High altitude F550 hexacopter crash after motors stop. Anyone know why?

[Mon0bLE]

Hey, so I just had the worse crash so far in my 7-8 months of flight. I went out today with a single battery for a quick flight. I wanted to see if I could reach the cloud base. On the descent, all the motors stopped. I presumed I'd throttled down too far and so immediately pushed to full throttle. The hex didn't seem to react, however, until several long seconds later, by which time it was too late to stop the fall and I smashed into the trees 250m away.

In terms of damage, I think I've been lucky. One arm snapped clean off and spun away into the forest (eventually recovered) and a prop broke. £22.50 in replacements. Also my video cloverleaf suffered heavy squishing, but I'm hoping it'll be fine after some careful reshaping. I'd just got it setup perfectly, and eliminated almost all vibrations.

I'm using 1.3GHz for video and 2.4Ghz Spektrum DX6i for control. Video was solid right up to the moment of impact. Horizontally, I've been out to about 750m without losing RC. I don't have any failsafe and so have been reluctant to push it any further. I was flying with the Naza's ATTI mode.

Looking at the video, I am line of sight as the hex is falling, so I'm confused as to why throttle didn't return. I thought at first the battery might have been used up by the heavy ascent, but I don't think this is the case. I usually have 8:30 flight time and this was less than a 6 minute flight.

Has anyone got any ideas of what might have happened?
I'd rather this didn't happen again.

Also, could anyone estimate my max. altitude reached at 1:05 ? I don't have telemetry and its hard to judge with the fisheye GoPro perspective.
Thanks!

 

[swisser]

What is the voltage of the lipo right now? And do you have Immediate or Intelligent configured for cut off mode?

(Just in case you didn't know, it's illegal to use 1.3GHz for airborne transmission in the UK, though I am not saying that's why your props stopped!)

 

[Benjamin Kenobi]

I think you were maybe 800ft high? Did you drop your throttle stick below 10%? Is failsafe setup?

 

[Mon0bLE]

What is the voltage of the lipo right now? And do you have Immediate or Intelligent configured for cut off mode?

I can't tell you right now as I don't have a suitable instrument and Windows isn't working for me to check in Naza Assistant. My first level warning is set at 10.5V and I'm pretty sure this didn't activate when I spun up the motors just after the crash. I'll try and get back to you on that one.

I use Immediate cutoff. The motors stop if throttle is <10%, but should start if >10% within 3 seconds (which it was).

I think you were maybe 800ft high? Did you drop your throttle stick below 10%? Is failsafe setup?

Thanks. Yeah I assumed at first that that was what had happened, and so pushed the stick up again expecting the motors to return, but seeing as that didn't happen I can't be sure. No, I don't have GPS, so no failsafe.

 

[gtranquilla]

Is your camera on a separate IMU controlled gimbal system? If not, then your Multirotor was somehow able to retain upright position all the way to the ground. If the motors stopped, it would tumble end over end.:dread:

 

[swisser]

I use Immediate cutoff

I think given that this is the case and your motors did (eventually) restart and you did lower the throttle it's the most likely explanation.

My question is why use immediate cutoff? Intelligent mode is a far better idea in almost every scenario (i.e. other than some crazy full stop aerobatics). It would have likely prevented this crash.

 

[FerdinandK]

Hard to imagine, that the motors stopped since you could hold the leveled position, also the "impact" was somehow slowed down compared to a free fall.

If (and only then) the motors stopped, I can only imagine, that the propellers started to rotate in the other direction and this was some sort of "autorotation", assuming that you COG was below the propeller-plane (which would be a great finding). However you were lucky, since if the copter would have started to flip, the impact would have been with much more speed.

This is how my "blade stop" looks like (and the almost successful recovery) starting at 1:15:
https://vimeo.com/47655300

best regards
Ferdinand

 

[Dewster]

I had a similar event happen. My Y6 dropped out of the sky shortly after hitting DJI's first stage voltage protection. Once it hit or indicated the second level voltage protection my craft just started falling:

http://youtu.be/DaCp1USGAGM

i thought that rapid descent had something to do with DJI's 2nd level voltage protection and my lipo settings for triggering it. It was simply old lipo batteries at the end of their life span. I tested the lipo on my test quad and had the same result. The lipo will provide power to keep the craft in flight, but once it hits the red zone it's sudden death. There's enough power to keep the blades spinning and the craft from doing a complete tumble, but not enough to create lift necessary to keep your craft in control and from falling.

