We recently crashed a large quadplane while trying to perform AUTOTUNE.
Long story short was that a series of unfortunate events (engine issues + bad piloting skills) led to the aircraft entering a stall spin; switching back to QHOVER did not help to recover from the spin and eventual crash.
However, after looking at the logs, we noticed something peculiar:
At the point when QHOVER was engaged, the aircraft was rolled almost 90 degrees to the right; intuitively, the VTOL Attitude Controller should be trying to roll in the opposite direction to level the aircraft. However, from the log, the desired roll is in the same direction as actual, and making the system roll to the right even more.
I am quite curious as to why the controller would respond this way. Is it being confused by the extreme angles, and unsure of which direction to correct? If that is the case, how is quadplane’s attitude controller configured to respond to extreme scenarios (e.g. 90 degree bank angles, flips)? Have tried looking through both the documentation and the code without much success.
Log file is here: https://drive.google.com/open?id=19A2Noj9LrTrJLkX3n6KsA01gWyOgS4mE
Onboard camera footage is here (stall spin occurs around 01:20): https://drive.google.com/open?id=1Qp5id6YZf4y1bHXGsKDgCU31_eYUC9yf
Some other useful info:
- I am using a Cube Black on ArduPlane 3.9.8, ChiBiOS
- Our quadplane has a wingspan of about 3m, with MTOW of 25kg
- All plane + quad response to sticks and stabilisation were checked and verified to be correct prior to flight
- Q_ASSIST was not enabled as we did not want the quad to interfere with AUTOTUNE maneuvers
Thanks in advance!