The Technological World

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The Technological World

• The Amazing World of Gears

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Gear Theory

• What is the purpose of gears?
• To increase torque and decrease speed
• To increase speed and decrease torque
• To change the direction of rotation by 90
• To reverse the direction of rotation

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Gear Theory

• Regardless of what you do you will only ever have
  two main types of gears
• Driving Gears and Driven Gears
• Driving Gears are connected directly to the power
  source and transfer the power to the Driven
  Gears.
• Driven Gears are in contact with the Driving
  Gears and either increase the torque or increase
  the speed.

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Principles of Gearing

• When a small gear drives a large gear you are
  said to have a gear reduction. Where the driving
  gear would turn several times for only one turn
  of the driven gear.
• When a large gear drives a small gear you are
  said to have an overdrive. Where the driving gear
  would turn only once and the driven gear would
  turn several times..

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Principles of Gearing

• When two gears of the exact same size are in
  contact, it is said to be direct drive. Where
  there is neither a torque increase nor a speed
  increase. An example of this would be the top
  gear of a transmission before they had overdrive!

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Principles of Gearing

• If you have an even number of gears in contact,
  regardless of their size, the last gear will
  always turn in the opposite direction of the
  first gear in the set.
• Example If the top gear drives the bottom gear,
  the bottom gear will rotate
• in the opposite direction!

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Principles of Gearing

• If you have an odd number of gears in contact,
  regardless of their size, the last gear in the
  set will always rotate in the same direction as
  the first gear in the set.
• Example If the first gear rotates clockwise
  every odd numbered gear must also rotate
  clockwise.

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How to determine Gear Ratio

• To calculate gear ratio you must always use the
  following formula
• Number of Teeth on the Driver Gear divided by the
  Number of Teeth on the Driven Gear.
• Example 1 If the driven gear has 8 teeth and the
  driving gear has 41 teeth, the ratio is said to
  be 5.131
• 41 8 5.13

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How Gear Ratio Affects Output

• If a gear ratio has a number numerically larger
  than 1 at the front of the ratio, you have a gear
  reduction. Example 4 1
• A gear reduction means that the speed of the
  output gear is ? times slower than the input
  gear.
• At the same time a gear reduction means that the
  output torque will be increase by X times over
  the input torque.

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• If a gear ratio has a number numerically smaller
  than 1 at the front of the ratio, you have an
  overdrive. Example 0.75 1
• An overdrive means that the output gear will be
  turning X times faster than the input gear.
• An overdrive means that the output torque will be
  X times smaller than the input torque.

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• If both input and output gears, driven and
  driving, are the exact same size then there is no
  advantage. There will be neither a speed increase
  nor a torque increase. There would simply be a
  direct transfer of power.

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Review

• To recap
• Torque is inversely proportional to Speed
• When there is a Torque Increase there is a Speed
  Decrease of the Same Amount.
• When there is a Speed Increase there is a Torque
  Decrease of the Same Amount.