This was a model aircraft connected to the ground by a universal joint. The tube, second mirror box, and universal joint survived. Lindberg's compass used an anemometer to spin the armature through a universal joint. In 1841, the English scientist Robert Willis analyzed the motion of the universal joint. One anticipation of the universal joint was its use by the ancient Greeks on ballistae. Power is transferred by an enclosed splined driveshaft with one universal joint. Suddenly the pink lights of "The Universal Joint," a bar, come on. The top link is the driving half-shaft with a universal joint at each end. Hitches for two-wheel trailers must incorporate some form of universal joint or flexible coupling. Kyosho changed the part numbering of BS20 universal joint to IFW62 in the later references. This universal joint mechanism was later called a scioptric ball. The universal joint is not a constant-velocity joint. More powerful engines and higher speeds required a mechanical universal joint. Alternative mechanics to the stationary (outer) swashplate are the hexapod and the universal joint. The outer universal joint allows greater angular changes but not changes in shaft length.