Large QuadPlane Crash in QAUTOTUNE
Tried QAUTOTUNE (Mode 22) on a large QuadPlane weighing 8.5 Kgs and 8-ft Wing Span.
The aircraft is fitted with Pixhawk2.1 Cube and HERE GNSS running Arduplane Latest 3.10.0-dev, and set up as an X Frame in the firmware (Q_FRAME_TYPE 1)
Quad drive is KDE3520XF-400KV coupled with KDEUAS55HVC (55A+HV) ESCs running T-Motor 18x6.1 CF Props, powered by a 16000mAH 6S Lipo battery. As per eCalc this setup provides a Thrust-to-Weight ratio of 1.7 at full charge and a hover time of 10+ mins.
In our first flight, QuadPlane was stable in QLOITER mode and held its position comfortably on a very calm day with all default PID gains. However, PID gains tunning was required as a small Roll/Pitch input from RC would result in oscillations in Roll/Pitch axis. Flight log is attached as QPlane_T1.BIN
Following parameters were set for the QAUTOTUNE Flight:
- AUTOTUNE_AXES = 1 (Roll Axis only)
- AUTOTUNE_AGGR = 0.06 (Reduced Autotune Aggressiveness)
- Q_ANGLE_MAX = 3000 (Limit Quad lean angle to 30 degrees)
- Roll/Pitch P gains (Q_A_RAT_RLL_P, Q_A_RAT_PIT_P) Reduced from 0.25 to 0.2
- Roll/Pitch D gains (Q_A_RAT_RLL_D, Q_A_RAT_PIT_D) Increased from 0.0036 to 0.005
QAutoTune (Mode 22) was engaged from QLOITER mode. Aircraft did not start twitching immediately because the throttle stick was not exactly centered (at 1530 PWM). Reduced the throttle to around 1490 PWM and the aircraft started to twitch as expected. All was good in the first 9 twitches, as the aircraft would recover to level position from the twitch with about 5-degrees overshoot. It did not recover from the 10th twitch and came down crashing. Sustained major structural damage to the wing and fuselage.
Here is the link to both log files: https://www.dropbox.com/sh/eh3d5lf7kw5imrt/AADqb469NAs4RRDXmX5PK7sia?dl=0
I am now trying to look into the log file and figure out the cause of the crash and how it could have been avoided. So far i have discovered two anomalies:
On 10th twitch, the throttle signal to Motor-1 (Front Right, CCW) & Motor-2 (Backward Left, CCW) i.e RCOU.C5 & RCOU.C6 went down to ZERO momentarily and then recovered to around 1700 PWM. Is this an ESC De-Sync scenario?
1.5 seconds after the above, the throttle signal to Motor-2 (Backward Left, CCW) RCOU.C6 goes to max (1900), while the throttle signal to Motor-1 (Front Right, CCW) RCOU.C5 goes to ZERO in perfect synchronization. The vehicle was still recovering from the overshoot of last twitch.
It seems like the Motor-2 is unable to provide the necessary lift and auto-pilot reduces the throttle on Motor-1 to ZERO in an attempt to keep the vehicle level. But it does not work as the vehicle keeps rolling to the left specifically dipping on the Motor-2 and starts loosing altitude and eventually hits the ground. Does this points to a Motor/ESC failure or an ESC de-sync?
Few More Questions
- Reducing the AutoTune Aggressiveness further down would have avoided this crash? Does the Autotune Aggressiveness limits the Max roll/pitch demanded by autopilot for twitching? Or it reduces the Rate (degrees per second) demanded by autopilot during the twitch?
- How about limiting the Q_ANGLE_MAX to 20-degrees to avoid excessive motor load during AutoTune? How would it impact the Autotune effectiveness and general flight later on?
- Assuming it is a Motor/ESC failure scenario, was this failure triggered because of the excessive motor load experienced in AutoTune mode? Should i consider increasing the T/W ratio in the design to give more headroom?
@Leonardthall and all: I might have missed something important so please look into the logs and provide your valued feedback.
Looking forward to great help as always!