Paparazzi UAS  v5.15_devel-58-g208c37b
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ahrs_int_cmpl_quat module

AHRS using complementary filter in fixed point.

Propagation is done in quaternion representation.

By default uses magnetometer for heading for rotorcrafts. For fixedwing firmware AHRS_GRAVITY_UPDATE_COORDINATED_TURN is enabled by default and magnetometer disabled (needs GPS).

To measure attitude angles, gyrometers measurements are integrated. The result of integration is accurate for short term, but gyro bias is accumulated, which results in long term errors (drift). On the other hand, accelerometers can be used to infer pitch/roll angles utilizing gravity vector measurement, but they suffer from noise due to vibrations. The measurement is then only accurate when averaged over a long term. Also, accelerometers alone are unable to give accurate angles when the vehicle is accelerating. Complementary filter takes advantage of both sensors, using a low-pass filter on accelerometer readings and high pass filter on gyrometers readings, to estimate attitude angles.

  • No danger of gimbal lock, since quaternions are used.
  • The arithmetic is fixed point and is thus suitable if the processor (on your board) has no FPU.
  • Estimates the gyro bias.

Example for airframe file

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

1 <module name="ahrs_int_cmpl_quat">
2  <define name="AHRS_MAG_UPDATE_ALL_AXES" value="FALSE|TRUE" />
3  <define name="AHRS_USE_GPS_HEADING" value="FALSE|TRUE" />
4  <define name="AHRS_GRAVITY_UPDATE_COORDINATED_TURN" value="FALSE|TRUE" />
5  <define name="AHRS_GPS_SPEED_IN_NEGATIVE_Z_DIRECTION" value="FALSE|TRUE" />
6  <define name="AHRS_PROPAGATE_LOW_PASS_RATES" />
7  <define name="AHRS_BIAS_UPDATE_HEADING_THRESHOLD" value="5.0" />
8  <define name="AHRS_HEADING_UPDATE_GPS_MIN_SPEED" value="5.0" />
9  <define name="AHRS_GRAVITY_HEURISTIC_FACTOR" value="30" />
10  <define name="AHRS_ICQ_IMU_ID" value="ABI_BROADCAST" />
11  <define name="AHRS_ICQ_MAG_ID" value="ABI_BROADCAST" />
12  <define name="AHRS_ICQ_GPS_ID" value="GPS_MULTI_ID" />
13  <configure name="USE_MAGNETOMETER" value="TRUE" />
14  <configure name="AHRS_ALIGNER_LED" value="1" />
15 </module>

Module configuration options

Configure Options

  • name: USE_MAGNETOMETER value: TRUE
    Description: set to FALSE to disable magnetometer
  • name: AHRS_ALIGNER_LED value: 1
    Description: LED number to indicate AHRS alignment, none to disable (default is board dependent)

Define Options

  • name: AHRS_MAG_UPDATE_ALL_AXES value: FALSE|TRUE
    Description: Use magnetometer to update all axes and not only yaw
  • name: AHRS_USE_GPS_HEADING value: FALSE|TRUE
    Description: Use GPS course to update heading
  • name: AHRS_GRAVITY_UPDATE_COORDINATED_TURN value: FALSE|TRUE
    Description: Compensation of centrifugal force via GPS speed (to fly in circles with a fixedwing)
  • name: AHRS_GPS_SPEED_IN_NEGATIVE_Z_DIRECTION value: FALSE|TRUE
    Description: AHRS_GRAVITY_UPDATE_COORDINATED_TURN assumes the GPS speed is in the X axis direction. Quadshot, DelftaCopter and other hybrids can have the GPS speed in the negative Z direction
  • name: AHRS_PROPAGATE_LOW_PASS_RATES value: None
    Description: apply a low pass filter on rotational velocity
  • name: AHRS_BIAS_UPDATE_HEADING_THRESHOLD value: 5.0
    Description: don't update gyro bias if heading deviation is above this threshold in degrees
  • name: AHRS_HEADING_UPDATE_GPS_MIN_SPEED value: 5.0
    Description: Don't update heading from GPS course if GPS ground speed is below is this threshold in m/s
  • name: AHRS_GRAVITY_HEURISTIC_FACTOR value: 30
    Description: Default is 30. Reduce accelerometer cut-off frequency when the vehicle is accelerating: norm(ax,ay,az) ~ 9,81 m/s2. WARNING: when the IMU is not well damped, the norm of accelerometers never equals to 9,81 m/s2. As a result, the GRAVITY_HEURISTIC_FACTOR will reduce the accelerometer bandwith even if the vehicle is not accelerating. Set to 0 in case of vibrations
  • name: AHRS_ICQ_IMU_ID value: ABI_BROADCAST
    Description: ABI sender id of IMU to use
  • name: AHRS_ICQ_MAG_ID value: ABI_BROADCAST
    Description: ABI sender id of magnetometer to use
  • name: AHRS_ICQ_GPS_ID value: GPS_MULTI_ID
    Description: ABI sender id of GPS to use

