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Motor repair

is it worth it?

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IanN06/07/2015 23:38:49
1675 forum posts
119 photos

My session was cut short this evening. First flight I thought "that sounds a bit louder and rougher than usual" but carried on without incident. When I launched for the second time I thought the same. In my defence, I'd recently had a couple of bits of covering work loose and make a heck of a racket until I fixed them so the noise didn't unduly worry me - until about a minute into the second flight I heard a "thwack" and lost power.. Got the model back no problem, to find the motor hanging off the front of the bulkhead.

motor hanging off.jpg

It looks like it simply vibrated out of the mounting screws


One wire was severed, another is nicked in two places.

motor wires.jpg

I have two questions

Firstly, is it worth attempting a repair? The can turns freely, so is it just a matter of simply soldering the wires? I can't help thinking the internals must have taken a serious heck of a tug at the point when the motor broke free and - albeit briefly - must have thrashed around quite violently until the wire cut. Is the vibration as the motor worked it's way free likely to have compromised the screw threads? I don't want to throw useable kit away, but neither do I want to waste time flogging a dead horse. It's not an expensive item

Secondly, does anyone go "above and beyond" to secure motors? This set up had over 7 hours flight time so I guess the four screws into the motor backplate were plenty tight enough initially. Does anyone use threadlock? As I'm about to fit out my first .46/.53 sized electric model I certainly don't want any repeat of today's incident. I'm thinking about drilling four holes through the firewall to allow access to the screws that go through the mount into the motor backplate. That will at least allow a periodic check, and tighten up if necessary. Any other methods or ideas?



Edited By IanN on 06/07/2015 23:45:18

Martin Harris07/07/2015 00:29:53
9332 forum posts
249 photos

I always use threadlock. I wonder if the prop was out of balance?

Dave Hopkin07/07/2015 00:32:14
3672 forum posts
294 photos

Personally, I would repair the wiring, then bench mount it and run it up without a prop and see what it sounds like - cant really see the screw threads, but if they look undamaged and screw back into the motor without feeling odd, then the chances are they did vibrate loose over a period of time, one comes loose and the remaining three get even more load/vibration, etc so its an accelerating problem.....

I always use a dab of SHMBO nail varnish over the heads and mounting plate to stop any movement

Phil 907/07/2015 05:48:38
4287 forum posts
255 photos


I would buy a new one and some threadlock

Frank Skilbeck07/07/2015 08:01:52
4727 forum posts
101 photos

I think we forget how much force these electric motors can excerpt, a friend had just installed a "32" size motor, 700kv, 4s and 13 x 6 prop on the first flight the commercial electric motor mount fractured and the motor fell out!

You biggest problem in repairing the above motor is going to be removing the enamel on the broken wire so you can solder them together.

I always use threadlock by the way.

AJ07/07/2015 08:37:31
143 forum posts
12 photos

Removing the enamel is easy enougth, just scrape it off with a sharp knife until you can see bare copper all the way around then not forgetting to add a bit of heatshrink first just solder the severed bit back on.

Always use threadlock on the mounting screws, use the blue stuff not re, and check your prop balance as that is probably what caused the screws to fall out.


iqon07/07/2015 08:43:33
1487 forum posts
239 photos

I would buy a new one at that price plus a new prop as that one looks out of balance......and I always use threadlock..

Cuban807/07/2015 09:46:43
2952 forum posts
1 photos

There's nothing to lose by attempting a repair, although I'd want to dismantle the motor as far as is possible to check for internal damage or shorts in the leads/windings. If nothing is amiss after all the thrashing around, a soldered repair shouldn't be too difficult. Threadlock is essential to avoid this problem, as is the occasional pre-flight waggle of prop/motor/firewall assembly, to double check the integrity of the unit to the airframe........................don't ask!sad

Dave Hopkin07/07/2015 10:13:20
3672 forum posts
294 photos

Vibration is a killer, I recently had the commercial motor mount fracture across ALL the holes where the screws fit into the motor base, I had been experimenting with props and put one on that was out of balance, didnt really notice it at low revs, took off and it sounded like an unsilenced IC engine, landed quickly ok, changed the prop and went to take off again, motor mount fractured and motor shot out of the plane!

