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Old Feb 03, 2013, 08:30 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Mini-HowTo
Outrunner Disassembly and Stripping - Gimbal Motor Rewind

Outrunner Disassembly and Stripping - Gimbal Motor Rewind

In a discussion on another thread, someone asked me to describe the process for disassembling and stripping a typical brushless outrunner. I had this B/06/12 that is running badly, stuttering intermittently, and needs to be rewound. So I'll use it for this demo.

This will be done in five posts, disassembly, removing the bearings, removing the shaft, removing the stator from the bearing tube, and stripping the windings.

The paragraphs in each post are numbered to match the images attached to the post.

We'll start with taking the motor apart.

Taking a Brushless Outrunner Apart

01- Magnet housing end of the the motor. The two screws are for the built in prop saver and they also bear on the 3.175mm/1/8” shaft to lock the shaft in the magnet housing.

02 – Backplate end of the motor. This motor has a shaft extending from the back for use in a firewall mounting. As seen in the photo the “X” mount is removed and the small screwdriver has been used to pry the Circlip off of the shaft. The screwdriver is magnetized to keep the clips from flying off and getting lost.

03 – The grub screws that lock the housing on the shaft will need to be removed to get the shaft out of the housing (if you don't need to remove the shaft, leave the screws in place). Most motors will have one or two 1.5mm headless hex socket grub screws holding the shaft in place in the magnet housing. This motor uses the two larger prop saver band screws to also retain the shaft. They are M3-0.5 socket head cap screws with 2mm hex sockets. The tools are a ball-ended (black) and straight shanked (silver) hex wrenches in the photo. Never use the ball-ended wrenches to loosen a tightened screw or you'll run the risk of stripping out the hex socket. Never use anything except the best fitting straight shanked hex wrench you have to loosen grub screws.

04 - The clip is off and screws out. The magnets and the sliding friction of the shaft in the inner bearing races is holding the magnet housing and motor together at this point. If you put your fingernails in the small gap between the baseplate and the magnet housing and push on the end of the shaft with your thumb you may get lucky. You have to overcome the magnetic forces initially and then the shaft will slide through the bearings and the shaft and housing will come away as a unit. Watch for and save any spacers or shims on the shaft inside the housing as you remove them.

05 - We get lucky! The shaft slides out easily and the magnet housing can be removed. It it had not, I would have rested the shaft end vertically on the bench and pressed the backplate down harder. If that did not work I would put the “X” mount back on the motor and pressed down on the ends of the mount. Beyond that sterner measures may be needed sometimes and the following posts and links show some of those.

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

Outrunner Shaft Replacement/Reversal - http://www.maxxprod.com/mpi/tips1.html

How to Change the Shaft & Bearings in a Scorpion Motor - http://www.scorpionsystem.com/buildi.../change_shaft/

We'll remove the shaft in the next post.

To be continued...

Jack
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Old Feb 03, 2013, 08:31 AM
Jack
USA, ME, Ellsworth
Joined May 2008
17,140 Posts
Removing Bearings from Bearing Tube

Removing Bearings from Bearing Tube

01 – Seen in the photo are the backplate and stator, a short length of aluminum tubing, and an short length of old 3mm shaft. The Ultrasky has a 3.175mm shaft, the 3mm shaft is needed so it will be a loose fit in the bearing races. It will be used as a pusher rod to push the bearings out. Any short, loose fitting rod will work for a pusher rod, a drill bit, a piece of welding or brazing rod, etc.

02 – The motor is seen with the pusher rod in place. Note that it is skewed in the bearing tube. That is so that the end inside is resting against the outer race of the bearing where it overhangs the central hole in the bearing tube.

03 - I'm going to use a small bench vise to push the back bearing out first. The small piece of aluminum tubing is held suspended in front of one vise jaw with a small piece of tape. The tubing is large enough that the bearing (seen on the back of the motor) will enter the tube easily as it is pushed out.

04 – The backplate is placed so that the back bearing is over the tube, the pusher rod is in place and tipped or skewed so as to stay in contact with the bearing, and the vise is closed to place a pushing force on the pusher rod. Hold the pieces in position and close the vice jaws together a little and it will push the bearing into the tube.

