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Old 12-16-2013, 01:10 AM   #1
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Default 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
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Old 12-16-2013, 01:34 AM   #2
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Originally Posted by cbreeze View Post
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.

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Old 12-16-2013, 01:50 AM   #3
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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.

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Old 12-16-2013, 02:12 AM   #4
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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.

slow stock prop reversal. it flies! easily! 543 watt dual motor bipe slow stick. push-me-pull-you. 242 watt 3 channel slow stick. 365 watt mini ultra stick. 415 watt mini contender. 810 watt ultra stick .25e. 220 watt alpha 450 sport (retired).
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Old 12-16-2013, 03:10 AM   #5
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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.

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Old 12-16-2013, 03:39 AM   #6
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also check to see if the shaft or bell is bent.

slow stock prop reversal. it flies! easily! 543 watt dual motor bipe slow stick. push-me-pull-you. 242 watt 3 channel slow stick. 365 watt mini ultra stick. 415 watt mini contender. 810 watt ultra stick .25e. 220 watt alpha 450 sport (retired).
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Old 12-16-2013, 03:55 AM   #7
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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.
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Old 12-16-2013, 04:06 AM   #8
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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.

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Old 12-16-2013, 05:16 AM   #9
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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.

Dave R, Proud PGR rider.
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Old 12-16-2013, 05:24 AM   #10
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Originally Posted by Wildflyer View Post
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.


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Old 12-16-2013, 08:00 AM   #11
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Originally Posted by Wildflyer View Post
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 ?



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Old 12-16-2013, 10:47 PM   #12
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Originally Posted by solentlife View Post
Cogging ?



Nigel
LOL
Cogging, NOT Clogging!

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Old 12-17-2013, 08:55 AM   #13
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Originally Posted by kyleservicetech View Post
LOL
Cogging, NOT Clogging!
??

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

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Old 12-17-2013, 01:49 PM   #14
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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.

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Old 12-17-2013, 08:51 PM   #15
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Originally Posted by solentlife View Post
??

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

Nigel
Oops
Sorry, clogging and country music kind of go together

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Old 12-20-2013, 04:07 PM   #16
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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
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Old 12-20-2013, 04:21 PM   #17
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Originally Posted by cbreeze View Post
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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