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Re: [Paparazzi-devel] aircraft path offset

From: Gautier Hattenberger
Subject: Re: [Paparazzi-devel] aircraft path offset
Date: Fri, 30 Mar 2012 14:41:20 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:11.0) Gecko/20120310 Thunderbird/11.0


Michel, a good to test to know if it comes from an imu alignment error (or command offset) is to fly in AUTO1, with the roll stick centered. If the aircraft always tend to turn in the direction, set the imu offset in the opposite direction. You can also check that measured and desired roll are (almost) the same. If not, tune your gains and command offset first.

Christophe, the "adaptive" and "new" control loops have roll (and pitch) integrators.


Le 29/03/2012 10:04, Christophe De Wagter a écrit :
If you do left circles and constantly fly outside the circle, but when you do right circles you fly inside the circle, you have a roll trim error or an imu alignment error.

If you always fly outside your circle regardingless of it being left or right, then you either need to check that phi gets close enough to your desired-roll, that your max_roll_angle is not too small for the desired circle or need to adjust the prebank correction a bit: normal prebank = 1 = 100%. Increase if you are outside your circle. 

This issue brings us to another discussion: could I add an integrator in the attitude command? In thermopile age this was a bit tricky, however we have seen several times that (foam) aircraft gradually deform, up to the point where they turn way to hard one way and only barely the other way. 


On Wed, Mar 28, 2012 at 7:39 PM, Felix Ruess <address@hidden> wrote:
Hi Mitchel,

as Christoph said the pre_bank_correction might be used to improve this.
However it sounds like there is a different issue as it should of course work the same, regardless which direction you are circling...
I presume you are using the master branch?

Having a quick look at nav_circle_XY in nav.c it seems like the circle_bank is not set if you are too far outside the circle... but that should not only depend on the distance to the circle, but the direction as well... Maybe this is the issue, maybe I'm missing something?
Gautier, Christophe or anyone with more fixedwing nav knowledge can clear this up?

Cheers, Felix

On Wed, Mar 28, 2012 at 6:46 PM, Christoph Niemann <address@hidden> wrote:

Hi Mitchel,

I would recommend using course pre bank correction to solve this.



Am 28.03.2012 18:22 schrieb "Michel MITCHELL" <address@hidden>:
Hello Paparazzi team,

I have done successul flights in AUTO2 (Lisa/M and Easy Glider), but things can be improved.

The aircraft is always slightly offtrack with the predicted path (about a 10 meters offset, always on the left).
Below here is a screenshot  from a real flight, when doing circles.

- Circle is 50m radius, and roll max is set to 35 degrees in the aircraft config file.
- If I ask to invert the circle (-radius), I can clearly see that the aircraft is able to make sharper turns, so I don't think the system  is saturated on the roll axis.
- Aircraft flies straight in AUTO1, straight in AUTO2 when doing lines (so I presume ROLL_NEUTRAL_DEFAULT is ok)

Do you have any idea of this problem ? Where can I look at in order to improve things ?


Images intégrées 1

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