Death of a motor this time ....

[Tony Smith 7]

Hi,

 

I flew my Fun Cub a couple of times this morning with its new ESC driving a Giant Cod 3530 1100kv motor (LINK) and 10"x5" prop.   After the last flight I had no power, and back in the workshop I found the motor had died.  The ESC was quite hot, and the motor was I would say very hot with a scorched smell.

 

Dismantling I found that that one of the three motor wires had failed inside the insulation halfway between the motor and the bullet connector.  The strands at the point of failure looked burned and melted.   One only of the windings looks scorched and blackened.

 

Checking with the meter, the resistance between any two of the three leads was pretty much the same, around 0.5ohm so there was no dead short in there.   Just for the hell of it I put a temporary connector on, linked it all up and the motor works, although I don't intend to use it again.

 

Any ideas what could have caused the fault?  I'm thinking possibly a short somewhere that drew so much current that it burned through that lead.  The fact that only one winding was overheated is odd.

 

Cheers,  Tony S.

 

[Steve W-O]

The motor should not have been a problem with a 10X5 prop

 

If it got too hot, it could have damaged the magnets, resulting in loss of power, more current draw, more heat and more damage.

 

The lead would have been a result, not the first thing to go

Edited By Steve W-O on 18/12/2010 15:22:57

[Plummet]

Tony,

 

Had you been somewhat generous with heat or solder when fitting the bullet?  Could the solder have crept back up the wire to the point of failure?  If so, the end of the stiffened wire would have been a point of stress concentration, and flexing of the wire could have gradually been breaking strands in the wire for some time. As less and less strands connected then they could have got hotter and then the whole lot failed.

 

Alternately, do you have mice?  Mice caused a similar fault for my Mother-in-law's washing machine a couple of months ago, and it was a sod to diagnose and fix.

 

Plummet

[Tony Smith 7]

Cheers.   I've flown the model a few times with that motor and prop, with no particular heat before so I don't see how it could have been over loaded. 

 

I don't think it was my soldering either, as the break was about quite a way back from the bullet, about half way along the lead.   The leads on that motor are pretty crappy, very loosely twisted strands and a loose filling insulation.   

[Steve W-O]

The leads on the motor are often just the windings extended out in silicone insulation tubing.

 

Did it seem to lose power before the failure?

 

When you say it is working now, have you checked the current draw, is it getting full rpm? did you check it with or without the prop?

[Tony Smith 7]

Posted by Steve W-O on 18/12/2010 16:20:19:

 

Did it seem to lose power before the failure?

 

I didn't notice it doing so.  I just landed, then had no power.

 

When you say it is working now, have you checked the current draw, is it getting full rpm? did you check it with or without the prop?

Just a quick check without the prop.  I'm not going to use that motor again with its heat-discoloured windings, and doing a full power test seemed like asking for it to burn out the new ESC or something.

I've just remembered that the bullets were ready-fitted to the leads, but I did have to replace one of them so the failed lead could have been soldered by me.  The re-terminated lead is 35mm shorter than the others, so the break must have been around 35mm back from the soldering.

[Steve W-O]

OK, if you checked it without the prop, it may well not work properly with the prop on, it may well turn, but badly lack power.

 

Sounds like it overheated, damaged the magnets, and after that overloaded the wires.

 

Is it the first time it has run with the shorter wire?

 

I don't think your soldering would have caused the problem in itself, but it is possible that you may not have taken the insulation off each individual wire completely.

[Tony Smith 7]

I just noticed something else on the motor.  In the picture you should just be able to see a bit of loose wire, almost as if one of the turns on the winding had missed the former and just been lying around loose.  Also I noticed that a couple of the other windings are scorched in places, not just the one at 4 o'clock that looks worst.

 

 

Edited By Tony Smith 7 on 18/12/2010 17:08:15

[Steve W-O]

The motor windings are long, not just round one former, and all the ends come out to the connections, so there shouldn't be any short pieces around. It is vaguely possibe it could have burnt off one of the windings.

 

Lots of possibilities, possible damage to the wire that you found broken, it could have broken and the ends touching until it got hot enough burn (or arc).

Possible that when you soldered, the enamel wasn't completely removed from one wire, resulting in a bad joint and the problems followed.

 

The magnets will almost certainly be damaged, and I would still guess that the damaged magnets indirectly caused most of the damage to the wires

[Tony Smith 7]

I guess I may never know.  I struggle to see how the cores could be damaged without damaging the insulation around them.  I've seen that very occasionally with flex, for example my soldering iron broke one of the mains wires inside the insulation, but that was after something like 30 years of use with lots of flexing.

 

Surely soldering problems would show up at the solder joint.  When I disconnected that bullet I was left with the bullet with a stump of wire soldered to it, with the break as I say around 30-35mm away from the bullet.

 

Are problems like this typical with cheap motors?   I need to replace this, but I'm having so much gear failure I really don't want to be worried every time I fly the model, wondering which bit's going up in smoke next.

