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Design & Technology

Mechanisms

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Types of motion

There are four basic types of motion in mechanical systems:

  • Rotary motion is turning round in a circle, such as a wheel turning.
  • Linear motion is moving in a straight line, such as on a paper trimmer.
  • Reciprocating motion is moving backwards and forwards in a straight line, as in cutting with a saw.
  • Oscillating motion is swinging from side to side, like a pendulum in a clock.

Many mechanisms take one type of input motion, and output it as a different type of motion. Below are some examples.

Chain and sprocket

A chain and sprocket changes rotary motion to linear motion - or vice versa. A wheel-and-axle, rack-and-pinion, rope-and-pulley, screw thread, or chain-and-sprocket could also be used for this.

Cam-and-follower

A cam-and-follower changes rotary motion to reciprocating motion. A crank, link and slider or rack-and-pinion could also be used for this.

Peg-and-slot

A peg-and-slot changes oscillating motion to rotary motion. A crank, link and slider could be used for this, and also to change rotary to oscillating motion.

Crank, link and slider

4. A crank, link and slider will change rotary motion to oscillating / reciprocating motion.

Rack-and-pinion

A rack-and-pinion changes rotary motion to reciprocating motion. A crank, link and slider could also be used for this. A cam-and-follower will change reciprocating to rotary motion.

Mechanical systems and sub-systems

Small systems can be combined to make more complex systems. A cam which is turned by an electric motor can operate a micro switch which could be used to turn a light on or off. Two mechanical systems can be connected together to give complex movements.

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