Auto-loaded modules

The following modules are automatically loaded (just as if you had added them in the airframe file)

Files

Header Files

The following headers are automatically included in modules.h

Source Files

Raw ahrs_int_cmpl_quat.xml file:

<!DOCTYPE module SYSTEM "module.dtd">
<module name="ahrs_int_cmpl_quat" dir="ahrs">
<doc>
<description>
AHRS using complementary filter in fixed point.
Propagation is done in quaternion representation.
By default uses magnetometer for heading for rotorcrafts.
For fixedwing firmware AHRS_GRAVITY_UPDATE_COORDINATED_TURN is enabled by default and magnetometer disabled (needs GPS).
To measure attitude angles, gyrometers measurements are integrated.
The result of integration is accurate for short term, but gyro bias is accumulated, which results in long term errors (drift).
On the other hand, accelerometers can be used to infer pitch/roll angles utilizing gravity vector measurement, but they suffer from noise due to vibrations.
The measurement is then only accurate when averaged over a long term.
Also, accelerometers alone are unable to give accurate angles when the vehicle is accelerating.
Complementary filter takes advantage of both sensors, using a low-pass filter on accelerometer readings and high pass filter on gyrometers readings, to estimate attitude angles.
- No danger of gimbal lock, since quaternions are used.
- The arithmetic is fixed point and is thus suitable if the processor (on your board) has no FPU.
- Estimates the gyro bias.
</description>
<configure name="USE_MAGNETOMETER" value="TRUE" description="set to FALSE to disable magnetometer"/>
<configure name="AHRS_ALIGNER_LED" value="1" description="LED number to indicate AHRS alignment, none to disable (default is board dependent)"/>
<define name="AHRS_MAG_UPDATE_ALL_AXES" value="FALSE|TRUE" description="Use magnetometer to update all axes and not only yaw"/>
<define name="AHRS_USE_GPS_HEADING" value="FALSE|TRUE" description="Use GPS course to update heading"/>
<define name="AHRS_GRAVITY_UPDATE_COORDINATED_TURN" value="FALSE|TRUE" description="Compensation of centrifugal force via GPS speed (to fly in circles with a fixedwing)"/>
<define name="AHRS_GPS_SPEED_IN_NEGATIVE_Z_DIRECTION" value="FALSE|TRUE" description="AHRS_GRAVITY_UPDATE_COORDINATED_TURN assumes the GPS speed is in the X axis direction. Quadshot, DelftaCopter and other hybrids can have the GPS speed in the negative Z direction"/>
<define name="AHRS_PROPAGATE_LOW_PASS_RATES" description="apply a low pass filter on rotational velocity"/>
<define name="AHRS_BIAS_UPDATE_HEADING_THRESHOLD" value="5.0" description="don't update gyro bias if heading deviation is above this threshold in degrees"/>
<define name="AHRS_HEADING_UPDATE_GPS_MIN_SPEED" value="5.0" description="Don't update heading from GPS course if GPS ground speed is below is this threshold in m/s"/>
<define name="AHRS_GRAVITY_HEURISTIC_FACTOR" value="30" description="Default is 30. Reduce accelerometer cut-off frequency when the vehicle is accelerating: norm(ax,ay,az) ~ 9,81 m/s2. WARNING: when the IMU is not well damped, the norm of accelerometers never equals to 9,81 m/s2. As a result, the GRAVITY_HEURISTIC_FACTOR will reduce the accelerometer bandwith even if the vehicle is not accelerating. Set to 0 in case of vibrations"/>
