Abstract: A drive mechanism of the type having a first pulley, a second pulley, and an endless flexible drive member extending therebetween for transmitting motion from the first pulley to the second pulley wherein at least one of the pulleys is a variable ratio pulley assembly. The variable ratio pulley assembly includes a planar and includes at least one circular row of apertures through the disk. At least one fixed magnet is affixed to the planar disk wherein the polar orientation of the fixed magnet is substantially transverse to the planar disk. A plurality of drive segments are positioned in the row of apertures and forms at least one circular row of drive segments wherein each of the segments is selectably translatable between a retracted position and an engaged position.