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Old Aug 10, 2012, 02:31 PM
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vtdiy's Avatar
Southern Vermont
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Removing old windings?

I've been reading enough in this forum to want to try to rewind a motor. I read the DT-750 thread start to finish, and have a few of those, but they work too well as is on the planes I have to want to tear one apart.

I do have some defunct motors, so I thought I'd try one of those -- a 2409 1200 kv CDrom type from EMP. This one had a very short life when it came loose from the mount and twisted the leads, breaking some of the winding wires.

I have it apart, but it looks like the windings are glued together. I've tried a hair dryer to heat it (probably not enough), and methanol (methylated spirits in UK), but that hasn't done it.

I've read that acetone will soften the winding cement, but will also attack the stator epoxy.

Early on I did use a Dremel with a cutoff disk on one of the winding bundle ends and cut through the wires almost to the stator, without touching it. After that I heated with the hair dryer. But it didn't seem to free the wires. What temperature do I have to get it to?

Also I was wondering if there are any other tips or suggestions for removing the windings before I try the acetone on it.

These windings are very tightly packed, very fine and look like 5 parallel strands. The stator is filled, and it may be as much a mechanical problem as a glue problem once I get the glue soft.

Anyway it's a learning experience for me.

Thanks!


EDIT and UPDATE:

There's lots of useful alternative info in this thread, however to save some grief please check out this video by rcAllDayLong showing an easy method of unwinding using heat from a stove top. After trying the thinner and re-coating method, I now think that heat is the way to go. A hair dryer is not enough heat to do it -- On my second motor, I ended up using a Harbor Freight plastic welder with an air regulator and a router speed controller to regulate temperature, but you don't need something that sophisticated -- I just happened to have it on hand. The first motor was stripped with lacquer thinner and tedious cutting and pulling out of wires. It looked "a right fright" to quote flydiver. It was successfully re-coated with epoxy and wound, and as a result a good learning experience. But I don't recommend any one follow suit, unless heat doesn't work.

Here's the video:

winding removal, prepping for new wind (2 min 14 sec)



Also a video on bearing removal:

Bearing removal from a brushless motor without damaging motor (1 min 40 sec)
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Last edited by vtdiy; Aug 29, 2012 at 07:54 AM. Reason: Added link to video
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Old Aug 10, 2012, 03:40 PM
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flydiver's Avatar
United States, WA, Seattle
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Good luck. It's mostly brute force and cussing.

I rarely bother with motors of that irritation level anymore. If you are new to winding I strongly suggest you get a better candidate to start and save that headache for later. It will raise your chances of success and lower your frustration level.
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Old Aug 10, 2012, 06:24 PM
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Bishopville S.C.
Joined May 2003
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I must agree with flydiver here. You could bake the motor @ 250f to soften the epoxy, but this means unwinding before it cools. Very messy, only worth the trouble on hard to find stators.

Acetone baths are easier, but either method can damage the stator coating. Not just on the surface, but between the laminations. What started as a stack of 20 lams can end up as one hunk of metal.

If you are determined, try using PVC pipe cleaner instead of pure acetone. It comes with an applicator in the can. The applicator can be removed, and the rod holding it then can be formed into a hook. This works very well for cleaning magnets/bells/bearings as the parts are submersed but not touching the bottom. Also the lid can be screwed on to contain the fumes.
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Old Aug 10, 2012, 06:52 PM
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vtdiy's Avatar
Southern Vermont
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Thanks flydiver and Ronh.

I didn't have acetone or primer on hand, but did have lacquer thinner. It did seem to break down the glue somewhat, but not enough.

Tried a hacksaw blade down through the spaces between teeth to nearly the stator. Still couldn't pick out broken strands. The winding was so tight and fine that solvent hadn't really penetrated enough after several hours to make it reasonable to continue. So I'm giving up. Looks like a copper brillo pad.
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Old Aug 10, 2012, 07:31 PM
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San Jose, California
Joined Dec 2007
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Looks like I'm too late to the thread, but if you do another one...

depends on what type of epoxy was used.
anyhow, hair dryer is not enough heat

if it's that black epoxy, you're looking at 700 degrees or higher
if it's anything else, the epoxy will break down after 300 degrees.

You can either put it in an oven, or put it on the stove top.
I like the stove top, since I can pop it on and work on it while it's hot. You'll find that when it's still hot, you can easily unwind just like there was no epoxy there. After doing about 25 motors, it's pretty easy and straightforward. The trick is just enough heat to soften, but not burn it.

winding removal, prepping for new wind (2 min 14 sec)
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Old Aug 10, 2012, 08:15 PM
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vtdiy's Avatar
Southern Vermont
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Hey rcalldaylong, really helpful video! Thanks a lot.

Well not necessarily too late. It so happens I have another bad motor of the exact same type. That one had grinding sounds after a crash. Replacing a bearing didn't seem to help it. So I could take that one apart too. Maybe I can mix and match parts, and try your stove top method on that stator. What have I got to lose -- both motors are bad.

I'm also leaving the first stator in thinner overnight just in case it loosens up enough to try one last time to pick the strands out. I do have WEST system epoxy. Don't know if that would be useful on the stator lams after the thinner treatment if the green insulating coat comes off.

btw, the glue used on the windings was transparent. Black glue only on the magnets on the rotor.
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Old Aug 10, 2012, 08:17 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Another way to apply heat to the epoxy is with a microtorch. You can see how I did that here on a D4023-850 motor:

http://www.rcgroups.com/forums/showp...7&postcount=40

With that, focusing the pinpoint flame at the bundle as it was pulled up and way worked very well. But those windings were not as heavily epoxied as the others I've done.

