Making The Reciprocating Rack & Pinion

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.
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