Carriage 1 with wheels 7 rolls along fixed rails 2. Two identical pulleys 3 and 4 rotate about axes F and E of carriage 1. Flexible links 5 and 6, attached with their ends at fixed points A, D, B and C, run crosswise over pulleys 3 and 4. When either pulley 3 or 4 is rotated, carriage 1 travels along rails 2.
$3539$CFL,ML$