2 Feet from landing then out of control: Logs provided

ArduCopter Copter 4.0
1

Hello!

TL;DR - Good 4 minute flight, then 2 feet from touchdown on landing, loss of control (yaw, side to side, then began to climb) and I switched to emergency motor stop and caught the darn thing as it fell from about 10 feet. TLOG replay shows EKF warning during the episode.

Logs: https://drive.google.com/drive/folders/1e5P62F5Z_f1pMRh5A1Y-99YVy0w4KdUj?usp=sharing

Logs are provided from both flight this evening… The second flight was glitchy one.

Here’s my build:
Holybro x500 Kit
Holybro Pixhawk 4 w/ Holybro GPS/Compass (BLHeli-S ESCs using Dshot150)
Holybro PM7 PDB
Futaba SBUS receiver (R2001SB)
Holybro 915mhz telemetry

PIC1
PIC2

I built this quad about 5 weeks ago. It flew great with default PIDs, and even better with autotune. Care was taken to mount the FC perfectly centered and facing forward. Its been solid in various flight modes.

Had two flights this evening. First was about 8 mins and all was well. Second was a quick 4 minute flight that went well using various modes (loiter, alt hold, drift, and stabilize), and while landing it gets sketchy within about 2 feet from the ground. Could not control it. It began to yaw and move side to side, then began to climb. I initiated emergency motor stop and managed to catch the thing as it fell… Total heart stopper!

I’ve yet to figure out how to use Mission Planner to analyze logs and graphs. I can’t zoom in and out on the graphs correctly… gotta be some trick to it?

I did manage to replay the TLOG and when the episode began, EKF turned amber in the HUD. So, I’m guessing a compass issue. Any help with these logs would be greatly appreciated!

Michael

2

Use http://plot.ardupilot.org to analize the dataflash log file. It allows non-experts to sellf instruct in the art of log file analysis

1 Like
3

Thank you so much! That is super easy to use and understand. I was able to see exactly where things went bad and maybe even how.

I was in loiter mode and descending for landing (battery was getting low), and then batt volt failsafe kicked in, triggering RTL. That’s when the compass went crazy, began to yaw and was uncontrollable. I suspect the climb was because of RTL, but it was still uncontrollable and yawing (spinning). Plotting RC6, I can see exactly when I enabled motor stop. The plots even show where I caught the death machine in mid air!

Thanks again, amilcarlucas!