Double Rack and Sector Pinion

This is a demonstration of a mechanical setup consisting of a double-rack plate surrounding a sector pinion. Rotation of the center pinion causes alternating linear motion of the rack.

Note that this is not reversible: driving the rack with alternating linear motion will not reliably drive the pinion, as there is a small amount of clearance in the middle of each rotation of the pinion where it is engaged with neither rack.

The setup can be optionally driven by a small hobby gearmotor, available for about $3.25 each on Amazon or about $1.70 each including shipping from AliExpress. They're advertised as Car or Robot motors, and have standard dimensions. This GrabCad Model has proved accurate.

Other hardware needed for assembly includes:

• 6 @ m3 x 5mm knurled insert nuts
• 2 @ m3 x 3mm knurled insert nuts (optional)
• 2 @ m3 x 22mm or 25mm Bolt (I used hex-socket bolts, cap head would also be fine).
• 4 @ m3 x 6mm Crown head machine screws
• Two small pieces of wire for motor
• Single AA Battery Holder
• Switch (optional)

Both the gear and the rack have a module of 3mm. The pinion has 6 teeth of a 20-tooth gear.

The largest single piece (the racks) fits within a 200mm x 200mm build place easily.