gear

''A crown !gear''backlash, which is the error in motion that occurs when gears change direction, resulting from hard to eliminate manufacturing errors. When moving forwards, the front face of the drive gear tooth pushes on the rear face of the driven gear. When the drive gear changes direction, its rear face is now pushing on the front face of the driven gear. Unless deliberately designed to eliminate it, there is slight 'slop' in any gearing where briefly neither face of the driving gear is pushing the driven gear. This means that input motion briefly causes no output motion. Assorted schemes exist to minimize or avoid problems this creates.In some machines it is necessary to change the gear ratio to suit the task. There are several ways of doing this. For example:

Manual transmission ('stick shift' in the US)

Automatic transmissionautomatic gearbox

derailleur gears which are actually sprocketsprockets in combination with a roller chain

hub gears (also called epicyclic gearing or sun-and-planet gears)

continuously variable transmission

transmission (mechanics)Friction and wear between two gears is highly dependent on the profile of the teeth. The tooth form used for most applications is involute gearinvolute but there are other tooth forms such as cycloid gearcycloidal (used in mechanical clocks) or Rack and pinionrack (used in automobile steering).

See also -

Antikythera mechanism

Epicyclic gearing

Hobbing machine

Non-circular gear

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