Meccano Animatronic updated to use one carriage drive motor instead of two. 

My Meccano Animatronic video (studio.youtube...) had two carriages one on top of the other which slid out when it was operated using two motors and two threaded rods. This video shows how by just driving the top slide and fastening it to the bottom one on the out stroke, only one motor and piece of studding are needed. Control would be easiest using a micro-controller, but here it is achieved with discrete components, although it is possible the circuit could be simplified.