log file attached.....running AC3.3.1 on Pix, was in loiter then guided mode just hovering at 5m for a while, all good, then sent the land command thru GCS and it just accelerated wildly to the right eventually ramming into my car and then into the ground, GPS masts broken, broken arm and motor mount, and nice gash on my car's door....

what the heck is Err: 0-44 mean? never seen that before but it happned just before I issued the land cmd, I dont see any mechanical issues and thou it appears there is some EKF issue right after the Err: 0-44 I dont see any specific EKF error 

Randy or Leornard? please help! thanks


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  • Have you ruled out multipath issues?

    Signal multipath:   Errors can be introduced when signals are reflected of buildings of geographical entities such as large rocks, etc. As the less direct path will be longer and take extra time, this can add errors into the system if the receiver recognizes the reflected signal.

    i.e. reflection from windows of house, car, etc.


    • actually i think i have no other left but to blame this on multipath issue....because of the low altitude i was flying at.

      the crazy thing is i have duplicated the landing scenario which caused the crash like 10 more times since then and not even a glitch....nothing...works flawlesly...

      I guess lesson learnt, auto landing is risky and 2 GPS is not safe yet

  • Make sure your throttle is set to 0 when you initiate auto land or if your auto mission has auto land as a final waypoint.

    • my two cent, when your UAV is  10m above the land ground, this is very critical moment. because all the satellites you tracking in the open sky now changes very dynamically when you are approaching house, car, mirror, lake, trees, since these objects can bring lot's signal noise and multipath and also block some good GDOP, HDOP satellites. GDOP or HDOP highly depend on your satellites span and volume. sometimes you only have 60 degree open sky in landing zone, the HDOP and GDOP will be very bad suddenly.

      we are developing low cost RTK for UAV.  Then you can setup a Base station in open sky (such as in your roof, or yard). and you can test the UAV with Rover installed. if the Rover give you very accurate height in you targeted landing zone, then you can the confidence to use RTK to auto landing. we are tracking tree constellation, GPS, GLONASS, Beidou, ,and both L1 and L2 frequency. which is more stable than usual GPS.

      checkout our website: tersus-gnss.com, I also attach some features here.

      RTK Accuracy       

      Horizontal ……………………….…....10mm+1ppm       

      Vertical …………………………….….15mm+1ppm

      Triple constellations, 5 frequencies support (GPSL1/L2+BDS B1/B3+GLONASSL1);

      192 GNSS channels;

      Centimeter level positioning accuracy;

      Rapid RTK integer ambiguity resolution;

      Up to10 Hz position/velocity/time solutions;

      Low power consumption;

      Compact design – 60mm x 130mm;

      Dual COM interfaces in TTL logic level;

      External antenna input through SMA connector;

      Data output: NMEA-0183;

      Correction: RTCM 2.x/3.x and CMR

  • Developer
    Randy did an analysis and suspects it was a mechanical failure.

    See https://github.com/diydrones/ardupilot/issues/3286#issuecomment-162...
    • and I replied to him to let him know this is not the case, what he was seeing was the vehicle impacting my truck and rolling 180 when doing so....there was no mechanical issue at all

  • hi all, i think i found the problem.....I run 2 GPS, and N8M and a 6M....for the duration of the flight the copter was tracking to GPS1 (N8M) but then suddenly (and for no apparent reason) you can clearly see right before the LAND command that the copter switches over to GPS2 (6M), am pretty sure this likely caused the drift in position...and the crash

    however the question remains, why did AC switch GPSs when there is no apparent reason? the HDOP was much lower on GPS1 than GPS2 the entire time, my understanding is it should only switch GPS if the primary HDOP becomes higher than secondary, I have also heard conflicting reports about using or not using 2nd GPS.....I did thoroughly tested the GPS switch function a few months ago (by receiver activated switch, shutting off the primary GPS in flight) and yes there were similar changes in position as what happened during the crash land. 

    Is running 2 GPS not recommended? are there issues with it such as this sudden and unexpected change in GPS?


    • Developer

      I don't think using 2nd GPS units is recommended at this time for the exact issue you have mentioned due to handover to the second reporting a slightly different position.

      • I did experiment with a second GPS puck, and found the response you mentioned.  The M7 acquires sats much quicker, but doesn't match the M8 in performance.  For the first 3-5 minutes in a new location, the 2nd sat would be primary.  Once the better unit acquired 2 more sats, it would be primary reporting,and the vehicle would think it is 3 meters where it last thought.  

        I envisioned that if I ever lost my masted puck, I would have a second as backup.  Unfortunately that behavior of a several meter jump would not be a viable mitigation.  I never flew it for that reason.

  • Developer

    what the heck is Err: 0-44 mean?

    I only see ERR, 1048373268, 12, 1 which means crash detected in your log. I used APM Planner 2.0 to look at the log

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