Brushless Motor Construction Discuss design and construction of custom Brushless motors

what makes a brushless motor burn out?

Old 03-09-2007, 05:59 AM
  #1  
peterkron
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Default what makes a brushless motor burn out?

well thats my question. im wondering because i have a small fiego inrunnerthats rated at 5 amps max and im only using about 3.5 amps with a 2 cell so im wondering if i can go to 3 cells if i just stay under 5 amps without burning up the motor
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Old 03-09-2007, 02:36 PM
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JWilliams
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I wonder too. It has no connected parts so I presume that as more and more juice is run through it, the wires creating the magnetic field get hotter and hotter to the point where they melt and/or start to deteriorate, similar to how if a lightbulb rated for a typical lamp has a thousand volts put through it its filament will burn out from too much heat.
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Old 03-09-2007, 02:58 PM
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crash_out
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Over-revving is a common cause of brushless motors going out. Magnets can be thrown off by too much heat or speed. Generally anything that can cause a brushed motor to destruct can destroy a brushless motor as well. Too much current, too many watts, too much heat...Of course these are all problems caused by over-propping, over-celling, or inadequate cooling.

I've got a small Feigao (IPS replacement) on an Edge RC Pocket Combat Wing. I can't remember it's numbers, but I do know with a 3x2 GWS prop and a 3s ~550 mah Tanic it pulls slightly more than the rated 5 amps. In the air it unloads to a more reasonable level. I generally don't run my equipment that close to the ragged edge, but the performance increase with the 3 cell was so significant, I decided it was worth it.

If you're worried about it, try a smaller pitch or diameter prop, and think on it from there. I don't personally think the increase from a 2-cell reading of 3.5 amps would be damaging if only run briefly to get an idea of the amperage.

-n

Last edited by crash_out; 03-09-2007 at 03:00 PM. Reason: stupidity
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Old 03-10-2007, 02:18 AM
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thanks
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Old 03-10-2007, 02:29 AM
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you can put 100,000 volt through the lamp and it will be fine as long the amps don't exceed the limits
Remember it not the voltage that kills it the amps
But like it's been said rpm can cause problems
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Old 03-10-2007, 02:33 AM
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thanks again
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Old 03-10-2007, 07:24 PM
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Bob_CO
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Originally Posted by peterkron View Post
im only using about 3.5 amps
Is that 3.5 amps WOT?
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Old 03-12-2007, 12:47 PM
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wattage is what kills em. power(in watts) is volts times amps. to stay at the same power imput, if u rasie voltage then current has to drop.
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Old 03-12-2007, 05:06 PM
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Originally Posted by skiman762 View Post
you can put 100,000 volt through the lamp and it will be fine as long the amps don't exceed the limits
Be assured, that if you did that to a 120V lamp filament, the current would be about 800 times the current at 120V
Pete
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Old 03-12-2007, 06:21 PM
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ron_van_sommeren
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Originally Posted by stroland View Post
wattage is what kills em. power(in watts) is volts times amps. to stay at the same power imput, if u rasie voltage then current has to drop.
Nope, only current. Or, if you like, power/wattage dissipated IN the coils and stator. But not power in or power out.
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Old 03-12-2007, 06:38 PM
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paranoia
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magnets, epoxy/enamel covering the wire, and bearings can all be damaged by the heat form the motor itself.

also low quality bearings can blow out
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Old 03-13-2007, 02:35 AM
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peterkron
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i see. and yes 3.5 amps wot static
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Old 03-13-2007, 06:01 AM
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every time the motor heats up it takes a bit out of the magnetic field strenght, so next time the motor will have to run harder and hotter to make up for the loss, and so on.....

better/costly motors should have more heat resistance magnets which should slow the rot.


so most new motors will run the same, ie super cheap motor vs costly motor on the bench

however the super cheap motor will fall off quicker and the costly will come through in the end.


so don't buy and cheap brand motor that is 2nd hand
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Old 03-13-2007, 03:26 PM
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Originally Posted by paranoia View Post
every time the motor heats up it takes a bit out of the magnetic field strenght, so next time the motor will have to run harder and hotter to make up for the loss, and so on.....

better/costly motors should have more heat resistance magnets which should slow the rot.


so most new motors will run the same, ie super cheap motor vs costly motor on the bench

however the super cheap motor will fall off quicker and the costly will come through in the end.


so don't buy and cheap brand motor that is 2nd hand
How much for the average user does that really affect things? Noticeable loss after one hour? 10? 50? Has anybody plotted it in a way relevant to our application of these motors?
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Old 03-14-2007, 12:05 AM
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Originally Posted by JWilliams View Post
How much for the average user does that really affect things? Noticeable loss after one hour? 10? 50? Has anybody plotted it in a way relevant to our application of these motors?


don't know, but my hi-end mega motors are still flying strong after +2yr of service, i use a heat sink, (which keeps it cooler) which increases the life

on the flip side i had a razor heli2 motor which i overloaded every flight in a micro heli w/o a heat sink, and after about 6months i when from using 45% power to hover to using 70% to hover. i sold that motor off cheaply...


i should start recording my numbers in excel, i would check my motors is with a wattmeter, with a given setup. Then record the date setup and amp/volt draw. but i don't have many cheap motors left, i have sold them off, and replaced them with aveox and mega, axi motors

i still have one or two justgofly outrunners.... i think outrunners do stay cooler anyway, and they tend to be installed in better vented areas. Because the outter case is moving you can't install stuff to close to them.

Last edited by paranoia; 03-14-2007 at 12:25 AM.
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Old 03-14-2007, 12:44 AM
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Well my old trusty 14 dollar beater must be a fluke it's still pulls like it was new and I'm not very nice to it either
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Old 03-14-2007, 12:51 AM
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Not sure if motors are like generators in that the power output is only limited by there ability to cool themselves I would think so as the heat builds the electrical resistance goes up and more amps are required to make the same power
sounds good anyway
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Old 03-18-2007, 05:14 PM
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aircruiser
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I read somewhere too that brushless motors cant go under water like brushed motors can...so dont nose dive your planes into the lake ya hear?
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Old 03-18-2007, 05:54 PM
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brushed motors can go underwater?

are you sure?

wouldnt the water short out the motor (causing burn out)?
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Old 03-18-2007, 06:05 PM
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Originally Posted by socal swimmer View Post
brushed motors can go underwater?

are you sure?

wouldnt the water short out the motor (causing burn out)?
Apparently some people break their brushed motors in with the thing dunked. I don't understand it, either. That's why I stick to brushless
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Old 03-18-2007, 06:20 PM
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I'm sure I read somewhere that brushless motors were pretty resistant to water. They had crashed planes into water, but still managed to power them back to shore, and once thay had dried out, there was nothing wrong with them.
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Old 03-18-2007, 09:14 PM
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Yep I break in my brushed motors underwater. You just put some leads on it to a AA battery and let it run til its done. The water will turn a semi-transparent dark grey and thats all the crap you are getting out of it. I also have waterproofed my R/C trucks and run them through mud and underwater and they do just fine!
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Old 03-19-2007, 06:14 PM
  #23  
ron_van_sommeren
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Both can run under water. Brushless even better because they don't have brushes.

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Old 03-19-2007, 09:49 PM
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Are you sure brushless can?

I know they can get a little wet but seeing as they dont use brushes, you'd think that water would screw up something..
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Old 03-19-2007, 10:13 PM
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Wet brushless motor, no problem. Wet ESC, not so good:o:p
Seriously though, this only applies to fresh water, salt water, not so good.
Pete
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