some of my motors have LOT of gogging, almost hard to turn, and some motors have a little, and some have no noticeable gogging at all, yet all motors run fine.

I have not figured a pattern to it, not size, not kv, not pole count. Some better people may know why, but not me.


Yeah
My $$$$ Hacker motors have very little or no cogging. As a wild guess, the amount of cogging might be related to how wide the stator pole sections right next to the magnets are. The wider those stator pole "Tops", the less cogging. And, the wider those stator pole tops, the narrower the gap the coil winder has to insert the windings, making the motor more difficult to wind up.

Does this make the Hacker's and similar type motors more efficient? Who knows. I've got some www.gobrushless.com motors that I wound up some 15 years ago that have a LOT of cogging. And, they run just fine under power. The gobrushless motors have 9 stator poles versus 12 magnet poles. That Hacker has 12 Stator poles and 16 Magnet poles. That's the same ratio, so that can't be it.

Note how wide the stator pole tops are in this motor. It would be interesting if other wattflyer readers could post photos of their motors insides, both top quality, and bottom of the line so we can make comparisons.

Note that top of the line motors like this one completely fill the copper winding area with copper wire. If this winding area is not completely filled, that requires the same number of turns of wire must be made with thinner wire. Some motors the same physical size as the Hackers have three times the winding resistance. I recently ran across a very expensive $299.00 motor at the local hobby shop that was supposedly rated at 3000 Watts. Problem was, less than half of the copper winding area was copper. The rest was air. This same motor had nearly four times the winding resistance than the smaller, less costly Hacker A60-5S motor I've got. You can run that A60 motor at its rating, and it will run quite cool. Per www.motocalc.com, running this name brand motor at 3000 watts would quickly burn up its windings, heating them up to some 450 degrees F.

solentlife 12-16-2013 08:00 AM

Quote:

Originally Posted by Wildflyer (Post 934553)
The jumpy motion caused by the magnetic fields is called gogging.

Some of my motors have LOT of gogging, almost hard to turn, and some motors have a little, and some have no noticeable gogging at all, yet all motors run fine.

I have not figured a pattern to it, not size, not kv, not pole count. Some better people may know why, but not me.

Try to put the motor close to your ear, slowly rotate, goging will just pull the shaft to the next point, gritty bearings will have a tiny sharp sound you would hear or feel through the metal parts. Gogging will be consistent, grit will not.

If it is grit in the motor, the only way I have been able to get it off the magnets is to use clay or chewing gum to absorb the parts and pull them off the magnets.

Cogging ?

;)

Nigel

kyleservicetech 12-16-2013 10:47 PM

Quote:

Originally Posted by solentlife (Post 934566)
Cogging ?

;)

Nigel

LOL
Cogging, NOT Clogging!

solentlife 12-17-2013 08:55 AM

Quote:

Originally Posted by kyleservicetech (Post 934644)
LOL
Cogging, NOT Clogging!

??

I wrote Cogging in response to other guys Gogging .... where's CLogging come from ?

Nigel

rcers 12-17-2013 01:49 PM

I married a clogger - o wait sorry....

It is indeed cogging not gogging. Gogging is something else altogether, not RC related. Do a search from home not at work. :)

Mike

kyleservicetech 12-17-2013 08:51 PM

Quote:

Originally Posted by solentlife (Post 934666)
??

I wrote Cogging in response to other guys Gogging .... where's CLogging come from ?

Nigel

Oops :oops:
Sorry, clogging and country music kind of go together :D :D

cbreeze 12-20-2013 04:07 PM

Just wanted to update this.

I decided that for the money I paid for the motor it wasn't worth a return. I went to headsuprc and wound up ordering another motor. When I got it, it appears to be the same motor I got from Hobby King. Removed the motor from its packing and turned it by hand, same issue. This tells me that what I am experiencing is normal and is either gogging or clogging, take your pick for a description.

Just want to thank everyone for their help. Also, in the process of researching this issue I stumbled on headsuprc. I wound up ordering another motor and some other items. They sell same items as Hobby King and I got the things I ordered in two days. Not saying that Hobby King is bad but their return/refund policy is a little awkward. headsuprc is just another option for us in the hobby.

Once again thanks for the help and everyone have a

Merry Christmas,

cbreeze

JetPlaneFlyer 12-20-2013 04:21 PM

Quote:

Originally Posted by cbreeze (Post 934900)
and is either gogging or clogging, take your pick for a description.

It's neither, it's cogging (with a 'C' and no 'L')


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