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Four-bar linkage

Crank, coupler and rocker on two ground pivots: the crank turns fully while the rocker swings. Drag any pin.

Slider-crank

A crank and connecting rod drive a piston along a ground axis; the stroke is twice the crank radius.

Gear pair

Two spur gears meshed by their centre distance m(z1+z2)/2: the small gear turns twice as fast the other way.

Gear train and rack

The driver turns an idler, the idler turns a pinion, and the pinion drives a rack that runs on a guide rail below it: the idler keeps the pinion turning the same way as the driver.

Belt drive

An open belt runs in the grooves of an 80 mm driver pulley and a 40 mm driven pulley: the driven pulley turns twice as fast (a 2:1 speed-up) the same way; crossing the belt reverses it.

Chain drive

A roller chain on a 17-tooth driver sprocket and a 34-tooth driven sprocket: the rollers seat in the tooth gaps, so the driven shaft turns at exactly half speed the same way, with no slip.

Planetary gear

A sun gear held still, a planet riding on an arm: the mesh is measured against the arm (the carrier), so the planet turns (1 + zs/zp) times per arm turn.

Scotch yoke

The crank pin slides in the slot of a yoke that runs on guides, so the yoke moves in pure simple harmonic motion x = r cos θ.

Quick-return (slotted lever)

A crank pin slides in a lever pivoted below the crank; the lever works a ram whose forward stroke takes longer than its return.

Cam and follower

A disk cam lifts a roller follower whose stem runs in a guide: the roller rides the cam's edge through a cycloidal rise, a dwell on the nose, a cycloidal return and a long dwell on the base circle.

Ratchet and pawl

A spring-loaded pawl rides over the teeth one way and catches them the other. Dynamic: set the wheel drive positive and the pawl locks it.

Toggle clamp

A handle crank drives a clamp arm through a short link; where handle and link line up the arm locks with a huge mechanical advantage.

Scissor lift

Three X stages of crossed bars: a crank pushes the sliding foot and the platform rises and falls several times as far.

Pantograph

A parallelogram of bars copies the tracer's path at twice the size: the pen always sits on the line from the pivot through the tracer.

Chebyshev walker

Two Chebyshev lambda legs (ground 2, crank 1, coupler and rocker 2.5, foot at twice the coupler) on one crank, half a turn apart: each foot runs flat along the ground.

Peaucellier straight line

The Peaucellier–Lipkin inversor turns the arc of the input arm into an exact straight line; a small crank rocks the arm.

Watt's linkage

Two equal rockers pivoted on opposite sides and a short coupler: the coupler midpoint moves on a nearly straight line. A small crank rocks the left rocker.

Stephenson six-bar

A crank-rocker four-bar whose ternary coupler drives a second rocker through a dyad: two ternary links that never touch (Stephenson type).

Geneva drive

A pin on the turning driver indexes a four-slot wheel a quarter turn per revolution; the locking disc holds it still in between. Dynamic.

Cam indexer

A stepped cam program pushes a slide forward in two equal steps with dwells between them, then returns it: indexing from a steadily turning shaft.

Oldham coupling

Two parallel but offset shafts turn together: the centre disc slides in a slot of each hub, the two slots at right angles.