Uncommanded switch to Qhover mode

ArduPlane VTOL Plane
1

Using 4.3.7 firmware version
I have a Quadplane VTOL with vectored yaw.
Successful takeoff, successful mission, VTOL landing is where the problem started.

About halfway done with the landing decent the aircraft rolled to the right sharply and then recovered. It then did this a second time. I then switched it from AUTO to QLAND mode via my hand held transmitter. The aircraft drifted hundreds of feet away before a soft landing occurred in some 6 foot tall weeds in a field. No major damage detected.

After reviewing my logs I found that the roll to the left was uncommanded (ch1). I also found that a split second after I commanded QLAND (because the aircraft started to roll to the right as if the front right motor was failing to produce thrust) the drone then went into Qhover mode without my knowing it. I do not have a Qhover mode option for my hand held transmitter (no flight mode set for it).

I also noticed the GPS data rate went to zero.

There was an emergency yaw reset.

The icon on the Data tab in the map view flipped 180 degrees.

I don’t know why any of those things happened as there was no solar activity (CMEs) to fault the GPS and the number of sats locked was between 13 and 15 and I even had RTK injection active.

Linked are the Tlogs/parameter/BIN files. Mission starts around the 30% mark, trouble starts at the 61% mark.

I plan on updating to 4.4.1 as well as changing the GPS mode parameter to 65 instead of 1 as soon as I get some understanding of what happened here.

Files linked here.

2

Doing some testing today:

  1. The right front motor is probably bad, it is sounding like there is a loose magnet.
  2. If the right front motor is bad that would explain the sudden down and to the right pitch/roll motion that I saw
  3. If that motion exceeds the default “hold this angle on takeoff” parameter value of 5deg then that might of been what kicked the vehicle out of Auto mode (VTOL landing phase) and into the next best mode that does not require the vehicle to remain in one place which would be QHover mode.

I’m not sure about this but it does make sense as GPS + RTK are working fine now.