ESC Failure.......

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PaulJ
Posts: 319
Joined: 16 Feb 2018, 19:01
Location: Ipswich, UK

ESC Failure.......

Post by PaulJ » 07 Jun 2019, 07:52

A member of my Club recently lost a beautiful scale Me109 due to esc failure. He has a theory that failure can be brought on by testing the failsafe........ The theory being that the frewheeling prop generates a reverse current, albeit for a short time, and that doing this every time you go flying gradually damages the esc eventually causing it to fail. I am not qualified to comment but what do the electronically literate think??? :?

Spike S
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Joined: 16 Feb 2018, 14:59
Location: Salisbury UK

Re: ESC Failure.......

Post by Spike S » 07 Jun 2019, 08:46

Unlikely !
Every time the ESC stops driving the motor, there is a reverse EMF as the prop windmills. This is deliberately stopped by the ESC "Brake" facility for gliders but many don't bother with that setting and things don't fail. Furthermore, when an ESC main motor drive fails, the BEC supply to the Rx often continues to function.
I have heard a few wild excuses for not testing Failsafe but that seems a bit spurious. It is probable that something more significant happened to your friend's model. It might also be worth investigating what his Rx does when forced into Failsafe mode - did it lose 'bind' ?
Spike S
(Tune for maximum smoke)

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PaulJ
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Location: Ipswich, UK

Re: ESC Failure.......

Post by PaulJ » 07 Jun 2019, 11:19

Thanks Spike, this guy is a very experienced and sensible chap who builds really beautiful, quite large "Warbirds". I don't think he would be likely to make wild excuses, this is just a theory which I wanted to put to the panel. ;) I didn't see the accident myself and I don't see him that often but I will ask him about the Rx losing bind next time I see him.

Paul.

Mike_K
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Joined: 16 Feb 2018, 06:35

Re: ESC Failure.......

Post by Mike_K » 08 Jun 2019, 12:53

Paul

In my view, testing the fail-safe is no different from closing the throttle when flying and my left stick works overtime when I'm flying aerobatics. And nobody that I'm aware of think twice about closing their throttle when flying. Except for my gliders, I never set the brake as I like the windmilling prop to slow the model down, so that isn't a cause either.

I also test my failsafe at the start of every flying session as I have been bitten by an incorrectly set failsafe and had a high profile "incident" at my club (I had "brain fade" and turned my transmitter off with the battery still connected on my edf model, the fail safe was incorrectly set and my model went at high speed across our patch luckily without damage). And none of my ESC has ever failed while doing failsafe tests.

From my experience, the most common cause of ESC failure is inadequate cooling. While modern ESCs are very efficient they still generate a surprising amount of heat and if they are hidden away in the depths of the fuselage then they can fail through over-heating. If the ESC has to be mounted out of the airstream, then you need to use one rated for probably double the motor current, maybe more, so they can cope with the heat generated. ARTF models designed specifically for electric often have the whole radio bay open to the front and a large outlet on the bottom of the fuselage behind the wing to ensure wherever the ESC is mounted, it will get cooled. All the E-Flite, Max-Thrust, Dynam and I think all Seb-Art sports models I have seen, have this feature. I wonder if a scale model would have such an outlet?

MIke

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PaulJ
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Re: ESC Failure.......

Post by PaulJ » 08 Jun 2019, 13:38

Many thanks all, I have forwarded the url for this thread to the member concerned so hopefully he will see all your comments verbatim.

Paul

Pchristy
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Location: South Devon, UK

Re: ESC Failure.......

Post by Pchristy » 06 Sep 2019, 13:58

Interesting point you make about over-heating, Mike. Not wishing to hijack the thread, but you may recall that I was a bit concerned about flying the Cobra at Ponty, as I'd been having some speed controller issues with it. Indeed, I had a long chat with Phil on the subject.

At Ponty (somewhat overcast), it operated fine, but during the course of the summer, I've had it cut out several times - fortunately all at low altitude, and with minimal damage caused.

Phil thought it might have been the timing being too advanced for the inertia of the rotor system, and retarding it did seem to help slightly, but at a cost of some power loss. However, my son, who flies electric helis competitively, immediately suggested overheating as the cause, and pointed out that he fits small 5V computer fans to all his ESCs.

A few weeks ago, on a cool, but sunny evening, I had the motor suddenly cut again! When I picked it up, the fuselage was almost too hot to touch! The drab camouflage green fuselage had absorbed enough sunlight to make it VERY hot - ambient temperature not withstanding - and the speed controller was mounted to the side of the fuselage!

I've now moved it to sit on the aluminium base-plate of the transmission, which should keep it cool, and also expose it to the movement of the air in flight. So far, so good, though the weather hasn't been kind enough for any extended test flying. I did manage an 8 and a half minute hover in sunshine a couple of weeks ago without problems, so I'm hoping I've now solved the problem!

--
Pete

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