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Old Dec 10, 2014, 04:39 PM
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Help!
SK3 motor: one cable disconnected

Today one of the 3 cables of my SK3 2836 disconnected while I was in the air, I managed to land my acro and now while I was checking the motor I've seen one cable falling apart:



Is there a way to repair it? Can I get inside of the chassis to solder it again?

Thanks!
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Old Dec 11, 2014, 03:57 AM
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Letchworth, Great Britain (UK)
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How new is the motor, and has it been in a crash? If new and not crashed, I would send it back, rather than try to fix it.

I can't see from the photo, but is the wire broken, or has a solder joint simply come apart? If you plan to repair it, first check if the motor windings look okay, not burned. I'm not familiar with your particular motor, but you can usually pull the "bell" (the rotating bit) off the windings if you remove the circlip that holds the shaft in place at the rear of the motor. That should give you access to the location where the lead should be attached. When you get there, re-soldering may be simple. If not, post a picture of what you find, and someone should be able to help further.
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Old Dec 11, 2014, 11:30 AM
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Thanks a lot Abenn

The motor has ~40 flights on a glider and ~15 on a 3D, never crashed and much beloved . Don't think that I can send it back, it's a shame 'cause I should probably buy again the same motor and this was perfect.

I think I will try to open as suggested and try to re-solder, I hope it should be a clean job as the motor did not take any shock, it was the cable a little to short I guess and after a while the solder joint gave up.

I'm looking to this thread: http://www.rcgroups.com/forums/showthread.php?t=1222788 and it gives me some hope

Thanks again for your help!
Cheers
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Old Dec 11, 2014, 03:07 PM
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Yes, that thread gives you a good idea of what's involved. One problem you might come across, which I'm not sure is mentioned there, is that if you need to solder to the stiff copper motor wires -- i.e. if the wire is broken, rather than just a solder joint come apart -- you'll need to scrape the varnish (or whatever they use these days for insulation) off the motor wire and get down to bare copper before you can successfully solder to it. I use a sharp blade to scrape the wire clean.
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Old Dec 11, 2014, 09:15 PM
WJH
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Hmm, think I'll stick to O.S.
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Old Dec 12, 2014, 01:46 AM
Wake up, feel pulse, be happy!
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Those leads look like regular stranded wire that's been soldered to the winding ends inside, in which case it would be easy enough to resolder if you could get in there. Unfortunately, it looks like the backplate is pretty enclosed. Taking off the bell won't grant access there. You'd have to pull the stator off the bearing tube to get at the wires, running the risk of trashing the windings or stator in the process.

If you haven't done much work on motors before, your best bet is to buy a new one.
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Old Dec 12, 2014, 08:55 AM
homo ludens modellisticus
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The Netherlands, GE, Nijmegen
Joined Feb 2001
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Removing insulation lacquer
In the Electric Motor Design and Construction subforum
-> Sticky: (Re)winding and building motors
-> opening post
-> tip/trick #27: Removing insulation lacquer using (real) Aspirin.

Prettig weekend Ron
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Old Dec 12, 2014, 11:57 AM
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Indeed, I'm holding on to it for the weekend as it looks like it's not a easy thing, there's no easy way to get to the soldering point.

To be fair to the vendor: the cable disconnected to a fault of mine: the wirings to the ESC where just the exact length and in fly that fuselage twists a lot , the motor had no trouble while it was on the glider it was supposed to stay on.

Thanks all guys, mybe I'll to upgrade to a 3530 for the 3D and a 2830 for the glider and I won't swap around.
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Old Dec 12, 2014, 01:27 PM
homo ludens modellisticus
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The Netherlands, GE, Nijmegen
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I'd say give it a try, you have nothing to loose. Maybe the stator will come off easily. You'll learn more about e-motors. And I refuse to believe that anyone living in/near Modena does not know anything about motors

Motor disassembly/repair videos
www.innov8tivedesigns.com
-> resources
-> video class room

Prettig weekend Ron
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Old Dec 12, 2014, 07:55 PM
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I tried to dismantle the motor and It didn't look very pretty so I decided to give a try with not-so-brute force by the outside.

After some cutting and pulling I was able to expose a small part of the inner joint, i decided to wet that edge with some fresh solder and then I soldered the other side with a hot tip for a small amount of time: I think the thermal capacity of the all-conducting-mass need more heat than what I was originally comfortable to use.


Then I used a small thermal skin to secure the cable from mechanical stress to just one of the others: this way you have less play than with 2 of them.

As safe is better than light I put some fiber tape to link the cable to the spare one too:


Do I thrust this motor for my shaky 3D plane? Not sure, I will sleep on it and maybe test it on my glider for a while: in case it's less trouble to bring that down without motor.

Thanks all for your help, Butane nailed it pretty well.
Special thanks to Ron: I've start reading some of your posts and you are quite the man about motors , nice job mate.
...he here in Modena they all go crazy for the smell of fuel and big car motors
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Old Dec 13, 2014, 11:22 AM
homo ludens modellisticus
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Next time, use a bigger iron for faster and better soldering. I hope your magnets did not get the time to get hot. Above 80C they start to weaken (irreversable) . Weaker magnets will give higher Kv, and current wants to go up cubed with Kv. I would test, initially, with a smaller prop, to be safe. Measure current, both with smaller and the prop you've been using.

And I would use it in your glider if I were you, given the way the soldering joint looks now. A loose motor-connection can fry your controller and/or controller.

Vriendelijke groeten Ron
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Old Dec 13, 2014, 09:33 PM
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Thanks again Ron, if that motor can hold it's own on my Phoenix 2K it would be fine, it used to be more than enough for it as I've been using a 2826 on it instead of that 2836.
...yet I don't like the idea of finding myself down wind with no motor , and I use the ESC included BEC with it...

I use zippy 1500x3s @25c (like 10C for real) and 1000x3s so it should not be able to get more than ~15amper anyway :P

So humm, yeah... The motor stays in a box right now. After I'll fly the hell out of my EPP 3D (now it has 140 flights) I'll put glass fiber on the nose to keep it firm, cover all the edges with LEDs and turn it in a clown-plane to entertain my nephews

What the hell, it will end that I'll buy a new motor for the old plane and a new plane for the old motor , merry xmax to you all
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