Crash Analysis Help Please

Pixhawk / APM 3.1.2 / Quad / Spectrum DX9 w/PPM Encoder

Flew great all morning… Stabilize, Alt-Hold and Loiter.

Then I go to recharge it and afterward it’s acting funny. I have a mini-crash or two. So I keep checking things and all the motors are spinning. Nothing is getting hot either.

I get it up in the air and it starts giving me trouble – almost impossible to control. So I trigger a RTL mode with my switch and it lands me safely (even though that seemed a little “glitchy” (but it could have been a mild breeze too).

Then I go up again – but slowly. I enter loiter mode and it begins behaving just fine (like it did earlier). Then a couple of minutes into the hover, I get a flip of death and it falls to the ground.

  • In my log, you can clearly see me enter loiter mode
  • Right around the time of the crash, you can see an “RTL” tag – and I’m 100% sure I didn’t trigger an RTL
  • Then right after the RTL tag, I see a “Stabilize” tag – and I’m 100% sure I didn’t change to stabilize either

Would someone mind looking at my log and seeing if they recognize the problem? I swear I wonder if the transmitter, receiver or PPM encoder was sending nonsense to the Pixhawk RC inputs. That would be the only explanation, because everything else appears to be mechanically sound.

So I answered my own question.

The connector pins on the RC input to the Pixhawk were loose for some reason. The connector was in the correct position, but the pins didn’t tightly engage the FCS’s pins.

So when I wiggled the connector, the switches were going crazy mid-flight. It looked like the craft was being bounced from Stabilize to Alt-Hold to Loiter and from RTL and Save Trim.

Now I need to go back and figure-out how to undo all those bad save trim values I was capturing. I’ll probably just revert back to an old parameter set and see if that works. That would also explain why it drifted so badly in Stabilize and Alt-Hold mode (it probably had bad save trim values).