Sounds like you saw those photos I posted on using the Dremel disc, that worked for me once. After making the cut I was able to cut down into the bundles with the nose of a small diagonal wire cutter and then peel the wire to each side in strips and by layers.

Seems like every time I have to learn a new way to do it because what worked last time is not working. But the next time it does not...

Jack
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Old Aug 10, 2012, 08:34 PM
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vtdiy's Avatar
Southern Vermont
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Well thanks jackerbes! That gives me another idea.

I happen to have an older Harbor Freight plastic welder that I added a router speed control to. It has adjustable airflow, and heat. It makes hot air.

But the nozzle is the size of a pencil so I can really direct it to a small spot, not like a hair dryer, and also control the flow and temp.

Wonder how that well that would work for this?
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Old Aug 10, 2012, 08:47 PM
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San Jose, California
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Quote:
Originally Posted by vtdiy View Post
Hey rcalldaylong, really helpful video! Thanks a lot.

Well not necessarily too late. It so happens I have another bad motor of the exact same type. That one had grinding sounds after a crash. Replacing a bearing didn't seem to help it. So I could take that one apart too. Maybe I can mix and match parts, and try your stove top method on that stator. What have I got to lose -- both motors are bad.

I'm also leaving the first stator in thinner overnight just in case it loosens up enough to try one last time to pick the strands out. I do have WEST system epoxy. Don't know if that would be useful on the stator lams after the thinner treatment if the green insulating coat comes off.

btw, the glue used on the windings was transparent. Black glue only on the magnets on the rotor.
don't soak it in thinner. I did that in my early winding days. when I did it, I only left it in thinner for like 30 mins and it ate up all the green enamel, well it softened it up to where it just came apart when touched. I'd imagine a whole day will strip it clean off. instead, put it on the stove top and when it comes up to temperature, you can just strip the pieces off.
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Old Aug 10, 2012, 08:58 PM
Jack
USA, ME, Ellsworth
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Quote:
Originally Posted by vtdiy View Post
Well thanks jackerbes! That gives me another idea.

I happen to have an older Harbor Freight plastic welder that I added a router speed control to. It has adjustable airflow, and heat. It makes hot air.

But the nozzle is the size of a pencil so I can really direct it to a small spot, not like a hair dryer, and also control the flow and temp.

Wonder how that well that would work for this?
Looks like it could work well. Any idea how hot it gets? I think you need 350-400F or so to get epoxy softening. If I had one around it would get tried, you betcha!

Jack
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Old Aug 10, 2012, 09:07 PM
Jack
USA, ME, Ellsworth
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I've stripped two stators down to bare metal. One out of stupidity and the second to prove that the first time was still stupid...

One of them ended up in the trash as a collection of loose stator laminations. The second is still awaiting a cure...

Here is a thread discussing the various potential cures for making the mistake of stripping a rotor to bare metal:

Stator coating - http://www.rcgroups.com/forums/showthread.php?t=1702834

Jack
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Old Aug 10, 2012, 09:08 PM
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rcalldaylong's Avatar
San Jose, California
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Quote:
Originally Posted by jackerbes View Post
I've stripped two stators down to bare metal. One out of stupidity and the second to prove that the first time was still stupid...

One of them ended up in the trash as a collection of loose stator laminations. The second is still awaiting a cure...

Here is a thread discussing the various potential cures for making the mistake of stripping a rotor to bare metal:

Stator coating - http://www.rcgroups.com/forums/showthread.php?t=1702834

Jack
It would be cost prohibitive to get into that for a couple of cheap chinese motors. Better to just not strip it.
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Old Aug 10, 2012, 09:11 PM
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vtdiy's Avatar
Southern Vermont
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@rcalldaylong that one is probably a lost cause anyway -- all wires frayed from dremel and hacksaw, yet the glue is still holding things down -- just soaking it now out of curiosity.

The other one is untouched and would be a better candidate for the heat method. Photo below.

@jackerbes

I think I will try it. I'm sure the welder can get to whatever temp I need, including red hot and burning out the element if you don't regulate the air properly! I don't think 400F would be any problem, certainly 250 would be easy -- it is designed to melt and weld polypropylene, nylon, PVC, etc. and can scorch black all of those if you don't keep it moving and use with care.
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Old Aug 10, 2012, 09:21 PM
Dude, I do fly all day long!
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San Jose, California
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Quote:
Originally Posted by vtdiy View Post
I think I will try it. I'm sure the welder can get to whatever temp I need, including red hot and burning out the element if you don't regulate the air properly! I don't think 400F would be any problem, certainly 250 would be easy -- it is designed to melt and weld polypropylene, nylon, PVC, etc. and can scorch black all of those if you don't keep it moving and use with care.
Just one more piece of advice- don't heat it too much. If you burn the epoxy too much, it welds the windings together, then it's just as hard to get out...Don't ask me how I know
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Old Aug 10, 2012, 09:24 PM
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Southern Vermont
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I'll try to start friendly, rcalldaylong!


Edit:

I kinda wonder if this thing was baked together at the factory, actually....
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