My Arducopter RC2 turned off all four motors at about 100' up today, and plunged to its death with no rotors spinning.
I believe there is a software bug or misguided feature at the root of it.
I was using GPS Hold to pin position, and the Arducopter was ascending. I brought the throttle stick down (while still in GPS Hold) to slow the ascent. I brought the stick all the way down. It was still a bit higher than I would have liked, so I switched GPS Hold Off and moved the throttle quickly to center/hover position.
This is when the motors turned off.
I can actually recreate this same scenario on the Configurator! In fact, any quick motion of the throttle stick from full down to mid-stick, while in flight, will kill all the motors and disarm.
Go try it and let me know if this is intentional/normal. It seems to auto-disarm if you bring the stick up quickly. That can't be good.
I have to get a new frame kit and a new motor/prop from Thailand now. I'm going to go look for the responsible bit of code and excise it.
Replies
I also noticed that the Safety code is engaging sooner than the comment indicates:
#define SAFETY_DELAY 25 // how long you need to keep throttle to min before safety activates and does not allow sudden throttle increases
// Safety logic: hold throttle low for more than 1 second, safety comes on which stops sudden increases in throttle
If units are 20mS, then the safety delay is really only 1/2 second.
So, if you bring the throttle stick down low for 1/2 second, then bring it up quickly, your bird falls out of the sky.
This is a deadly combination with the GPS Hold mode, where the throttle behaves quite differently than normal flight, and more severe deflections are normal.
I'm surprised I'm the only one to hit this, and on my very first Magnetometer flight with a working GPS Hold.
That was intentional, but maybe not well-advised. It was a safety measure to avoid "instant on" catastrophes on the benchtop, such as when people turned off their RC transmitter, which on some RC sends an all-on signal. Perhaps we set it to be too sensitive, or perhaps it wasn't a good idea at all, but it was designed to ensure that your quad won't hurt you if you do something wrong.
It is not in ACM, and the ArduPirates may decide to take it out or modify it in NG.
Just to clarify, to reproduce the bug in Configurator (with ESCs disconnected or props removed):
1) ARM the Arducopter so all motors are idling.
2) Bring the stick up to mid-stick/hover. Motors should be at mid-speed.
3) Now bring the throttle to full descent (down).
4) Now bring it back up to hover quickly. All four motor signals will go full-off and disarm.
I can't see how this would be desirable.