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Brushless Motor Construction Discuss design and construction of custom Brushless motors

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Old 10-16-2007, 03:14 AM   #1
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Default Rewinding Help Please.

I'm rewinding a motor, The plane was to get some more efficiency out of it but I don't think that's gonna happen ):

Emax cf2805 15T of 3 strand 30awg wire in dLRK.
It was recommended I use 17T of 24awg but that's not going to happen.
I was barely able to get 13T on two teeth.

So the question is can I use 10T and terminate it Wye and get similar performance? Or I suppose I could just use a LRK wind(?).

Suggestions Please,
Thanks.

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Old 10-16-2007, 05:22 PM   #2
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LRK or DLRK does not matter much. DLRK is better for thin motors, LRK for longer motors.

17wind in delta is equivalent to 10 winds in wye. Use the thickest wire possible or wind 2-3 in parallel if that's easier.
The only way to get efficiency up by rewinding is by getting a better statorfill i.e. with copper.

About winding wire
Go to your local friendly motor/transformer rewinder/refurbisher or repair shop. Excellent quality, all gauges, penny stuff, you'll probably get it for free if you bring your motor along. They love it when they can handle a motor without an overhead crane And maybe let them have a spin with your plane once you finished your motor? You know, in case you need wire again for your next motor

In general:
Whether you use star or delta makes no difference, you can get the same motor (Kv, Kt, Io, Ri) with both configurations: 17 winds in delta/triange is the same as 10 winds in star/wye (factor 1.7 = v3 ). (Wire diameter has to be changed accordingly of course)
However, delta is a closed circuit all by itself, differences between the wound phases (#winds, wire-length or -diameter) may lead to differences in the voltages induced in the coils/phases. Useless circular currents will flow through the delta circuit, which leads to higher temperature and lower efficiency.
Therefore: star/wye.

About (D)LRK
12 statorpoles, 6 (lrk) or 12(dlrk) wound, 10 or 14magnetpoles:
DLRK winding tutorial
http://www.rcgroups.com/forums/showthread.php?t=736580
LRK winding
http://www.rcgroups.com/forums/showthread.php?t=523039
http://www.torcman.de/peterslrk/index_eng.html
http://www.torcman.de/motoren/manual...o_200e_scr.pdf


Excellent motor building articles by Brian Mulder, a must read, will prevent you from asking a lot of questions you even did not know you were going to ask
http://www.southernsoaringclub.org.za/
-> Articles by SouthEasterners.
-> Electric Motors - part 1-5

Do-it-yourself motor homepages, manuals/tutorials, checks and tests in this motor builders tips and tricks thread. The checks and tests may save you from frying your controller or motor. Thread is active, bookmark it for future reference and subscribe to it:
http://www.rcgroups.com/forums/showthread.php?t=240993 (sticky thread, at top of subforum)


Vriendelijke groeten Ron
diy motor building tips & tricks
diy brushless motor discussion group
Drive Calculator download & discussion group
int. E fly-in & diy outrunner meet, Nijmegen, the Netherlands
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Old 10-16-2007, 10:12 PM   #3
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Originally Posted by fr4nk1yn View Post
I'm rewinding a motor, The plane was to get some more efficiency out of it but I don't think that's gonna happen ):

Emax cf2805 15T of 3 strand 30awg wire in dLRK.
It was recommended I use 17T of 24awg but that's not going to happen.
I was barely able to get 13T on two teeth.

So the question is can I use 10T and terminate it Wye and get similar performance? Or I suppose I could just use a LRK wind(?).

Suggestions Please,
Thanks.
As Ron said 17T delta and 10T Y are basically the same. So if the orig. wind was 15T and you wind 10T you will be reducing the Kv and get lower power, speed and max. current draw, if you keep the prop. and battery the same. Less power (higher turns) is not normally the direction rewinders go. It would only be desireable if your plane has too much power now and you are willing to sacrifice power for improved flight time. Again that is not common, but if you are into ariel photo, or duration maybe it makes sense.

15T delta is the same as about 8.6 T Y so if you wind 8 or 9 T you will have about equal performance (speed and power) as the orig. If you want more power, and speed you can wind 6 or 7 T connected in Y, but current will go up.

