What Happened!

[Biggles' Elder Brother - Moderator]

OK, just putting the finishing touches to my second electric model. Finding these electric jobbies quite handy in the winter! But, alas something very, very bad has happened.

 

Now, let me explain. I've pretty well finished the model - I just need to set up the control throws. Everything has been tested and works OK - all the controls move - and in the right direction. The motor spins up fine, I've programmed the ESC (Hey I'm getting the hang of this electricity stuff - its not so difficult).

 

I then remember, prior to setting the throws, that I would like to put some aileron differential in for this model - everything is connected, the model is live remember. Differential is best I find if I have the model set up on "2 ailerons" on channels 1 and 6. So I'll change over to that - currently I have a Y lead and both ailerons going into channel 1. Ok before I jiggle the servo leads round (removing the Y lead) I'll just reset the model type on the tranny to "2 aileron".

 

At this point, just as I press "OK" on the tranny to change the set up, my universe fell apart! The motor suddenly started up - full throttle, fortunately the model was in a cradle and so semi restrained. I slam the throttle stick WOT and the engine stops spinning - wow. That was exciting! What happened there? Well I hardly had time to think before white smoke started pouring out of the ESC! It starts glowing! The LIpo is just below it and I'm in an upstairs bedroom!!! Panic!

 

I get halfway down the stairs when the drastically overheating ESC melts the solder joints on the battery leads - effectively cutting off the power. I take a deep breath.

 

What happened? I only changed the model type - surely that can't have done this - but it seems it did! OK I know that fiddling with something as fundemental as the model type in the tranny with the model live wasn't smart (or at least I know it in retrospect) but I'd just like to understand why it happened!

 

Any electric power bods out there that can enlighten me? I'm sitting here shaking!

 

BEB

[Allan Bowker]

I can't imagine what caused the ESC/Battery to have a meltdown BEB, changing the model type shouldn't do that.

 

How new/old were the electronic components (ESC, Battery, RX, Servo's)?

How long had they been plugged together and powered up live?

 

As I understand it ESC's are hardest at work when on low throttle, I wonder if a little throttle was trimmed in, not enough to turn the prop, but enough to make the ESC work. Even though the ESC should have got warm/hot, certainly not go up in smoke!

 

This may be a job for Timbo!

[Biggles' Elder Brother - Moderator]

Its all brand new Allan. I first installed everything yesterday, programmed the ESC, waggled all the control surfaces round, reversed the ailerons because they were backwards. Then I ran up the motor to full throttle for few seconds then checked I was getting full and stop etc. Everything was fine. For that I suppose it was hooked up for 10-15 mins.

 

Tonight I just had to set the throws and sort the CoG (its a liitle tail heavy) - so the model would be ready for the weekend and its maiden. I guess everything had been connected for 5, 10 mins at the most. I'd literally just connected the battery then picked up the tranny and dailled in the set up change when all hell broke loose!

 

BEB

Edited By Biggles' Elder Brother - Moderator on 27/01/2011 01:07:54

[Martin Harris - Moderator]

Will you be removing the prop before your next "live" setting up session BEB?

 

One of my clubmates scared himself stupid when his motor started while performing a similar exercise, nicked his nose IIRC - and that was after he'd (only just) removed the prop for some reason other than safety...needless to say he resolved to always do it that way in the future!

 

We tend to be more aware of the real and present danger of i.c. props where electrics are actually potentially a lot more dangerous, lurking silently awaiting the opportunity to bite - and bite again once any obstruction is removed - especially with the power levels becoming more common as prices fall and new technologies are developed. It's incredibly important to try to imbue new fliers (and more established ones for that matter) with the mindset that a model with a connected flight battery should be treated like a running i.c.model at all times.

[Biggles' Elder Brother - Moderator]

Too right Martin! Lesson learnt believe me

 

But to learn the lesson even more effectively I'd love to know why it happened!

