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Old May 03, 2014, 07:49 PM
Little Red Plane
United States, TN, Knoxville
Joined Dec 2012
559 Posts
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Need help rewinding MVVS glider motor

I have a MVVS 3.5/960 motor that I would like to rewind.
I don't really know where to start, what size wire . or how many turns on each pole.
Has anyone rewound one of these motors?
Thank you in advance for your help,
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Old May 04, 2014, 05:11 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,790 Posts
What is the purpose of the rewind? Burnt, higher/lower Kv, higher efficiency?
Has the motor overheated?

Don't unwind it yet! Have to figure out first star- or delta-hookup, number of winds, number of parallel wires, winding diagram.
How many stator poles, how many magnet poles.
Pictures?
Your first rewind, or do you already have rewind experience?

This will help you understand the answers you are going to get from us
(Re)winding and building motors, tips & trick, manuals, do's and don'ts

Vriendelijke groeten Ron van Sommeren
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Old May 04, 2014, 06:16 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,995 Posts
Kind of an interesting motor, like Ron suggested, it looks like we will need and full and detailed autopsy on it.

If you get it out of the can and find the windings are heavily epoxy saturated, give us a report on it before you proceed much further. We can probably help get you through the process from there.

Esprit says "Poles (Rotor/Stator) = 12" so I am guessing it is probably a 9N12P motor.

Images compliment Esprit Model...

Jack
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Old May 04, 2014, 07:37 AM
Little Red Plane
United States, TN, Knoxville
Joined Dec 2012
559 Posts
The reason that I want to rewind it is that I overheated the motor and smoked the windings. Now all that the motor will do when power is applied is kind of shake, it will turn by hand, but not with power.
Yes I can purchase a new stator/ windings from Esprit, but I would really like to use this as a learning exercise and rebuild it myself.
The windings do not appear to be epoxied in place. I will take it apart and take some pictures of it so you can see what it looks like.
I have seen where other hobbyists have rewound the similar Turnigy Glider Drive motors. To me once you remove the outer housing a motor is still a motor...
I have not unwound it yet, and will wait until I have a good plan on what sixe wire to rewind it with, how many turns , etc.
I like to have a reasonable plan before I start a project, this one included.
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Old May 04, 2014, 09:42 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,995 Posts
Quote:
Originally Posted by GarryOgilvie View Post
The reason that I want to rewind it is that I overheated the motor and smoked the windings. Now all that the motor will do when power is applied is kind of shake, it will turn by hand, but not with power.
Yes I can purchase a new stator/ windings from Esprit, but I would really like to use this as a learning exercise and rebuild it myself.
The windings do not appear to be epoxied in place. I will take it apart and take some pictures of it so you can see what it looks like.
I have seen where other hobbyists have rewound the similar Turnigy Glider Drive motors. To me once you remove the outer housing a motor is still a motor...
I have not unwound it yet, and will wait until I have a good plan on what sixe wire to rewind it with, how many turns , etc.
I like to have a reasonable plan before I start a project, this one included.
Sounds like a good plan and it will be interesting for all of us. As you complete the dis-assembly your plan will gel as part of that and with a little bit of experimenting and it will lead you to the thing like the wire size options too.

If that is a 9N12P (9 stator arms, 12 magnets) motor there is really only one winding scheme that comes into consideration. That is the ABCABCABC wind seen in the image.

And if you can look at the transit runs on your motor now and as you strip it you can probably tell if that is what you have there now. If there is not a small Wye bundle with half of the ends soldered together and insulated then you have a Delta termination now.

Separate the strands in one of the ends or transits to get a count on the strands in each bundle (all will have the same strand count). Measure a strand and multiply and that will give you the approximate wire size you want for a single strand wind of the same area:

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

And if you know the prop you want to use we'll help you pick a Kv that is good for that prop and that will lead to your choosing a turn count and termination that will give you the best Kv.

Jack
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Old May 04, 2014, 10:16 AM
Little Red Plane
United States, TN, Knoxville
Joined Dec 2012
559 Posts
When you take the cover off of it the look is about the same as any other outrunner motor.
I'll have to learn the different termination types, but I do not see any wye termination, so I suspect that you are correct. I'm positive that you have seen many more motors than I have, I've seen two...
here are multiple wires in each bundle, if that is the correct terminology, that is wound around each pole. I suspect that each wire is wound individually, not as a group.
Now if I can figure out how to remove the stator from the backing plate.
I've read that maybe overnight in the freezer would help. but it may be glued on to it. Also the 3.5mm barrel connectors will need to be removed from the backing plate, once again they appear to be glued in place.
Humm, what to do next...
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Old May 04, 2014, 10:50 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,995 Posts
Quote:
Originally Posted by GarryOgilvie View Post
When you take the cover off of it the look is about the same as any other outrunner motor.
I'll have to learn the different termination types, but I do not see any wye termination, so I suspect that you are correct. I'm positive that you have seen many more motors than I have, I've seen two...
here are multiple wires in each bundle, if that is the correct terminology, that is wound around each pole. I suspect that each wire is wound individually, not as a group.
You're off to a great start. The bundle thing goes to two purposes. For one it makes for an amount of copper that is equivalent to a large single strand of wire. The total cross section area of all the strands in a bundle is the key component as far as current capacity. A single large strand of the same cross section area would be or might be impossible to wind with.

