Machines & motion

One part rotating relative to another: pins, hinges, ball joints and couplings.

• Print-in-place pin joint: born already articulated
• Assembled pin joint with clevis: separate lugs and pin
• Living hinge: a thin wall that flexes
• Knuckle hinge (piano and barrel): interleaved knuckles on a shared pin
• Print-in-place captive hinge: born articulated off the printer
• Concealed cabinet hinge: the cup hinge hidden in furniture
• Friction hinge: holds at any angle
• Detent hinge: holding at defined angles
• Spring-return hinge: the hinge that closes itself
• Cross-axis flexure pivot: a pivot with no axle and no play
• Notch and cartwheel flexures: thinning down to make a pivot
• Ball joint: multi-axis articulation
• Universal joint (Cardan/Hooke): transmitting rotation between angled shafts
• CV joint: constant velocity through an angle
• Gooseneck: a ball-joint chain that holds its shape
• Embedded bushing and bearing: let the bearing spin, not the plastic
• Rolling-contact joint: surfaces that roll, no axle

Guides, slides and mechanisms that carry something in a straight line.

• Sliding dovetail: male and female trapezoidal rail
• Generic rail and carriage: T, slot, or tongue
• Rod and bushing (linear bearing): sliding on a smooth shaft
• Linear guide variants: V-groove, telescoping tubes, slides, and crossed rollers
• Parallel flexure stage: a linear guide with no contact or wear
• Sarrus linkage: rotation to straight translation without guides
• Scott-Russell linkage: exact straight line from a rotation
• Lead screw stage: turning rotation into linear motion, with force

The base of transmission: ratio, module and teeth.

• Spur gear: the foundation of it all
• Internal ring gear: teeth facing inward
• Planetary reducer: compact coaxial reduction
• Compound gear train: stages in series
• Mutilated gear: missing teeth to drive only part of a turn
• Worm drive: high reduction and self-locking
• Helical and herringbone gears: angled teeth, smooth and quiet
• The bevel family (straight, spiral, crown, hypoid): drive at 90 degrees
• Rack and pinion: rotation to linear and back
• Special gears: non-circular, cycloidal, harmonic, nutating, and differential

Carrying rotation at a distance with belts, chains and cables.

• Timing belt and pulley (GT2/HTD): backlash-free drive
• V-belt and round belt: friction drive
• Roller chain and sprocket: high torque over distance
• Capstan cable drive: smooth, backlash-free reduction
• Friction drive, Bowden, and block and tackle: three lesser-known flexible drives

Turning rotation into reciprocation or linear motion.

• Cam and follower: any motion law from a profile
• Crank-slider: turning rotation into reciprocation
• Eccentric drive: reciprocation from an offset center
• Acme and ball screws: rotation to linear, with force
• Trammel of Archimedes: drawing an ellipse
• Scotch yoke, quick-return, and special cams: the conversions crank-slider can't cover

Joining shafts, or connecting and disconnecting rotation.

• Rigid shaft coupling (sleeve or flange): joining aligned shafts
• Oldham coupling: correcting parallel misalignment
• Jaw (spider) coupling: torque through elastic inserts
• Dog clutch: engaging and disengaging rotation
• Flexible couplings and clutches: beam, bellows, cone, friction, centrifugal, and limiter

Turning continuous rotation into indexed steps.

• Geneva drive (Maltese cross): one step per turn
• Ratchet and pawl: one tooth per stroke, no backdrive
• Star wheel: the indexer cousin of the Geneva
• Escapement and cam indexer: clockwork and precision

Advance one way, lock the other.

• Wrap-spring clutch: grips or releases depending on direction
• Ratchet and pawl, no-back: forward yes, return no
• Self-locking worm: won't backdrive from the output
• Smooth one-way drive: sprag, roller-ramp, and cable clamp

Convert, guide or amplify motion by connecting bars.

• Four-bar linkage: the queen of motion chains
• Scissor and lazy tongs: a lot of extension from very little
• Toggle lever: huge force near the dead point
• Bell crank: turning force through 90 degrees
• Pantograph: scaling and copying paths
• Parallelogram linkage: keeping orientation while it moves
• Approximate straight-line motion: the four-bar family (Chebyshev, Watt, Hoeken, Roberts)
• Walking legs: Klann and Jansen linkages
• Special linkages: the exact straight line (Peaucellier, Hart) and spatial motion (Bennett, Bricard)

Combining several families: showcase pieces.

• Iris and aperture diaphragm
• Composite gadgets: spring box, secret box, combination lock, and more