Abstract: An energy transfer device includes a rotatable driveshaft supported within a cylinder and including first and second pistons slidably mounted within the cylinder. The driveshaft has first and second generally helical tracks formed thereupon and extending in opposite rotational directions about the driveshaft. First and second ratcheted cam clutches are coupled to the first and second pistons, respectively, and engage the first and second tracks within the driveshaft for converting reciprocating sliding motion of the first and second pistons into rotational motion of the driveshaft. The first and second pistons may be reciprocated by a valving mechanism which alternately admits pressurized fluid to one end portion of the cylinder while exhausting fluid from the opposite end portion thereof. The first and second pistons may also be reciprocated by magnetizing the first and second pistons and surrounding the cylinder by an alternating electromagnetic field.