05 – The pusher rod falls away as the bearing comes out and the bearing removal is obviously done. It takes very little force to get bearing out normally and they will not be damaged by this kind of removal. The bearing can be seen laying in the tube.

06 - I got lucky on the front bearing. I put the rod against it and pushed and the bearing popped right out. This is a good time to put the bearing on the exposed end of shaft in the magnet housing and turn the shaft by hand to see if they are damaged. Put a small twisting or side force on the bearings as you do that, if you feel any minor clicks or ticks or any roughness at all replace the bearings.

These bearings not metric sized, they are 5/16” OD x 1/8” ID x 9/64” WIDE . They almost look like 8mm x 3.175mm x 3.5mm bearings but they are not. Measured metric they are 7.94mm x 3.175mm x 3.57mm. You Can't be too careful when measuring bearings...

To be continued...

Jack
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Old Feb 03, 2013, 08:31 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Removing Shaft From Magnet Housing

Removing Shaft From Magnet Housing

01 – Shaft removal is optional if you are just rewinding the motor. The shaft is a light to medium pressed in fit in the magnet housing. It will not come out easily and needs to be pressed out. This shaft has a short length exposed at the prop saver so props can locate on that. We'll press the shaft flush with the end of the magnet housing first. Then we'll use a smaller object to push it until it is out.

The piece of tubing seen there is a piece of steel brake line tubing, that is why it is flared on the end. The tube needs to be slightly larger than the shaft. The “dome” end of the magnet housing is easily bent or deformed. You need to support the dome on the tube as you press the shaft down into the tube. That keeps the pressing forces right around the shaft and prevents bending.

02 - You can use a vise, drill press, C-clamp or other similar method to press the shaft out. I'll use a large C-clamp because this won't fit in the bench vise. In this photo the shaft is in the tube, the dome is resting on the tube, and the exposed shaft end is against the fixed jaw of the C-clamp.

A turn on the screw will move the adjustable jaw and push the shaft down and flush with the end of the prop saver. It is about half way there in this photo

The shaft is flush with the end of prop saver on the dome and I need to use a pusher to continue the pushing.

I put an old hard drive magnet on the fixed jaw and used it to hold a m3-0.5 machine screw in place. That will rest on the end of the shaft to continue the pushing and be small enough to easily clear the hole bored for the 3.175mm shaft. A couple of turns on the screw and the shaft fall into the tube.

To be continued...

Jack
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Old Feb 03, 2013, 08:31 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Removing Stator From the Bearing Tube

Removing Stator From the Bearing Tube

01 – Seen here are the stator and bearing, two type of butane micro torches, and the bench vise. The torches are used to soften the adhesive that hold the stator in place on the bearing tube. The stator is easily bent, the coating on it is fragile, and bending the stator or damaging the coating can really complicate the project. Or it can even end it here...

02 - An “X” mount is put on the backplate with the plate offset to one side so that it can be clamped in the vise.

03 – The backplate is clamped in the vise and ready for the heat to be applied. The thin bladed, wide, flat screwdriver will be used to move the stator on the tube. The end will fit between the back of the stator and the edge of the backplate and rotating the screwdriver will move the stator away from the backplate. But brute force will not do it!

Do not apply any force until the heat has been applied for 10 seconds or so. Even then, apply only a gentle rotating force and wait for the glue to give up. As soon as the stator moves away the heat can be removed.

04 – As seen here the stator has moved and is being allowed to cool off a little. The micro torch flame was directed just down through the bearing tube and it only took 10-15 seconds for the stator to move. This will not damage any of the parts

05 - The glue will not normally grip again and the stator is easily removed by hand when it has cooled a little. It is seen here hanging from the motor leads. At this point I snip the bullet connectors off because they won't pass through the openings in the backplate. Leave 1/4” or so of wire in the connectors when you snip them off so you can grip that to remove it and use them again.

06 – The stator is removed and ready for stripping. This is the back of the stator, note that this motor has a Wye bundle for the termination (the small bundle with three soldered and insulated wire ends).

07 – And the front of the stator is seen here. This motor is a little unusual in that the transit runs between the phase halves on the dLRK windings are done on the front of the motor. That is not a common practice but it is a good idea for relieving the crowding and congestion on the other side of the stator. It can effectively add a turn or partial turn to the turn count and change the Kv a little.

