Hi Mats,
According to IMU Location the CG input is to be provided in a coordinate frame that is fixed to the body. However, the IMU Location parameter and CG input are NOT defined in the same body-fixed axes in which the Ab and omega and omega_dot inputs are defined. According to Algorithms "The orientation of the axes used to determine the location of the accelerometer group (xacc, yacc, zacc) and center of gravity (xCG, yCG, zCG) is from the zero datum (typically the nose) to aft, to the right of the vertical centerline and above the horizontal centerline. The x-axis and z-axis of these measurement axes are opposite the body-fixed axes that produce the negative signs in the lever arms for the x-axis and z-axis." (emphasis added).
Strongly suggest developing some basic test cases for stimulating the IMU model where you know what the output should be to make sure you get all of the inputs defined correctly.
I suspect that CG is defined as an external input for applications where the CG location changes over time (relative to a fixed point on the body), such as a solid rocket burning fuel.
Looking at your diagram, I was quite surprised to see those derivative blocks on velocities to form accelerations as opposed to the accelerations being output from the 6DOF block. According to Version History, the omeg_dot and A_be outputs were removed from that block in 2025a. That seems like a very peculiar decision and I'm quite curious as to why it was made.
