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. \n
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
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Number of teeth on the driven pulley
Velocity = -------------------------------------------------------------
Number of teeth on the driver pulley
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