To be continued...

Jack

20 August 2014 - Added Note:

I want to document another stator removal technique that worked for me recently.

This was on a 24N22P iFlight MT4114 gimbal motor and I tried the heating technique first for stator removal with no luck at all.

Then I mounted the motor to an aluminum flat bar, put some PB Blaster penetrant on the top of the stator, put it in a bag, and left it in the freezer overnight.

When it came out I clamped the stator with a leather strap and pump pliers and rocked it and the stator turned. I gave it a little more PB Blaster, continued rocking it and doing a little prying with a padded lever, and the stator came off pretty easily.

The last four images show the PB Blaster removal process.

Jack
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Old Feb 03, 2013, 08:32 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Stripping Windings from the Stator

Stripping Windings from the Stator

01 – Take a short length of dowel that will easily fit in the stator and mount it vertically in something to restrain the stator as you apply heat with one hand and pull on a winding with the other. As seen here I've already stripped one of the arms.

Start by setting all six ends free. There will three bundles of wire and six ends. At the Wye bundle remove the insulation and cut two of the bundle ends free as close to the solder as you can. With a Wye termination the other three ends will be at the ESC and are, for that reason, already separated. These six ends are the handles for removing the windings.

If it is a Delta terminated motor (that is the most commonly seen one) the six ends will be gathered into three pairs with some length of that soldered, placed in heat shrink tubing, and an ESC connector placed on the end. For those, make a light cut on the insulation with a Exacto knife and peel back some or all of the insulation, then divide each the strand bundle into two bundles. Which is which will be obvious as they will come from different places on the stator. The point here is to leave yourself six bundle ends that you can pull on to remove the windings.

If you are very lucky the windings will not be epoxy or CA saturated and will simply unwind. Otherwise you need to study the ends a little before you start trying to remove the windings. There are two different situations, starting ends and ending ends. Starting ends will often have riding turns over them where they started around the arms. They will emerge from the bottom of the “V” which is crowded with turns from two arms and if you pull on an end that has riding turns on it the wire will break and you are turning this into the disaster as seen in photo 04.

Count the turns on the arms as you unwind them so you can get the same Kv again. Or you can use that to calculate a change in the Kv. Keeping some notes on wind type, termination, turn counts, stator size and weight, lamination count, length of a strand, etc., can be useful to yourself or others in the long run. If you ask questions here about rewinding you will be asked for info like that.

Note the wind type too. A dLRK wind will have two side by side arms wound, then a transit across to two more opposing arms. Each strand bundle will be wound on four arms on a 12 arm stator. An ABC wind will wind one arm, skip two arms, wind another and skip two more, and repeat that until four arms are wound. The other two strand bundles will repeat that same pattern, each one starting on one of the first two skipped arms. A LRK wind will only have six of the 12 arms wound and the other six will be empty. Note the termination. If there is no Wye bundle it is a Delta termination. If there is a bundle it it is a Wye termination. References to Wye, Star, or Y all refer to the same termination.

02 - Look for any one of the three ending ends to start with. It will also emerge from the same area near the bottom of the “V” but it will be on the surface of the winds and not buried under riding turns. Pull on that gently, it it does not pop out of the “V” it is time to apply heat. Dim the lights for this part so you can see the flame better. Get the torch going with a small steady flame, maybe 1/2” or so of visible blue flame. Test the torch by pointing it up and down to make sure it will not go out when you make that change. Drop the stator over the dowel restraint, apply a gentle steady pull to the end of a bundle and put the tip of the flame (the most heat is just beyond or at the point where the flame becomes least visible) on the spot where the strand bundle is adhering to the windings. In this photo the adhesion point is where the red “x” is on the stator and I am going to pull on the strand bundle end at the other red “x”.

03 - The strand is repositioned for heating now. Apply a gentle pull on the “x” on the strand bundle, put the flame tip on the “x” at the point of adhesion, and in just 2-3 seconds the wire will pull away from the adhesion point. If this your first one ever, act surprised and pleased!

From this point on it is a case of applying gentle tugs at each adhesion point and applying heat when it is needed. All the subsequent adhesion points may just pop free with a gentle tug. But don't be stubborn and break the bundle, if it becomes buried under riding strands check the other five bundle ends and one of them will be ready to be pulled away. You cannot expect to remove each phase one at a time and from one end to the other. Work the ends alternately getting the one that will come away easily.

