Front flip while mapping??? --> CRASH

No idea what went wrong today (which is why I'm here). I have (had) this awesome Alien 560 quadcopter. As soon as I put it up in the air for the maiden, it flew beautifully. I actually flew an auto mission my very second flight.



Anyways, I've put about 5 flight hours on this guy. It flies great in stabilize, and for the most part is great in auto as well. One mission last week I noticed the quad rose about 30m (several times in a row) for no reason while in auto mode, but then it descended and finished the mission. Here is another thread were I give more info about that mission and about the craft itself:

Two days after that, I took it out for another mapping mission. It was super windy and the quad seemed to be struggling to keep a straight path on the way to the first waypoint. I tried several times, but every time once I switched to auto it seemed very confused and would wander around and yaw weirdly. I attributed the issues to the wind, so I just packed up and decided to do it later.

Today I went back to try that mission again. Step by step breakdown:

  1. I popped it up in stabilize and everything was perfect.
  2. Put it into Pos Hold. Very slight circular drifting (possibly due to bad compass orientation?) but no major issues.
  3. Switched to auto. First 4 or so waypoints were fine. Not super precise, but tolerable. The quad had slightly incorrect heading on two legs, and, seemed to not be doing such a great job keeping a constant velocity.
  4. The quad flies behind the stone structure I was mapping, cutting off my Mavlink. The last data point I get shows the quad upside down at 30 meters up in the air.

I have the failsafe set up to complete a mission if it's in auto. Never had any issues with that before.

Looking at the DataFlash logs, I see that the quad flipped forward and went down with throttle. Needless to say, this guy won't be flying again.

I'm super upset, but I also really want to know what could have gone wrong. I'm inclined to believe I messed up the set up, but then again I've put together at least a dozen autonomous aircraft by this point and I've never had any issues like this while in Auto Mode. I've attached the dataflash log and KML, so please let me know if you have any ideas.

2015-06-30 15-47-31.kmz

2015-06-30 15-47-31.log

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  • you are flying that thing in this condition in huge areas near people (the post you link to)? 

    bad magnetometer calibration, stuff that fall apart..- and BLOS.  I can bet on an accident soon.

    Enough about being irresponsible:

    Before the crash, you can see IMU.AccZ vibrations go bad, so bad, it actually detected a "landing" 

    (simplified detection that expects motors at lowest setting in next release)

    Apparently something started to fall apart.

    • I agree, it was irresponsible. I had had successful and much longer mapping missions in the past, so I had some faith in the craft.

      When you say, "fall apart," do you mean physically? The frame was actually fine upon recovery, so I don't think anything in the frame fell apart. It just smashed all my props and 1 motor mount. 

      Concerning the magnetometer alignment: that is my current theory after the fact. I had never had a PosHold issue like that before, so I had no reason to believe at the time that my magnetometer had suddenly gone bad.

      As for BLOS, the stone structure I refer to is the prospect hill monument. It is literally 15 feet across, so I had no reason to expect that I would lose any radio link. Especially considering that the craft was no more than 100m from me at the time (I could check the exact value but I didn't see the distToHome param fast enough). I was really surprised to have anything other than a strong link, actually.

      Regardless, that does not excuse the fact that it was a bad idea to fly there, and fortunately not my own idea. I am however guilty of attempting to carry out the mission.


      Looking at the log again, I see what you mean with the accZ, spiking rapidly. This occurs mainly after the craft entered "land" mode. It hit a tree on the way down, which is what I think triggered land mode. I think the subsequent spiking of the accelerometer can be attributed the props hitting the branches and then the sidewalk. I thought they would throttle down on "land," but looking at rcou.Chan2-4 you can see that the motors keep spinning. This probably explains why all 4 props were broken on both blades. 

      But I still don't understand why the thing descended down to where it would be able to hit a tree at 6m alt in the first place...

      • Of course, I cannot tell you that I am 100% sure, as that would require a god-level as log reader, and preferably to have seen the accident  :)   - but this is how I think it went down (why I wrote what I did)

        After line 32200 you can already see vibrations IMU.AccZ increase, it's even easier to see on CTUN.ThrOut that something is not right.  then ,  despite the increased average ThrOut  after line 32600 - you start to loose altitude (see BARO.Alt)   first after the BARO.Alt dropped from 33meters to 4.5meters, the Landing is detected - at line ~33700

        So I see a good period of shaking, throttle hunting, and altitude loss.

        At first - I thought a prop came loose, an motor vibrated , a prop had structual damage ( a part fell off or cracked etc)   But I don't see that in the RCOU.Chan1-4    But the vibrations are usually an indication of something mechanic.

        Also, the increased throttle and dropping altitude made me look at batteryvoltage and current, but unfortunatly, you have no logging of that.   but the symptoms *may* have been (depending on ESC's) the effect of too little power, and PID's not being suitable anymore for ESC's that are starved and do not respond as expected.

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