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Crash! Can you help me find out the reason?

Posted by Harapan on April 20, 2014 at 2:56am

Hello all

Yesterday, after one previous successful mission, our MAJA drone crashed after acting very strangely, and contrary to the mission which we had planned and uploaded.

We have tried to do some analysis of the log files, and so know that these occurrences preceded the assumed stall and subsequent nose-spin from which it couldn't recover:

1. The drone listed to the right, off its planned flight path

2. Throttle suddenly flooded to 100%

However, we don't know if these are causes or effects of the crash.

We recovered the drone and (luckily) it was ok, although in need of a little hot glue. The battery (lipo 3 cell) had puffed up significantly which we've never experienced before -could this have been an issue?

The tlog, rlog and graph of the throttle v altitude is attached here, any ideas as to why our drone suddenly crashed would be very much appreciated. 

Thanks!

140420 tlog throttle v alt.jpg

2014-04-19 10-51-30.tlog

2014-04-19 10-51-30.rlog

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Replies

  • Harapan April 25, 2014 at 12:57am

    UPDATE: 

    Since the crash we have found that the rudder servo is not working, and we are replacing. However with the tlog you can clearly see that it was working during its last mission up until the crash, so we've ruled this out as a possible reason. Most likely it was broken during the fall?

    If anyone with more seasoned eyes could take a look we'd really appreciate it... we're now a little nervous about throwing it in the air again until we know what went wrong.

    Thanks.

    • Andre K. > Harapan April 25, 2014 at 1:25am

      without the .log , it's very difficult to say what happened, - you CTUN messages, no RCOUT etc..

      The unusual flight before crash seems to start with a rapid climb then a dive without expected attempts to level.

      I could guess  that a defective servo or control surface, or even a part like horizontal stabilizer that got loose, changed angle, could cause that.

      A rudder servo failure would not cause this. AP uses ailerons for main control, and this can usually cancel out very big rudder errors.  - Also, AP does not deflect rudder very much.

      Of course, if a the rudder or vertical stabilizer came loose and changed angle, - anything could happen.

  • Andre K. April 20, 2014 at 8:12am

    post .log from APM/Pixhawk.

    • Harapan > Andre K. April 20, 2014 at 8:47pm

      Sorry, we can't find the .log file, only the .tlog, .rlog, .bin, .tlog.kmz, and PARAM file.

      Could the issue be similar to this one?: http://ardupilot.com/forum/viewtopic.php?f=44&t=6117

      The activity of this UAV preceding its crash sounds very similar to what we experienced.

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