another crash on auto land, mad, hit my car scratched it all up!

log file attached.....running AC3.3.1 on Pix, was in loiter then guided mode just hovering at 5m for a while, all good, then sent the land command thru GCS and it just accelerated wildly to the right eventually ramming into my car and then into the ground, GPS masts broken, broken arm and motor mount, and nice gash on my car's door....

what the heck is Err: 0-44 mean? never seen that before but it happned just before I issued the land cmd, I dont see any mechanical issues and thou it appears there is some EKF issue right after the Err: 0-44 I dont see any specific EKF error 

Randy or Leornard? please help! thanks

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Strange, A plot of the GPS shows that both GPS units followed each other until the end where one drops out.  The plot shows only one going for the front of your garage where I assume your car was.  I think the other GPS did not follow....

I noticed that thou honestly didnt think much of it as I thought GPS wasnt used during a LAND mode, only the althold controller is used or something like that....I dont even think land uses EKF as land is a failsafe mode for EKF...so i have no idea what could have gone so wrong during a land if it doesnt rely on any navigation? 

Hi Ivan,

All this happened just as you lost 3 satellites (20 to 17) so I assume your gps moved off. I can also see that the copter is reacting because it thinks it has moved, not because it is trying to move. So from the controlers perspective it was trying to stay stationary but the GPS was telling it that it was moving.

How close were you to the car when you started to land and how far did it move in total?

Thanks for looking into Leonard.... Thats an M8N GPS and it always fluctuates between 14 to 20 sats all the time,  I have never had an issue with it doing that during auto flight. What is the error 0-44 about which shows up right before the land command?  I can't find reference to it anywhere... 

Copter was about 25ft away from the car at the time,  the copter was suppose to land about 15ft away from me when it suddenly veered off towards the vehicle for like 25ft,  and I believe was still descending at the land descent rate while veering off

GPS will be used on "land" mode if the FC has a lock.

From the wiki:  

  • If the vehicle has GPS lock the landing controller will attempt to control it’s horizontal position but the pilot can adjust the target horizontal position just as in Loiter mode.
  • If the vehicle does not have GPS lock the horizontal control will be as in stabilize mode so the pilot can control the roll and pitch lean angle of the copter.

http://copter.ardupilot.com/wiki/land-mode/

If the GPS coords move there is no way to tell if they are accurate and valid or if the quad has moved. So some bad readings give a worse result than a failed gps with no lock.

I've found that the RTL works beautifully in an open field.  Any obstructions (hillside, car, building) it loses the GPS & out of nowhere will crash, just when you think you're home free.  If you know there's going to be interference, either land in loiter or manual.   

Thanks Tony and Ben... There was GPS lock and no indication of otherwise... There still no valid reason I can see for the copter behaving how it did... There was a mysterious error code 0-44 right before the land command was issued which I can't find what that error code means anywhere... I suspect that code has something to do with it.. Does anyone know what it is?

Hi Ivan,

As I said in the post below, I can see that the GPS location moved and the controler and copter was simply following that and as far as it could tell was staying stationary. So it is very clear why it did what it did.

As for the error code, as you said, there is no error in the code that corresponds to these numbers. I suspect that the code is a write error or a corruption in the file. We see this from time to time in the form of an infinite spike in one of the graphs.

An information from discussion: http://diydrones.com/forum/topics/copter-3-3-beta-testing

may be an answer to your crash...

Warning #2: an issue has been found in Copter-3.3.1 which can lead to hard landings in RTL or AUTO if the WPNAV_SPEED_DN is set too high (i.e. >400 or 4m/s) and/or the WPNAV_ACCEL_Z is set too low (i.e. <100 or 1m/s/s).  We hope to resolve this in Copter-3.3.2-rc1.

Thanks for the reply Randy, where do you see the GPS position change?  because I look at the GPS LAT and LONG and they only changed "after" the copter had already entered the unexpected right roll, but before then they dont seem to change much if at all.....

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