I think you'll find you have parallel strands, not individual single strand windings.

The second consideration is that the Chinese factories can get away with only buying one size of wire (0.25mm in most cases) and adding strands to get the best fill. The better motor makers will use a range of strand sizes and may vary the count and sizes from one motor model to another. But, in all cases I have seen so far, all strands are always the same size.

We "man knitters" of motors feel that we can replace almost any multi strand wind with a single strand wind and do that with the same or better current capacity. Worst case, when we have to do it, we will reduce the strands count to two or three larger strands instead of 16 or so smaller strands and keep the strands as close to perfectly parallel concentric as we wind . So in the end we get a higher current capacity and also better harmony in the magnetic flux fields. And more power and smoother running motors. And we are willing to experiment with winds that cannot be bought off of the shelf in the pursuit of better motors.

Quote:
Now if I can figure out how to remove the stator from the backing plate.
I've read that maybe overnight in the freezer would help. but it may be glued on to it. Also the 3.5mm barrel connectors will need to be removed from the backing plate, once again they appear to be glued in place.
Humm, what to do next...
Those are the two primary solutions. Removing the bearings and heating the inside of the bearing tube will soften adhesives. Here are a couple of threads that will help with dis-assembly:

Outrunner Disassembly and Stripping - Gimbal Motor Rewind - www.rcgroups.com/forums/member.php?u=211021

How to repair an electric motor. - http://www.rcgroups.com/forums/showthread.php?t=1079423

And for pressed fits, I recently discovered that putting drops of PB Blaster penetrating oil on the seam where the bearing tube and stator meet and giving it the overnight in the freezer soak works. Then next day wrap a heavier leather strap around the stator, grip it close with a pliers, and rotate the stator on the tube to set it free and work it off.

When I do that I have the "X" mount on the base plate and attach that to a board. On your motor, you'll have to figure out a way to either immobilize one of the parts or maybe use a pair of strap type wrenches in opposite directions.

I like the heat down the bearing tube technique for glued on stators. Once you get the stator to move at all you can let it cool then maybe use the oil and freezer trick to open the clearances a little too.

There some motors that use internal snap rings or Circlips, others that have a bearing tube that screws into the baseplate. But it your motor appears to have a typical one piece base plate and bearing tube the hot or cold tricks should do it.

When I put stators back I never glue them. Most will have an aligning groove inside the stator and you can add a matching groove to the bearing tube and use a pin to prevent rotation.

You have a much better than average motor there, you might not be able to improve it's performance a lot for that reason. But on inexpensive motors I generally think in terms of being able to get increase in power that range from 50% to 100% or more. And when I know the prop and battery I want to use I get a Kv rating that is perfectly matched to the prop. And that can make a big difference in performance.

Jack
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Old May 04, 2014, 11:19 AM
Little Red Plane
United States, TN, Knoxville
Joined Dec 2012
559 Posts
At this point, looking at the complexity of the project I think that my best course is to purchase the replacement stator and reassembly the motor back to it's stock configuration. Then in the future after I have researched rewinding more and understand the process better I can take another look at it. I will keep the current failed stator so that I can rewind it if I'm comfortable with the project.

Jack you are correct about the MVVS motor being much better than average. They are not manufactured in China and are some of the higher priced motors available. That is one of the reasons that I need to progress slowly and knowledgably with this.

I have much to learn.
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Old May 04, 2014, 05:54 PM
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Fourdan's Avatar
Antony (France)
Joined Sep 2003
2,991 Posts
Hi
For our info ..
Could you measure stator diameter and axial length of the laminations ?
Are laminations 0.2 or 0.35 mm thick ? (take a macro picture jpg and count on the screen the number)
MVVS are perfect on the mechanical point of view and machining.
On the side of heat (losses) extracting, the design is not the best.
(compared to an outrunner with a lot of ventings holes and air in/off room)
For the same thermic properties (power out) the MVVS is heavier.
Louis
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Old May 04, 2014, 07:30 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,995 Posts
Quote:
Originally Posted by GarryOgilvie View Post
At this point, looking at the complexity of the project I think that my best course is to purchase the replacement stator and reassembly the motor back to it's stock configuration. Then in the future after I have researched rewinding more and understand the process better I can take another look at it. I will keep the current failed stator so that I can rewind it if I'm comfortable with the project.

Jack you are correct about the MVVS motor being much better than average. They are not manufactured in China and are some of the higher priced motors available. That is one of the reasons that I need to progress slowly and knowledgably with this.

I have much to learn.
Once you can get it apart the winding is really an easy part of the process. It is intolerant of mistakes, and working neatly and carefully has it's rewards.

