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Old Jul 24, 2006, 07:20 AM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
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AXI 2820/10 burn out on 3s Lipos

Looking for a few clues here men.

I've been running AXI 2820/10s on 10 Nicds and 10 NimHs since the motors first came out, usually with 11x7 APC "e" prop and they have worked superbly for me in funfighter type models at 3.25-3.75lbs weight.

Yesterday I tried one of my old 2820/10s in an aerobatic model, the Esprit Models Supra-E, at about 4.25lbs weight. I'd previously seen the second hand model fly well on a 2820/10 and 10xCP1700s. The set-up I'd arrived at was a 3s1p 3300ma FP Lipo pack, Jeti Advance 40 esc and, in view of the better voltage hold up expected of the pack under load, had propped down to a 10x6 MA wood prop.

We put the meters on the model before flight and the static numbers came out more or less as expected = 37amps WOT, fresh off the charger, 9000 rpm and the voltage settling down at something around 10.7v. Take off was brisk and the climb out was fine. The model had no shortage of power and I flew around for five minutes or so, being very happy with the performance.

Then, as the model was pulled vertical and the vertical held, she hung in the air for a couple of seconds and suddenly all power was lost. I still had radio and landed the model deadstick with no damage. On recovering the model there was a strong smell of something burning and I initially thought that the ESC had burned out- further investigation showed that the motor had burnt out a winding and was dead as a dodo. It's the first problem of that type that I've encountered.

The battery was cool, the speed controller was cool but the motor was very hot indeed. The motor has an abundance of cooling supplied, through a big open hole in the front of the cowl, with good airflow through the model.

Two other factors that might be relevant, or not, are that the motor had been in a model that had crashed and this was the first time it had been used since that crash. There is the merest hint of a wobble in the rotation of the can, which might be a very slightly bent shaft, towards the rear. However, even if that was the case, I'd have thought that the current draw of 37 amps WOT static, really ought to be well within the limits for the motor and I can't envisage a situation where that current draw would be increased in the air.

The other thing was that a cable tie, located through the motor box to hold the speed controller was found to be touching the rear or the motor. It hadn't melted or shown any sign of any mechanical damage but I wonder if friction from contact with the tie could have been involved in any way.

I'm going to remotor the model, as I was very pleased with the performance. However if there is something inherently wrong with the set-up, that I'm missing, then I don't want to burn out another of my 2820/10s and would maybe go for a 2820/12. If someone with experience of using either of these two motors on 3s Lipos could chip in with their prop size, current draw and the details of the models that they are using them in then that would be great.
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Old Jul 24, 2006, 07:36 AM
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vintage1's Avatar
East Anglia, UK
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1/. You forgot to mention that this is the hottest July on record..

2/. Why not rewind what you have there? Or get a new stator for it..

3/. I've heard that a 10x7 is a safer bet..

I'd say that you have been on the edge for a time..and a combination of hot weather and maybe a little extra bit of load pushed it over the edge..maybe the magnets finally partially demagged...
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Old Jul 24, 2006, 07:46 AM
All under control, Grommit!
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United Kingdom, Aberdeen
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Vint

I don't think the ambient temperature was really a concern to be honest, I waited for conditions to improve before making that first flight, as we had a strong crosswind for much of the afternoon, and this was early evening with the temperatures quite tolerable.

Life's too short to rewind motors mate - Paul McCartney stuck at it for just a morning before escaping over the wall and I'm of much the same mind, if not of the same wind

I've used those 11x7 props right from when the motors came out and when those were the recommended props. A while later, presumably after the burned out motors started coming back, the recommendation changed to 10x7 but I so rarely use full throttle in these models that I saw no need to prop down and haven't had any problem. The 10x6 that was actually fitted ought to be well within spec.

You might be right though, it might have just been a bridge too far for the motor, in which case replacing it with another one with the same spec wouldn't be the best option.
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Old Jul 24, 2006, 08:00 AM
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If the magnets aren't damaged, John Emms can allegedly supply a new stator IIRC at about half the cost of a new motor.