04 – This DAT-750 stator is an example of the consequence of attempts at brute force removal. Of just grabbing glued bundle ends and pulling until they break. In this case four of the six ends have been broken off, two ends are remaining, but all the strands are still solidly epoxy glued together where they touch or nearly touch in the “V” between arms. I was reduced to grasping each visible strand end (there were hundreds of them now) one and a time and hoping they wouldn't break again. In most cases I was wrong...

Here is a link to a post that shows one method of dealing with the mess seen in this image. But in the long run it is best to apply heat and work the ends free as described above:

http://www.rcgroups.com/forums/showp...postcount=1122

If you have a motor with heavily epoxied windings look at the post above. It shows how you can use a Dermel tool (carefully!) to deal with windings like that.

05 - And here it is with all the windings removed. The wire is useless and will be thrown away but the stator is still in perfect condition. And it has no damage from the stripping process. Any glue residue can be picked off and the stator is ready to be rewound.

We're ready to rewind now, this may be continued later...

Jack
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Old Feb 03, 2013, 08:32 AM
Jack
USA, ME, Ellsworth
Joined May 2008
17,140 Posts
Test Winding

Test Winding

This is a test wind to see how many turns can be put in a full, one layer, wind. When we remove it, it will also give us the length of wire needed to wind a full arm.

00 – A piece of 5/16" (7.94mm) wood dowel was close to a friction fit in the stator. I wrapped 2-3 layers of clear package sealing tape around the dowel to make it fit snugly and put it in the stator to serve as a handle.

01 - A 1/8" hole (not seen) was drilled in the handle near one end and that end was colored with a marker to make it more easily distinguished from the other end so as to aid in turn counting.

As seen here, my home made 3rd Hand motor rewinding accessory is clamped to the bench top, the spool of 32 AWG wire is laying a few inches back, and the Exacto knive stuck through the spool of wire keeps it there as wire is pulled.

With the 3rd Hand accessory, you can put a dowel through the stator as a handle and when you are winding the wire is coming straight off of the spool, through the 3rd Hand, and the stator is rolling up the wire under light tension so no turning or twisting is involved.

The wire is brought forward through the gasket material lined clamping jaws of the 3rd Hand. The wing nut is adjusted to clamp the wire and apply a light drag when the wire is pulled through the jaws. This same thing could be done using a book for wire this light.

The goal on the clamping force is that it let you pull gently on the wire to so to keep the turns in snug contact with the stator arm. But you do not want to stretch the wire or break it.

02 - The wire is put through the small hole in the handle and a toothpick (not seen) is stuck in the hole to keep the wire there. Make a few turns around the dowel and descend down and along side one of the stator arms. The wire wrapped around the dowel will be your "working length" for making terminations and motor leads so don't go too short as far as leaving some extra wire at the ends.

We are now ready to start winding turns on the arm.

Counting turns requires some concentration and it is easy to lose your place. My process is at follows:

The colored end of the dowel is the end I count on, I count a turn when I see the strand cross the top of the stator arm and the blue end is seen. As you see it in the photo, there are 0 turns there now.

I pull 15" to 18" of wire through the jaws and hold the stator back a ways to put tension on it, the wire will come from the 3rd Hand in a straight line and under light tension, and come to the stator without getting snagged on the hammerheads.

I put the arm to be wound to the left (at 9 o'clock) and, start rolling the dowel up and around to pick up a turn. As I do that I watch the wire at the stator and turn, twist, and move the stator as necessary to let the wire drop down into the slot without getting snagged or nicked by the hammerheads.

I use my index finger tip to nudge the wire into the slot and my fingernail shield the sharp corners on the hammerhead as the turns are applied. The wire will slide off of your fingernail undamaged.

Keep the lightly tensioned wire coming through the jaws in a straight line and onto the stator as you work and bring the stator closer to the 3rd Hand as you roll the stator up the wire to put turns on.

03 - I have a few turns on now. If you zoom in on that photo, you will see the starting wire dropping down from right and there are four strands crossing the top of the stator arm. The strands that cross the top each represent one complete turn and those are what I count. And I count them the colored end of the dowel is also seen so I know I am not counting the wrong end and losing 1/2 a turn.

