Madgwick Algorithm With Magnetometer: Issues in True North Detection #495
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How are you calibrating the three sensors?
…On Fri, Dec 20, 2024 at 12:15 AM gafa7758 ***@***.***> wrote:
Hello,
I am currently calculating quaternions using the Madgwick algorithm with
magnetometer data. The calculation works well, as the quaternion values
change correctly when the sensor is rotated. I have verified the results
using a quaternion calculator and visualized them with a 3D cube model.
However, I am encountering an issue with the qz value (yaw/heading).
When the sensor is powered on while lying flat, with the magnetometer's
X-axis pointing north, the initial quaternion is (1, 0, 0, 0). If I power
off the sensor, rotate it 90 degrees about the Z-axis (so the
magnetometer's X-axis points west), and power it back on, the quaternion
remains (1, 0, 0, 0).
This behavior seems incorrect since the magnetometer readings have to
change after the rotation. I also tested rotating the sensor so that the
magnetometer's X-axis points south or east, but the quaternion still does
not change (still 1, 0, 0,0) when the program is restarted.
Could I have missed something that prevents the quaternion's Z-axis
rotation from updating properly, even after changing the sensor's position
and restarting the system (turning off the sensor, adjusting its position,
and turning it back on)?
Note: Restarting means turning off the sensor, adjusting its position, and
then powering it back on.
Thank you for your attention.
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First of all, I would like to thank you, for the respon Sir
So, the calibration I did is like that, do you think it’s correct or not? Here, I am using the 9DoF Razor IMU sensor from SparkFun to get raw data from each sensor, and it is done in real-time. Thank you |
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It looks like you're doing the right thing for the accel and gyro. Here,
when the sensor is flat and motionless, subtracting the average bias values
should give a good result. To check, you should see 0, 0, 1000 mg on the
accel and 0, 0, 0 dps on the gyro when the sensor is flat and motionless
after calibration to ~1% or so.
For the mag, this doesn't work
<https://duckduckgo.com/?q=poor+mans+magnetometer+calibration&t=brave&ia=web>.
You have to move the sensor in all three dimensions sampling every possible
orientation multiple times while collecting bias data. Generally, the mag
response surface will be non-spherical so ellipsoidal corrections (3 x 3
matrix) are needed for best results, but OK results can be achieved just by
recentering
<https://github.com/kriswiner/MPU6050/wiki/Simple-and-Effective-Magnetometer-Calibration>
the response surface on the origin (subtract the average of the three axes
like for the accel).
As a quick check for the mag, after calibration you should see that the
magnitude of the magnetic field is ~0.5 Gauss (Earth's average magnetic
field). Better is to find out the expected field in your location (use USGS
magnetic data or equivalent) and verify that the mag shows the expected
values on all three axes.
It really doesn't matter what sensor fusion algorithm you use if your
sensors are not properly calibrated. Once they are, I think you will find
the best results using the Mahony algorithm...
…On Fri, Dec 20, 2024 at 10:07 AM gafa7758 ***@***.***> wrote:
How are you calibrating the three sensors?
… <#m_7331028583157023171_>
On Fri, Dec 20, 2024 at 12:15 AM gafa7758 *@*.*> wrote: Hello, I am
currently calculating quaternions using the Madgwick algorithm with
magnetometer data. The calculation works well, as the quaternion values
change correctly when the sensor is rotated. I have verified the results
using a quaternion calculator and visualized them with a 3D cube model.
However, I am encountering an issue with the qz value (yaw/heading). When
the sensor is powered on while lying flat, with the magnetometer's X-axis
pointing north, the initial quaternion is (1, 0, 0, 0). If I power off the
sensor, rotate it 90 degrees about the Z-axis (so the magnetometer's X-axis
points west), and power it back on, the quaternion remains (1, 0, 0, 0).
This behavior seems incorrect since the magnetometer readings have to
change after the rotation. I also tested rotating the sensor so that the
magnetometer's X-axis points south or east, but the quaternion still does
not change (still 1, 0, 0,0) when the program is restarted. Could I have
missed something that prevents the quaternion's Z-axis rotation from
updating properly, even after changing the sensor's position and restarting
the system (turning off the sensor, adjusting its position, and turning it
back on)? Note: Restarting means turning off the sensor, adjusting its
position, and then powering it back on. Thank you for your attention. —
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First of all, I would like to thank you, for the respon Sir
For calibration, I used bias error correction for the gyroscope and soft
iron and hard iron calibration for the magnetometer. I did not calibrate
the accelerometer because I believe its values are already good enough.
Below are the equations I used in the code for calibration.
1.
Gyroscope Calibration
//Finding the total value with a certain number of samples.
avr_gyroX = avr_gyroX + gyroX;
avr_gyroY = avr_gyroY + gyroY;
avr_gyroZ = avr_gyroZ + gyroZ;
//Finding the offset value by dividing the total value by the total number of
//samples
offset_gyroX = avr_gyroX/sample;
offset_gyroY = avr_gyroY/sample;
offset_gyroZ = avr_gyroZ/sample;
Result:
Sample: 752
Average X: -227.23
Average Y: 825.67
Average Z: 825.24
Offset X: -0.30
Offset Y: 1.10
Offset Z: 1.10
Gyro X Calibrated: 0.03
Gyro Y Calibrated: -0.00
Gyro Z Calibrated: -0.03
2.
