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Brushless Motor Construction Discuss design and construction of custom Brushless motors

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Old 09-13-2011, 02:40 AM   #1
neorules
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Default Home built large brushless NEWBIE

Hello everyone,
My first thread has about 75 questions in it LOL...

No really....

Here they are.
Is there a formula for the correct number of magnets vs coils in a brushless
motor?
Right now I have 18 magnets and 27 separate coils.
Yes this is a huge motor.
I have done searches and I keep coming back to LRK combination table in german.

Is that only for a LRK skip tooth winding?
if I use that table it gives me ABCABCABCABCABCABCABCABCABC.
I mean that looks like a standard three phase brushless repeated several times so it should work right?
Or am I translating wrong.
Thanks JC
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Old 09-14-2011, 03:38 AM   #2
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Did you write me a mail message about direct drive motors yesterday or the day before yesterday:
"... are you the guy who is heavily involved ...?"

Check this post for 27 statorpole motors
www.rcgroups.com/forums/showthread.php?t=587208

What dimensions are we talking about? Where did you get the motor from? It may be too big for a first build (prop, high currents, shorts) in/with large motors. In that cause would start with a smaller motor to learn the trade, you don't want errors/accidents to happen.

ABC winding diagram is for #magnetpole/#statorpole ratio 2:3 or 4:3, if seems your motor fits the bill You cannot use LRK/dLRK/adLRK in your stator.

LRK/SPS winding diagram, straight from horse's mouth, two posts by Christian Lucas, the father of diy motorbuilding and outrunners (earns his beer at www.magnet-motor.de, slightly larger motors than we are used to )
http://www.rcgroups.com/forums/showt...0#post19194671

Veryvery improved winding diagram 'calculator':
www.rcgroups.com/forums/showthread.php?t=1434363

Motor winding/building tips, tricks, videos, manuals. The checks and tests will one day save a newly wound motor and/or controller and/or battery:
www.rcgroups.com/forums/showthread.php?t=240993 (sticky at top of diy motor subforum)

The bibles:
www.powercroco.de (English & German)
www.aerodesign.de/peter (English & German)

Vriendelijke groeten Ron
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Old 09-14-2011, 04:31 AM   #3
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Originally Posted by neorules View Post
Hello everyone,
My first thread has about 75 questions in it LOL...

No really....

Here they are.
Is there a formula for the correct number of magnets vs coils in a brushless
motor?
Right now I have 18 magnets and 27 separate coils.
Yes this is a huge motor.
I have done searches and I keep coming back to LRK combination table in german.

Is that only for a LRK skip tooth winding?
if I use that table it gives me ABCABCABCABCABCABCABCABCABC.
I mean that looks like a standard three phase brushless repeated several times so it should work right?
Or am I translating wrong.
Thanks JC
Some years back, I rewound a standard automotive alternator to put out about 60 Volts DC, for charging a 38 cell Nicad Pack, feeding an Astroflight 90 geared brush type motor.

This was used to check it out before using it as a high voltage three phase alternator: (All automotive alternators are three phase units)
Drytesting brushless motors
http://www.wattflyer.com/forums/showthread.php?t=35216 Found out I'd reversed polarity on one winding. It did make a difference, a big difference.

Actually got one to run like a motor by putting in a 15 VAC three phase voltage direct to the windings. Only problem was it had many poles so did not turn over more than a few hundred RPM. Power output was zilch. It needed a much higher frequency for performance. But this thing is as heavy as a lead brick compared to the modern brushless motors.

DennyV
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Old 09-14-2011, 01:27 PM   #4
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@ Ron, Nope... this is my first post on this forum unless I was a member about 5 years ago.. I was on several forums then but mostly robotics and battlebots stuff.
And thanks for the AWESOME links! Yes this is one of my first builds. You are right and I will build a smaller motor first. I have done some tweaking on EV warrior motors (clocking, isolating the case etc.) and have wound some smaller stuff just for fun but never for a real live flying machine.

@Kyle, I played with alternators at one time too. I didn't rewind it but removed the regulator and fed some voltage into the armature. I found that I could weld with it at about 18 volts with fair results.

The biggest thing with automotive alternators (at least the old dodge I had) is the stator has those trapezoidal teeth. I think they do that to smooth out the output some. It definitely would improve as a motor if the teeth were straight.

Supposedly you could get close to 100 volts 3 phase without a regulator if you fed the armature well and removed the regulator.

Thanks JC
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Old 09-14-2011, 01:43 PM   #5
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@ Ron, Also I have a post on the LRQ forums a while back about Hammer heads.
I got conflicting responses from another board on that one.
Several people told me that if I used closed hammers (The stator is cut reversed and wound from the inside then bolted to the a laminated flux ring on the shaft) I would get a 1 - 2% increase in performance.

Then someone else told me I could get a magnetic short circuit doing that and it was bad.

So I definitely am still in the learning mode!

