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Old Sep 13, 2009, 04:20 PM
Lookin' up at the centerline
taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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let the theories begin!

I'm really unsure of what's going on here and hope the electric pros will jump in just one more time.
The youtube thread at the end of this first entry will show exactly what happened, I finally got lucky and had a confusing event happen when the camera was running.

My 1/4 scale sig clipped cub had three good flights on it's 6 cell A123 packs. I changed to lipos because:
A123 packs would only give 3 - 4 minute flights.
New 6 cell 5000mah packs with 2C charging abiility. introduced at well under $100. So with 2 packs in parallel, I could get an 8 - 10 minute flight and still charge in 30 min.

My setup was:
Scorpion 4020-16, good up to 70 amps continous.
Scorpion 6-cell 60 Amp ESC, max voltage 26 volts.
Prop is a Master Airscrew classic 16/8.
Batteries were 2 ZIPPY Flightmax 5000mAh 6S1P 15C wired in parallel.

Voltage at the ESC plug is 25.5 volts.
Full throttle showed 41 amps WOT.
giving 7200 rpm and giving 7 lb. of thrust.

Batteries were tested at home while measuring three different props for amp vrs rpm. and measuring thrust. plus a little running up and down the yard with the tail up.

At the field, (as the vid shows right at the beginning) I started to taxi out and heard a sound that sounded like the prop was loose or something was rubbing.
I taxied back and checked that everything was tight and free spinning.
Then I did another runup and shook the tail trying to get the strange noise. Without the stick being moved, the motor slowed to about half then stopped. I cut the throttle and left it there while spinning the prop to see if it had bound up. while I was doing this, she caught fire , burning through a 1/2" balsa floor and melting the cowl a little.
Motor windings looked ok and felt ok while turning.
ESC fried big time....
Any ideas?
http://www.youtube.com/watch?v=i2M-7_prMyE
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Old Sep 13, 2009, 08:45 PM
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lmopar69's Avatar
United States, NE, Doniphan
Joined Feb 2005
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What kind of BEC did you have in it? On anything over 3S you want to use an external BEC instead of the one in the ESC.

I would guess that the internal BEC in the ESC could not handle dropping the 22 volts down to 5 volts to run the servos. It then overheated and caught on fire.

On a Castle Creations ESC I remove the red wire from the connector, then wire in a BEC to power the servos. It takes the load off of the ESC.

Laine.
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Old Sep 13, 2009, 09:09 PM
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Ed Lyerly's Avatar
Rutherfordton, North Carolina, United States
Joined Apr 2001
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I think you need more headroom on the ESC ...... say an 80 amp 6S one.
I believe you were pulling more than 41 amps, the ESC got hot and had no cooling air so it fried. The motor slow down you heard was the ESC trying to slow things down and cool off. Scorpion Calc says this setup will pull in the mid 50's (amp wise).
Ed
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Old Sep 14, 2009, 03:49 AM
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Peter M's Avatar
Newcastle, New South Wales, Australia
Joined Sep 2007
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Mr Dragger,
My first theory and experience with burning expensive electrical equipment ( ) is that the strange noise is in fact the motor and speed controller losing commutation or "timing". When this occurs the current skyrockets, the motor slows or stutters to a halt and would easily cause damage to the controller or the motor.

I've had this occur while I've had my watt meter attached and have seen the normal peak current double instantly, all the wiring get hot and the magnet bell on the outrunner became distorted!

My second theory is that sometimes, speed controllers for no apparent reason just decide its time to turn back to carbon. In you case, your controller didn't go quietly and caused the loss of commutation on its way to the grave!

I agree with Ed about you peak current reading and personally would have expected a peak closer to 60amps than your measured 41 with that prop, voltage and motor kV. Might be worth trying another watt meter on your new set up just to be sure.

If you find your new set up makes a similar noise, shut off the power straight away and I suggest you try in the following order:
a higher timing setting for your controller,
slow down the motor acceleration (can be changed in some better ESC's or just dial in say 1 second of servo slow for ESC channel into your TX),
smaller prop (diameter or pitch) or
a different ESC!

Beautiful model by the way!

Cheers
Peter
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Last edited by Peter M; Sep 15, 2009 at 02:57 AM. Reason: Clarity
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Old Sep 14, 2009, 11:18 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,681 Posts
Can you tell where the fire started on the ESC? There will normally be a field of identical MOSFETs on one side that hand the current for the motor, the BEC circuitry is usually one small square IC on the other side and near the where the BEC wires connect.

If can spot which of the IC's burned it maybe you can narrow it down to the BEC. At the low throttle setting involved here and in view of the 42A max it pulled at full throttle, I'd leaan towards the theory that the BEC started the fire.

Jack
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Old Sep 14, 2009, 01:03 PM
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My guess: From static loads, you fried it. I've seen a couple guys do this before, where they ran their setup static at full throttle for just a minute, but that minute was plenty of time for the ESC to go south. They were using an ESC that was well above the motors max amp draw too.

People don't really realise just how much of a load can be put onto a power system by static testing. Their power systems may be conservatively rated, but then when static testing, they can just fry. I would only run WOT for a couple seconds, to make sure all is well.
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Old Sep 14, 2009, 07:08 PM
Lookin' up at the centerline
taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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Thanks to all for jumping in.
The motor and esc are on their way back to Scorpion for close examination.
I'll post what I hear here...

