How I built the Reciprocating Rack & Pinion mechanism. Prototype model, layout, timing, a failed motor application, modification of a Roomba drive motor using a lathe turned drum attachment.Usually the pinion is stationary and the double rack section moves back and forth and would be connect at one end or at both ends like a connection rod. In the case of my model a connecting rod could be connected to the pinion axle. Either way, the mechanism delivers straight-line push and pull.Also see the video: "Reciprocating Rack & Pinion" http://youtu.be/ScB6Wd4r9Jc