The controller prototypes used in the electrical development lab employed a yoke and gimbal mechanism that came from an RC airplane controller kit. The design of the analog joystick, which used a weak rubber boot rather than springs to provide centering, proved to be ungainly and unreliable. They quickly became the Achilles heel of the system because of their combination of an overly complex mechanical design with a very low-cost internal flex circuit system. Another major flaw of the controllers was that the design did not translate into a linear acceleration from the center through the arc of the stick travel. The controllers did, however, include a pause button, a unique feature at the time. Games were shipped with plastic card overlays that snapped in over the keypad. The card would indicate which game functions, such as changing the view or vehicle speed, were assigned to each key.
