Worst Crash ever, Log analysis needed!

Hey folks!


Yesterday I had my biggest, worst and most scary crash with my 3DR Quad.

Our local firefighters had an open day for public and presented their equipment, did some presentations, they had a jumping castle for the kids, BBQ and beer for the bigger ones.

A friend of mine who is always acting as a spotter for me when doing video flights planned to do some aerial footage of the place and in a second flight film the firefighter team during a car rescue.

So I picked up my quad with full loaded batteries, pre checked everything in my office and went to the starting locations. Here I powered the quad up und waited to get a GPS lock. I didn't need the GPS, but I just wanted to make it absolutely right, because I would be flying over a crowded place.

So after 2 minutes of patience I had a stable GPS lock, made sure I had the right flying mode dialed in, in this case I used stabilize with simple mode, so I could concentrate on the flying location while my spotter would give me advises how to align the camera.

A quick spin up test, everything was fine, so I took of, stabilised the copter in mid air 2 meters from the ground for a couple of seconds and pulled the throttle up to get some height.

First position was reached (no mission, no fpv, just plain odd manual control) so I headed to the second position and yawed the copter 90 degrees to the left. After the yaw I felt the copter beginning to drift a little so I pushed him backwards towards me and reverted yaw so the copter looked away from me.

I wanted to fly back to me whitch meant backwards for the copter but the quad started to lean more and more forward. I had fully deflected the stick backwards, but the copter would not come back, ist slowly increased pitch for some reason.

Because of the kids and the people under the copter the only way to recover safely from this situation was to apply throttle and let the copter drift away over the firehouse, keeping it in the line of sight until I could be sure it was over the building towards free space and then shut the motors down.

The result: most important: nobody injured, for gods sake!!!

2 Motors broken

2 arms damaged

GPS unit destroyed

IMU shield defective

maybe more to come, I didn't disassemble and tested everything right now

I have absolutely no clue what happened! So any help in order to understand what went totaly wrong would help!

Greets

Marc

P.S.: Board Version 1.4, Quad with 850 motors, all settings to stock, Firmware version 2.7.1

2012-09-03 14-17 9.kmz

2012-09-03 14-17 9.log

2012-09-03 14-17 9.log.gpx

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Replies

  • Hello - I have some questions on  using Mission Planner with SITL:

    1) Is it possible to maneuver the copter manually as you would with an Remote Controller ?

    2) How would I use SITL with my own customized copter  build or a beta version of a

    copter build ?

    Robert

  • Ok, it's time to get things to the end and come to a conclusion.

    I have checked every singe component of the copter and found nothing except that the sensors on the IMU are not working correctly. Could be due to improper solder connections or a defect of the sensors themselves. Take a look at the video, than you will se what I mean.

    And here comes the rest of the stuff.

    First, the copter himself.

    3692503385?profile=originalThe motors.

    3692503461?profile=original3692503603?profile=original3692503483?profile=originalThe GPS. It has been torn off the copter and laid about 2 meters away.

    3692503616?profile=originalA closer look on the arms and the screws, pretty much force must have been used "redesign" them.

    3692503654?profile=original3692503572?profile=originalAnd last but not least the charging state of the lipo cells.

    3692503639?profile=originalConclusion:

    As the board shows odd behavior, it probably could have been the source of the problem. The variant from Jason, the dcm init error is plausible, but a closer look from Dan with the log visualiser shows that the yaw calculation seems ok. And, as the copter started to "lean" i pulled back, which was the exact opposite direction it was leaning to and orientated. So the yaw error must have been nearly 180 degree, summed up from two turns in the opposite direction.

    If it's the sensors on the board and they werde not soldered properly, they could be resoldered. If not, the IMU would be the most expensive part, relative to the arms and the motors.

  • Hi Marc

    I looked at your video, and your log file using APMLogVisualizer 1.34, and I've determined that your roll but mainly pitch sensors failed mid flight.

    I wish you had logged your motors, you need to turn them on using the CLI, but even without that data, Ervine was right in saying that the roll/pitch was one way, and it was flying the other.

    I suppose it could be a fierce wind that would do the same thing, but I see no evidence of that anywhere else in your video.  

    So to summarize, after you pulled it back toward you, it starts moving away from you.  At that point the log file says you're pitched backwards, and in fact, looking at the video, you're pitched forward.

    Dan Gray

  • I don't know if this means anything to anyone, but I had yaw drifts with 2.7.1 when flying in ANY mode...

  • Hello Marc, Everyone,

    I am not an ArduCopter Expert (soon i'll order one :-) ) but I have already worked on plane UAVs and with guys with big yamaha helicopters (~100 kg) and now involved in ground field robotics.