BTW, details left out in first post:
The cowl has three inlets that catch the prop blast and a scoop at the back of the cowl, all feed through a hole in the firewall where the ESC is suspended, air exits out of the cockpit window.
During the run ups I checked the temps of the ESC and batts. (and the prop shaft) and throughout the tests of 20 - 30 secs, the batts stayed cool, the motor was barely warm and the ESC was warm but nowhere near hot.
I don't think it was the bec because the controls still moved after the motor stopped. but I'm not positive because the fire started after I checked the controls.
I'm leaning with Peter M's theory of the ESC going back to carbon, since on the temps were all cool on landing on the first three flights, and never got more than warm on the extensive runups.
re: wattmeter not giving accurate readings...
It matches my flying buddy's meter in readings, so I guess it's good.
I don't know if it makes any difference but the MA Classic is a gasser prop. I've always used gasser props on all of my larger models. Just like the way they perform, and in this case, the look.
Never had any problems from them though.

Nick
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Old Sep 14, 2009, 07:53 PM
Lookin' up at the centerline
taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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Quote:
Originally Posted by lmopar69
What kind of BEC did you have in it? On anything over 3S you want to use an external BEC instead of the one in the ESC.

Laine.
I got the motor/esc as a set as the esc is designed to not need a separate bec.


'Each Scorpion 6-cell Speed Controller includes a built-in Switching Style BEC circuit. This BEC provides a regulated output of 5.7 volts, and can deliver 3 amps of continuous current with 4 amp bursts. With a Switching type BEC, you do not need to de-rate the BEC as the input voltage increases. The full 3 amps of BEC current is available for any input between 2-cell and 6-cell Li-Po operation."
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Old Sep 14, 2009, 07:58 PM
Lookin' up at the centerline
taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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Quote:
Originally Posted by Peter M
Mr Dragger,
If you find your new set up makes a similar noise, shut off the power straight away and I suggest you try in the following order:
a higher timing setting for your controller,
slow down the motor acceleration (can be changed in some better ESC's or just dial in say 1 second of servo slow for ESC channel into your TX),
smaller prop (diameter or pitch) or
a different ESC!

Beautiful model by the way!

Cheers
Peter
Thanks I'll keep this handy for when we get it going again.
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Old Sep 14, 2009, 08:00 PM
Lookin' up at the centerline
taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
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Quote:
Originally Posted by jackerbes
Can you tell where the fire started on the ESC? There will normally be a field of identical MOSFETs on one side that hand the current for the motor, the BEC circuitry is usually one small square IC on the other side and near the where the BEC wires connect.

If can spot which of the IC's burned it maybe you can narrow it down to the BEC. At the low throttle setting involved here and in view of the 42A max it pulled at full throttle, I'd leaan towards the theory that the BEC started the fire.

Jack
the fire seems to have started between the two boards.
the single chip on the backside seems ok.
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Old Sep 15, 2009, 02:50 AM
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fly_boy99's Avatar
San Jose, California, United States
Joined Oct 2004
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Definately a candidate for a wattmeter run-up before trying this again.

I'm sure George will take care of you though.
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Old Sep 15, 2009, 10:09 AM
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Joespeeder's Avatar
Davison, MI
Joined Sep 2007
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Hi taildragger1589,

The noise sounds to me like a timing issue as others have mentioned before. I had the same exact noise happen on a Hurricane of mine. It only happened intermittently and was the cause of an aborted take off that collapsed my landing gear. After adjusting the timing to high the noise and stutter went away. The watts my motor pulled changed as I swapped props and changed timing to get it dialed in.

I ran your combo through Scorpion Calc and got 56amps using an APC 16x8 as a comparison. Reading are readings but closer to 60amps is what I would have guessed without putting a meter on it.

Keep us posted and be sure to post the maiden!!

Joe





www.thecaterhamproject.com
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Old Sep 15, 2009, 12:21 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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"..the fire seems to have started between the two boards.
the single chip on the backside seems ok.."

With the additional info about the twin boards and that your ESC has a switching mode BEC, that sort of rules out an over heated BEC or failure of the BEC.

Sounds like it might just have been a coincidental and spontaneous failure of a weak or faulty component that happened at that moment in time. When IC's, resistors, caps, etc. go up in smoke the flare can be quite big and can destroy or ignite other things in the area (labels, heat shrink, other surfaces, etc.).

That is a quality ESC and from a company with a good reputation, hopefully they will take care of you.

Jack
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Old Sep 15, 2009, 06:38 PM
Lookin' up at the centerline
taildragger1589's Avatar
Lawrenceville, Georgia
Joined Feb 2005
2,163 Posts
*************************************
That is a quality ESC and from a company with a good reputation, hopefully they will take care of you.
*************************************


Lucien Sent me a product return form to printout and a return number, Sent it in today along with the motor for a check up.
I'll report on this thread when I hear from him.

BTW, here are the "calc" numbers Lucien sent me when I was looking for a motor:

******************************************
the 4020-16 motor in Scorpion Calc with an APC 16x8E prop at 17 volts, I get the following performance numbers:

Amps 33.5
Watts 570
RPM 6046
Thrust 110 ounces (6 pounds 14 ounces)
Pitch speed 46 MPH
**********************************************

With 6 more volts the gasser prop pulls 6.5 more amps but with 10 amps of batt power, I can handle it.
The look of the prop is worth it to me.
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Old Sep 15, 2009, 07:44 PM
Recruiter - 60 Amp Club
Ed Lyerly's Avatar
Rutherfordton, North Carolina, United States
Joined Apr 2001
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If you go from 17 volts to 23 volts ..... and don't change anything else .... your amps will go from 33.5 to 61.
Ed
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