Paper mechatronics & automata, or "Paper Mech," encompass a variety of mechanical objects allowing directional motion to be translated into other movements. For example, rotating a crank produces a back-and-forth rocking motion that at first seems separate from the circular motion being used to create it. Automata can be hand powered or operated via motors. PaperMech exist at the intersection of paper, mechanical engineering, and electronics.

Some basic mechanisms include: rack & pinions, cranks, cams, spur gears, planetary gears, and jansen mechanisms. 

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Spur Gear

Spur gears transfer motion from one axis rod to a parallel rod or shaft. The teeth of the gears interlock. When one gear rotates, it causes the interlocking gear and shaft to rotate in the opposite direction.

This illustration of spur gear and pinion gear shows that the two gears rotate towards one another in opposite directions
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Diagram of a yellow pear shaped cam topped by a grey vertical follower sandwiched between blue slide guides. As the cam rotates, it causes the follower to rise and fall based on the profile of the cam.

Cam and Follower

A cam and follower mechanism converts rotary motion into reciprocal linear motion. The follower rises and falls as it comes into contact with different points on the rotating cam. It maintains contact with the cam through either the force of gravity or by a spring. The total range of the follower's movement produced by the cam is called the stroke. The motion of the follower is restricted to a pre-determined pattern by a guide and the specific shape of the cam. Pear, snail, and off-center circle cams are common cam shapes.

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Crank

A crank is an arm attached at a 90° angle to a rotating shaft. When the shaft rotates, the circular motion is translated from the arm into reciprocating motion (repetitive up-and-down or back-and-forth linear motion) of a connecting rod.

Diagram of a crank mechanism. One end of a connecting rod is attached to the circular crank by a pin. The other end is attached to the slider. As the crank rotates, the pin rotates which causes the connecting rod to push or pull the slider based on the location of the pin within the rotation.
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A large grey ring gear encloses three planetary gears rotating around a smaller sun gear. The three blue planetary gears are attached by a lime green carrier arm.

Planetary Gears

Planetary gears consist of multiple gears (planetary gears) attached to a carrier arm rotating around a central gear (sun gear). This structure is enclosed by a large ring gear. Planetary gears allow for faster speeds and greater lubricant retention.

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Rack and Pinion

The Rack and Pinion produces linear movement. Within the mechanism, a circular pinion gear engages the teeth of the linear rack. As the gear rotates, the rack travels up and down or side to side, depending on the orientation of the mechanism.

Diagram of a rack and pinion mechanism. The rack is a bar with teeth along one side. The gear's teeth interlock with the rack's teeth.