And I chant my counts aloud as I work. Here is exactly what I said as I worked. When the first strand crossed the top I said "1...", as I started down the other side I said "1 and...", as the strand crossed the bottom of the arm (it was the first one to cross there) I said "1 and..." again. As the strand started up the other side and back towards the top, I said "1 and..." once more. And then as the strand crossed the top of the arm I said "2 ...". And there were two strands see. Then it was

"2 and..." - down the other side

"2 and..." - across the bottom (two crossing strands there now)

"2 and..." - up the other side

"3..." - as the strand crosses the top and 3 strands are seen there

The chanting thing seems silly but it works for me. Do whatever works for you.

As I complete each turn I use my thumbnail or the end of a popsicle stick to push the turn just applied up against the other turns, and I do the same thing as I cross the bottom of the stator arm. Don't push too hard, just until the turns are all flat and touching. Crossing strands are a bad thing for the magnetic harmony in the motor. It is bad Karma for the motor!

04 - And now here we are with 28 turns on and a full arm. It might hold one or two more turns as I start back with the second layer of turns. If you zoom in you can count the turns and see that there are no crossing turns.

Crossing turns will happen occasionally as more turns and layers are added. I try to avoid having any but am sure I'll have a few in the course of getting three layers onto this arm. Can you imagine how many crossing turns there are in a average quality cheap motor? Anyone can do a lot better than they do average motor.

05 - Here are the turns seen up close. I snipped the end at the end of the last turn and where it dropped down to start the first turn. I unwound those turns and the wire meaured 17"/431.8mm. That works out to 0.63"/16mm per turn. This info will be used for estimating the resistance in the windings.

This was a test wind on one arm and that is a no-brainer. When winding a stator I have an image of the wind at hand and attention has to be paid to getting the strands on the correct arm and getting the turns going around the arms in the correct (clockwise or counter clockwise) direction.

Jack
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Old Feb 04, 2013, 03:07 AM
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Great work, thank you very much for that
Now I see that rewinding a motor is itself a science!
I'll take care of reading all this once again when I'll start to wind one.. I guess I'll wait till some datas will appear to be valuable for a given motor, regarding gimbal use.
Thanx again for your time.
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Old Feb 04, 2013, 09:31 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by milouze View Post
Great work, thank you very much for that
Now I see that rewinding a motor is itself a science!
I'll take care of reading all this once again when I'll start to wind one.. I guess I'll wait till some datas will appear to be valuable for a given motor, regarding gimbal use.
Thanx again for your time.
It's a hobby, I'm interested, and am here because I enjoy being here.

I did it here to get the motor winding guys involved. To give them some background here, is the story on this "gimbal motor rewind."

I got involved in this when I read some things about rewinding motors in a thread on the Multirotors Electronics forum and I contributed some posts to the discussion. So it all started here:

Simple AlexMos brushless gimbal from Viacopter - http://www.rcgroups.com/forums/showthread.php?t=1815204

In that thread they are developing a product that will be a motion stabilized controller called an IMU (IMU means "Inertial Measurement Unit" I think) and gimbal for cameras. And the gimbal will be motorized with two brushless outrunners that will control the pan and tilt axii.

The motors they are experimenting with now have been mostly thinner 22mm stators (although many other sizes are being considered). When I got involved was when I read about them winding motors with a single strand of small wire of 0.16-0.20mm or so (down in the AWG 3x range and even smaller). And they were winding with turn counts that were like 60 to 90 to even 130 turns of that small wire.

The best motor they have found so far is the T-Motor MT2208 motor rewound dLRK-Wye with 60 turns of 0.16mm (.0063" or 34 AWG) wire. That is a $40 plus motor, many here are looking for other and cheaper motors and some of the new 40-50mm pancake style motors are being considered too as candidates for a gimbal motor.

I started helping them with re-winding questions and have been encouraging them to do it here so as to get the best motor minds involved. And eventually I wound up starting it here...

So now I guess we have to say that the discussion in this thread is now shifted from a discussion about how to take a motor apart to "How to rewind a motor for a camera gimbal" or some to that effect.

