Using Arduino to Obtain Absolute Orientation from a 6-Axis Gyro

[Leo Liu]

The gyro has 6 inertial axes and 3 magnetic axes. How do I make them work together to get the orientation of the rocket in the reference fixed to the ground? I found something from Matlab but I am not sure how it works: https://www.mathworks.com/help/fusi...sing-Inertial-Sensor-Fusion-and-MPU-9250.html. Also it doesn't suit my purpose since I would like to compute the absolute orientation in real time on the Arduino.

Could someone help me out please?

PS My end goal is to build a model rocket with attitude control, but for now I just want to record orientations and accelerations. I will be using Arduino for my project.

PS2 I realized the real question is how to obtain the absolute orientation from the gyro angular speeds.

 

[Baluncore]

There are three perpendicular accelerometers.
There are three perpendicular rotation rate-meters.
There are three perpendicular magnetometers.

Start with the rocket vertical, and with a reference to North.
Use the accelerometers to find the vertical axis. Measure g.
Use the magnetometers to find local magnetic field orientation.
Record the zero values for the three rotation-rate channels.

Launch the rocket.
Measure 3D acceleration, and 3D rotation.
Integrate those to map the changing orientation and path of the rocket.
Check the computed orientation against the local magnetic field orientation.

 

[Lnewqban]

What method of control will you use?
Servos combined with thrust vectoring or fin angling?

 

[Leo Liu]

Integrate those to map the changing orientation and path of the rocket.

Does integrating the body rates give the true orientation? How do I convert body rates to angular speeds under an inertial frame?

 

[Leo Liu]

What method of control will you use?
Servos combined with thrust vectoring or fin angling?

Haven’t decided yet. Most likely TVC without fins. But for now I just want to record data during a flight.

 

[FactChecker]

Does integrating the body rates give the true orientation? How do I convert body rates to angular speeds under an inertial frame?

No, there is a lot more to it. You can use the MATLAB link that you included or make your own code.
The MATLAB code might even adjust for a rotating Earth and Coriolus force, but that is not needed in a short-range rocket. On the other hand, it might not keep track of rotations of the rocket around its long axis if it is assuming that the rocket is asymmetric in that axis and a rotation does not matter.

 

[Leo Liu]

No, there is a lot more to it. You can use the MATLAB link that you included or make your own code.
The MATLAB code might even adjust for a rotating Earth and Coriolus force, but that is not needed in a short-range rocket. On the other hand, it might not keep track of rotations of the rocket around its long axis if it is assuming that the rocket is asymmetric in that axis and a rotation does not matter.

My IMU module is actually able to do a sensor fuse though all the calculations are done in a black box. I have made this post to understand what's going on behind the scene, but I guess I will just use that for now. Thanks for the help.

 

[FactChecker]

My IMU module is actually able to do a sensor fuse though all the calculations are done in a black box. I have made this post to understand what's going on behind the scene, but I guess I will just use that for now. Thanks for the help.

The actual sensor fusion and inertial reference calculations of a purchased IMU are likely to be proprietary. That being said, if you are interested in calculations of that general nature, MATLAB usually does a pretty good job of documenting their algorithms.

 

[Baluncore]

The mass and the moment of inertia about different axes will change during flight, as fuel is consumed. That does not change the integration of the accelerations and rates, to get the position and orientation, but it will change the dynamics of the control response, needed to correct the flight path.