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Old Jul 07, 2012, 12:44 AM
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AleG's Avatar
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Help!
Rewinding C20 1550Kv motor, some help needed.

Some time ago I bought four C20 1550kv motor to make a small quadcopter, alas, one didn't work (broken or shortened wire perhaps) so I took it apart and now I'm seeing about rewinding the whole lot.

I have 0.45mm copper wire and on testing I can put 12 turns on a stator (it has nine). Very tidy I should say, much better than the spaghetti-on-a-fork original winding fork.
So, the question would be, is that wire thickness and turn, on a Delta configuration OK? I have no idea what Kv it would yield, around 1000kv I guess?
Since I have pretty much no experience in rewinding and only a flimsy grasp of the relationship between teeth number, wire, turns, kv, RPM and whatnot I'd be grateful if someone would chip in with some advice.

I'm also thinking of making a PCB to solder the solid wires and the stranded leads, I'm just bored of wires breaking at the base of the motors.
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Old Jul 07, 2012, 02:08 AM
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If the motor started out as a 1550Kv motor and you rewind with twelve turns, the new Kv will be (Told/12)*1550 = Kvnew assuming you use the same termination as the original winding scheme. How many turns did the motor have originally? It appears that in your post you mean to say it has nine stator arms, but I'm also able to read it as nine turns.

Rewinding the motors will bring the actual Kv values very close together. In stock form these cheaper motors can vary widely due to uneven turn counts and such, but when they're rewound all nice and tidy they end up almost exactly the same. That's good news for a multicopter.

The PCB thing is a good idea. I've also had good luck with just tinning the solid winding wires and then soldering stranded wire to them, but that's scary cause you have to chop the winding wires down to little nubs. Good winding wire won't break easily, and if you use heatshrink to bind the leads together where they exit the motor then you probably have nothing to worry about.
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Old Jul 07, 2012, 04:33 AM
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The stator has nine teeth, sorry for the confusion.
I'm afraid I didn't count the original turns as I was gutting the motor, I should do it with the next one.
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Old Jul 07, 2012, 08:54 AM
Jack
USA, ME, Ellsworth
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Quote:
Originally Posted by AleG View Post
The stator has nine teeth, sorry for the confusion.
I'm afraid I didn't count the original turns as I was gutting the motor, I should do it with the next one.
Your options for winding schemes on a nine arm stator can be seen here:

http://www.powerditto.de/Kombinationstabelle.html

If it is a 9 arm 10 magnet (9N10P) motor it was most likely would with an AaABbBCcC (not ABCABCABC as I said originally) wind originally. And if you did not find a Wye bundle (three of the six winding ends soldered together and insulated) then it was a Delta termination.

So your wind choices really come down to ABCABCABC or AaABbBCcC with the magnets really deciding which one to use.

You can copy those winding schemes from the table and paste them into the winding scheme calculator here:

http://www.powerditto.de/bewicklungsrechner.html

Then choose the slot (arm or Nuten) magnet (pole) count and termination and it will show you the wind and give you the winding factor for it. The closer the winding factor is to a value of 1 the better the torque and power of the motor will be.

9N10P AaABbBCcC winding factor = 0.94521

9N12P ABCABCABC winding factor = 0.86603

If you measure the strands in the original wind they were probably 0.25mm or so and to get the same current capacity you wold want the new single strand wind to be that much or more. You can look up the surface area here:

http://en.wikipedia.org/wiki/American_wire_gauge

I looks like the surface area on your 0.45mm wire (0.162 mm2) would be equivalent in area to four strands of 0.25mm wire (0.0404 mm2). Once you figure out the turn count that will give you the termination you want you may be able to use an even larger wire, the largest size that will let you get the needed turns on, to get the best surface area.

There are some turn calculator spreadsheets here that will show your the results on the various wind, turn counts and terminations. Turn Calculator 6 need the input (turn count and Kv) from a dLRK wind so that won't work for you on this motor but the Simple Turn Calculator will help you if you have a known turn count and Kv:

http://www.rcgroups.com/forums/showp...&postcount=266

Added note: And on further consideration, I think the Simple Turn Calculator only works for dLRK winds. So neither of those turn calculators will help you...