I think you pushed your lipo too far. There's a point (which changes wi the age of the battery) where you'll have a decent voltage (meaning you should land) and free fall moment.

 

[kristiaj]

I believe the sound you hear from propellers when descending are not the motors that start, it's autorotation that kicks in when the speed get high enough. I have experienced this myself when shutting off motors by mistake. The sound is different when propellers going backwards, and they will stabilize the machine when autorotating. After landing in the tree you can hear the propellers stop and then the motors spin up the right way. It's possible that the motors shut down because of low battery voltage or esc's overheating, and they did not manage to fight the Wind.

 

[djneils98]

what firmware were you running when the crash happened?

 

[haha49]

Well it all depends on how high the clouds are....

1 day it was 800 meters and I was above them another day it was 1300 meters and I wasn't even close to the clouds.

Here are some gimbal highlights at the start you can see the 800 meters up

Here is the 1300 meters as you can see not even close to the clouds yet...

 

[Benjamin Kenobi]

The legal limit is 122m (400ft) above ground level in the UK and the USA. You have just posted videos of you committing a crime if in one of these countries. Where did these flights take place?

(it's better that I say it than someone who matters) :nevreness:

 

[Scott Drysdale]

All the 99% of the fun and 100% money making opportunities for aerial use of Multirotors is well below the 400 foot level.......
So why fly higher and put commercial and public air travellers at risk?
And create an opportunity for FAA and other federal regulators an opportunity to crush MR flying out of existence because of such irresponsible and treacherous acts.

 

[haha49]

The legal limit is 122m (400ft) above ground level in the UK and the USA. You have just posted videos of you committing a crime if in one of these countries. Where did these flights take place?

(it's better that I say it than someone who matters) :nevreness:

More north were the laws are lax and freer...

I contacted transport Canada were they not only said it was legal were I was they said go for it.

So HA! Some planes do fly to low and break the rules for safety it happens a lot. It's not just someone sending something up it's the planes them self flying to low when they're told not to but it's never inforced.

I broke no laws what so ever...

 

[Benjamin Kenobi]

Kind of the response I expected from you to be honest...

As long as you don't mean Canada where the law states:

The letter of the law states: (We make no interpretations of this)
602.45 No person shall fly a model aircraft or a kite or launch a model rocket or a rocket of a type used in a fireworks display into cloud or in a manner that is or is likely to be hazardous to aviation safety.

http://diydrones.com/profiles/blogs/uav-faqs-for-canada

 

[haha49]

Kind of the response I expected from you to be honest...

As long as you don't mean Canada where the law states:

The letter of the law states: (We make no interpretations of this)
602.45 No person shall fly a model aircraft or a kite or launch a model rocket or a rocket of a type used in a fireworks display into cloud or in a manner that is or is likely to be hazardous to aviation safety.

That old law went poof....

They changed it to don't fly in a designated flight path.

They did this so the Canadian Military can fly unmanned drones and experiment with them. They fly them self and are full size aircrafts.

I contacted all the agencys that over see the laws and enforment of the laws. They sent it back to me in writing. I checked the flight paths people submit for approval and made sure no planes would be in the area that day. I also have radios that you can talk to the planes with it's AM radio stuff. So I moniter the sky I moniter the flight plans and I also tune into the radio so I can hear what is going on up there. I also have a spotting scope that you can see how many fingers someone is holding up 2km away. Then add live video feed with voltage ect then add I still had 6 minutes of flight left when I was on the ground. I did way more checking before I did anything.

 

[Benjamin Kenobi]

Now that is a proper response. Keep it up. :02.47-tranquillity:

 

[OneStopRC]

The legal limit is 122m (400ft) above ground level in the UK and the USA. You have just posted videos of you committing a crime if in one of these countries. Where did these flights take place?

(it's better that I say it than someone who matters) :nevreness:

Beat me too it.

 

[haha49]

So if I take off here in Detroit and fly over to Windsor Canada do you think that the authorities would get pissed?

Well if your dropping drugs, guns or money they might... Not illegal per say but everything that cross the border is subject to an inspection buy border control. So they can inspect it legally but reallisticly nothing will be done.