Re: [Paparazzi-devel] turning AP upside down (installing it reversed)

[Felix Ruess]

Another hint:

If the AHRS does not properly support body_to_imu and you don't want to add an upside down option to the imu, you can also simply invert the signs on the y and z axis:

<section name="IMU" prefix="IMU_">

  <define name="GYRO_Q_SIGN" value="1"/>

  <define name="GYRO_Q_SIGN" value="-1"/>

  <define name="GYRO_R_SIGN" value="-1"/>

  <define name="GYRO_Q_SIGN" value="-1"/>

  <define name="ACCEL_X_SIGN" value="1"/>

  <define name="ACCEL_Y_SIGN" value="-1"/>

  <define name="ACCEL_Z_SIGN" value="-1"/>

  ....

</section>

Cheers, Felix

On Mon, Sep 8, 2014 at 5:18 PM, Felix Ruess <address@hidden> wrote:

Hi again,

or do something like adding an APOGEE_UPSIDE_DOWN option:

https://github.com/flixr/paparazzi/commit/58e6cf78f69eb6e49501a5774513cc0abf2c3e06

Cheers, Felix

On Mon, Sep 8, 2014 at 5:08 PM, Felix Ruess <address@hidden> wrote:

Hi Andreas,

if you only want to turn it upside down (keeping the x-axis to the front), just turn it 180deg around the x-axis:

    <define name="BODY_TO_IMU_PHI" value="180" unit="deg"/>

    <define name="BODY_TO_IMU_THETA" value="0" unit="deg"/>

    <define name="BODY_TO_IMU_PSI" value="0" unit="deg"/>

But please not that not all AHRS algorithms properly take this into account: https://wiki.paparazziuav.org/wiki/Subsystem/ahrs
Which one are you using?

Cheers, Felix

On Mon, Sep 8, 2014 at 5:01 PM, Andreas Philipp <address@hidden> wrote:

Dear list,

in order to mount an AP reversed (upside down, for accessing the plugs
easily), what do I have to change in the airframe file? I couldn't find
any hint in the archive or wiki.

For an Apogee I changed this:

  <section name="IMU" prefix="IMU_">
    <!-- Calibration Neutral -->
    <define name="GYRO_P_NEUTRAL" value="0"/>
    <define name="GYRO_Q_NEUTRAL" value="0"/>
    <define name="GYRO_R_NEUTRAL" value="0 "/>

    <define name="ACCEL_X_NEUTRAL" value="0"/>
    <define name="ACCEL_Y_NEUTRAL" value="0"/>
    <define name="ACCEL_Z_NEUTRAL" value="0"/>

    <define name="BODY_TO_IMU_PHI" value="0" unit="deg"/>
    <define name="BODY_TO_IMU_THETA" value="0" unit="deg"/>
    <define name="BODY_TO_IMU_PSI" value="0" unit="deg"/>
  </section>

to that (just changing BODY_TO_IMU_THETA and BODY_TO_IMU_PSI):

  <section name="IMU" prefix="IMU_">
    <!-- Calibration Neutral -->
    <define name="GYRO_P_NEUTRAL" value="0"/>
    <define name="GYRO_Q_NEUTRAL" value="0"/>
    <define name="GYRO_R_NEUTRAL" value="0 "/>

    <define name="ACCEL_X_NEUTRAL" value="0"/>
    <define name="ACCEL_Y_NEUTRAL" value="0"/>
    <define name="ACCEL_Z_NEUTRAL" value="0"/>

    <define name="BODY_TO_IMU_PHI" value="0" unit="deg"/>
    <define name="BODY_TO_IMU_THETA" value="180" unit="deg"/>
    <define name="BODY_TO_IMU_PSI" value="180" unit="deg"/>
  </section>

This works in principle, however, the GCS (PFD) shows that the AP is
initated reversed first and then needs a long time for slowly drifting
to the correct position (actually it drifts beyond the right roll
position and then back like controlled by a low-pass filter).
And maybe associated with this: When flying circles in the flightplan,
the plane of the circle is tilted about several meters (may be 20m or
more), leading to one side of the circle being lower than the other,
which is strange and annoying for climate measurements. The tilt is
always in the same direction.

What am I missing?

Thanks for any reply,
Andreas

--
--------------------------------------
Dr. Andreas Philipp
Institute of Geography
University of Augsburg
Universitaetsstrasse 10
D - 86135 Augsburg
Germany

Phone:  ++49/821/598-2266
Fax:    ++49/821/598-2264
Email:  address@hidden
http://www.geo.uni-augsburg.de/lehrstuehle/phygeo/personal/philipp/
--------------------------------------

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