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Old Feb 17, 2015, 11:01 PM
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Is there a easy way to find the number of motor poles?

Since I have several motors of unknown KV, I purchased this device from H. K. that installed on one of the leads from the esc to the motor, and plugs into the battery. It will tell me the KV of the motor, if I know the numbers of poles. Since I can usually count the number of motor laminations, is there an easy way to figure out how many poles. I had taken apart two motors for repairs on shafts, and broken motor mount screws, and found one had 14 magnets, and 12 windings, the other had 6 magnets and 9 windings. That is the hard way, is there an easy way. Thanks for any help with this.

H.
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Old Feb 18, 2015, 03:12 PM
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The only easier way I know of is to consult the motor spec sheet. But most cheap motors dont have that kind of info.

Often you can count magnets without pulling the motor apart though.
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Old Feb 18, 2015, 03:58 PM
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Counting the number of magnetpoles, a picture is worth a thousand words:
The number of poles in BLDC

And the similar threads section at bottom of this page.


Vriendelijke groeten Ron
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Old Feb 19, 2015, 07:22 AM
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You can usually see the ends of the magnets that are up inside the magnet housing in the gap between the housing and baseplate. Make a mark on one and count them around. It will always be an even number and never the same as the number of stator arms.

The image shows the practical combinations, your motors will almost certainly be one of the ones shown in light blue.

Worst case you can remove the magnet housing and count them...

Outrunner Disassembly and Stripping - Gimbal Motor Rewind - http://www.rcgroups.com/forums/showthread.php?t=1823636

Jack
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Old Feb 19, 2015, 10:07 AM
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The problem is, the ones I don't know anything about are not marked in any way, so there is no way to consult a data sheet. Sometimes I can see the magnets, but usually not. Thanks for the replies, it is useful to know how the most common motors are made. At one time, I used a solid stable 10 volt supply, ran full throtle, and measured the prop speed, using a no pitch flat stick, but that was only a guess. Thanks again.

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Old Feb 19, 2015, 01:16 PM
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himeros,

I replied in the post that Ron linked to. But there is another way that only requires a power supply (preferably with a current limit). Here is the procedure:

1) Hook the positive lead of the power supply to 1 stator lead.
2) Hook the negative lead of the power supply to the other 2 stator leads.
3) Slowly increase the applied voltage until you have enough current to lock the rotor in place but not too much current that you can't still rotate the shaft by hand. Usually this is around 10% of the rated current of the motor.
4) Mark the shaft with a line.
5) Keeping the motor in the same orientation, turn the shaft to the next "cog."
6) Mark the shaft again.
7) Repeat this until you come back to your original mark.

The number of pole pairs is the number of marks you have on your shaft. The number of poles is 2 times the number of pole pairs.
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Old Feb 20, 2015, 08:55 AM
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Originally Posted by learningrc View Post
himeros,

I replied in the post that Ron linked to. But there is another way that only requires a power supply (preferably with a current limit). Here is the procedure:

1) Hook the positive lead of the power supply to 1 stator lead.
2) Hook the negative lead of the power supply to the other 2 stator leads.
3) Slowly increase the applied voltage until you have enough current to lock the rotor in place but not too much current that you can't still rotate the shaft by hand. Usually this is around 10% of the rated current of the motor.
4) Mark the shaft with a line.
5) Keeping the motor in the same orientation, turn the shaft to the next "cog."
6) Mark the shaft again.
7) Repeat this until you come back to your original mark.

The number of pole pairs is the number of marks you have on your shaft. The number of poles is 2 times the number of pole pairs.
I do have a good variable power supply that I can limit the current, I will try that, sounds like an easy way to me. I will have to think about why that works, and how motors are wound, so that works.

Thanks

H.
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Old Feb 20, 2015, 11:28 AM
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I have to say, I am excited, and the voltage though the winding work very well. The higher kv motors seem to take more current for this test to work, up to 10 amps at 1 volt, the lower kv seems to be as low as 4 amps at 1 volt. Now knowing the poles, I can test the motors that are not marked to find out the KV. Thanks so much for the help here. Life is good once again.