I have to say my instinct is to always test a motor to 'that's bloody hot' and then go down to 75% of load from there..batteries likewise.

But then I fly stuff that doesn't need massive power...

MPjet have in interesting outrunner in the same class..might try Fanfare...on paper it looks a tad sharper..

If you are chucking the motor, chuck it my way..might be interesting to pull it apart and try and puzzle out why it blew, and/or rewind it ...
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Old Jul 24, 2006, 08:15 AM
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You didn't say the vintage of this particular 2820/10. If it is a couple of years old, you may have thrown a magnet. They had some problems with that a while back that seemed to be cleared up now.
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Old Jul 24, 2006, 08:19 AM
All under control, Grommit!
leccyflyer's Avatar
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Ken

It's an old one, and predates the time of the magnet chucking ones. On examination all the magnets are fine and all are in place. I'm going to pass the motor onto a clubmate with a lathe for him to measure the truness of the shaft.

Vint - that's an interesting option that I hadn't actually thought of, I've already contacted John this morning to ask about the 2820/12s, so I'll see what he comes up with.
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Old Jul 24, 2006, 08:30 AM
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Quote:
Originally Posted by leccyflyer
Ken

It's an old one, and predates the time of the magnet chucking ones. On examination all the magnets are fine and all are in place. I'm going to pass the motor onto a clubmate with a lathe for him to measure the truness of the shaft.
Oh, the value of a mate with a lathe!

I actually borrowed my mates simply to push a shaft squarely into a bell..never even switched it on...just used teh tailstock with the bell squared up in the main chuck..

Quote:
Vint - that's an interesting option that I hadn't actually thought of, I've already contacted John this morning to ask about the 2820/12s, so I'll see what he comes up with.
Someone else had the same problem, and ordered a new one..a week ago..in here somewhere...bearings? new ball races shouldn't be hard either. Biggest worry is 'did it demag, or did it just blow?'

Not sure how you would test for that, oher than with a new stator and seeing if the idle current and KV were on spec...expensive experiment..if the results are negative.
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Old Jul 24, 2006, 08:41 AM
Kou
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lecc:

I had a 2826/10 with the same problem. It was also in a crash before the winding burned. What happen is that in the crash, I did not notice that the stator glue is loosen in the crash so when I use the motor again, the winding actually rubbed against the rotating can and short the winding after a short run. You may have the same problem.

MK
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Old Jul 24, 2006, 09:03 AM
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Quote:
Originally Posted by Kou
lecc:

I had a 2826/10 with the same problem. It was also in a crash before the winding burned. What happen is that in the crash, I did not notice that the stator glue is loosen in the crash so when I use the motor again, the winding actually rubbed against the rotating can and short the winding after a short run. You may have the same problem.

MK
That is a more than plausible scenario.

Windings shorting to the can would produce exactly those symptoms.

removing the bell and inspection of the magnets would probably prove it one way or the other.

And a new stator would entriley fix the problem..assuming the magnets were not damaged and the bell still ran true..which a run out test on the lathe would establish..
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Old Jul 24, 2006, 09:17 AM
All under control, Grommit!
leccyflyer's Avatar
United Kingdom, Aberdeen
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Quote:
Originally Posted by Kou
lecc:

I had a 2826/10 with the same problem. It was also in a crash before the winding burned. What happen is that in the crash, I did not notice that the stator glue is loosen in the crash so when I use the motor again, the winding actually rubbed against the rotating can and short the winding after a short run. You may have the same problem.

MK
MK

Thanks- that does sound like a feasible scenario. If the windings touched against the back of the can as the motor warmed up then that could explain it.
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Old Jul 24, 2006, 09:34 AM
Kou
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lecc:

Let us know what you find out. If you pull on the winding, it will slip out of the shaft if the glue is loosen.

MK
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