Good whatever time of day it is, dear colleagues and readers! About a week ago I came across a Leopard 4082 2000kv, which is well known among RC boat builders. I found it on one of the forums, it was being parted out, because, the seller told me, it had gone through water and soaked completely, and would heat up even on a 4S battery. I decided to restore it, so I did not hesitate to buy it.
I’ll start my story with a not so funny thing – the Russian Post. It took them a whole month to deliver the pack from St. Petersburg to my place. I’m still wondering how they could have lost it as it had already crossed the Russian border. I was all shocked and shaking, because I had never faced such a situation before. Good start!
Now down to business. Finally, the package did arrive, so I took it and decided to open it in that same evening to see what was in there and what I’d have to do about it.
Well, as to appearance, I’d rate it four on a scale of five - there was nothing but a few scratches. Never mind, let’s repair it. I chose to connect and test it right away prior to disassembling it, so I went for broke and gave it 6S. After five seconds it was scalding hot. Then I took it out and scheduled my further operations:
1. Rinse and clean the stator.
2. Polish and rewind the rotor.
3. Replace the bearings.
4. Replace thermal wire insulation.
5. Solder connectors.

Now let’s go through each stage one by one.
Rinse and clean the stator. When I disassembled the motor, I realized that it had taken a good series of soakings. The stator was all rust and the coiling was covered in brown stuff and dust (it was shooting out of it when I was testing it). I decided to rinse it out in spirit. I put the whole stator into a glass filled with spirit and left to sit for a couple of hours. After two hours I began to clean it, and the cleaning took about half an hour. The waste spirit was all brown. Down the drain it went (that was not cognac! =)). Then I waited until the stator dried. The old thermal insulation looked bad, so I removed it from the wires.


As long as the stator was drying, I went about the rotor. It was an even sorrier sight. However, much to my joy, all four magnets were well intact.
I removed the old winding using a box cutter, so that I could polish the rotor and the shaft before rewinding it.

Now I was in for the most subtlest and most exciting part of it – rewinding the rotor. Why should I do that?! Because I wanted the magnets to stick firmly to the rotor, so that they wouldn’t come off at high rpm, block the engine, or, worse still, drag the governor down into the wastebasket as well. I considered two types of thread – capron and Kevlar. I chose a 0.1 micron capron thread, because Kevlar was thicker. Honest, it pretty much drained me, because I spent an hour or two fitting every little coil to each other without a single gap.
Now that I had wound it, I was only to soak it in epoxy. I chose the good old plastic glue. Well, to soak it properly, I covered the winding in a thin layer of glue in such a way as to prevent dripping. Then I put it into a heated oven, and the result was a smooth and shining surface. As long as it cooled down, I’d do the wires and connectors. I had bought shrinkable plastic tubes at a very sweet-tasting price, and now I was to heat-shrink the wires.




Now the stator is ready, so let’s put the whole thing together.

Finally, I replaced the bearings and started assembling it. The rotor span smoothly without hitting the stator, thanks to my choice of a thinner thread. Just a few minutes of bolting, and there it was. Now, one more check: the same 6S battery got it working, and I ran it at maximum rpm for about 30 seconds. The motor was warm, and there was a little noise at the beginning, as the bearings were seating. After five minutes it was all spick and span.
Conclusion: not quite so challenging and pretty cheap, and the motor will run for more than one season – there are ways around the trashcan, aren’t there =)
Thanks for reading, I hope you’ve liked it – I just wanted to tell you that not everything that fails deserves the wastebasket (I’ll post a vid later).
This is the translated version. You can read the original Russian article here.