15T of triple #30 gives a copper cross section that provides about the same fill as:
18T #26
14T #25
11T #24 (It is no wonder you had trouble with #24 at higher turns)
9T #23
7T #22


As Ron said, peak efficiency of the motor will improve only if the new winding has more fill or copper. However the efficiency with a particular battery and prop can also be changed by selecting the best number of turns.

So, if you want a slower motor to match up to a big prop wind #26 and if you fit over 18T Delta you will gain on fill (peak efficiency) also.

If you want equal power and speed with better peak efficiency wind #25 with 15 turns Delta or 9T #23 Y.
#24 is not a good size--You end up with 11-12T Not enough for Delta and too many for Y

For a modest power and speed increase (also higher peak current) wind 7T #22

Have Fun!
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Old 10-17-2007, 01:18 AM   #4
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THANKS Guys!(:

I wish I had know about the 24awg before I bought 1/2lb of it. ):
Maybe I'll place it in the for sale section.

Now I'll run to RS and buy their $5 spool and report back shortly.
I'll try 22awg and see the fill then try 2 strands of 26awg.

There's different opinions on using multiple strands. Some say it's good some say it's bad.

I've followed a lot of those links Ron Some don't translate well using Babelfish. Even still I have a lot of questions, Like:

Is it my imagination or does the second consecutive tooth on a dLRK wind lose 1/2 a turn when the wind direction is changed?

BTW Stator diameter is 22mm, and length is a little over 5mm (.3 according to my caliper).

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Old 10-17-2007, 03:18 AM   #5
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I tried the 7T of 22awg and it was a little sloppy.
So I tried the 9T of 26awgx2 and it was much cleaner.

I haven't decided on which to finish it with.


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Old 10-17-2007, 03:58 PM   #6
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Glad things are working for you now.

Have Fun!
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Owner, www.strongrcmotors.com
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Old 10-18-2007, 05:11 AM   #7
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Thanks for the help.
I went with your recommendation, 7T of 22awg. My fingers are kinda numb and my fingernails are broke ): I spent a lot of time practicing.

Here's the motor before terminating, and before checking for shorts o:
I need to read up on how to do it.


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Old 10-18-2007, 03:57 PM   #8
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.
Careful not to overstretch the wire


picture from www.torcman.de
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Old 10-18-2007, 04:41 PM   #9
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Originally Posted by fr4nk1yn View Post
Thanks for the help.
I went with your recommendation, 7T of 22awg. My fingers are kinda numb and my fingernails are broke ): I spent a lot of time practicing.

Here's the motor before terminating, and before checking for shorts o:
I need to read up on how to do it.
Lookin' good !


To check for shorts:
Scrape the insulation off a 5 mm length on each end of each wire (six locations).
If you have a Multi -meter, set it to measure OHMs or resistance. The test leads should be pluged in to the common (-)terminal and the terminal labled resistance, or Volts, or +.
If the meter has and audio beep for a continiuty check turn it on.
Touch the ends of the two test leads together. I f you have a continuity check beeper you should hear it now. The readout should be some very small value (never exactly zero, but close to it). That is the indication of a direct short, and that is what you do not want to see or hear when testing your winding.

Now you are ready to test!
Touch one lead to the bare metal on the outside of the stator. Touch the other test lead to the end of each wire. You should never get the indication you got when you touched the two leads together. If you do there is a short between the wire and stator.

If there are no shorts to the stator, then it is time to look for a short between wires (these are very rare). With one lead connected to the first wire to be tested. Touch the other lead to all the other wire ends. Only one should indicate a connection, (same as continuity, or very low resistance). When you here a beep or see the low resistance you have the leads touching the opposite ends of the same wire! That is supposed to be a solid connection, but there should not be a solid connection to any other wire end.

I sell a video DVD on motor building which has a great explaination on testing for shorts and measuring volts and amps during bench testing using low cost meters. It's only $12 and many good tips and tricks for building and testing motors. It is shown on this page of my website. http://www.strongrcmotors.com/Kits.htm


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Old 10-18-2007, 04:49 PM   #10
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First test for shorts between the phases before you hook them up in delta or wye. If you do it the other way round, you will certainly measure shorts, after all, the phases are connected now.

