Mechanical Devices

• Mechanical movement


  The way a structure moves to create movement
• Types of mechanical movement

  • Linear motion
  • Rotary motion
  • Reciprocating motion
  • Oscillating motion
• Linear motion


  • Movement in a straight line in one direction
  • A train uses linear motion to move along a track
• Rotary motion


  • Rotary movement follows a circular path around a centre point
  • Such as a bicycle wheel
• Reciprocating motion


  • Movement of in/out, up/down or left/right
  • Found in a car engines piston
• Oscillating motion


  • Motion of left to right (or backwards) from a single point
  • Found in a grandfather clocks pendulum
• Lever


  Used to lift loads with the least amount of effort
• Classes of levers


  • First order (Class one)
  • Second order (Class 2)
  • Third order (Class 3)
• First order (Class one) lever


  • The fulcrum is placed centrally between the force and the load
  • Such as a pair of pliers or a crow bar
• Second order (Class 2) lever


  • The effort comes first, then the load at the same side of the fulcrum
  • Such as a wheelbarrow, where the wheel is the fulcrum
• Third order (Class 3) lever


  • The load is first, effort in the centre and fulcrum at the end
  • Examples include tweezers, mouse traps and a hammer hammering a nail
• Linkage


  A mechanism which creates movement around a fixed pivot
• Types of linkages


  • Reverse motion linkage
  • Parallel motion linkage
  • Bell crank linkage
• Reverse motion linkage


  • The pivot is fixed in the centre of a Z shape, when moved the top moves in the opposite direction to the bottom
• Parallel motion linkage


  • Two fixed pivot points vertically make the horizontal movement parallel
• Bell crank linkage


  • Looks like an L shape with a pivot point in the corner, horizontal force changes into vertical movement
• Rotary system


  Uses circular movement to move and create power
• Components of rotary systems

  • Cams
  • Gears
  • Pulleys
  • Belt drives
• Cams


  • A cam and a follower create movement, the follower rests on the cam and moves in the shape of the cam
  • Circular cams rely on the centre of the circle being offset, a pear cam creates a gentle rise and fall as the follower flows the pear shape
• Gears


  • Wheels which interlock to move the force, different sized gears increase and decrease the speed they turn
  • Power turned the driver gear clockwise which turns the next gear anticlockwise, if you add a centre gear (called and idler) it turns the gears on either side in the same direction
  • If gears are different sizes the smaller gears turn faster
• Pulleys


  • Can help lift a load by transferring the weight through a wheel, a single pulley makes something easier to move by pulling down rather than up, using 2 pulleys can lift a weight using half the effort
• Belt drives


  • Belts can transfer movement from one rotating shaft to another, working like gears a smaller wheel spins faster when attached to a bigger wheel, this is used in washing machines