Pulley and slotted wheel for opto sensor fits onto output gear on surplus 12V 4 RPM gearmotor for car vent louver. This motor was previously sold by AllElectronics.com and on Amazon as http://www.amazon.com/12VDC-designed-operate-Chrysler-product/dp/B003XKVNUA/ref=pd_sxp_f_ptA version of the pulley to fit a 1/2" Sch.40 PVC pipe, and standoffs for the motor's three mounting holes, are also included, with OpenSCAD files provided. Works with opto-sensor bracket here: https://youmagine.com/designs/opb917-optosensor-bracketYou can see it in motion here: https://www.youtube.com/watch?v=OWIdMYjCm1M