RC Plane Flyer07/07/2015 10:39:18
730 forum posts
10 photos

Although it may feel smooth to turn by hand I have had a similar motor and the bearings had failed after a broken prop on a rushed landing. Very easy to get hold of and change

Shaunie07/07/2015 12:18:31
951 forum posts
78 photos

As a minor point, most winding wire is now "self-fluxing". You will find if you hold a hot well-tinned bit onto the exposed end of the wire for a few seconds the enamel will burn back and allow you to tin the wire without scraping. If you can't get to the end make a small scrape to expose the copper and if the iron is sufficiently hot the enamel should melt back.


Andy4807/07/2015 12:22:57
1539 forum posts
9 photos

New Emax BL2815, £15.

Cost of new plane when repair fails.........

Its a no brainer really.

Dave Bran07/07/2015 12:32:39
1896 forum posts
5 photos

Repaired a number of motors, even rewound them fully, not just repair but also tuning.

For a laugh, try it................Break down one motor, use the wire in a smaller one, what was a cooking 12 or 14 becomes a hot 6/8 wind.......................Simples...............

But then I used to do the same to slot car motors in my youth. nerd

Not had a failure to a repair, ever....................

Komodo used to sell kits for motors to wind yourself, they worked well, but have not looked recently

IanN07/07/2015 23:27:03
1675 forum posts
119 photos

As always, when faced with a problem you haven't encountered before this forum comes up trumps thumbs up Many thanks to all

Those that suggested an out of balance prop are probably right. I had a perfectly balanced 11x7 fitted. But when a clubmate asked to try that on his plane I happily let him have it, but then replaced it with a 10x7 I had in the flight box, straight out of the packaging. I probably told myself I'd balance it when I got home - but never did

Dave Hopkin is almost certainly right in that one screw then came loose, which then accelerated/multiplied the problem with the remaining three

Some good tips re soldering/repairing the wires: thanks for those. I'll have a crack at repairing it, but mainly for interest/experience as I haven't done that before. If that works AND it runs smoothly I'll use it again but will confine it strictly to disposable models - hacks and "bitsas". If not, I'll harvest the shaft and circlip and the magnets!

And lastly, it's 100% definitely threadlock from here onwards - every time, without fail. The SHMBO nail varnish solution would I'm sure be equally effective - but it would HAVE to be my colour wink

PatMc08/07/2015 00:31:42
4405 forum posts
527 photos

It hasn't been mentioned but the potential for vibration could be minimized if the overhang was reduced. Could the prop driver be mounted so that it's hard up against the motor body ?

IanN08/07/2015 07:41:07
1675 forum posts
119 photos

That's as far on the shaft as the driver goes,

I suppose it could be drilled out - or take a bit off the end of the shaft instead? Hadn't thought of that

Another fair point

Edited By IanN on 08/07/2015 07:41:31

Edited By IanN on 08/07/2015 07:41:49

Mike Blandford08/07/2015 09:53:11
629 forum posts
25 photos

Regarding vibration, also consider mounting the motor behind the firewall. I had a EMAX 2832 mounted as you do, and had a lot of vibration problems, even with a balanced propellor. This motor is very long, so any imbalance (mass or aerodynamic) caused trouble. I solved this by moving the shaft so it protruded from the "fixed" end of the motor, then mounting the motor behind the firewall. The propellor and spinner are now VERY much closer to the mounting position.


gangster08/07/2015 10:18:48
1027 forum posts
29 photos

Another cause could be a slightly bent shaft, the shafts on those motors bend easily but on the bonus side are easy and cheap to replace, (from memory about 60p) Looking at the state of that prop definitely check its running true!

In my opininion it is worth repairing the motor, if for no other reason than "you can". Imho very unlikely to jeopardise a model.

On the other hand, have you seen the price of hatch magnets?, if you scrap a motor you get most of your money back by harvesting the magnets, real touch little blighters they are.

Edited By gangster on 08/07/2015 10:20:58

Engine Doctor08/07/2015 10:23:04
2508 forum posts
39 photos

Well worth a try to repairing it . Do make sure that windings or tails cannot short onto case or mounting. New heat shrink should do the job but If in doubt try some 24hr araldite. It will hold wires in place and insulate them . Definitely use some threadlock on mounting screws .

Gordon Tarling08/07/2015 11:49:38
237 forum posts
4 photos

OK, I'll be first to say it, as I feel it must be said.frown All four screws are not going to have vibrated from fully tight to completely undone on one flight. A simple preflight check for motor security would have picked the problem up before it became catastrophic. I'd agree with the others though - what have you got to lose by trying a repair? Threadlocker on the screws next time. smiley

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