[Stephen Grigg]

Ive never  gone for cheap motors and never remember having a problem,youve really had  a hard time

[Steve W-O]

I have had one cheap motor fail, from GC, but it did not even get off the ground, not enough power. Replaced it with another identical bought at the same time, and it is perfect.

 

It is easier for a cheap motor to fail in this way, as the magnets are not as good quality in as much as they get damaged at a lower temperature.

 

But if it doesn't overheat, then this doesn't matter for normal hobby flying.

 

It is possible that this was going before your ESC went, and could even have caused that.

 

The magnets start to fail at just over 80C, as they become less efficient, the motor draws more current, so gets hotter, so the magnets work less well, so more current............................

 

Until the current is too great for the wires, and they burn out.

 

The only cheap motor I have not been happy to use, is the one that came in my Wot4. FoamE

 

But I have replaced it with another cheap motor from HK.

 

Using an Ohm meter to measure the motor windings isn't very accurate. Most digital meters don't read zero when touching the probes together, and even if you deduct that, you can only get a rough indication. You need a milliOhm meter to measure with any meaning.  Most will have four wires going to the probes/clips to properly eliminate test lead resistance

 

[Tony Smith 7]

Agreed about using the multimeter low resistance, although its a decent instrument (Fluke 75) and can certainly distinguish between half an ohm and a dead short. 

 

On Giant Cod they think the motor could be rated only 15A, and might be overloaded with 10x5.   With the skis on the soft snow it maybe had full power for 10 sec or so at take off, whereas previous days its been only a couple of seconds to lift off.   I guess the GC motors might be lower rated than for example the Turnigy 35-30s that were tested HERE

 

Any suggestions for mail order sources of better quality motors?   I don't want to pay three times as much (for example from Purple Power) to just get the same thing.

[Steve W-O]

Posted by Tony Smith 7 on 18/12/2010 17:50:30: I need to replace this, but I'm having so much gear failure I really don't want to be worried every time I fly the model, wondering which bit's going up in smoke next.

 

 

Just followed the link to your motor on DC, and underneath I found t h i s link. It explains the magnet - wire situation nicely. You didn't over-prop, but something else could have followed the same path.

 

As for buying another motor, if you decide to buy a more expensive one, it might be worth thinking about a 3536, as it would be usable in a larger model later, and you can always use less throttle for now.

[Tony Smith 7]

Cheers.   I was thinking the same regarding maybe going 35-36, and propping down to start with.   I saw a 910kv version somewhere.

[Steve W-O]

Posted by Tony Smith 7 on 18/12/2010 19:36:22:

Cheers.   I was thinking the same regarding maybe going 35-36, and propping down to start with.   I saw a 910kv version somewhere.

 

 

With a 3536 910 you will need a different prop (12X6), and you will have vertical performance, with an 11X7 you wouldn't quite have the performance (but still very powerful) but you would get better duration at lower throttle.

 

I rarely use full throttle, or climb vertically, but I do like to fly for a long time between battery changes.

 

 

I haven't tried any expensive motors, so can't comment, when a I see the prices, I switch off.

 

 

I always try to test motors, first on the bench before installation, and then in the plane for max current and static thrust.

 

I run the motors for about 15 minutes on low throttle, then 15 on about 30%, then 10 on full.

My logic for this is that the bearing have lubricant in them, but it may not be distributed round the bearing. The bearing when assembled into the motor may be sitting very slightly out of true in the housing, and they may has some pre-load because of being a bit tight on the shaft and in the housing. All of these will sort themselves out with running, but I would rather it was without the load of a prop at full RPM as you take off for the first time.

 

You certainly have had a run of bad luck, but I wonder if it wasn't really just one problem that first caused the ESC to go, and then the motor.

 

 

I would hope that the more expensive motors are more consistent in manufacture, and the QC is better, and maybe higher quality bearings etc., but the motor is still only one part of a system, and even the best quality things fail sometimes.

[DH 82A]

Posted by Tony Smith 7 on 18/12/2010 19:24:58:

Agreed about using the multimeter low resistance, although its a decent instrument (Fluke 75) and can certainly distinguish between half an ohm and a dead short. 

 

On Giant Cod they think the motor could be rated only 15A, and might be overloaded with 10x5.   With the skis on the soft snow it maybe had full power for 10 sec or so at take off, whereas previous days its been only a couple of seconds to lift off.   I guess the GC motors might be lower rated than for example the Turnigy 35-30s that were tested HERE

 

Any suggestions for mail order sources of better quality motors?   I don't want to pay three times as much (for example from Purple Power) to just get the same thing.

               ----------------------------------------------------------------------------------------------

     I  have bought several  motors/esc   from  Purple power over the last 2-3 years, and have been quite satisfied with them.   They  did " what it said on the tin ".

 

     Speaking as a happy customer. 

