Engineering PLTW

What is a mechanism?

A machine component where motion of one part controls others; changes direction; speed; type of motion; or force/torque.

Simple Gear Train

Parallel shafts; meshed gears rotate oppositely; larger output gear = slower speed/higher torque. Ex: Watches; sewing machines.

Simple Gear Train with Idler

Idler gear aligns input/output direction; speed/torque constant (1:1 ratio). Ex: Paper transport rollers.

Bevel Gear

Transmits motion at 90° angle; constant speed/torque unless gear sizes differ. Ex: Hand drills; car differentials.

Worm and Wheel

Irreversible (wheel can't drive worm); reduces speed; boosts torque (24:1 ratio). Ex: Winches; tuners.

Lead Screw

Converts rotary to linear motion; amplifies force (Ex: Car jack); non-reversible power flow.

Rack and Pinion

Converts rotary to linear motion; larger pinion increases rack travel. Ex: Car steering systems.

Chain Drive

Transfers power over long distances; smaller drive gear = slower speed/higher torque. Ex: Bicycles.

Belt Drive

Quieter/cheaper than chains; open belt (same direction) or crossed belt (opposite). Ex: Car engines.

Crank and Slider

Converts rotary to reciprocating motion; longer crank increases slider distance. Ex: Engines.

Cam and Follower

Converts rotary to reciprocating motion via cam shape; symmetrical cams are reversible. Ex: Camshafts.