Help a Newbie Understand First Crash

[Teirdome]

Hey gang. I had my first crash over the weekend, and it was entirely my fault. Footage of the crash from a mobius on the underside of the Storch is here:

What I observed happening at the time was a pop while starting a turn and bank to the right, then I completely lost control of the plane (it wasn't responding to inputs). If you watch the footage, it's obvious that the prop collet somehow came loose as they both bop into the camera.

My question is, why would the plane go completely dead when the prop disconnected? Everything seemed to be connected and the battery still had 3.9v on all cells. Should I be concerned about the ESC?

I've since tried to power the motor, and it did run fine, but the beeps were quieter than normal.

 

[joshuabardwell]

I have had nuts work loose on my quad if I hit a prop on something and it stops the prop suddenly. What if the ESC had a flake-out moment such that it suddenly braked the motor hard enough to loosen the nut and collet? Like if the ESC's timing got messed up and it tried to spin the motor backwards all the sudden. This could have caused a huge power surge and a brown-out. Just a theory... see if any smarter folks than me buy it. I can't see any way that a loose prop would have caused a receiver brown-out, so I'm just trying to hypothesize the other direction.

 

[Teirdome]

That's an interesting theory. Maybe I was being too twitchy with the throttle, and that caused the prop to break loose. If the motor was spinning faster without the friction of the prop, could the ESC have overheated and that lead to the brownout?

I was running the Suppo 2217/7 1200kv Brushless Motor (Park 425 equivelant) on a Suppo 30A ESC with a 10x4.7 prop. While I haven't explicitly tested it with a watt meter, I think that motor/esc/prop combo should be just fine (it's essentially the FT recommended).

 

[joshuabardwell]

That's an interesting theory. Maybe I was being too twitchy with the throttle, and that caused the prop to break loose. If the motor was spinning faster without the friction of the prop, could the ESC have overheated and that lead to the brownout?

No, not at all. It's possible, if you didn't tighten the collet down enough, that it could have worked loose simply from vibration. It's very unlikely that the power system had enough torque to loosen the nut by spiking the throttle. If the motor was spinning without the prop, the current draw would drop to almost nothing, because there wouldn't be any load on the motor, so the ESC could spin the motor without the prop all day long and not overheat.

My hypothesis is based on an unexpected and catastrophic failure of the ESC itself, not anything you would have done. And it's pretty far-fetched, so take it with a big grain of salt. I know that it's physically possible for an ESC to change its timing to as to spin a motor backwards. I'm just guessing that if an ESC were to do this by accident (due to a hardware failure, probably) then it would have a big problem and might cause a dropout on your receiver. There are a zillion people who have lost a prop during flight and there's no reason I can think of why it should cause a receiver dropout.

EDIT: Oh, and PS, this all depends on the assumption that your prop shaft is threaded such that the spinning prop will loosen the nut. I believe this is the case for a standard (clockwise) turning motor, along with a standard-threaded shaft.

 

[mjmccarron]

I have had 4 stroke IC engines cough or backfire and throw the prop. Although it is unlikely, it is possible that something failed in the ESC that caused an electronic equivalent to a backfire and could cause the prop to come off if it was a threaded adapter. What's puzzling to me is that the BEC portion of the ESC is usually a completely separate circuit and a failure of the motor control should have little effect on the part that powers the radio. My theory is that whatever may have happened to the motor controller may have pulled the battery voltage down below the BEC's low voltage threshold causing the loss of control. This is based on a guess but the bottom line is, I would be cautious of that ESC.

The power setup you have is well matched and well suited to the Storch. With the 10x4.7 prop I would expect about 15-20 amps at full throttle with a 3s battery. Well within the 30A ESC's specs.

I recently had an ESC failure that burned up the servos. The BEC circuit had shorted and put battery voltage (12v) on the radio system. It was intermittent at first and then failed completely leaving my FT-22 about 80 ft up in a tree. But that's another story.

 

[OttoPilot]

Check out the BEC output of the ESC with an old pack and voltmeter. If it's not outputting anything that points to ESC failure.

The chances of the prop coming off and electronics failing at the exact same time from unrelated circumstances is very low.

An ESC failure would explain both. Could have failed and sent straight DC to the motor stopping it dead in its tracks. Big failure could nuke BEC too resulting in instant loss of control.

The other possibility is a magnet failure in the motor at full throttle, stopping it (throwing the prop), cooking the ESC. But that would have most likely cooked the FETS and control circuit leaving the BEC working and your plane gliding. It would also not have been as instantaneous a loss of control.

 

[makattack]

What receiver are you using and what failsafe setting does it have? On my planes without autopilot, with rx's with programmable failsafe, I set them up to cut throttle and put the plane in a left spin. Yours almost looks like that, but it also could be that power was cut from the servos while you were banking right.

 

[Teirdome]

Thanks a ton for the responses everyone. This has been really helpful in understanding more about the ESC.

What receiver are you using and what failsafe setting does it have?

This is a basic 6 channel Tactic receiver. The failsafe holds the last recognized positions for all channels except throttle. The throttle can be changed, but I believe I left it at the default of 0. Unfortunately the other channels cannot be programmed.