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

From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.
Date: Sat, 8 Sep 2012 21:44:12 +0200

We have implemented the acceleration feedback in 

It has flown several times, including catapult launches but with the complexity of all aspects involved (e.g. gps latency etc.) that is not a guarantee. If you would be so kind to help test it it would be highly appreciated. 

copy the file to your repo, add USE_AHRS_GPS_ACCELERATIONS to your airframe (should pop a message during compile)


On Sat, Sep 8, 2012 at 8:58 PM, Marc Schwarzbach <address@hidden> wrote:
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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