Re: [Paparazzi-devel] Paparazzi EKF- and compelmentary- filter

[Felix Ruess]

Hi Andrew,

Whether you represent your angles in a way that they have
singularities (like euler angles) or not (like quaternions or dcm) has
nothing to do with the choice of your estimator (e.g. EKF or
complementary filter or your PI controller). In any case you have to
transform your IMU measurements from the IMU frame into the navigation
frame (assumed to be the same as the inertial frame considering the
quality of the sensors).
The paparazzi KF uses quaternions as angle representations (you really
don't want to use dcm here) but also converts the latest quaternion
attitude estimate to euler angle and dcm representations for ease of
use.

Cheers, Felix

2010/4/6 Andrew S <address@hidden>:
> Hi
> For my view, EKF is unnecessary as it loads microcontroller. You can use even 
> simple PI controller. It works worse than EKF, but quite well. For good 
> results PI regulator should be adjusted for 10 seconds of correction after 
> 180 degrees error. Also I can say cheap two axis gyros by ST are unusable 
> because of cross axis interference and whey do not have tolerancy against 
> vibration. Complementary one axis Z-gyros are better.
> For correct angles EKF is not a solution, you need for example Directional 
> cosine matrices for calculations between body and earth frames. The problem 
> is that gyros works in the body frame, but accelerometers works in the earth 
> frame. In fact when pitch is near 90 degrees, the roll gyro indicates jaw :)  
> EKF will not helps for this.
> Andrew
>
> 02.04.10, 17:41, "Prof. Dr.-Ing. Heinrich Warmers" <address@hidden>:
>
>> Hello,
>>  we made same experiments with a EKF based  on the rotomotion solution in
>>  combination with the tiny13 and a low cost analogue IMU from sparkefun.
>>  By the test i saw that the software is not  possible to  deal with
>>  pitch  angeles over  90°. So  to fly a looping is impossible.
>>  If  90° arrives it is  impossible to get the correct angeles by the g
>>  force since static  z acceleration is zero.
>>  If the pitch angels is more than  120°  the roll angeles rotate fast.
>>  What is about the  paparazzi  booz ekf and complementary filter. Can
>>  they deal  all angeles ?
>>  In the video from 2006  i saw only small  angeles.
>>
>>  Cheers
>>
>>  Heinrich
>>
>>
>>
>>
>>
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>>
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