The crash occurred while flying a grid survey auto mission for mapping purposes. I believe the crash is my fault possibly due to powering (plugging in) the copter with copter shaking. I had placed the copter on the flat cover of my pickup bed where I was going to take off from and land because I was in a field of tall grass. I plugged it in and then jumped down from the tailgate and just didn’t recognize that this would shake the copter as it was initializing and calibrating things. I had set AHRS_EKF_USE to 1 a while back and had no problem with it. This day I kept getting BAD AHRS messages on MP when I was setting things up so I would climb up and unplug and the plug the copter back in and jump down again. I decided something must be goofy and just went in and changed AHRS_EKF_USE to 0 and of course the message went away. The copter flew the first strip of the mission fine and about halfway into the second strip it lost altitude and went into a tree at about 60’ up. When I looked at the log I can see that the gyro and mag go crazy then it starts losing altitude and takes a sharp turn. I am thinking that the initial calibration was off and it was able to compensate on the first leg of the mission but once it headed back the other direction it just could no longer handle it. Am I close?
Hate learning the hard way but it happens. Luckily I am also a tree climber so I went home and got my gear and was able to get it out of the tree before dark.
Any help in analyzing the log for crash determination is much appreciated. I have been flying missions with pixhawk for a while and never have had to do much log analysis so I’m a little uncertain of how to best identify the cause.
Bummer, looks like the batteries took a beating too. Sorry, but I’m just learning this Pixhawk stuff, so no help from me, but watching. Good luck. Common sense says that your suspicions of the cause, is pretty possible. The Pixhawk does it’s self calibrating thing pretty quick after plugging in. After the blue red thing, I think it’s OK to move around.
Thanks cootertwo! Yep, batteries are trashed, When the copter hit the tree the batteries were ejected and fell 60-70’. Three arms broke, both gps masts, one gps cable, both battery trays, UV filter on camera lends, and pretty much all prop blades. Could have been a lot worse though. Just wish someone would help me confirm what caused the crash.
I don’t think this was due to how you armed it, everything tracks as it should for 3minutes then goes crazy, I’d have thought it would have had acc errors from the beginning if it was due to a shaky arming.
Was the pixhawk still firmly attached to it’s mounting point after the crash?
Have you tried powering up the pixhawk since the crash to see if the accelerometers respond normally?
[quote=“MarkM”]I don’t think this was due to how you armed it, everything tracks as it should for 3minutes then goes crazy, I’d have thought it would have had acc errors from the beginning if it was due to a shaky arming.
Was the pixhawk still firmly attached to it’s mounting point after the crash?
Have you tried powering up the pixhawk since the crash to see if the accelerometers respond normally?[/quote]
After reading some more about BAD AHRS warning it appears to have to do mostly with GPS. The Pixhawk was still attached to the mounting plate of the anti-vibration rig but that plate had separated from 3 of the 4 rubber dampers. I will power up the pixhawk at lunch and see what I get.
I think there may be one other possibility. I live in Central Texas and we get widely varying temperatures. The last time I did all the calibrations of this unit it was probably in the mid-60’s and the day it crashed it was in the upper 90’s. The flight controller is exposed on the top plate and was certainly getting hot in the sun on that black surface. I’m not sure that’s enough of a difference to cause an issue.
I plugged in the Pixhawk and all seems to be fine. I had everything disconnected from it except for safety switch and the AZ value sits a -1004. It allowed me calibrate accel and compass. I then restarted it with the secondary GPS (neo7m) I had connected to it plugged in and it won’t come on. There appears to be no damage to it from the crash. I then plugged in a stock GPS (LEA-6H) and all seemed fine. I can’t plug in the primary GPS (m8n) because the wires got pulled from the plug in the crash and I need to repair. Any chance an external compass or GPS failure might have caused what is seen in the logs? Guess I need to spend some more time with the log.
