Abstract: The invention provides a motion transfer mechanism for transferring motion between a first and second component, the mechanism comprising an elongate track mounted to the first component, the track having a polar axis and an external actuation surface along a portion of the length of the track, the track having at least one portion of the actuation surface inclined at a predetermined spiral angle about the polar axis; track riding device, mounted to the second component in guided contacting relation with the actuation surface, for longitudinal displacement relative to the actuation surface, and for predetermined rotational displacement in response to the longitudinal displacement, the track riding device comprising: an actuating surface follower mounted within a rider housing; and biasing device disposed between the follower and the housing for resiliently urging the follower into continuous engagement with the actuation surface; track mounting device for mounting the track to the first component in predeterm