Magnetometer Calibration
//hard iron
offset_x = (max_magX + min_magX)/2;
offset_y = (max_magY + min_magY)/2;
offset_z = (max_magZ + min_magZ)/2;
//soft iron
avg_delta_x = (max_magX - min_magX)/2;
avg_delta_y = (max_magY - min_magY)/2;
avg_delta_z = (max_magZ - min_magZ)/2;
avg_delta = (avg_delta_x + avg_delta_y + avg_delta_z)/3;
//Scale
scale_x = avg_delta/avg_delta_x;
scale_y = avg_delta/avg_delta_y;
scale_z = avg_delta/avg_delta_z;
Result:
avg_delta: 46.44
Max X: 89.72 Min X: 6.30
Max Y: 41.71 Min Y: -42.46
Max Z: -63.17 Min Z: -174.19
Offset X: 48.01
Offset Y: -0.38
Offset Z: -118.68
Scale X: 1.11
Scale Y: 1.10
Scale Z: 0.84
3.
Example of accelerometer value that i think it's already proper value,
so i decide didn't calibrate it.
ax: -0.01, ay: 0.04, az: 0.97 g
ax: -0.02, ay: 0.03, az: 0.98 g
ax: 0.01, ay:0.04, az: 0.98 g
So, the calibration I did is like that, do you think it’s correct or not?
Here, I am using the 9DoF Razor IMU sensor from SparkFun to get raw data
from each sensor, and it is done in real-time.
I have also uploaded the code and a short video related to the simulation
that might help in understanding the issue I am facing. If you are willing
to visit it, you can open my GitHub link:
https://github.com/gafa7758/Quaternion_heading_issue.git
Thank you
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Hi Sir, thank you. My quaternion values are now changing correctly when I face the sensor towards the south, west, or east (it no longer stays at 1,0,0,0 continuously when program is first run) after you suggested using the Mahony algorithm. It is quite stable for flat positions and rotations around the Z-axis. However, when I make sequential changes to the pitch, roll, and yaw values, the values sometimes continue to change even after I stop moving the sensor. Additionally, could you provide me with references to learn more in-depth about the Mahony algorithm? I am using the algorithm from this code: https://github.com/PaulStoffregen/MahonyAHRS/blob/master/src/MahonyAHRS.cpp As for the magnetometer calibration, I have followed the steps described in the article you shared, and it matches what I have been doing. I have also tried recalibrating multiple times, but the result remains the same (the quaternion values always start at 1,0,0,0 when the program is first run). Is there any other way to calibrate the magnetometer? Thank you |
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Did you check the magnetometer output against the expected values for your
area as I suggested? In other words, how well (accurately) are your sensors
calibrated?
Then, what is the fusion rate you are using? Laggy behavior will occur with
slow MCU speeds...
…On Mon, Dec 23, 2024 at 3:33 AM gafa7758 ***@***.***> wrote:
Hi Sir, thank you. My quaternion values are now changing correctly when I
face the sensor towards the south, west, or east (it no longer stays at
1,0,0,0 continuously when program is first run) after you suggested using
the Mahony algorithm. It is quite stable for flat positions and rotations
around the Z-axis. However, when I make sequential changes to the pitch,
roll, and yaw values, the values sometimes continue to change even after I
stop moving the sensor. Additionally, could you provide me with references
to learn more in-depth about the Mahony algorithm? I am using the algorithm
from this code:
https://github.com/PaulStoffregen/MahonyAHRS/blob/master/src/MahonyAHRS.cpp
As for the magnetometer calibration, I have followed the steps described
in the article you shared, and it matches what I have been doing. I have
also tried recalibrating multiple times, but the result remains the same
(the quaternion values always start at 1,0,0,0 when the program is first
run). Is there any other way to calibrate the magnetometer? Thank you
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Hello,
I am currently calculating quaternions using the Madgwick algorithm with magnetometer data. The calculation works well, as the quaternion values change correctly when the sensor is rotated. I have verified the results using a quaternion calculator and visualized them with a 3D cube model.
However, I am encountering an issue with the qz value (yaw/heading).
When the sensor is powered on while lying flat, with the magnetometer's X-axis pointing north, the initial quaternion is (1, 0, 0, 0). If I power off the sensor, rotate it 90 degrees about the Z-axis (so the magnetometer's X-axis points west), and power it back on, the quaternion remains (1, 0, 0, 0).
This behavior seems incorrect since the magnetometer readings have to change after the rotation. I also tested rotating the sensor so that the magnetometer's X-axis points south or east, but the quaternion still does not change (still 1, 0, 0,0) when the program is restarted.
Could I have missed something that prevents the quaternion's Z-axis rotation from updating properly, even after changing the sensor's position and restarting the system (turning off the sensor, adjusting its position, and turning it back on)?
Note: Restarting means turning off the sensor, adjusting its position, and then powering it back on.
Thank you for your attention.
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