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[Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only

From: Mitchell SLOWER
Subject: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.
Date: Sat, 8 Sep 2012 20:37:18 +0200

Dear all,

I encounter a really strange behavior on a fixedwing. 
I had a look at the logs, made a lot of flights in order to find out what's wrong, but I really don't understand what's happening. 
So here is the situation:

First, the setup:
Lisa/M 2.0, PPZ Version: 4.0.1. I'm using an airspeed sensor, 
I'm launching the plane with a bungee, in manual mode.
Before launch, current clock is set to circle over home, 150m AGL.

What's happening:
After launch, when I change to AUTO2 , the plane does not pitch up with motor on as expected in order to reach the desired altitude, but pitches down, gaining airspeed and loosing altitude (I checked that airspeed is near or over desired airspeed when I switch mode).

As things get dangerous, I switch to MANUAL, get some altitude, engage AUTO2, and the same behavior occurs.
Then, after a few tries like this, everything works ! And it works really fine, as I have a very good airspeed control and climb rate. 
After that, I can switch from MANUAL to AUTO2, and the plane behaves normally (get some altitude at the right airspeed and climbrate).

I did a lot of tests (I initially thought of a I-term winding up), all were unsuccessful.
The only clue I found: this problem might be related to the airspeed specific control loops, because when I disable the airspeed sensor from the airframe config file the plane seems to behave correctly (no pitch down when engaging auto2).

Did anyone encounter the same behavior ?
Do you have any idea about what could be happening ?

Of course, I can provide further details, setup and logs.


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