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Re: [Paparazzi-devel] Calibrate the IMU/GYRO


From: Gautier Hattenberger
Subject: Re: [Paparazzi-devel] Calibrate the IMU/GYRO
Date: Fri, 01 Jun 2012 10:11:08 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.23) Gecko/20110922 Thunderbird/3.1.15

Hi,

I did some test with the float_dcm filter and I observed this:
- when doing full roll, the attitude takes some time to recover correctly (some degrees of error after 360° of roll) - when turning the plane upside down and going back to normal changing direction of rotation (+180°, then -180° on roll axis), there is almost no error As Felix said, this should not append as the rotation matrix should not have singularity. At least for normal flight (no roll or loop) it works well, even at high bank angle. A possible issue is a bad gyro sensitivity calibration (and it's most likely the case of everybody since we use datasheet values). The result is an angular error when integrating the gyros. If you turn your plane in one direction and then go back to initial position turning in the opposite direction, the error is compensated. But if you do a full turn, it doesn't and you end up with a final angle too small or too big. Then it slowly converge to the correct angle thanks to the accelerometers.

Gautier

On 31/05/2012 13:17, Felix Ruess wrote:
Hi,

While the rotation matrix representation of float_dcm should have no
problems dealing with an inverted IMU, I have never much used or
checked this algorithm.
If you have problems with float_dcm you may want to use int_cmpl_quat instead.
See http://paparazzi.enac.fr/wiki/Subsystem/ahrs

Cheers, Felix

On Sat, May 26, 2012 at 3:44 AM, wang yao<address@hidden>  wrote:
hi i use the weasel.xml and have that problem

have you got the problem i mentioned?

when the plane is inverted and turn to upright again,  the PFD screen is
hard to>recover to its original position.


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