 

BEB

[Martin Harris - Moderator]

Luckily you learnt your lesson the easy way - I'm still getting over my stupidity with my lathe nearly 4 months ago.

 

What radio do you use?

[Biggles' Elder Brother - Moderator]

Futaba 8FG - had it about 8 months - faultless so far. The RX was a pukka Futaba 617.

 

BEB

[Martin Harris - Moderator]

Did it go into failsafe perhaps? Default for Futaba is throttle closed but that's the wide open position for most ESCs...

 

...or did changing the model type put the throttle back to default?

Edited By Martin Harris on 27/01/2011 01:48:05

[Steve W-O]

When you reset the TX, it changed all the setting to default, so the throttle was reversed.

 

It's not a good idea to make any basic changes, like stick mode whilst the model is live, in the same way you would not change the model memory when a model is live.

 

If you had done it with a glow engine running, the exact same thing would have happened.

 

I do all my set-up with an ordinary flight pack connected to the receiver, with the ESC unplugged from the receiver. I use the same flight pack for the servo tester, so it is convenient.

 

Had you have switched off the model first, changed the transmitter and switched the model back on, it would have been safe, as the ESC would have detected the throttle position as non zero, and wouldn't have activated. The beeping would then have alerted you to the reversed throttle control.

 

I also have a cheap 5g servo marked with the direction of a standard ESC, which I plug into the receiver when setting up, so that I have a visual indication of all channels. Worth the couple of pound.

[David Ashby - Moderator]

Steve is right one of the Futaba traits being that the throttle channel always seems to require reversing for electic models.

 

I've got an 8FG and found this to happen when you change the model type. I always connect a small Rx batt to the system for making throw adjustments etc. so the prop only goes on the model for the very first time just prior to balancing and power system measuring.

 

Not sure why your ESC burnt out though BEB, perhaps that sudden surge just did for it (what make is it?) or perhaps it's not up to the power demands of the system? Have you taken a wattmeter reading? The Li-Po should be ok - it probably went quite warm during the process but a cell checker will confirm that the cells are fine.

 

All good fun eh?

 

 

 

 

 

Edited By David Ashby - RCME Administrator on 27/01/2011 07:07:26

[BB]

Not so into leccy meself, after realizing too late we are screwing up the planet, I have gone to 'Petrol' - oops!

 

But, I have seen a number of in (im)promtoo (tue) burnt outs of the leccy variety: And for no apparent reason. Perhaps like 'plugs' ESC's are 'consumables' & carry no garanttee (I have never spelt that word the same way twice!). It's been a long shift

 

Purely coincidence perhaps.... though I like the bit where you tell the modelling fraternity that you 'wet' yourself & ran away .....

 

" The LIpo is just below it and I'm in an upstairs bedroom!!! Panic!

I get halfway down the stairs when the drastically overheating ESC melts the solder joints on the battery leads - effectively cutting off the power. I take a deep breath."

 

In my day you'd run towards it and headbutt the flame clean out !!

 

BB

Edited By Basildon Biggles on 27/01/2011 07:36:27

[David Ashby - Moderator]

Posted by Basildon Biggles on 27/01/2011 07:32:15:

Not so into leccy meself, after realizing too late we are screwing up the planet, I have gone to 'Petrol' - oops!

 

But, I have seen a number of in (im)promtoo (tue) burnt outs of the leccy variety: And for no apparent reason. Perhaps like 'plugs' ESC's are 'consumables' & carry no garanttee (I have never spelt that word the same way twice!). It's been a long shift 07:36:27

All ESCs burn out for a reason BB

Edited By David Ashby - RCME Administrator on 27/01/2011 12:57:03

[BB]

Though I can't see a connection between a programme change between tx & rx . Since the amps/volts remain the same. Unless the original 'connection' was 'somehow' wrong.

 

I have seen a flight/land & restart of a leccy model that resulted in a smoking ESC. It was replaced at the field. The new ESC behaved fine for the remainder of the session ?