[Steve W-O]

Posted by Tony Smith 7 on 18/12/2010 19:24:58:

Agreed about using the multimeter low resistance, although its a decent instrument (Fluke 75) and can certainly distinguish between half an ohm and a dead short. 

 

On Giant Cod they think the motor could be rated only 15A, and might be overloaded with 10x5.   With the skis on the soft snow it maybe had full power for 10 sec or so at take off, whereas previous days its been only a couple of seconds to lift off.   I guess the GC motors might be lower rated than for example the Turnigy 35-30s that were tested HERE

 

Any suggestions for mail order sources of better quality motors?   I don't want to pay three times as much (for example from Purple Power) to just get the same thing.

 

 

 

Missed this post.

 

The 75 is good, that is my general knock around that is always on my desk, as you say, it can give an indication between a short and 1/2 ohm, but on the motor we really need to tell between  .050 and .055 ohm. I use a Rhopoint M210, which is reasonable, resolution os .001 ohm and accuracy .1%  not perfect, but my bank balance doesn't go to perfect

 

 

I don't think the motor could have been over-propped, I think it would be very wrong to use what are becoming standard numbers with a totally different spec.

 

 

If you are in a hurry, I guess the decision will be more to do with what you can get, otherwise I would suggest HK. They may not be much slower than local people taking into account the holidays and snow.

 

 

[Steve W-O]

Just had a quick look, a Turnigy SK 3536 will cost you aout £22.50 locally on ebay, and about £14 on HK, you could get two from HK for £26, or maybe one 3536 and one 3530. May just be worth waiting!

[Tony Smith 7]

I reckon the motor failure comes down to a number of possibilities - maybe it was overloaded in that my particular example wasn't happy with more than 15A.  It's quite likely that motors from a budget source might be variable, and for example mine's branded "EMP" rather than XYH as advertised.   Maybe there was some damage from the dying ESC, or maybe the motor just failed in some way setting off the sequence.

[Eck]

I use the XYH 3536 1100Kv motors from GC in a number of models, from a Seagull Edge 540EP to a Black Horse B-25 Mitchell. They provide plenty of power on a 10x7 3-blade or 11x7 2-blade, and get barely warm during a flight. They're around £15.

[Tony Smith 7]

Posted by Steve W-O on 19/12/2010 13:45:15:
Just had a quick look, a Turnigy SK 3536 will cost you aout £22.50 locally on ebay, and about £14 on HK, you could get two from HK for £26, or maybe one 3536 and one 3530. May just be worth waiting!

 

That's the motor I'm coming round to thinking of, propped right down to maybe 11"x4" to keep to not much over 20A, and with a 40A ESC.    I don't know if Turnigy really counts as "up market" but I'm not getting another GC motor in this case.   Dunno if I can face the wait from Hobby King, my last order took eight weeks.

 

Purple Power are recommending their own-brand 3536 (1000kv) with a 13x4" (!!) prop and only 33A ESC.

[Steve W-O]

Posted by Tony Smith 7 on 19/12/2010 20:36:38:

Posted by Steve W-O on 19/12/2010 13:45:15:
Just had a quick look, a Turnigy SK 3536 will cost you aout £22.50 locally on ebay, and about £14 on HK, you could get two from HK for £26, or maybe one 3536 and one 3530. May just be worth waiting!

 

That's the motor I'm coming round to thinking of, propped right down to maybe 11"x4" to keep to not much over 20A, and with a 40A ESC.    I don't know if Turnigy really counts as "up market" but I'm not getting another GC motor in this case.   Dunno if I can face the wait from Hobby King, my last order took eight weeks.

 

Purple Power are recommending their own-brand 3536 (1000kv) with a 13x4" (!!) prop and only 33A ESC.

 

 

A 3536 1000 with a 13X4 prop will give you great helicopter performance, but dodgy flying performance, and would still draw nearly 30A.

 

But they are the experts with their motors, so best to go with what they say.

 

I would use an 11X5.5,  or an 11X7 which would sacrifice vertical performance, but giv longer duration at lower throttle.

 

And I would still use a minimum of 40A esc

[C Norton]

I had a similar sort of thing in a brushless powered Twin Star, had no problems previously but halfway through a slow roll one of the motors gave out a funny sort of squeak, both motors stopped and I was very pleased that I managed to do a rather nice deadstick landing, albeit at some distance away.

 

That is, until I was walikng up to retrieve it, when I noticed smoke coming from the 'plane and by the time I got to it one of the nacelles was nicely ablaze! I quickly put out the fire but one wing was ruined, the motor and its wiring totally burnt out and I still have no idea why.

 

They were Chinese cheapy motors but until then had run very sweetly. Very odd! Needless to say a replacement wing costs not much less than buying a whole new model

[Stephen Grigg]

I find BRC hobbies very reasonable and reliable.I converted a TwinStar to brushless andcoulnt get it to run well.Brc advised mt to use gold plated connections which I did.It ran perfectly but I gave it to a club mate who does all sorts of things with it.