If we assume that the robot is only affected by gravity so that the
fx, fy, fz base on world coordinates is
0, 0, ~9.8m/s^2.
We also know the
fx, fy, fz of robot coordinates which is returned from the accelerometer. Based on these we can calculate the angles difference between robot coordinates and the world coordinates.
As an example you can try this BalanceSkill.
However, it’s our problem that the description of
ax, ay, az is not clear enough to understand, we will try to find a way to clarify it and update the documentation soon.
Thanks for your feedback!