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Water Ingestion & Brushless Motors

Old 10-30-2006, 03:37 PM
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DinoR
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Default Water Ingestion & Brushless Motors

Hi All

Our club is investigating what could have potentially ben a quite serious accident with a members plane coming down and narrowly missing people and cars.

Eyewitness accounts suggest the motor was cycling on off rapidy just prior to impact and there is a suspicion that water may have enterd the front cowling ( YAK55D ) and been ingested or somehow entered the brushless outrunner.

Flying conditions were a moderate drizzle at the time, so some water entering the cowl/motor seems possible.

My question is how is a brushless outrunner affected, if at all, through exposure to such ' drizzle ( lets ignore an obvious 'drenching' say in heavy rain )...is it something to be avoided, how does a problem manifest itself ( ie does the motor cycle on and off as observed ?) ?

Thnaks in advance - DinoR
Old 10-30-2006, 07:09 PM
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jdetray
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Default RE: Water Ingestion & Brushless Motors

DinoR-

I can't answer your question about water in brushless motors; I've never seen it happen. But is there any chance the pulsing motor was caused by a depleted battery triggering the ESC's low voltage cutoff (LVC)? Some ESCs pulse the motor when LVC is activated.

- Jeff
Old 11-02-2006, 05:55 PM
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Default RE: Water Ingestion & Brushless Motors

Remember that motors are FREQUENTLY broken in submersed in WATER.

With brushless motors the hookups are often far better enclosed.

With all motors the winding wires are covered.

Water getting into the motor is more likely to adversely affect the bearings, but that would happen over time as rusting occur, etc. This is something you would not see right away.

A short due to water would also tend to be all or nothing, not intermittent functioning.

The low voltage cutoff sounds much more plausible.

I was running a brushless config and my LVC turned on while flying a .40 sized plane.

I had programmed the ESC to reduce power. The LVC kicking in was immediately apparent. The plane could not gain any more altitude and I was barely able to land it. I would not have had enough power for a second go around of the field.

Had I programmed the ESC to cut off power I would have been in a dead stick situation, etc.

Did the member properly program the ESC?

Is it possible that they merely used the defaults, as so often occurs?

Old 11-02-2006, 06:10 PM
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jdetray
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Default RE: Water Ingestion & Brushless Motors

Good points, opjose.

I would simply add the BRUSHED motors are frequently broken in by running them under water. I have never heard of a BRUSHLESS motor being broken in that way. Brushless motors don't need any break-in, anyway.

- Jeff
Old 11-02-2006, 06:17 PM
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Default RE: Water Ingestion & Brushless Motors

Yes.

If anything brushless motors have their wiring more tightly enclosed so would tend to be less prone to moisture problems that quickly.

Of course moisture and metal don't mix over time.


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