<define name="AHRS_ICQ_IMU_ID" value="ABI_BROADCAST" description="ABI sender id of IMU to use"/>
<define name="AHRS_ICQ_MAG_ID" value="ABI_BROADCAST" description="ABI sender id of magnetometer to use"/>
<define name="AHRS_ICQ_GPS_ID" value="GPS_MULTI_ID" description="ABI sender id of GPS to use"/>
</doc>
<settings>
<dl_settings>
<dl_settings NAME="AHRS">
<dl_setting var="ahrs_icq.gravity_heuristic_factor" min="0" step="1" max="50" module="subsystems/ahrs/ahrs_int_cmpl_quat" shortname="g_heuristic" param="AHRS_GRAVITY_HEURISTIC_FACTOR" type="uint8" persistent="true"/>
<dl_setting var="ahrs_icq.accel_omega" min="0.02" step="0.02" max="0.2" module="subsystems/ahrs/ahrs_int_cmpl_quat" shortname="acc_omega" param="AHRS_ACCEL_OMEGA" unit="rad/s" handler="SetAccelOmega" type="float" persistent="true"/>
<dl_setting var="ahrs_icq.accel_zeta" min="0.7" step="0.05" max="1.5" module="subsystems/ahrs/ahrs_int_cmpl_quat" shortname="acc_zeta" param="AHRS_ACCEL_ZETA" handler="SetAccelZeta" type="float" persistent="true"/>
<dl_setting var="ahrs_icq.mag_omega" min="0.02" step="0.01" max="0.1" module="subsystems/ahrs/ahrs_int_cmpl_quat" shortname="mag_omega" param="AHRS_MAG_OMEGA" unit="rad/s" handler="SetMagOmega" type="float" persistent="true"/>
<dl_setting var="ahrs_icq.mag_zeta" min="0.7" step="0.05" max="1.5" module="subsystems/ahrs/ahrs_int_cmpl_quat" shortname="mag_zeta" param="AHRS_MAG_ZETA" handler="SetMagZeta" type="float" persistent="true"/>
</dl_settings>
</dl_settings>
</settings>
<autoload name="ahrs_sim"/>
<header>
<file name="ahrs.h" dir="subsystems"/>
</header>
<makefile target="!sim|fbw" firmware="fixedwing">
<configure name="USE_MAGNETOMETER" default="0"/>
<define name="AHRS_USE_GPS_HEADING" cond="ifneq (,$(findstring $(USE_MAGNETOMETER),0 FALSE))"/>
<define name="AHRS_GRAVITY_UPDATE_COORDINATED_TURN"/>
</makefile>
<makefile target="!sim|fbw">
<configure name="USE_MAGNETOMETER" default="1"/>
<define name="USE_MAGNETOMETER" cond="ifeq (,$(findstring $(USE_MAGNETOMETER),0 FALSE))"/>
<define name="AHRS_ALIGNER_LED" value="$(AHRS_ALIGNER_LED)" cond="ifneq ($(AHRS_ALIGNER_LED),none)"/>
<define name="USE_AHRS"/>
<define name="USE_AHRS_ALIGNER"/>
<file name="ahrs.c" dir="subsystems"/>
<file name="ahrs_aligner.c" dir="subsystems/ahrs"/>
<file name="ahrs_int_cmpl_quat.c" dir="subsystems/ahrs"/>
<file name="ahrs_int_cmpl_quat_wrapper.c" dir="subsystems/ahrs"/>
<raw>
ifdef SECONDARY_AHRS
ifneq (,$(findstring $(SECONDARY_AHRS), icq int_cmpl_quat))
# this is the secondary AHRS
$(TARGET).CFLAGS += -DAHRS_SECONDARY_TYPE_H=\"subsystems/ahrs/ahrs_int_cmpl_quat_wrapper.h\"
$(TARGET).CFLAGS += -DSECONDARY_AHRS=ahrs_icq
else
# this is the primary AHRS
$(TARGET).CFLAGS += -DAHRS_TYPE_H=\"subsystems/ahrs/ahrs_int_cmpl_quat_wrapper.h\"
$(TARGET).CFLAGS += -DPRIMARY_AHRS=ahrs_icq
endif
else
# plain old single AHRS usage
$(TARGET).CFLAGS += -DAHRS_TYPE_H=\"subsystems/ahrs/ahrs_int_cmpl_quat_wrapper.h\"
endif
</raw>
</makefile>
</module>