Abstract: A determinate positioner assembly comprises a helical cam, such as a threaded lead screw, a follower element which continuously contacts the lead screw in a predetermined number of places for a determinate condition (neither over- nor underconstrained), an elastic member connecting the follower element to the leadscrew, and a driven element. The elastic member maintains continuous contact between the follower element and the cam, yet the combination of the elastic member and the follower element exert substantially zero net force on the cam in the x and y directions. The follower element is attached to the driven element with pivot structures which transmit axial movement from the follower element to the driven element and permit the follower element to “float” in the x and y directions while prohibiting its rotation about the x, y and z axes.