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Author Topic: Brushless motor strange behaviour?  (Read 638 times)

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Offline cheddar-caveman

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Brushless motor strange behaviour?
« on: October 15, 2018, 09:27:48 AM »
Power train for my new build (when it gets here).
Turnigy D2836/8 1100Kv outrunner.
25Amp ESC - from an old Walrus glider.
3S Lipo.
11 X 6 prop.

First run, for about ten seconds, all well. Ran up to full speed - ila_rendered - everything normal.
Second run and the motor just jerked round - see video - wouldn't go up to speed - ila_rendered
Gave the prop a spin before applying throttle and it ran up OK again but getting rather hot.
Ran it again with the 40amp ESC from my other plane and a bit jerky to start but ran up all right, same parameters, but again getting a bit hot.
Never exceeded the 265 Watts which is well within the motor range.

ESC or motor problem?? 
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« Last Edit: October 15, 2018, 10:00:38 AM by cheddar-caveman »


Offline pooh

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Re: Brushless motor strange behaviour?
« Reply #1 on: October 15, 2018, 11:04:23 AM »
If two ESCs give much the same result, I'd suspect the motor. I'd try another motor with both ESCs, which would eliminate the ESCs as part or all of the problem.

If the motor is getting hot as well as running badly, I'd be thinking "shorted turns" rather than a loose connection in the motor.

If adjacent coil turns are shorting together, you get a transformer effect - if just one turn has becomes a single loop adjacent to 50 turns of normally connected wire, that can equate to a 50:1 ratio, 20 amps in the 50 turns means 1000 amps in the single turn - hopefully not as this would get a bit more than hot! Fortunately the transformer efficiency would be very low.

Very difficult to prove as the windings are very low resistance so a standard testmeter won't be much use.
Confucious he say "more than one aircraft in the same airspace leads to structural failure"

Offline Chippie

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Re: Brushless motor strange behaviour?
« Reply #2 on: October 15, 2018, 11:16:42 AM »
Shorted turns would affect the moto'r'sback emf sensed by the esc too, and if the short is sufficient to give rise to large currents flowing, chances are it may blow the mosfets......is your esc getting hot? Is the current draw similar to that shown on the meter?

You could check the soldered connections on your motor wires, make sure the connections are good and solid, no broken ends....take the heatshrink off to do this.
« Last Edit: October 15, 2018, 11:19:28 AM by Chippie, Reason: »
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Offline cheddar-caveman

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Re: Brushless motor strange behaviour?
« Reply #3 on: October 15, 2018, 12:24:52 PM »
Thanks guys. I do have another similar motor so will try that this PM. I'll also check out the ESC's and connectors - pouring with raIn so nice indoor activity!


Offline pheasant_plucker

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Re: Brushless motor strange behaviour?
« Reply #4 on: October 15, 2018, 14:17:40 PM »
I have seen this happening on a multicopter and it was caused by timing/sync issues. It burnt out a sec very quickly. Try setting the timing higher.

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Offline cheddar-caveman

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Re: Brushless motor strange behaviour?
« Reply #5 on: October 15, 2018, 14:52:53 PM »
I have seen this happening on a multicopter and it was caused by timing/sync issues. It burnt out a sec very quickly. Try setting the timing higher.
Gerry

Thanks Gerry but Timing?? This is an electric motor not a petrol engine so not sure what you mean??

Any way, just tried the ESC with two other motors and both ran correctly, tried the suspect motor with another ESC and same result so duff MOTOR!!  :banghead:

As it happens I've got a replacement on order already  :co


 

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