Its basically just tube with a rod running down the middle.
When the moment is applied at the bottom depending how much reaction to the moment means the out tube will rotate or the inner rod will rotate. One of them is attached to the control surface directly the other one is attached to the servo tab.
Thanks.
Its a slow !!!! hauler
That's subjective.
which is suited to rough short strips. Its pro's are more linked about how cheap it is and how robust it is.
That's important.