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. Various third-party replacement joysticks were also released, including those made by Wico.