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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Matt Brown on May 14, 2018, 08:26:21 PM
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This past weekend I attempted to maiden my new Twister. It had a Scorpion Commander 45A ESC, KR timer and a generic IFly 2820 850kv motor spinning an APC 11x5.5 pusher prop. I had the esc all set up and had everything set on the KR timer except the rpm. I was using my tach to set it with the programming stick. I noticed the rpm wasn’t real steady. I figured maybe the gain setting needed adjustment. I reached for the battery to disconnect and the motor screeched for a half second or so and both the motor and esc rolled smoke.
I admit, I forgot to bring my watt meter so no idea how many amps I was pulling at that moment. I’ve ran that motor and prop before maxing out at 41A.
I now have a ZTW 50A esc and a Cobra 2826 930kv motor on it ready to test. I ran it up from an RC receiver and everything seemed good to go. My only concern at this point is the gain setting on the KR governor. I think I set it to 3 which was the middle of the range. There was nothing in the instructions as to a starting point for the gov. I’m wondering if too much gain is why it was varying rpm and possibly caused the smoke release.
Suggestions?
I know both the Cobra and the ZTW are overkill on a Twister but I really needed a little nose weight. I might still be a touch tail heavy but it’s definitely in a flyable range.
Thanks, Matt
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Doubt it was the governor. More info here
http://www.keithrenecle.co.za/Electric%20CL.htm#Govtimerinfo
I found the governor useful, but not overly critical or powerful, and used all settings. I had a ZTW 50 but a 3520 14 Cobra and 5 cell pack. ZTW and KR seemed fairly bullet proof.
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I’m surprised the KR timer didn’t shut down due to the RPM variances. I believe that’s how it senses a prop strike.
Did you have the governor turned off in the ESC? If not, maybe the timer and ESC were both trying to “govern” the RPM and it was a toxic mix.
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No governor active in the Scorpion esc. I was setting the rpm for 9800. It was varying from 9500-9800.
Matt
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For anything on the ground, use an undersized prop - around 2" smaller on diameter works well. The system will strive to get to that RPM - or die trying - when you reinstall the flight prop, but in the air the load is somewhere around 15% to 20% lower.
FWIW, I did the same thing a long time ago while checking watts vs RPM on a set-up using the intended flight prop. Never did find a way to get the smoke back in...
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I’ve been flying electric RC since early 2000’s. Only smoked one esc and one motor prior to this and this was back in my early days. I am not counting my race quad motors in that as they tend to smoke fairly regular because they are being ran way beyond “normal” weight/watt ratios.
I wish I knew what happened. I suspect it was a timing issue when it screeched. The esc may have lost sync with the motor and caused the meltdown.
After reading the info on Keith’s site, the governor gain isn’t like the gain I’m familiar with on my helicopters. Gain there can cause serious issues.
Matt
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I'd be pointing the finger at a loose motor connection, that got worse as the motor was running, the engine lost timing and then just fried - or a dead short.