 

BB

[Chris Bott - Moderator]

Hi BEB this is a strange one!

 

In the moments while the motor was up and running, the model "semi restrained", when you had the speed of thought to first realise that the throttle channel was reversed and then decide that slamming it to full would help, could the plane have moved enough for the prop to be stopped by something physical so the motor was stalled ?

 

If this happened the current in the ESC would shoot up. This has the possibility of causing output FET's to fail short circuit, then you have a short across the battery that you can do nothing about.

 

[Danny Fenton]

Electric flight seems so calm and safe until you are reminded of the potential. Ic engines shout at you "I am dangerous" all the time. when they are actually running that is

Leccy just sits there waiting to chew your arm off lol

BEB you may want to take a look at the motor, the sudden start from zero to full throttle may have dislodged a magnet or the like. thus causing the current to be much higher than on your previous tests. I presume nothing had been changed like prop size, spinner rubbing on airframe etc? Take a look at the bearings too.

 

they don't short for no reason imo.

 

Cheers

Danny

 

[BB]

Posted by Chris Bott on 27/01/2011 08:43:44:

Hi BEB this is a strange one!

 

In the moments while the motor was up and running, the model "semi restrained", when you had the speed of thought to first realise that the throttle channel was reversed and then decide that slamming it to full would help, could the plane have moved enough for the prop to be stopped by something physical so the motor was stalled ?

 

If this happened the current in the ESC would shoot up. This has the possibility of causing output FET's to fail short circuit, then you have a short across the battery that you can do nothing about.

 

Except runn away !

 

BB

[Biggles' Elder Brother - Moderator]

Hi Guys,

 

thanks for the advice. I will certainly be using the temporary Rx battery pack for set ups from now on - that's a good (and in retrospect ) obvious idea!

 

OK I understand why the throttle reverted to it normal state - I had indeed reversed the throttle and ailerons originally. Obviously selecting a new model type causes the Tx to switch back to default. So that's fine - I now know what happened there.

 

But of course the ESC burn out is still an unknown. The model was inverted in a cradle I use in the workshop to support the planes when I want access from all sides - like for setting control throws. The prop definately wasn't stalled and there is no sign that it is "sticking or rubbing". All the connectors were fine - in short I can't see a mechanical reason for what happened. The ESC was rated at 50amps continuous - 60amp burst. The spec I'm running should be at 30-35amps max. So it was well within spec. Is it possible that the extraordinary nature of the "restart" did something to re-initialise the ESC into some unacceptable mode which led to it drawing loads of current I wonder?

 

One thing I have learnt - skills from IC don't always easily transfer to electric and there are definitely issues the IC modeller needs to think about. I think one of my problems is years of conditioning that "if it isn't making a noise its not dangerous"! It doesn't matter how many times you say to yourself "this is live I must treat it as such", once you get absorbed in some other task, instinct and years of IC custom and practice takes over without you realising. Another mind set us die hard IC'ers used to running 90 four strokes etc. suffer from is the "its only a little electric jobby - almost a toy really" syndrome. That has to be fought against!

 

So its the Rx flight pack for testing servos etc for me from now on, no fiddling with the main battery connected and treat this thing with respect!

 

The good news is that except for a slight sorch mark on the wood internally the model is OK. Just ordered a new ESC - when you fall off the horse, get striaght back in the saddle!

 

BEB

 

 

[David Ashby - Moderator]

Nice one BEB, hey, you can't call yourself an electric flyer until you've fried something

Edited By David Ashby - RCME Administrator on 27/01/2011 12:58:44

[Chris Bott - Moderator]

Good news BEB that everything else survived. Does the motor feel OK? A coincidental fault in the motor could possibly have taken out the ESC. Unlikely though.

[Biggles' Elder Brother - Moderator]

On a quick look the motor seemed OK - but I'll give it thorough examination tonight.