Here is a manual that describes the process for winding a 9 arm stator for a kit motor. That will give you a little more insight to the winding process:

http://www.micronradiocontrol.co.uk/.../KH-278-v2.pdf

The image is an example of the method of counting laminations that Louis mentioned. That stator is called a 8mm and it had 42 (or is it 41?) laminations. It will measure a little more than 8mm because of the coatings and adhesive between the laminations but it identifies the material as 0.2mm and not 0.35mm. And thinner is better.

Jack
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Old May 09, 2014, 09:05 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Autopsy on MVVS motor...

Garry send me this motor to look at and maybe mess with some for him.

The baseplate and stator are 26mm x 18.7 long

5 laminations appear to be equal to 1mm = 0.2mm laminations

base plate bearing tube with stator and windings = 65g

The stator looks to have been rubbing on one side, the finish is chaffed off there. There is some evidence of overheating between the windings in the slots in one or two places. The coating on the wire is cooked a little and crumbling off.

There is one strand visibly melted leaving a gap in that strand.

So far have only removed the bottom bearing and looked at it and taken these photos. Have sprayed it down with PB Blaster and have it in the freezer for now. Will try to see if the stator can be turned on the bearing tube tomorrow or so.

Not sure but I think the bullet were pushed into place in the base plate and then epoxied in place.

@ Fourdan,

Louis I think this answers the questions you had. If you have any suggestions I welcome them!

Jack
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Old May 11, 2014, 10:43 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,995 Posts
Just to not keep everyone in suspense, I made some headway on this motor today. I got the stator off of the base plate and started stripping the windings. I'll finish that up tomorrow and post some more photos and the details.

@GarryOgilvie,

I think we're going to be able to salvage a motor out it this OK. It will be a little bit different but should be OK. I'll file you in tomorow...

Jack
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Old May 12, 2014, 08:21 AM
Little Red Plane
United States, TN, Knoxville
Joined Dec 2012
559 Posts
Jack,
This is good news!
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Old May 12, 2014, 09:24 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Stator dimensions = 26mm x 18.7 long, 5 laminationss = 1mm = 0.02mm laminations

Base plate bearing tube with stator and windings = 65g

I heated the tips of the bullet ends to soften the epoxy and pushed the bullets up into motor.

Then termination bundles (each had two winding ends twisted together) were cut at the bullet sockets so stator could rotate and maybe come off.

Heated bearing tube by directing flame from a micro torch up into the tube, takes about 20 seconds or so, no damage from flame or heat.

Had leather strap tight around stator and got bearing tube/stator to rotate in base plate. The bearing tube appears to have been epoxied into place.

Soaked with PB Blaster again, and got tube looser in plate, then tapped the back with a dowel and hammer and baring tube came out of base plate. Bullet then pushed out easily.

Managed to remove windings from the heat damaged arm cleanly. The wind is ABCABCABC and turn count was 11 turns with a Delta termination.

Separated a strand bundle, it was seven strands of 0.25-0.26 mm wire

Windings were epoxy saturated, the overheating winding came off fairly easy but most were just slow steady and stubborn removal. It is hard to get any heat down into the area of the windings to soften the epoxy so as to make winding removal easier. In the end I just had to cut and break the crossing turns on the ends pick them off as carefully as I could.

The removed windings were about 15g of copper, bare stator with bearing tube still in it is 36g.

Now to crunch the number using the wiki awg page numbers:

Strand bundles = 7 strands 30 AWG = 0.0100"/ 0.255 mm
30 AWG cross section area = 0.0509 mm2
7 strands @ 0.0509 mm2 = 0.3563 mm2 = total cross section surface area in original 7 strand bundle

Single strand surface area comparisons from the wiki AWG page:

21 AWG = 0.410 mm2
22 AWG = 0.326 mm2
24 AWG = 0.205 mm2 (2 strands = 0.410 mm2)
26 AWG = 0.129 mm2 (3 strands = 0.387 mm2)

I tried a test wind with 22 AWG wire (0.0253"/0.644mm) from scrap bin
layer 1 - full arm = 6 turns
layer 2 - 5 turns back = 11 turns

This is a small decrease in surface area from original wind, maybe 92% or so of the original area. But there is a little room left and maybe some increase in surface are is possible later. 24 AWG might work for 11 turns, it will require some turn threading and patience.

The 22 AWG looks OK, 21 AWG would be too stiff to wind with on this smaller stator and it would be too crowded for the turns, to improve on this maybe two strands of 24 or three strands of 26 AWG in parallel would work and also give a small increase in surface area.

I'm going to look at this a little more, see what the options are for fastening the tube back into the base plate with some set screws maybe. And then I'll get it back in the mail to you...

Jack
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Old May 12, 2014, 09:28 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by GarryOgilvie View Post
Jack,
This is good news!
Yes, it went OK once I figured things out a little. I am still baffled by the apparent lack of insulation between the bullets and the base plate. They seemed like they would all be shorted together.

But when you wind it you can just bring the winding ends out (insulated with heat shrink) through the cooling openings and put rugular 3.5mm bullets on those. The bullets that MVVS uses are 3.5mm too but they are made to fit those sockets in the base plates and I don't know if you can find those or if you even want to try the nicely done but much more complicated method used in the original work.

Jack
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