Systems for facilitating conversion between reciprocating linear motion and rotational motion include a continuous undulating track circumscribing a circular profile and generally defining a cylindrical volume having a central axis; a reciprocator that is configured to linearly reciprocate along the central axis; a converter coupled to the reciprocator to reciprocate with it, configured to rotate about the central axis, and engaged with the undulating track; and a rotator engaged with the converter and configured to rotate about the central axis with the converter but not to linearly reciprocate along the central axis.