Plane goes vertical in FBWA or STABILIZE

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1

Hey all, I have a brand new PixHawk and when I switch to FBWA or STABILIZE in the air, it immediately goes vertical and stalls until I switch back to MANUAL.

The strange thing is that I can switch to FBWA or STAB on the ground and I don’t see any abnormal movement on the elevator.

I’ve attached the log, and here’s what I can see:

Near the beginning of the log file you see I switch to FBWA while on the ground and the RCIN->C2 and RCOU->C2 are nicely inline with each other, other than a small amount of movement as I jiggle the plane.

Then at around line 55179, you can see I switch to FBWA (while I’m in the air) and you’ll notice RCOU->C2 jump up, then I try to fight it (with opposite RCIN->C2) until I give up and switch back to MANUAL. Same thing happens again when I try at around line 59048.

All I can think of is that maybe it’s airspeed related? I have a pixhawk airspeed pitot tube installed, but I completely disabled it (in the onboard params) and it didn’t seem to make any difference.

Any ideas? I’m new to APM so I don’t quite know what all the parameters are that are being logged. Is there any online reference for the parameters in the flash logs?

Any help would be greatly appreciated!

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Are you certain that the elevator direction isn’t reversed? It can be correct in manual, but inverted for the APM. On the ground, while in FBWA mode, when you raise the tail, the elevator should also go up. Sorry if this reponse is too obvious, but that’s the usual cause.

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Aaand of course as soon as I post this, I go back to check the ground mode one more time and realize the elevator is moving in the wrong direction. Turns out the elevator was reversed.

I didn’t realize that the APM worked differently in MAN vs FBWA. I just assumed that if the elevator was working in the proper direction in MAN it would be working correctly in FBWA. Maybe a documentation clarification would help.

Anyway, I think my problem is solved. Sorry for the false alarm!