On the rudder and elevator the arm does not go 90 degrees to the servo. It goes 90 degrees to the direction the cables go. The cables go at a angle before they go into the fuselage. Your servo arm needs to be 90 degrees to that angle. Another way of putting it, say you servo arm has 40 arms on it all at 90 degrees. With the pull pull cables attached to opposite arms, the other arms need to be pointing the same direction as the cables. I built mine and I made the arms perpendicular to the servo and I could not get full throw in one direction.