A drive mechanism is provided for converting linear motion into a rotary motion. The drive mechanism includes a slider which is linearly movable in response to linear actuation. A rotatably mounted helical member is connected to the slider such that linear movement of the slider causes rotation of the helical member. A clutch may be connected to one end of the helical member and surrounded by a pinion gear. The clutch is arranged so that, when the helical member rotates in a first rotary direction, the clutch drives the pinion gear in the same rotational direction. However, when the helical member rotates in an opposite direction, the clutch disengages the rotation of the helical member from the pinion gear. The pinion gear thus "free-wheels" or idles with respect to the helical member. The pinion gear meshes with a rotatable output mechanism which can be connected to any device which is to be driven by the resulting rotary motion. Actuation of the slider in a first linear direction causes rotation of the output mechanism in a corresponding direction. However, when the slider is actuated in the direction opposite to the first linear direction, the clutch disengages the resulting rotary motion of the helical member from the pinion gear. Two or more such drive mechanisms may be combined to provide an overall combination of drive mechanisms. Also, the drive mechanism may be modified to provide unidirectional rotation in response to bidirectional linear actuation of the slider.