AQA GCSE Product Design: 1.5 - Mechanical Devices
Mechanical Devices:
Types of Movement:
- Linear - * Forward
- Reciprocating - * Up and down movement
- Rotary - * In a circle
- Oscillating - * Side to side
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Levers:
- Mechanism - * A device that changes an input motion into a different output motion.
- Lever - * A mechanism that moves around a fixed point (pivot) * The oldest type of mechanism * Changes an input movement and force (effort) into an output movement and force (load)
- Load - * The object that needs to be moved
- Effort - * Force applied to move the load
- Fulcrum - * The point at which the load is pivoted
- 3 classes of levers - * Class 1: L-F-E * Class 2: F-L-E * Class 3: L-E-F
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Linkages:
A linkage is used to transfer force and can change the direction and movement. They are an assembly of levers. 
Cams:
A cam mechanism has 3 parts: a cam, a slide and a follower. A cam mechanism can either go up, go down or stay still.
- Torque - * The turning force that causes rotation
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Gears:
Number of teeth on the driven gear
Velocity = -----------------------------------------------------------
Number of teeth on the driver gear
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- Friction - * Can cause thermal energy * Usually a problem that needs to be resolved * Breaking systems and pulley systems need high coefficients of friction
- Coefficiency * How resistant a material is
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Gear Trains:
Rack and Pinion Mechanism:
- Pinion = circular gear
- Rack= long gear
- Linear motion
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Crank and Slider Mechanism:
- Rotary motion to linear motion
- Used in pistons in car engines.
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Chain and Sprocket Mechanism:
- Rotary motion to rotary motion
- Used in bike chains
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\ Number of teeth on the driven sprocket
Velocity = ------------------------------------------------------------------
Number of teeth on the driver sprocket
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Pulleys and Belts:
- Pulley Systems - * Rotary to rotary motion
\ Number of teeth on the driven pulley
Velocity = -------------------------------------------------------------
Number of teeth on the driver pulley