Subsystem/imu

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Revision as of 14:05, 1 December 2011 by Flixr (talk | contribs) (Defining the orientation of the IMU)

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Currently possible IMU subsystems are

  • aspirin
  • b2_v1.0
  • b2_v1.1
  • b2_v1.2
  • yai
  • crista
  • analog
  • ppzuav

Other IMUs can be used through modules or you can just add a subsystem makefile for your own. Also see the IMU calibration page.

File: conf/airframes/myplane.xml
  <firmware name="fixedwing or rotorcraft">
     ...
    <subsystem name="imu"       type="aspirin"/>
  </firmware>

Defining the calibration

In the IMU section the IMU calibration is defined and looks something like this:

File: conf/airframes/myplane.xml
  <section name="IMU" prefix="IMU_">
    <define name="GYRO_P_NEUTRAL" value="32362" />
    <define name="GYRO_Q_NEUTRAL" value="32080" />
    <define name="GYRO_R_NEUTRAL" value="32096" />

    <define name="GYRO_P_SENS" value="1.1032765" integer="16" />
    <define name="GYRO_Q_SENS" value="1.1360802599" integer="16" />
    <define name="GYRO_R_SENS" value="1.1249874614" integer="16" />

    <define name="ACCEL_X_SENS" value="2.45932966" integer="16"/>
    <define name="ACCEL_Y_SENS" value="2.45106376" integer="16"/>
    <define name="ACCEL_Z_SENS" value="2.47825717" integer="16"/>

    <define name="ACCEL_X_NEUTRAL" value="31886"/>
    <define name="ACCEL_Y_NEUTRAL" value="32162"/>
    <define name="ACCEL_Z_NEUTRAL" value="32941"/>

    <define name="MAG_X_SENS" value="3.17378921476" integer="16"/>
    <define name="MAG_Y_SENS" value="3.14663275967" integer="16"/>
    <define name="MAG_Z_SENS" value="3.26531022727" integer="16"/>

    <define name="MAG_X_NEUTRAL" value="2059"/>
    <define name="MAG_Y_NEUTRAL" value="1944"/>
    <define name="MAG_Z_NEUTRAL" value="2099"/>
  </section>

See the IMU calibration page for the actual calibration instructions.

45deg Mag hack

If your magnetometer axes are rotated by 45deg around z. (e.g. with external mag on booz imu v1.0)

File: conf/airframes/myplane.xml
  <section name="IMU" prefix="IMU_">
    ...
    <define name="MAG_45_HACK" value="1" />
    <!--define name="MAG_X_SENS" value="5.14821844457 * sqrt(2)/2" integer="16"/-->
    <!--define name="MAG_Y_SENS" value="5.11810156597 * sqrt(2)/2" integer="16"/-->
    <define name="MAG_X_SENS" value="3.640340173" integer="16"/>
    <define name="MAG_Y_SENS" value="3.619044324" integer="16"/>
    <define name="MAG_Z_SENS" value="5.07618333556" integer="16"/>
  </section>

Defining the orientation of the IMU

Paparazzi has a parameter to define the orientation of the IMU with respect to the body of the vehicle.

Important This is coming from the rotorcraft codebase and was only intended for small corrections and not for complete 90deg rotations. See the issue on github. Currently the only way to properly deal with 90deg rotations is to just change the sensors channels (e.g. so that what are normally the x-axis gyros and accels become the y-axis sensors, etc.)

Not defining these values is the same as setting them to zero:

File: conf/airframes/myplane.xml
  <section name="IMU" prefix="IMU_">
    ...
    <define name="BODY_TO_IMU_PHI"   value="RadOfDeg(0.0)"/>
    <define name="BODY_TO_IMU_THETA" value="RadOfDeg(0.0)"/>
    <define name="BODY_TO_IMU_PSI"   value="RadOfDeg(0.0)"/>
  </section>