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

From: Felix Ruess
Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.
Date: Sat, 8 Sep 2012 22:35:46 +0200


the pitching down after a bungee takeoff is definitely noticable, however from what you describe I'm not sure if that is the only effect you are seeing.

But please note that AHRS_GRAVITY_UPDATE_NORM_HEURISTIC in v4.0 does not really have a big effect.
As already mentioned previously in
you can test the improved gravity norm heuristic from my int_cmpl_quat_gravity_heuristic branch which is up-to-date with v4.0 otherwise.

Would be great to get some feedback on this as I can't test this with a real bungee takeoff myself.

Cheers, Felix

On Sat, Sep 8, 2012 at 10:19 PM, Eduardo lavratti <address@hidden> wrote:
I have the same behavior.
i am using float_dcm and bungee but i think this is not due bungee.

this behavior occur if i engage auto2 when pitching up.
If i pitch up, stabilize altitude and engage auto2 this behavior not occur.
this seem that some I term are working but i not have time to search the cause.

i have to make this test.
takeoff in manual then engage auto2.
this will reset the integrator.


Date: Sat, 8 Sep 2012 21:57:52 +0200
From: address@hidden
To: address@hidden
Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.

Marc, Christophe: initially, I thought it could be an AHRS related problem, but I'm think it's something else.
(I'm using int_cmpl_quat and the  AHRS_GRAVITY_UPDATE_NORM_HEURISTIC flag).

I think it's not related to AHRS because:
- I had a look at the estimator (theta), and pitch seems to be correct.
- If I lauch with the capatult, fly some time in manual, and engage AUTO2, diving also happens.
- When I disable the airspeed from the airframe config file, everything seems to work (I say "seems" because I did only one try that was successful).


2012/9/8 Christophe De Wagter <address@hidden>
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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