Checking for shorts during winding, item #24:
http://www.rcgroups.com/forums/showthread.php?t=240993
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Old 10-19-2007, 12:44 AM   #11
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I checked at lunch today and there was no shorts to the stator or other phases. I tied every other leg together, soldered them and covered with heat shrink. I was not able to read resistance even using my ϋber-meter which apparently doesn't measure below 0.1Ω, although it did fluctuate in graphing mode.Motocalc, with my fudged numbers said the kv would be 3521rpm/v.
Using a cordless drill that spins at 1170rpm, and a freshly charged battery, the measured AC was .34v so it works out to 3440kv(?).

I have to solder on some leads then test it using my "junk" 25amp and a discharged pack.

This is really exciting thanks guys!

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Old 10-19-2007, 02:40 AM   #12
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I solder some wires and tested on the cheap ESC with a dead pack.
It started up fine under no load but seemed like it stuttered under full power.
I then tried a Graupner 5.5x4.3 prop. Again ok up until full throttle where it "didn't sound right".
So the full 1320 2s pack went on along with a T-Bird 18. No stuttering but it feels weak.
With a bit of playing I start smelling the magic smoke. Then I see the magic smoke ): But upon taking the motor apart I see no obvious hot spots.

I took a few macro photos to help me out since I have no magnifying glass at the house. And I spot something that does look right. I'll take a look at it tomorrow under the glass. *sigh


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Old 10-19-2007, 02:52 AM   #13
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Another way of testing. Use the cordless drill and measure all three voltages, preferably at a higher rpm this time. Al three voltages must be the same.
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Old 10-19-2007, 05:19 AM   #14
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Originally Posted by fr4nk1yn View Post
... I tied every other leg together, soldered them and covered with heat shrink. ...

I have to solder on some leads then test it using my "junk" 25amp and a discharged pack.

This is really exciting thanks guys!
Sorry to hear about the smoke, but don't get discouraged. Most of us have seen it a few times. It happens.

I am wondering if you made a connection error when you made the "Y". Each phase wire has a start end and a termination end. To make a "Y" connection you can connect the three starting ends or the three termination ends. Is that what you did when you "tied every other leg together"? It sounds like you may have connected a mix of starts and terminations. When I wind, all three starts are adjecent and all three "ends" are adjecent. And, the three starts are adjecent the three ends. So if I connected every other end, I would be connecting either two terminations with a start or two starts with a termination end. Either way is wrong. Two make a "Y connection I would connect either the first three wire ends, or the last three.
Let me know if that is not clear.
Don

EDIT: Sorry, The information above is for a16 magnet motor with 12 arm stator wound ABCABCABCABC (or a 6 or 12 magnet motor with nine arm stator wound ABCABCABC). It is exactly correct for the dLRK winding. See post #18.

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Old 10-19-2007, 05:51 AM   #15
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I think I understand. I looked at a chart and thought I had it correct but now I'm 2nd guessing it.
*epiphany I understand it clearly now.

I took the e-clip off, since it's a pusher for now, started it up with the prop then took it off quick and felt the stator.
It was "smokin'" right where I zoomed in the photo.
180 away and it was cool to the touch.
I was thinking I sawed the wire against the stator while winding it.

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Old 10-19-2007, 08:24 AM   #16
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I decided to start over, besides it's more practice.
That one tooth that got hot had the insulation flaking off.

In my effort to get the winds neater, which I think I did, I'm not sure if I've messed up.

I find winding like in the first photo easier since winding tightens the first loop.
However trying to be neat and symmetrical I staggered the wires like the second photo.


My brain is hurting now trying to be sure or the termination, it's time for a nap x_x

Images are from powercroco.de


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Old 10-19-2007, 02:21 PM   #17
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What did you do about the sharp stator edges?
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Old 10-19-2007, 04:44 PM   #18
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Originally Posted by fr4nk1yn View Post
I decided to start over, besides it's more practice.
That one tooth that got hot had the insulation flaking off.

In my effort to get the winds neater, which I think I did, I'm not sure if I've messed up.

