ahrs_float_dcm module

AHRS using DCM filter.

No direct gyro bias estimation, but also compensates for attitude drift. Uses GPS speed for heading. Compensation of centrifugal force via GPS speed (to fly in circles with a fixedwing). Careful, it doesn't handle all BODY_TO_IMU rotations (mounting positions) correctly!

The algorithm was developed by William Premerlani and Paul Bizard. The algorithm is also used in the AHRS systems of the AdruIMU. The name DCM for the algorithm is really a misnomer, as that just means that the orientation is represented as a DirectionCosineMatrix (rotation matrix). But since people already know it under that name, we kept it.

Example for airframe file

Add to your firmware section: This example contains all possible configuration options, not all of them are mandatory!

<module name="ahrs_float_dcm">
  b'<define name="USE_MAGNETOMETER_ONGROUND" />\n    '
  b'<define name="USE_AHRS_GPS_ACCELERATIONS" />\n    '
  b'<define name="ACCEL_WEIGHT_FILTER" value="8" />\n    '
  b'<define name="ACCEL_WEIGHT_BAND" value="1." />\n  '
  b'<configure name="AHRS_DCM_TYPE" value="AHRS_PRIMARY|AHRS_SECONDARY" />\n    '
  b'<configure name="USE_MAGNETOMETER" value="FALSE" />\n    '
</module>

Module configuration options

Configure Options

• name: AHRS_DCM_TYPE value: AHRS_PRIMARY|AHRS_SECONDARY
  Description: set if the AHRS is the primary source (default) or one of the secondary sources
• name: USE_MAGNETOMETER value: FALSE
  Description: set to FALSE to disable magnetometer

Define Options

• name: USE_MAGNETOMETER_ONGROUND value: None
  Description: use magnetic compensation before takeoff only while GPS course not good
• name: USE_AHRS_GPS_ACCELERATIONS value: None
  Description: enable forward acceleration compensation from GPS speed
• name: ACCEL_WEIGHT_FILTER value: 8
  Description: adjust accel drift heuristic filter (default 8, 0 to disable filter)
• name: ACCEL_WEIGHT_BAND value: 1.
  Description: band size of accel filter: 1. means that there is no correction when accel magnitude exceeds +/- 0.5G around 1G (normal flight)

Module functions

Init Functions

These initialization functions are called once on startup.

• ahrs_dcm_wrapper_init()

Files

Header Files

The following headers are automatically included in modules.h

• ahrs_float_dcm_wrapper.h

Source Files

• modules/ahrs/ahrs_float_dcm.c
• modules/ahrs/ahrs_float_dcm_wrapper.c

Raw ahrs_float_dcm.xml file:

<!DOCTYPE module SYSTEM "module.dtd">
 
<module name="ahrs_float_dcm" dir="ahrs" task="estimation">
  <doc>
    <description>
      AHRS using DCM filter.
      No direct gyro bias estimation, but also compensates for attitude drift.
      Uses GPS speed for heading.
      Compensation of centrifugal force via GPS speed (to fly in circles with a fixedwing).
      Careful, it doesn't handle all BODY_TO_IMU rotations (mounting positions) correctly!
 
      The algorithm was developed by William Premerlani and Paul Bizard.
      The algorithm is also used in the AHRS systems of the AdruIMU.
      The name DCM for the algorithm is really a misnomer, as that just means that the orientation is represented as a DirectionCosineMatrix (rotation matrix).
      But since people already know it under that name, we kept it.
    </description>
    <configure name="AHRS_DCM_TYPE" value="AHRS_PRIMARY|AHRS_SECONDARY" description="set if the AHRS is the primary source (default) or one of the secondary sources"/>
    <configure name="USE_MAGNETOMETER" value="FALSE" description="set to FALSE to disable magnetometer"/>
    <define name="USE_MAGNETOMETER_ONGROUND" description="use magnetic compensation before takeoff only while GPS course not good"/>
    <define name="USE_AHRS_GPS_ACCELERATIONS" description="enable forward acceleration compensation from GPS speed"/>
    <define name="ACCEL_WEIGHT_FILTER" value="8" description="adjust accel drift heuristic filter (default 8, 0 to disable filter)"/>
    <define name="ACCEL_WEIGHT_BAND" value="1." description="band size of accel filter: 1. means that there is no correction when accel magnitude exceeds +/- 0.5G around 1G (normal flight)"/>
  </doc>
 
  <settings>
    <dl_settings>
      <dl_settings NAME="AHRS DCM">
        <dl_setting var="ahrs_dcm_enable" min="0" step="1" max="1" module="modules/ahrs/ahrs_float_dcm_wrapper" values="DISABLE|ENABLE" handler="enable"/>
        <dl_setting MAX="100" MIN="0" STEP="1" VAR="imu_health" shortname="health" module="modules/ahrs/ahrs_float_dcm" />
        <dl_setting MAX="100" MIN="0" STEP="1" VAR="renorm_sqrt_count" shortname="err_norm" module="modules/ahrs/ahrs_float_dcm" />
      </dl_settings>
    </dl_settings>
  </settings>
 
  <dep>
    <depends>ahrs_common,@imu,@gps</depends>
    <provides>ahrs</provides>
  </dep>
 
  <header>
    <file name="ahrs_float_dcm_wrapper.h"/>
  </header>
  <init fun="ahrs_dcm_wrapper_init()"/>
  <makefile target="!sim|fbw">
    <configure name="AHRS_DCM_TYPE" default="AHRS_PRIMARY"/>
    <define name="AHRS_DCM_TYPE" value="$(AHRS_DCM_TYPE)"/>
    <configure name="USE_MAGNETOMETER" default="0"/>
    <define name="USE_MAGNETOMETER" cond="ifeq (,$(findstring $(USE_MAGNETOMETER),0 FALSE))"/>
    <file name="ahrs_float_dcm.c"/>
    <file name="ahrs_float_dcm_wrapper.c"/>
    <test firmware="fixedwing">
      <define name="AHRS_DCM_TYPE" value="AHRS_PRIMARY"/>
    </test>
  </makefile>
</module>