Quaterion Creation In Simulink

Hello,

I am just starting to work with quaterions and I am currently confused as to how they are defined in Simulink. From what I have read so far are have a basic understanding of how they can be used to define rotations in 3D space. I understand the mathmatical form of a+bi+cj+dk, I just don't undestand how they are inplemented in matlab.

I would like to define a quaternion by specifing an axis + angle and then building the quaternion. I assumed that it would be as simple as using a mux block with the angle first and then the three elements of the vector. However this does not seam to be the case.

I ran this test and it does not show the same results.

Can anyone help explain where I went wrong. Or help explain the following deffintion from the doc page.

"Quaternions in the form of [q0, r0, ..., q1, r1, ... , q2, r2, ... , q3, r3, ...],"

Thanks

Answer 1

[James Tursa]

See these posts for discussions of the MATLAB quaternion convention:

https://www.mathworks.com/matlabcentral/answers/352465-what-is-the-aerospace-blockset-quaternion-convention

https://www.mathworks.com/matlabcentral/answers/465053-rotation-order-of-quatrotate

If they don't answer your questions then feel free to post some follow-up questions here in this thread.

[James Mulhern]

Your referneces did help to expain my issues. I would also like to point out that my creation of the quaternion was incorrect becasue it is not normalized to 1. The quaternions should take the form

[James Tursa]

I presume you meant Y * S in the 3rd spot instead of Y * X.

[James Mulhern]

Good catch. I updated it.