I asked all the questions you motor minds are going to ask. What Kv do you need? What prop or load will you put on it? And things like that. Believe it or not, the best descriptions I have as to how this motor needs to be wound is in these two statements from that thread:

"..You are aiming to get a resistance of between 5 and 15 ohms between two phases on the finished motor..."

"..The basic principle is that the motors work on constant current. If we have 8-12V onboard, we can reduce it by PWM, but not much (say to 4-6V). Motors will dissipate all power to heat. But the Motors can not dissipate more than 5-10 Watt. According to Ohm rule we can get the max. current. And then resistance for a given motor..."

So as it stands right now, right or wrong, I'm thinking in terms of the need being a rewind that will have a DC resistance measurement in that 5 to 15 Ohm range when the resistance is measured across any two of the three ESC connectors with a standard multimeter. Right, wrong, or otherwise I think that is what they want. But this is still a developing process...

After I disassembled this B/06/12 I played around with rewinding it's 27mm x 13mm stator with the smallest wire I had on hand (32 AWG) just to see what a practical turn count for it might be. I came up with some numbers and stuff from that trial and they are like this (this is quoted from a post I made on the gimbal thread), and user JussiH is owner of the gimbal thread.

I asked Jussi to tell me what he could about what the current or load requirements were and he said:

Quote:
Originally Posted by JussiH View Post
I´ll do my best, but some of this stuff is new to me too.

The termination is a Star aka WYE.

Here is a transcript of what Alex told me:

In very basic terms that means that the calculation for the 2208 is as follows, assuming 3 watt maximum and Ohms law:

I=P/E

3W/6V = 0.5A

Then, assuming 6V and 0.5A we get:

R=E/I:

6/0.5= 12ohms

http://www.onlineconversion.com/ohms_law.htm
And if there is a clear answer in that it is over my head.

So I told Jussi what I had learned so far and it is as follows:

Based on messing with that Ultrasky 27mm x 13mm stator, I think I could get 80 or 90 turns on it with the 32 AWG wire I had. But that will not get the DC resistance, as measured across two phase ends, up high enough. Here is why I say that, and I am open to correction on any or all of what I say.

When I measure DC resistance across any two connectors on a dLRK wind I think I am basically measuring the resistance in a length of wire that is two of the three strands. So on that stator with turns of 0.78"/19.8mm length and 80 turns I would have a length of wire in each phase that is 10.4ft/3.168m

0.78" x 160 turns = 124.8" / 12" = 10.4 feet @ 164.1Ω/1000 feet = 1.71Ω
19.8mm x 160 turns = 3168mm = 3.17m @ 538.3Ω/km = 1.71Ω

If I have this figured out right, changing to 37 AWG wire would change the numbers as follows and work:

0.78" x 160 = 124.8" / 12" = 10.4 feet @ 523.1Ω/1000 feet = 5.44Ω
19.8mm x 160 = 3168mm = 3.17m @ 1716Ω/km = 5.44Ω

I'll leave it to you to decide if that will will handle the current or not. Your dandy calculator says that 5.44Ω at 6V draws 1.1A . So you would have to add the load to that yet and that may be too much for the wire, no?

As far as the resulting Kv, I ran the Simple Turn Calculator on the B/16/12 motor and it indicated that 40 turns will give me a Kv of 558 Delta and 332 Wye so 80 turns will cut that in half again and give a 279Kv on Delta and a 166 Kv on Wye.

When I wound the test layer I used my 3rd hand thing to put a little drag on the wire and that worked good. For 37 AWG I would try using a book to get a little more subtle feel on the drag on the wire.

So now I am going to invite JussiH to read this thread and become a participant here in determining if a brushless outrunner can be rewound to serve as a gimbal motor. JussiH is the interface between us and the guy (Alex Mos?) who is developing the IMU and controller.

Jack
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Old Feb 04, 2013, 09:46 AM
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Hi Jack

Thanks for taking out this thread, should be very helpful for DIY people wanting to rewind their own motors. Hopefully we can build a motor DB here.

I´ll do my best to help, but I am gonna be a bit busy the next few days - we have some big AQ demonstrations coming up.

