Step by step guide to rewinding your 1100kv/1500W motor!

[Kailee]

Hi all,

In another thread (https://www.helifreak.com/showthread.php?t=219061) I already explained how I killed my 1100kv/1500W motor, and asked for some info on how to rewind it... I got some excellent posts on that thread and while they were going on I managed to get started on my first attempt at rewinding a brushless motor. This was very confusing initially, then daunting as I learned more about brushless motors, but as soon I really got going it became interesting and - wait for it - fun!

So, here it goes - my own personal experience of rewinding a brushless outrunner that has mostly black multistrand, beaded (!) wire into one that runs!

Some of you might consider rewinding you motor in this way (or any other way you might see fit) as reports are increasing that the 1100kv Gaui motor might have regular winding mistakes in them. In particular, JimLerch reports that one phase was connected the wrong way, which would certainly explain the amp-drawing nature that many are seeing with this motor. Also, the kv is regularly higher that 1100 (as on mine and JimLerch's), so if you want to adjust your kv rewinding is the way to.

Before I begin, let me thank all on this forum and on rcgroup.com for posting their related information. There is no question that I would not have been able to fix my motor without the information posted by, there are too many to mention but you know who you are ;-) ! Also, a lot of what I know now (which is not much yet btw) came from www.powercroco.de, regularly (and accurately) described as being "The Bible" for brushless outrunners. The amount and quality of the info there is second to none, so a special Thank You goes to Dr. Ralph.

I'd like to dedicate this thread to the memory of my late uncle Johann v.d. Heide, who was something of a brushless genius, designing all sort of electric motors for all sorts of applications, ranging from power steering systems to hard drives. Unfortunately he passed away this february before I even got particularly interested in these little machines. It's the irony of nature and the nature of irony that only now do I appreciate and understand what he was trying to relate to me before his untimely death.

Now - let's finally begin with ...

[Kailee]

Clean up that mess! I won't go through the details of how to take this motor apart, as it's actually straightfoward. Undo a few grubscrews that fix the stopper ring to the axle and pull out the bell with the axle. You'll have to pull quite hard to overcome the magnetic pull of the bell to the iron of the stator, but nothing major. If you want, undo a couple more grubscrews at the base of the bell and pull out the axle. If you can't move it, point a heatgun at the bell for a few secs and it should go.

[Kailee]

Next, point the heatgun at the statorpacket (the round bit that has all the copper wire threaded though it), don your leather gloves and try to twist the stator off of the stator holder (the brownish golden anodized bit). It should come off with some force, but try to be gentle with it anyway, so you don't accidentally scratch the stator insulation (the green stuff). This is also why I use leather gloves rather than a hard metal clamp. Now you should make a note of how your motor is wound and connected internally, i.e. star/wye or delta. If it's star connected you'll see a very distinct point where three bundles of wires are soldered together - these are the ends of the wires that make up the individual phases. If you don't see such a soldering point then it's probably connected as a delta, i.e. the end of phase 1 goes to the beginning of phase 2, the end of which goes to the beginning of phase 3, the end of that then connects to the start of phase 1. The motor connection to the esc are actually these connection points. Anyway, you can now unwind the motor, or, if you're in a hurry just cut the phases at the top of the slots and lift out the wires.

[Kailee]

Clean up that stator, remove any black sludge you find with nail polish remover or acetone, but be carefull with this as the acetones, when left on the green insulating coating too long, will make it soft or even dissolve some of it. If it does, you'll need to either fix the bits where the metal is showing through with cyano or (better) heat resistant epoxy, or if only the front and back surfaces are affected like with mine you can cyano some thin (0.5mm) grp on top…

[Kailee]

I could only find this thickness grp material as raw pcb, so I had to sand away the copper after glueing it to the stator. Start by marking out the circle a little oversized…

[Kailee]

... then glue it to the stator with ample cyano - make sure to cover all of the metal with the cyano, you'll be filing away at this later and there's nothing more annoying than chipping this stuff as you'll have to start again. Do this on both sides of the stator if both have chips in their insulating covering.

[Kailee]

Now sand away the copper. This is important as you *cannot* have any electrically conducting material touching your coil wires.

[Kailee]

… almost done …

[Kailee]

Here's the stator with the now cleaned up grp plate on the end.

[Kailee]

Now carefully dremel the slots in. Make absolutely sure you don't dremel into the green insulation at the base of the slots as you're trying to completely insulate the stator iron.

[Kailee]

Get your fine files out and carefully file the slots to the contour of the stator slots. Again be careful of the green insulation when doing this!

[Kailee]

Sooner than you think you'll have them all done and it should look like this…

[Kailee]

if you're new to winding motors, you might like to like me and practise using some unwound servo wire. This is nice and flexible, maybe a little thick, but it will certainly help understand the winding scheme. Servo wire is ideal for this because you get 3 colours of the same wire… one for each phase. Here, I wound phases 1, 2 and 3 onto their respective first teeth. It helps to mark out the teeth on the side of the stator with an edding so you know exactly which phase should go on which tooth. Experienced winders will spot a mistake in the way I wound these btw… Also note the bits of tape on the start of the phase wires. These will also help because they show you where the start of the whole wind is.
It's important that you wind the same way on all phases on all teeth btw, so don't do like Gaui sometimes do and wind one phase counter clockwise and the other clockwise… It'll run, but it will run hot and draw lots of current (sound familiar?). This is because it's a motor with 12 slots and 8 magnet poles, which has to be wound in this way. Other motors (with 10 magnets for instance) will require different schemes, but this one is actually one of the simplest winding schemes. in our case, all phases will be wound clockwise on all teeth, so it's easy to keep right. You start winding at the bottom of each slots and coil you way upwards, then do the same with the next phase on the tooth next to the one you just did, again starting at the bottom of the slot working your way up. In this case, I did 4 turns. It looks like only 3, but if you count the number of wires running through each slot you'll see there's 8, including the wires going in and out of the slot. These also count and make up for the 4th turn.

[Kailee]

This is all 3 phases on two teeth each…

[Kailee]

After another a few more teeth wound you'll have completed the test wind. As stated before, the brown and orange starting wires shouldn't have been where they were. It would have been much neater and tidier had they been on the outside of the slots, but this is how we learn…

[Kailee]

This is what the back of the stator now looks like. You can now much more clearly see that there are 4 turns on each tooth. You can see how the wire don't quite fit into the slots, and the top turn is laying slightly on top of the 3rd turn. This wouldn't have been a problem, multi-layer winding is quite common but i will try to prevent this by using wire of a thickness that *just* fits 4 turns into the slots in one layer. Once you're happy with your winding you can unwind (excuse the pun), have a beer and prepare for the real thing…

[Kailee]

First, create some small helpers; cut some pvc strips of about the height of the slots, and bevel one corner so it's sit quite snugly in the side of the slot. This will help keep the slot tidy - as you wind the wire in, you can't fill the bit on the other side of the slot…

[Kailee]

… do this on both sides and it will make packing in the wire much easier.

[Kailee]

Also, when doing the testwind I noticed the top edges of the slots were quite sharp, so I'm going to pull their teeth by laying a layer of kapton into the slot, and let it sit over the edge. This will also provide one extra layer of insulation, probably unnecessary, but it's so thin that it shouldn't prevent me using the wire I chose.

[Kailee]

I went around the whole stator, and …