APM 3.3.2 quadcopter in Auto suddenly veers off course


I hope that someone can identify what’s wrong with my setup. I’ve done my own analysis and also asked at DIY drones first but there is no reply.

Posted in the wrong forum, should go to “Log files, Tuning, and Analysis of Log files”. Sorry - help?

Problem: My DIY H-frame Quadcopter in Auto or RTL suddenly veers off course / seems to lose control / bumbles through the air for about 1 or 2 seconds before I switch to Stabilize and land it manually.

I’m attaching a log file where this happens (Auto -> Stabilize) around line 282.000. The second occurrence is later, where I switch from RLT to Stabilize. For the first event I’ve looked at the topics listed in copter.ardupilot.com/wiki/common … using-logs but could not find much. The DesPitch vs. Pitch, DesRoll vs. Roll and DesYaw vs. Yaw seem to show the course deviation but I can’t identify a reason:

  • EKF4.SMX/Y/Z are all normal (below 0.1) at that time
  • IMU.AccX/Y/Z are oscillating between -1.1 and -2.0 (X), 0.2 and -0.8 (Y), -8 and -11 (Z) (not a vibration issue)
  • MAG.MagX/Z show bumps which may well be caused by the course change and not the other way around
  • GPS.HDop is at 0.83 until after the switch to Stabilize (not a GPS issue)
  • CURR.Vcc/Volt are normal as well (no brown-out)
  • All motors, ESCs and batteries are cold to the touch right after emergency landing.
    In both cases the event occurs while the copter is supposed to fly a straight line. It looks as if it’s hit by a strong gust of wind - but it’s not, I’m fairly sure of that. The wind was blowing only slightly and from the other direction.

Any ideas?? Thanks in advance!


Log: dropbox.com/s/gnxe1kt7upb8xsi/17.BIN?dl=0
SW: APM Copter 3.3.2
HW: DIY quadcopter (H frame), pixhawk clone, power module clone, 915 kHZ telemetry clone, ext. compass + GPS (the HK clone combo pack - sorry…), 30A SimonK Afro ESC, 2.4 GHz RC, 2x 4S battery
Flight video (same place, different time, only to give an idea): instagram.com/p/BAxvqBiDwRB/
Conditions: Soccer field, some trees on one side, not much wind, no power lines.

For my own analysis (graphs) please look at http://diydrones.com/forum/topics/apm-3-3-2-diy-h-frame-copter-in-auto-or-rtl-suddenly-veers-off.