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

From: Marc Schwarzbach
Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.
Date: Sat, 08 Sep 2012 20:58:12 +0200

Hi Mitchell,

your problem seems to be an AHRS calculation thing related with the high 
acceleration at bungee take-off.
See the conversation one month ago: Subject: Re: [Paparazzi-devel] 
int_cmpl_quat and bungee takeoff

As a short note, I had a similar, but very light behaviour when hand throwing 
my Easystar also with Lisa/M. It does a little pitch down before starting to 
climb after the throw...

Probably we should look into the ACC signals for fixed wing..



-------- Original-Nachricht --------
> Datum: Sat, 8 Sep 2012 20:37:18 +0200
> Von: Mitchell SLOWER <address@hidden>
> An: address@hidden
> Betreff: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2,  
> only after launch.

> 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.
> Regards,
> Mitchell

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