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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Don't use Loiter because that does use GPS, use Altitude Hold or Stabilize.

As the copter lowers to the ground the GPS signal coming from the satellite bounces off your roof line and will cause position error.  If the error is towards your house the copter will correct for that by moving away from your house.

When this glitch happens it's very fast and I have seen my GPS position change by several hundred meters in less than a second.  The copter will fly horizontally very fast in the opposite direction of the error.

I was only 1 meter from the ground in Stabilize in front of my garage just playing around when the battery failsafe kicked in unexpectedly and my copter went dead left into my car which was 10 meters away.

You're right, loiter does use GPS.  I just use it to get it close & when it's near the obstacle I switch it to alt hold to land.  There's no warning & there's nothing you can do once it decides to veer off.  It's just lost some sat communication for the horizontal accuracy.  

I remember before EKF , when INS was used there was GPS glitch protection. If the GPS had a sudden change that couldn't be real due to outrageous accelerations that would be required,  the loiter controller would just reset to the new wrong position. This was introduced to prevent this exact type of fly away condition. This was dropped when EKF was introduced. I thought the EKF was supposed to handle GPS glitches making the simple glitch protection no longer necessary ? I have seen some pretty serious GPS glitches while connected on the bench. Lucky for me I never had one in the air. I have been landing in RTL or Loiter mode mostly within ~ 10 meters of me. If GPS glitches are back I will have to rethink my landing procedure and only use Alt Hold or Stabilize.

is this reaction a result of the 'new' EKF filters in 3.3x?, or has that always existed in the algorithm?

It is surprising to me, as I have a M8N on one of my PixHawks, and since reading your post on Thursday, I have been watching the GPS status on my bench.  It does fluctuate Sat locks. . . dropping from 1 or 2 in a 5 minute interval, to an occasional drop of 3 or 4 Sats.

Will we possibly see this reaction in 'land', 'loiter', and 'RTL' modes below, say, 30' AGL?

Should we be, as suggested below, landing only in non-GPS modes?

what the heck is Err: 0-44 mean?

I only see ERR, 1048373268, 12, 1 which means crash detected in your log. I used APM Planner 2.0 to look at the log

Interestingly looking at the param you have set for the copter you have for glitch protection

PARM, 137008601, EKF_GLITCH_ACCEL, 250
PARM, 137009688, EKF_GLITCH_RAD, 40

The defaults in the code for Copter3.3.1 are link

EKF_GLITCH_ACCEL, 150

EKF_GLITCH_RAD, 25

And the master (3.4) they have been lowered to 100 and 15 respectively.

Would be interesting to play back the recorded data and see if the new params trigger glitch detection in the EKF.

Do you have an idea why your params are set larger than the defaults?

PS: I'll have more of look later, run out of time for now!

i am not convinced is a GPS issue honestly...my M8N fluctuates between 15-20 sats in the air and it has never been an issue, I didnt see any different behaviour when this crash happened, my EKF filter is also on the "relaxed" setting, but I didnt even get an EKF error

i for one wont be landing auto for a long time until this is all sorted out!

thanks Bill, glad you are helping. 

I recall changing those parameters in july I think when I had a GPS glitch and  by recommendations that the larger GLITCH radius would tolerate a larger GPS discrepancy thus handling a longer glitch, and the ACCELL was default at 350 back then and it was suggested to bring it down to 250 to reduce sudden jerks in acceleration during position changes using 2 GPS (I use 2 GPS)

how do i play back the data using different parameters? that sounds very cool....I use SITL but no expert with it

i see it in MP....Leonard indicated it could be a log parsing error or something, not a real error

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I don't think it's a glitch, I think it's # of sat's.  The RTL holds vertical & horizontal, it hovers for a sec while it finds the horizontal.  It gets confused if something blocks it.  I also think it claims 10 meters of accuracy, and it does a really good job in an open space.  My RTL, if I'm all calibrated, will land less than a foot from where it took off.  

The way I look at it is like an airplane autopilot GPS.  It'll take you down to 200' before you have to land the plane.  They're pretty accurate, but for a landing near objects you have to remember it's a signal from the satellite that's not going to cut through a building, tree, hillside or other obstacle.  

hi all, i think i found the problem.....I run 2 GPS, and N8M and a 6M....for the duration of the flight the copter was tracking to GPS1 (N8M) but then suddenly (and for no apparent reason) you can clearly see right before the LAND command that the copter switches over to GPS2 (6M), am pretty sure this likely caused the drift in position...and the crash

however the question remains, why did AC switch GPSs when there is no apparent reason? the HDOP was much lower on GPS1 than GPS2 the entire time, my understanding is it should only switch GPS if the primary HDOP becomes higher than secondary, I have also heard conflicting reports about using or not using 2nd GPS.....I did thoroughly tested the GPS switch function a few months ago (by receiver activated switch, shutting off the primary GPS in flight) and yes there were similar changes in position as what happened during the crash land. 

Is running 2 GPS not recommended? are there issues with it such as this sudden and unexpected change in GPS?

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I don't think using 2nd GPS units is recommended at this time for the exact issue you have mentioned due to handover to the second reporting a slightly different position.

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