Jack
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Old Jul 07, 2012, 09:56 AM
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...thanks Jack, for editing...
Magnus
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Last edited by MagnusEl; Jul 07, 2012 at 07:28 PM. Reason: Problem solved..
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Old Jul 07, 2012, 11:02 AM
Jack
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Magnus,

Thanks for pointing that out, I hate it when that happens. It wouldn't even work that way!

Jack
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Old Jul 07, 2012, 12:18 PM
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Am I understanding correctly that an ABC wind can have 3 arms wound opposite from the other six? sort of LRK
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Old Jul 07, 2012, 12:49 PM
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Ah... erm... I'll read that a couple more times.

I checked the motor and it has 12 magnets. I haven't disassembled another one to count the original windings.

In the meantime I spent some time rewinding a AXN2213 I had laying around, after finishing the second winding I realized it was all wrong. No big deal it was a practice run to gain some experience anyway.
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Old Jul 07, 2012, 02:34 PM
Jack
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Quote:
Originally Posted by zeroback View Post
Am I understanding correctly that an ABC wind can have 3 arms wound opposite from the other six? sort of LRK
That is the way that generally reliable and accurate table at powercroco has it shown. It has one variation for 4 magnets (ABaCAcBCb), a second variation (AaABbBCcC) for 8 and 10 magnets, and tbe ABCABCABC for 6 and 12 magnets.

We need to get three identical motors and try it all three ways, right?

The winding scheme table on the Motor Building Info page presents the same info but in a little different manner. They use a black/blue/white/red scale (credited to Dr. Ralph Okon) for grading the winds as meaning:

black- does not work,
blue - good combination,
white - it works,
red - it works, but not very well

The powercroco page grades the blue fields as "works well", the red fields as "not tested" and empty gray fields to mean there is no functional wind.

I think the powercroco table is the newer of the two so I have been using that one for the most part.

Jack
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Old Jul 07, 2012, 05:50 PM
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Having rewound a couple or 4 C20's in the past, 8 turns is (?) ~2000kv on those, it's 4 strands of V thin wire oem. Quite easy to replicate using ( IIRC?) 24 ga which gave more density than the oem but it does look a bit skimpy actually.
No matter, perf is improved as result.
Simple ABC wind is fine. There are no observable disadvantages to the simpler wind scheme.. true enough.
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Old Jul 09, 2012, 09:30 AM
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How interesting, new (to me) winding technique. Is there any motor kits available with 9 arms and loose magnets to experiment with. The RCer kit I bought has a 9 tooth stator but the magnets come glued in the bell.
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Old Jul 09, 2012, 04:17 PM
Jack
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Strong Motors has some:

http://www.strongrcmotors.com/Motors.htm

And Komodo Hobby, at least in theory, sells some kit motors and the KH-278 has a 9 arm stator and comes with loose magnets.

http://www.komodohobby.com/

But I can't ever get their web pages to work in Firefox so I'm not allowed to shop there or even see what the prices are like...

I don't have another browser to try, IE might get it up for you.

If you google the KH-278 motor it brings up some info on it:

http://www.komodohobby.com/cgi-bin/s...categoryID=181

But I can't get anywhere from there.

Jack
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Old Jul 09, 2012, 09:17 PM
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Unfortunately DIY Motor kits are yesterday's news. Looong gone.
Either old stock or foolishly expensive for what you get
Simplest more cost effective approach is to rewind an existing motor.. albeit , often these are glue slathered . Just to add insult to injury.
IMO (gasp! a Heretic) it's a slowly dying Fad.
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Old Jul 10, 2012, 07:33 AM
Jack
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The kit motor days peaked before I got into this so I skipped that phase. I came in during the Tower Pro CD-ROM style motor glory days I think. And those are still viable candidates for rebuilds and rewinds. But getting hardwer to find and some of the parts for them, like the end bell fittings and stuff are probably getting hard to find.

Jack
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Old Jul 10, 2012, 10:08 AM
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There is a life time supply of burnt up motors/parts that folks will sell for cheap or give away just pay for shipping. I posted 1 request and I have acquired a pile of motors. The selection includes cheap to top tier.
I'll check out the links and see if I have any luck.
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