Editing Machine (section)

=== Gears and gear trains ===
[[File:Antikythera Fragment A (Front).webp|thumb|The [[Antikythera mechanism]] (main fragment)]]
The transmission of rotation between contacting toothed wheels can be traced back to the [[Antikythera mechanism]] of Greece and the [[south-pointing chariot]] of [[China]]. Illustrations by the renaissance scientist [[Georgius Agricola]] show gear trains with cylindrical teeth. The implementation of the [[involute gear|involute tooth]] yielded a standard gear design that provides a constant speed ratio. Some important features of gears and gear trains are:
* The ratio of the pitch circles of mating gears defines the [[gear ratio|speed ratio]] and the [[mechanical advantage]] of the gear set.
*  A [[epicyclic gearing|planetary gear train]] provides high gear reduction in a compact package.
*  It is possible to design gear teeth for gears that are [[non-circular gear|non-circular]], yet still transmit torque smoothly.
* The speed ratios of [[chain drive|chain]] and [[belt (mechanical)|belt drives]] are computed in the same way as gear ratios. See [[bicycle gearing]].