what's this funny noise?

[Dillzio]

Hi All,

First of all, MERRY CHRISTMAS!

And now for my problem, I had a rough landing today where the plane nosed into concrete and bent the prop shaft. Now the brushless is intermittently making a nasty grinding noise. I've attached a vid of what it's doing.

When it's purring along quietly, that's what it's supposed to sound like, but when it cuts in and out getting louder, that's where my problem is. Anyone know what it is, or how to fix it?

-Thanks

[toff]

Sounds like one of the magnets is working loose, and grinding. Also why it seems intermittant.

[Dillzio]

Dec 24, 2010 23:07:58 GMT 1 toff said:

Sounds like one of the magnets is working loose, and grinding. Also why it seems intermittant.

I suspected that might be what's going on. Any idea if it can be fixed?

I've never dismantled a brushless motor before

EDIT:

I've figured out how to take it apart, and there were some scrape marks on some of the magnets. When I put the bell and shaft on my magnetic prop balancer it seemed to be a little wonky too. I forgot to check if the shaft was bent when I had it out (dow!)

The magnets well all glued down by a tarry sort of stuff. I just squashed all the magnets down with some needle nose plyers to hopefully get a bit more clearance for them. I also cleaned out some little metal filings that were stuck to the magnets, and put a very fine layer of vasoline over the manets (wiped 99% of it off with a tissue).

I've put it back together now, and it does seem to be better than it was. It made the grinding noise only briefly, after which it hasn't made it again. I guess time will tell.

Just in case, I went and ordered the Turnigy 35-36 today, a little christmas present for myself :-)

[toff]

I think I've read on one of the posts on RCgroups about using epoxy and a mini G clamp to repair this problem. Also filing down the metal armatures would help a lot, as these tend to be minutely mis-aligned, so they tend to catch on the magnets if they get moved ( as happens in nose first earth re-entry)

[Dillzio]

part of the problem seems to be that the whole bell wobbles a tiny bit when it spins now, I think I may have bent the shaft. Anyone know where I might be able to get a spare shaft for the Turnigy 35-30?

[flydiver]

Squishing the magnets down? Not a good idea. If it's loose glue it, otherwise it's probably where it should be. Squishing is more likely to break the glue bond and wreak havoc if not break the magnets outright. They ARE brittle. If broken they ARE TOXIC!!!

Cleaning out metal fragments - If they were in there it indicates a problem. Tape works well to clean them out.

Vaseline? For what, lubrication? Stator should not touch the magnets. Lubrication will not help. If it touches, something is wrong and needs to be fixed.

The problem of crashing a much heavier plane is good old physics. The bigger they are the harder they fall. Going in that hard on the motor could very well have bent the shaft and even bent the bell/shaft attachment. Getting replacement parts for cheap motors can be a problem often not worth the hassle.

[Dillzio]

giantcod.co.uk

all the necessary parts for the turnigy motors :-)

I'm hoping all I did was bend the shaft on my 35-30, and not the bell.

I managed to minimize the wobble by rotating the shaft in the bell a bit, now it doesn't make the noise anymore. The motor does still wobble a bit though, and it makes it look as if it has a bent prop shaft. It makes the motor draw an extra couple of amps too (20a vs 18a). At least it's flying pretty well for now though :-)

Thanks for the warning on the magnets fly, had no idea they were toxic. The glue holding these magnets down looked like sort of a tar, seemed like it could flex a fair bit without letting go. I applied a little vas to prevent the scratched magnets from rusting, and to provide a little lube just in case they started rubbing again (would hopefully minimise the damage)

[flydiver]

That black stuff is probably loctite 410.
www.gobrushless.com/shop/index.php?app=ccp0&ns=catshow&ref=ADHESIVE
It's some kind of goop in CA. I use it for magnet gluing in motors and covering chipped stators before rewinding.

Not all the rare earth magnets are toxic but these are Chinese, not subject to any disclosure, and I'd treat them as a potential problem if broken.
www.rareearth.org/magnets_safety.htm

Hopefully a new shaft will fix it up.

[ginginho]

I'd treat them as toxic if I were you. If they have been scratched and lost parts I'd be wary of using the motor anymore.
An alternative often used instead of replacement shafts is to use some hardened steel rod of the correct diameter. I believe the most common form is known as "drill steel". Much less likely to bend.
Did you manage to move the shaft on the bell? Often this is held in place with a glue, as well as the grub screws. If this is the case you'll need to break that grip before being able to remove it. It may also be a very tight friction fit. Some have success using a centre punch and carefully pushing it out, others have had to revert to applying some heat as well. Others just haven't succeeded in breaking this bond between the shaft and bell without causing irreparable damage.

Drawing more amps for the same power output? This may be due to the friction as it's rubbing. Another possible reason is that the magnets have been compromised (normally due to overheating), in your case by the removal of some material, if this has happened. If you do manage to swap the shaft check this again. The motor might be on it's way out.

[Dillzio]

I managed to move the shaft on the bell fairly easily (with the right tools).
I just grabbed the bottom of the shaft with vice grips and twisted it whilst holding onto the bell.

I think it's drawing more amps because the propeller is wobbling now, and is hence less efficient.