How to wind a motor?

[John Rist]

I have unwound a burnt out Cobra 2820/12 motor.  It had 3 wingdings of 4 wires each.  It had 6 turns per section.  The armature has 12 slots.  Each of the 3 leads had 8 wires.  So that accounts for all 24 wires.  I believe  the 3 wingdings were probably in a delta pattern.  Does any one have a link on winding motors?  I had trouble getting the old wire out and did not quite get the pattern down pat.  I have magnet wire and believe I can rewind the motor if I knew the wind pattern.  I am guessing the pattern is per the sketch attached.  The sketch is for one of the 3 segments.

[Tim Wescott]

I'm guessing, based on winding home-made motors as a kid, and some time making motors work in industry, but without any real experience rewinding motors:

Dunno where your "segments" comes from, but if you take a felt pen and mark "A B C A B C" on the poles, all the way around your armature, then you should put four turns of winding "A" around each of the four "A" poles, four turns of winding "B" around each of the four "B" poles, and so on.

When you're done, hook the motor up to a voltmeter and give it a spin -- it should read some AC voltage.  It should also spin down about the same with windings as it did without -- if it feels like it's filled with molasses when you spin it, you probably shorted a winding or did something else wrong.  To get an idea of what I mean, short the wires on a spare motor and give it a twirl.

Actually capturing how it was originally wound would have been best, but I understand how sometimes that doesn't work out.

[John Cralley]

This may help.

http://m.instructables.com/id/How-to-Wind-a-12N-14P-Brushless-Outrunner/

[Larry Renger]

Chuck a hook into a hand drill, lube the motor with a mix of green soap and glucerin. Stretch it to about 2x length and start cranking. 

[Howard Rush]

Chuck a hook into a hand drill, lube the motor with a mix of green soap and glucerin. Stretch it to about 2x length and start cranking.

I wondered if John would get the joke, then I looked at his age.  Sadly, I can't imagine anybody younger than us winding either type of motor himself.

[William DeMauro]

If you do a search on RC Groups in the power section  http://www.rcgroups.com/power-systems-13/ you should be able to find some info as I remember reading about that about 5-6 years ago. I do know that not only the number of turns matter but also the gauge of the wire. With the cost of these motors being as cheap as the are these days. I don't see much practical purpose in rewinding one unless you just want to do it for the sake of learning how.

[Tim Wescott]

Thanks to Science Olympiad, there's a supply of rubber-power-savvy kids out there.

[John Cralley]

John, Alan Hahn rewound an outrunner or two a few years ago. I seem to recall that he wanted to change the KV or some such. Alan left the Stunt Hanger forum but I think I have his email address. PM me and I will look for it if you want to pick his mind on rewinding motors.

Howard, Yes, geezers like me have wound a few motors in our day and successfully knocked the sides out of models when they broke! 

[John Tate]

I found info a few years ago on electric motor rewinding on the following: http://www.gobrushless.com/shop/index.php?&tgt=top

I even obtained the wire to rewind the motor from them. I liked dealing with them.

[ericrule]

I checked with the folks who rep Cobra motors here in the uSA. They confirm that it is indeed a delta pattern.

[John Rist]

I checked with the folks who rep Cobra motors here in the uSA. They confirm that it is indeed a delta pattern.

I had figured out ( by looking at the motor) that it is a delta pattern.  I figured out that mine is a 6 turn winding.  I also learned that it is 4 strands of 26 AWG.  When I unwound the motor it appeared that each of the 3 windings was wound on 4 adjacent slots.  However the web sight John Cralley recommended shows the 4 slots of a winding are 2 sets of 2 180 degrees apart. I am going to test wind this pattern and see if it works.  But I would like to wind it back to the original Cobra configuration.

Some  suggested that at the cost of a motor it is not worth rewinding.  This is somewhat true but it cost $5 to rewind a $50 Cobra motor.  If you have a $100 motor it is really a cost savings.  But the real deal is I want to do it just for fun.  As a retired engineer I have lots of time to tinker - and I love tinkering.  

[John Rist]

Chuck a hook into a hand drill, lube the motor with a mix of green soap and glucerin. Stretch it to about 2x length and start cranking. 

                

I get it!!!!

[John Rist]

Well I figured it out!  

I had a second motor that was also burnt out.  I basically destroyed it to see if I could determine the wind pattern.  So what I figured out is that a Cobra 2820/12 motor is a 6 turn motor. It has 12 stater bars and 14 magnets. It has 3 windings wired in a delta configuration.  Each winding consist of 4 strands of 26 awg wire.  As it turns out the configuration as described at http://m.instructables.com/id/How-to-Wind-a-12N-14P-Brushless-Outrunner/ will not work with my motor.  This How-To shows winding 4 stater bars in groups of two bars 180 degrees apart. My motor has each phase wound in a group of 4 adjacent bars.

I didn't have any 26 AWG magnet wire so right now the motor is wound with wire that is way too small.  So far I have just ran it no-load.  I do plan to put on a small prop to check the KV rateing.  I have the correct wire on order (good old EBAY) so one day next week I should be able to see if I can actually wind a working motor.  Attached is a drawing of the winding pattern that worked for me.

 

[John Cralley]

Great John!

That pattern turns out to be quite different from the one in the link I posted. Give us an update when you get the correct wire on it.

[John Rist]

I just ran the rpm test.  At 13.4 volts (measured at the speed controller input) I am reading 14400 RPM.  That would be 1074 KV.  The speck is 970 KV. So at 13.4 volts the RPM should be 13000 RPM.
I wound the motor as a 6 turn motor.  So 14400 RPM divided by 6 gives 2400 rpm per turn. I am 1400 RPM high.  This is about 1/2 turn off.  The 14400 RPM may be OK because I set RPM at 95000 with a KR timer.  I am running a very light load (1/2 A prop).  I don't have a working factory fresh Cobra motor to test for comparison.  Right now the 2820/12 is on back order.  It will be two weeks before I get one.

Any thoughts and comments would be appreciated.  

[John Rist]

It is doubtful if I will be able to wind this motor.  The stator is press fitted to the baring support/end-bell. I would bet money, that at the factory the stator is wound and then installed on the baring support/end-bell assembly.  Because the end-bell is close to one end of the stator it is almost impossible to get the windings tight enough to get all 6 windings in place.  Anyway I have ordered a new motor.  This time I will try a Cobra 2826/10 instead of the 2820/12 that burnt up.  The 2826 is the same diameter and bolt patter and  is only a 1/4" longer.  It has a slightly lower KV rating but a higher power rating. By the way I discovered that I burnt up to old motor because I was running too large of a prop.  Anyway it was fun to deturmine the wind pattern of a Cobra motor.