    We once had a plane crash we didn't understand at first sight: the plane just pointed to the ground from an altitude of 75 meters at speed >~ 50 m/s. Nothing much was left but fortunatly nobody was around.

    Our autopilot was relying on GPS signals and altitude estimation from the GPS got wrong and the estimated was 100 meters higher than it should have been for a few second(s) so the plane decided to pitch down... The ground stopped it :/

    It was too fast for the pilot to swich back to the manual mode and do something.

    Now for any mission (ground or air) we are always at least two persons to operate. One pilot and One guy monitoring logs/sensors to see if everything is nominal. A third guy with the "emergency alternative/stop" is a must-have with some spectators around.

    GPX : I have checked your GPX log because I didn't really understand if you didn't need GPS or if the autopilot was in fact using it (Like a default behaviour if GPS-Signal-is-present).

    By checking the ArduCopter code I've seen there is a variable *initial_simple_bearing* that is updated at every GPS read.

    So the GPS was used (correct me if I'm wrong, I am just a ArduCopter new-starter :D ).

    I don't really understand now the mix between Stabilize and Simple mode when you say I used stabilize with simple mode but you seem to have started on a home point that is behind you, the GPS indicating a point in the the middle of the road but If I do not mistake you seem (from the video) to have started on the parking part that is the closest to the pavement, that's about 5m far from the road.

    In ArduCopter.pde version 2.7.1 (yours at the time of the crash) I see this :

    ////////////////////////////////////////////////////////////////////////////////
    // SIMPLE Mode
    ////////////////////////////////////////////////////////////////////////////////
    // Used to track the orientation of the copter for Simple mode. This value is reset at each arming
    // or in SuperSimple mode when the copter leaves a 20m radius from home.
    static int32_t initial_simple_bearing;


    And your troubles seem to appear after these 20 meters of radius (accounted from the middle of the road).. and GPS keeps "jumping". This variable, wrapped with the yaw reading, only seems to be used to update  roll and pitch  when applicable (simple_counter > 0) and jasonshort examination about Yaw looks perfect.

    Well I still have a lot to read to understand everything about the flying modes so this is just my 2 cents ! You can delete if its non-sense. :)

    Anyway congratulation for your manoeuvre avoiding kids and people and thank you very much for the data.

  • good job clearing the crowd..  I know alot of people that would have been fighting to save the aircraft first without worrying about were it was.

    some advice.  learn to fly in acro mode...  if an accelerometer goes out or the calibration gets wonked out, if you are proficient in acro mode, you can flip to that and take more manual control without the controller fighting you.

    just my $0.02

  • I am curious of the conclusion - if you ever get one - but this is basically what I've experienced several times, it pulls harder and harder to one side, until stick input is unable to compensate, if I - however - landed, then take off again - it would be fine - for a while.

  • Developer

    Hi Marc, i'm sorry about your crash, I advise you to not fly over people with four engines, is already risky to do it with 6 or 8, but with 4 chances that something nasty happening increase greatly, if you lose an engine in flight you half mad that falls swinging wildly.

  • Developer

    I've reviewed the logs here for about an hour trying to piece together what happened and I think I know now.

    When you armed, the actual Yaw was incorrect. It was about 20° off of the true Yaw value. The DCM inited at zero and should have inited at the Compass heading. This has been fixed in 2.7.2 and caught a few testers off-gaurd as well. It was fixed right away after we pinned down the init issue.

    The Yaw seemed to drift again in flight leaving you with an incorrect Yaw. I believe this happened when you Yaw'd back and forth quickly. This can happen if the Magnatometers aren't fully calibrated or the calibration isn't right.

    Then your roll and pitch became partially transposed due to Simple mode having the wrong yaw and the magnetometer induced yaw drift. The hard left roll you were inputting was becoming pitch forward. 

    You may not have noticed since you attributed it to Gyro drift. In fact the quad was under full control the entire time.

    I lost a few under similar circumstances in the past. I've gotten pretty good at checking mid flight for Simple mode yaw issues by doing quick check of pitch and roll to verify all is OK in the air. It's a shame it happened to you and I'm sorry to hear about your crash.

    Jason

  • My guess is fw 2.7.1 -  I had several times testing this where the copter would slide off in some direction and I would find the stick completely opposite - it was usually 3-4 min into flying and not apparent at takeoff.

    Happily, 2.7.3 is a thing of beauty - I am approaching 100 mission runs without failure (well, some pilot failures):

    The $  and time loss really sucks, but one great thing about the quad hobby is that you can rise from the ashes much easier than a model you spent hundreds of hours on or a TRex 600 life threatening crash!

    Something that has saved me damage in my numerous crashes are the spring loaded legs on the x525 frame. I have seen it fall 20 feet to cement without major damage (except to my heart!)

This reply was deleted.

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