the prototypes used to design the controller's electrical systems used a so-called "yoke and gimbal" taken from a radio control system used to fly model airplanes. this simple design gave very nice control and was highly reliable. the actual controllers sold with the game were quite different and a great disappointment to the development teams. the design of the analog joystick, which used a weak rubber boot rather than springs to center the stick, caused many joysticks to have no ability to center. another major flaw of the controllers was that the design did not provide smooth control through the travel of the stick. this made controlling games awkward. the controllers did, however, include a pause button. this was a novelty at the time, but would become standard on almost all future game systems. replacement joysticks were also released by other manufacturers.