 

Thanks again guys for, as ever, the excellent info and advice!

 

BEB

[Steve W-O]

Posted by Biggles' Elder Brother - Moderator on 27/01/2011 12:24:54:

 

One thing I have learnt - skills from IC don't always easily transfer to electric and there are definitely issues the IC modeller needs to think about.

 

BEB

 

 

 

 

At the club I was at last year, one of the "expert" flyers, thought it was a disgrace that people should be able to take their A test in an electric plane, because "what would they do when they came to fly a proper aeroplane"

 

Well, the flying is the same, and to my mind the electric has the same caveats as IC plus a couple of extras. I think I said the other day that if I wanted to stop a glow motor in a hurry, I would throw a rag in the prop (always at hand to wipe off the gunge). Do that with electric, and it will draw more power to try and keep going, so if it was your hand, it would slice even better than a glow motor.

 

Glad it did not attack you, and that all it needs is a new ESC.

 

I think the most common cause of ESCs failing well under specified load is the fact that the heatsink often does not make good physical contact with all the fets, so one pops, the others have to share the load, then the next pops etc.

[Biggles' Elder Brother - Moderator]

Ah, now that is an interesting comment Steve.

 

When I removed the ESC after the incident the heatsrink covering was split, as I parted it to examine the damage to the ESC the heatsink just fell off! I assumed the glue holding it had just melted - but maybe it was already loose and the demand of the full throttle start followed by the throttle back was enough to push it over the edge, then as you say one FET blows and it just cascades?

 

BEB

[leccyflyer]

Posted by Danny Fenton on 27/01/2011 09:27:06:

Leccy just sits there waiting to chew your arm off lol

 

 

No I don't

 

Sounds like a few lessons to be learned here and, as Simon pointed out, making such a change with an IC model with the engine running ght have had a similar effect and every electric model that is live should be thought of as being a tiny step removed from having the engine running.

 

So - prop off when working on a model on the bench. Every time. No exceptions. The only time you need the prop on, with the model on the bench is if you;re balancing the model or, if you;re bonkers enough to run the motor to measure current draw on the bench. At all other times everything can be done with the prop off, much more safely.

 

Major changes to the set-up - model memory, model type etc, should not be made with the model live to the extent that the power to the motor is enabled.

 

If the motor is to be run at all, make sure that it is completly free to turn and cannot foul on anything and stall - so, for instance, don;t try to run a motor in your hand, just for a second, just to check rotation direct. It could be done, if you were bonkers enough, in the days of sp400s, but it's asking for it these days with so much power at the prop.

 

Running the motot on the bench is to be discouraged anyway. Unless your bench is spotless there a very good chance of sucking something into the prop, or blowing something away with the prop wash. Things get even more serious with a ducted fan. A clubmate had a serious hand injury last year when he reached out to feel if the ESC was getting warm and the fan just sucked his hand straight into the fan.

 

 

[Biggles' Elder Brother - Moderator]

Thanks for that leccy - as you say lessons to be learned.

 

In retrospect I think I've got off lightly and been given the opportunity to learn the lessons only at the cost of an ESC, a bit of delay and a funny burning smell about the house that Mrs BEB went on about all night!

 

It could so easily have been much worse!

 

BEB

[Biggles' Elder Brother - Moderator]

Well the Big Fish came up trumps and my replacemnt ESC arrived today. So I treated myself to an early dart from work and got stuck in.

 

Soldered the connections on and refitted the ESC. I was good boy and set up using an old rx battery pack I had lying around in the "that'll come in handy one day" draw. I also followed the advice and programmed the ESC and set up the throttle etc without the prop on. (I don't get caught twice! - Well not often!).

 

And I'm pleased to report - all appears to be well and the "magic smoke" has remained inside the device.

 

Thanks again to everyone for their advice - much appreciated. Weather looks good up here tomorrow - for a change - so the maiden could very well be on!

 

BEB