H.
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Old Feb 21, 2015, 06:52 AM
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Quote:
Originally Posted by himeros View Post
I do have a good variable power supply that I can limit the current, I will try that, sounds like an easy way to me. I will have to think about why that works, and how motors are wound, so that works.

Thanks

H.
The winding image calculator here:

http://www.bavaria-direct.co.za/scheme/calculator/

gives some insight as to the steps in a wind with it's "cogging steps" number. And if you play with the Advanced modes and animations it really gets into some interesting things.

It would be wonderful if someone that understood it all would post a page that explains Felix Niessen wonderful contribution in more detail. But in the meantime it is still very useful for us knuckle dragging motor heads in the Simple modes

Jack
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Old Feb 21, 2015, 02:49 PM
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Even though I used the word cog, it isn't the same as the number of cogging steps at that website. That value is based on the least common multiple of the number of stator slots and the number of poles.

The method I outlined above basically sets up a number of magnet poles in the stator equal to the number of poles on the rotor. Because only norths and South's attract, you end up with pole pairs instead of poles.
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Old Mar 09, 2015, 11:23 AM
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Sorry if I'm oversimplifying but if you just need to know the kV of the motor, why don't you simply do this:
- Remove any prop and adapter from shaft;
- Put a piece of masking tape on the outer casing and draw a line using a black marker;
- get a compatible lipo and measure its voltage
- Plug everything and power up at full throttle
- Grab a digital tacho and measure the rpms

The motor kV=rpm/V (aproximately)

If you have a good wattimeter you can get more accurate values as the voltage will drop a bit when under load.
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Old Mar 09, 2015, 11:29 AM
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That works very well, it will be close enough to the "laboratory" Kv for all of out purposes here. If possible, I would measure the voltage under load and use that and the RPM reading. If there was (as is not untypical) a lot of variation in the RPM reading I would use an average value.

Jack
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Old Mar 16, 2015, 01:02 AM
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Aren't poles always in multiples of 3 with these three phase motors?

Does more poles solely equate to a higher kt. Lower kv. And more...dare I say torque?

Can I run a 15 or 18 pole motor with a typical esc?
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Old Mar 16, 2015, 06:17 AM
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Yes, on the first question, I don't know for sure on the second, and a standard ESC will run any of these RC motor regardless of the arm count. I have run up to 24 arm motors so far.

More arms means there will be more permutations as the ESC is running the motor so you can't rule out that at some RPM you may exceed the maximum permutation rate that the ESC can operate at. The motor will scream and not run right when that happens, the cure is a better/more capable ESC.

Manuel_v did a very nice rewind on a 24N22P motor in this thread:

Rewind Iflight MT 4108-720 - www.rcgroups.com/forums/showthread.php?t=2126516

His wind was Half Parallel dLRK-YY so, in reality, he has a pair of 12N11P motor running in parallel there. That being a two part motor does lower the burden on the ESC a little as far as the permutation rate goes.

In the end there Manuel finished up with a 130g 690 Kv motor that can run at 400W or so without even getting more than barely warm. That is not a major increase over what the motor would handle originally but the efficiency was much improved and the motor is running much cooler so the load could be increased even more.

Jack
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Old Mar 16, 2015, 07:21 AM
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Quote:
Originally Posted by Hummina View Post
Aren't poles always in multiples of 3 with these three phase motors?
No, poles are always a multiple of 2. You always need a north and a south.


Quote:
Originally Posted by Hummina View Post
Does more poles solely equate to a higher kt. Lower kv. And more...dare I say torque?
Yes, more poles in general leads to a higher Kt. Remember that Kt is torque per Amp, so just because you have a higher Kt motor doesn't necessarily mean you will get more torque than a lower Kt motor. If your lower Kt motor can handle more current, it could produce more torque.
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