Thanks JC
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Old 09-14-2011, 02:08 PM   #6
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@ron or anyone else that knows german?...
_________________
Es komt zu einer deutlichen Verstärkung des magnetischen Flusses, der vor allem im gleich dick gebliebenen Rückschluss zu Übersättigung führt.
Diese Simulation liefert die Erklärung dafür, warum im hochdrehenden Segmentmagnetcroco (extreme Magnetstärke(1,8mm N52 Segment) gepaart mit minimalem Luftspalt) im Leerlauf eine massive Aufheizung des Rückschlusses statfindet!
Der 1,2mm dicke Rückschluss ist bei hohen Leerlaufdrehzahlen durch den hohen Fluss und die hohe Zahl der Feldwechsel schlichtweg völlig überfordert.
_______________
is translated by google to
_________________________
It komt in a significant amplification of the magnetic flux, leads mainly remained in the same thickness conclusion to supersaturation.
This simulation provides the explanation for why the high-revving Segmentmagnetcroco (extreme magnetic strength (1.8 mm N52 segment) coupled with a minimum air gap) at idle a massive heating statfindet of inference!
The 1.2 mm thick rear end is at high idle speed by the high flow and the high number of field changes simply overwhelmed.
_________________

Are they saying here that the really powerful magnets with minimal air gap over-saturate the end bell and thus cause heating? Or what?

Thanks again JC
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Old 09-14-2011, 05:14 PM   #7
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Originally Posted by neorules View Post
@
@Kyle, I played with alternators at one time too. I didn't rewind it but removed the regulator and fed some voltage into the armature. I found that I could weld with it at about 18 volts with fair results.

The biggest thing with automotive alternators (at least the old dodge I had) is the stator has those trapezoidal teeth. I think they do that to smooth out the output some. It definitely would improve as a motor if the teeth were straight.

Supposedly you could get close to 100 volts 3 phase without a regulator if you fed the armature well and removed the regulator.

Thanks JC
Yeah, alternators are fun to play with. Didn't think you could use one as a welder through!

As for the trapezoidal teeth in the rotor, methinks that would reduce "Cogging" at low RPMs while charging. I just bought a rebuilt alternator for a project, and that unit also had those trapezoidal teeth, same as one that was mfg 30 years ago.

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Old 09-14-2011, 06:08 PM   #8
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Originally Posted by neorules View Post
@ Ron, Also I have a post on the LRQ forums a while back about Hammer heads. I got conflicting responses from another board on that one. ...
Do you have a link to that thread?

Originally Posted by neorules View Post
... Are they saying here that the really powerful magnets with minimal air gap over-saturate the end bell and thus cause heating? ...
Correct. Also keep in mind that the stronger the magnets, the higher the eddy current losses in the stator.

Vriendelijke groeten Ron
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Old 09-21-2011, 02:49 AM   #9
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[QUOTE=ron_van_sommeren;834130]Do you have a link to that thread?

well... I can't find the link on both threads.. one is from RFL I think...
The whole deal was how wide does the gap have to be between the hammer heads on the end of poles.

One person said that it could be continuous lamination's and it would give me 1 to 2% efficiency but very hard to wind.

Someone else warned me of a magnetic short circuit...

That made me wonder what the (larger than we use) stators I saw with slots cut in them and continuous inner and outer rings of material were for.

If I can find them I will send you the links...
JC
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Old 09-21-2011, 03:02 AM   #10
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@ Ron,

Here is a link to one of the documents I found back in the day when I first posed the question.

http://test.scripts.psu.edu/users/d/...blication1.pdf

I don't understand the math but I read the conclusions LOL...

"IV. CONCLUSION
An effective method for determining eddy currents in the
rotor of a synchronous machine in which insulating barriers
exist in the rotor is presented. The use of the GMRES method
in determining steady-state operation significantly reduces required
computations and runtime. Simulation results show that
rotor losses can be reduced significantly by using one or all
of the following methods: laminating the rotor backiron, segmenting
the permanent magnet poles, increasing slot number,
and “closing” the stator slots."

Thanks JC
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Old 09-21-2011, 09:55 AM   #11
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W ww.powercroco.de/bewicklungsrechner

Here you will find NP configuration and windings. More importantly, you will se what is a good NP combination by checking the winding factors in terms of efficiency.
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Old 09-21-2011, 09:58 AM   #12
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But you may not rely on the winding factors wholly. Sometimes u may wanna have more rpm by sacrificing torque and more importantly, efficiency
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Old 09-21-2011, 01:45 PM   #13
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Originally Posted by kyleservicetech View Post
Yeah, alternators are fun to play with. Didn't think you could use one as a welder through!

As for the trapezoidal teeth in the rotor, methinks that would reduce "Cogging" at low RPMs while charging. I just bought a rebuilt alternator for a project, and that unit also had those trapezoidal teeth, same as one that was mfg 30 years ago.

Some companies that sell modified alternators or alternator hook ups for existing high amp alternators for welding...

http://classicbroncos.com/homemade-welder.shtml
http://www.zena.net/
http://www.premierpowerwelder.com/
http://www.4crawler.com/4x4/CheapTri...er/index.shtml
http://www.essexmfg.com/MobiWeld/index.stm
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