# Rotary Motion A Pulley Mechanism uses rotary motion to transmit rotary motion between two parallel shafts.

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Rotary Motion A Pulley Mechanism uses rotary motion to transmit rotary motion between two parallel shafts.

Mechanisms using Rotary Motion

Pulley mechanisms can be used to increase or decrease rotary velocity

Velocity Ratio Velocity Ratio = Velocity Ratio = Velocity Ratio =
Distance moved by Effort Velocity Ratio = Distance moved by Load Distance moved by the driver pulley Velocity Ratio = Distance moved by the driven pulley Diameter of Driven Pulley Velocity Ratio = Diameter of Driver Pulley

Velocity Ratio Pulley Shaft Rotary Velocities can be calculated using the following formula rotary velocity of driven pulley x diameter of driven pulley = rotary velocity of driver pulley x diameter of driver pulley rotary velocity of driver pulley x diameter of driver pulley rotary velocity of driven pulley = diameter of driven pulley

What is the rotary velocity of the driven pulley shaft?
rotary velocity of driver pulley x diameter of driver pulley rotary velocity of driven pulley = diameter of driven pulley 450 x 30 = revs/min 90 = revs/min

Pulleys and Belts Vee pulley and section through a vee pulley and belt
A section through a grooved pulley and round belt Stepped cone pulleys provide a range of shaft speeds

Flat belts and pulleys A section through a flat pulley and belt
Jockey pulley in use Flat belt in use on a threshing machine

Bicycle chain and sprockets
Chains and sprockets Bicycle chain and sprockets Graphical symbols

Velocity Ratio = = = number of teeth on the driven sprocket
number of teeth on the driver sprocket 12 = 36 = 1 : 3

Example

Pulleys and Lifting Devices
The pulley is a form of Class 1 lever

Movable single pulley

Distance moved by Effort
Pulleys Distance moved by Effort Velocity Ratio = Distance moved by Load Velocity Ratio = the number of rope sections that support the load

Distance moved by Effort
Two Pulley System Distance moved by Effort Velocity Ratio = Distance moved by Load 2x Velocity Ratio = x Velocity Ratio = 2:1

Distance moved by Effort
Four Pulley System Distance moved by Effort Velocity Ratio = Distance moved by Load 4x Velocity Ratio = x Velocity Ratio = 4:1

Cams Rotary Cam Linear Cam Barrel or Cylindrical Cam

Cams More complex cams Box cam Swash cam

Pear shaped cams are used in valve control mechanisms
Uses Pear shaped cams are used in valve control mechanisms

Cams used in a four cylinder engine

Cam motions Rotary to reciprocating / oscillating Not other way round

Types of cam follower Point Sliding and oscillating Roller Angled foot

Types of cam follower Flat Knife Edge Sliding yoke

Springs are used to keep the follower in contact with the cam

Cam Profiles Pear shaped Circular Heart shaped
Uniform acceleration and retardation cam

Displacement graph for a pear shaped cam
Very common cam Long rest (dwell) period Quick rise and fall

Displacement Graphs Desired displacements can be used to construct cams

Bearings Flat bearings consist of two or more sliding flat surfaces
Journal Bearing is a bearing that supports a cylindrical shaft

Nylon bush Bronze washer - alloy of copper and tin commonly used type contain phosphorous known as phosphor-bronze hard but softer than steel

Bearings

Bearings Bronze Nylon PTFE Air White metal Cast Iron Sintered
Bronze - alloy of copper and tin commonly used type contain phosphorous known as phosphor-bronze Nylon plastic cheep to produce quiet running PTFE Polytetrafluoro-ethane coating resistance to high temperatures hard – good friction qualities Air Air pressure is sometimes used to support a moving part hovercraft vacuum cleaner lawn mower White Metal tin alloy with copper and antimony it is soft and will adapt to the shape of the shaft if the bearing over heats the metal melts and runs leaving the shaft undamaged and gives a warning of what has happened Cast iron forms a flat sliding surface high graphite content no other metal will run on itself Sintered made from oil soaked powder of copper, tin and graphite that are pressed together (in shape) when hot

Gears Drawing gears- note the spline

Gears Gears are not only used to transmit motion.
They are also used to transmit force.

Gears Mechanical Advantage = Velocity Ratio = Gear Ratio =
Number of teeth on the driven gear Mechanical Advantage = Number of teeth on the driver gear Number of teeth on the driven gear Velocity Ratio = Gear Ratio = Number of teeth on the driver gear

Gears Guess the ratio. How many turns of the driver = a turn of the driven? Try different idlers

Gears Gear Ratio = Product of teeth on the driven gears
Calculate ratio Product of teeth on the driven gears Gear Ratio = Product of teeth on the driver gears

Gears Spur gear- straight cut Parallel Helical Double helical

Gears Face cut Bevel gears Spiral bevel

Gears Crossed helical Worm and wormwheel Rack and pinion

Gears Internal Differential

Basic Gear Geometry

The inclined plane

The inclined plane

The inclined plane M.A. = 1000/10 = 100
Effort required to pull trolley up slope F = effort E F = 1000 x sin F = 1000 x 0.01 F = 10N E = 10N sin = 1/100 = 0.01 M.A. = 1000/10 = 100 Follow link to see effects of steeper incline:

B.S. PD7308

Newton’s Laws First Law
A body continues in its state of rest or uniform motion in a straight line unless compelled by some external forces to change that state. (sometimes know as the law of inertia)

Newton’s Laws Second Law
Rate of change of momentum is proportional to the applied force and takes place in the direction in which the force acts. (Continued force means continued acceleration)

Newton’s Laws Third Law
To every action there is an equal and opposite reaction

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