I find winding like in the first photo easier since winding tightens the first loop.
However trying to be neat and symmetrical I staggered the wires like the second photo.


My brain is hurting now trying to be sure or the termination, it's time for a nap x_x

Images are from powercroco.de
I see now at www.powercroco.de many variations of winding end patterns and even the one shown below which would be correctly connected "Y" by joining every other wire as you did. EDIT: This one is wound AabBCcaABbcC.
There are many variations I did not know about. I think I should be quiet. And suggest you wind your motor using the information at www.powercroco.de


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Old 10-19-2007, 04:53 PM   #19
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I have to wind it AGAIN. The first pahse I did is now shorted to the bearing tube.
I'm wondering if the insulation on the Radio Shack wire is too delicate.
Perhaps thats why it's $5 compared to $12 at the electronics store.
There's one place that winds motors locally and I think it might be too far to reach on my lunch period, But I may have to try anyway.

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Old 10-19-2007, 06:35 PM   #20
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Originally Posted by bz1mcr View Post
I think I should be quiet. And suggest you wind your motor using the information at www.powercroco.de
Don't do that I'm learning a lot here. But theres still confusion. A lot of it.

I think that wind was AaBbCcAaBbCc which sent me into a spin.
Should there be two teeth with counter clockwise, and clockwise, winds next to each other? i.e. AaBbCcaAbBcC

-edit-
I made it to the motor rebuilders. This wire is far superior to the RS and the wire from the electronics shop.
It's softer than than even the 26awg Radio Shack wire and the varnish insulation is tough it took some good scraping to get off.
They gave me 9' for free just as mentioned (:

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Old 10-19-2007, 10:30 PM   #21
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I edited my post with the attached wiring illustration to in clude the wiring patern notation AabBCcaABbcC. I only copied this from http://babelfish.altavista.com/babel...ma12N14Pv.html. I do not know about it myself.

It says on that site

"AaBbCcaAbBcC Thus actually WRONG wound!"

You say "I think that wind was AaBbCcAaBbCc which sent me into a spin." I do not see any referance to this winding pattern for a 14 magnet motor.

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Old 10-20-2007, 05:42 AM   #22
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With the GREAT wire I went back to the very basics.
I followed exactly a dLRK tutorial on RCG, instead of half following that tutorial and half "improvising" from another site.

Seven turns of 22awg. No shorts to the stator, I was really anal about that this time around. No phase shorts either so I'm doing good (:

I hooked a drill up, 1200rpm, for 1st run:
  • Stock: .371vac/.371vac/.382vac
  • Rewound: .311vac/.311vac/.320vac
Then I connected them to a Dremel, estimated 11krpm:
  • Stock: leveled off to 3.72vac (2956kv)
  • Rewound: 2.41vac (4560kv!?!)
Connected to a discharged battery and cheap ESC the motor was very quiet and smooth.
The LHS will measure speed and watts on a motor/prop for a couple bucks I may do so I have "real" data on it. 4560kv seems a little high.

-update- Somebody borrowed the test equipment from the LHS so no actual test.
I did make a makeshift thrust stand and measure the voltage with a 4.5x4.1 APCe.
Over 10 ounces of thrust at 7.6v with a Thunderbird ESC 18(?!?).
I mentioned the ESC since the cheap ESC was stuttering at full throttle with the prop and had less thrust.

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Old 10-22-2007, 03:15 AM   #23
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I flew this today with 4.5x4.1 and a 4.2x4.0 APC props on a scaled down, 24", Mugi.
Once on step with either prop this motors screams.
The 4.2x4.0 was quite a bit faster with hardly any loss of thrust.
It looks like smaller props only before efficiency drops, same as MotoCalcs' simulation.

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Old 10-23-2007, 06:25 AM   #24
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I hate to bump this again but I did some some readings using the same "thrust-stand", a clamp-on DC probe connected to a scoping multimeter and measured the voltage with a second multimeter at the Li-Pos balancing tap.

Here's the results.

I'm pretty happy with that.
RPM was calculated using Thrust_XL from the thrust measurement.

No load current was 1.8 amps for whatever that's worth.

"If you stand behind me... You gonna get kicked." - Zebraman.
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