When I am back, I will compile a spreadsheet with our results and try to gather some more results from the russian forums.
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Old Feb 04, 2013, 11:18 AM
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Old Feb 04, 2013, 06:49 PM
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Old Feb 04, 2013, 08:15 PM
Jack
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Estimating the Resistance in the Rewind

Estimating the Resistance in the Rewind

The sizes (O.D. x height) of the stators we have is going to be a factor in these gimbal motor rewinds. As is it now we are working to obtain a measured resistance and not a specific Kv as would be the normal winding practice.

JussiH has said that they have tested the T-Motor MT2208 motor and that has worked with 60 turns of 0.16mm (.0063" or 34 AWG) wire. So we are basically trying to accomplish the same thing. The MT2208 has a 22mm x 8mm stator.

The Ultrafly B0/06/12 stator I am working with is a 27mm x 6.25mm stator. So this stator has longer arms but is not has high as the MT2208. The length and height of the stator arm will be a factor in determin the number of turns you can get in each layer. And the width and shape of the "V" between two arms will be the other limiting factor. The normal jamming point in winding is that the

I'm going to crunch the numbers on this to see if it looks like I can get it rewound to have a DC resistance of 5-15 Ohms as measured across any two of the phases with a multimeter. For the record, I think that when you measure the resistance like that you are measuring the length of the wire in two of the phases.

So if we know the length of the wire in each turn, the total turns and layers, and the size of wire, we should be able to estimate or predict that measurement.

The test wind with 32 AWG wire got 28 turns on a full arm, the wire length for those turns was 17"/431.8mm. I estimate the length for each turn as being 0.61"/15.5mm.

The wire length for one arm with three 28 turn layers (a total of 84 turns) would be 51"/1295.5mm = 1.296m. These numbers do not include or allow for the small amount needed for the transit runs or for the 4" or so needed for the Wye bundle and motor leads.

Each phase would have four arms wound with a single length of wire so the total length of wire in a phase would be four times the above or 204"/5.184m. I get the resistance for the wire used from the wiki AWG table and estimate the resistance in a phase:

204" = 17 feet @ 164.1Ω/1000 feet = 2.79Ω
5.184m = 0.005184km @ 538.3Ω/km = 2.79Ω

And since I think a DC resistance measurement will be the resistance in the lenght of two phases, the measurement is estimated to be 2 x 2.79 or 5.58Ω

So it looks like if I do a dLRK wind on this stator with the 32 AWG I have on hand it will be within the 5-15 Ohm range needed. And having on the lower end is a good thing as that means that there will be less resistance in the windings than there would be if we measure it at closer to 15 Ohms.

If the number had come out below 5Ω I would have done the above calculations with a smaller size of wire. For example and comparison, if I had done the wind with the 34 AWG wire that was used on the MT2208 the calculations would have been as follows:

204" = 17 feet @ 260.9Ω/1000 feet = 4.44Ω
5.184m = 0.005184km @ 856Ω/km = 4.44Ω

And that would have raised the resistance in the length of two phases to 8.88Ω.

I don't have the details on the length of the wire in a phase on the MT2208 rewind that Jussi mentions. But I would suspect that it is similar to what I used on the stator I have. My stator has longer but lower arms, his has shorter but taller arms, so the length of the wire must be similar.

Jack
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Last edited by jackerbes; Feb 05, 2013 at 10:05 AM.
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Old Feb 04, 2013, 08:28 PM
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Can a DLRK wind be terminated delta?
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Old Feb 04, 2013, 08:41 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by IloveFLIGHT! View Post
Can a DLRK wind be terminated delta?
Yes. The images show two ways to do the dLRK wind. The first tells you how to join the ends for either Delta or Wye. The second one, commonly know at the "dLRK for Delta" wind, is wound differently bring the two wires that will be joined in the Delta termination out side by side. That makes for a little neater termination.

There are several different way to do the dLRK wind.

For these gimbal motor rewinds, most or all of them have been terminated Wye. I think the reason for that is that, with the same turn count, a Wye term produces a lower Kv, uses less current, and has a little better torque. If you change any wind mentioned here from Wye to Delta it would raise the Kv by a factor of 1.73, and increase the current draw and and decrease the torque by the same 1.73 factor.

Jack
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Old Feb 04, 2013, 09:13 PM
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The reason I asked is because for a Delta connection you will only be reading the R of 1 coil vs the Y which is 2?
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