Gear train

A gear train or gear set is a <a href="/facts/Machine_element/cV69bkb9">machine element</a> of a <a href="/facts/Mechanical_system/wTCxFRfs">mechanical system</a> formed by mounting two or more <a href="/facts/Gear/9KVHRfUR">gears</a> on a frame such that the teeth of the gears engage.
Gear teeth are designed to ensure the <a href="/facts/Pitch_circle_diameter_(gears)/9KVHRfUR">pitch circles</a> of engaging gears roll on each other without slipping, providing a smooth transmission of rotation from one gear to the next. Features of gears and gear trains include:

<ul><li>The gear ratio of the pitch circles of mating gears defines the speed ratio and the <a href="/facts/Mechanical_advantage/tWX3c82Q">mechanical advantage</a> of the gear set.</li>
<li>A <a href="/facts/Epicyclic_gearing/FMz8Fjg8">planetary gear train</a> provides high gear reduction in a compact package.</li>
<li>It is possible to design gear teeth for gears that are <a href="/facts/Non-circular_gear/JrTT52Mc">non-circular</a>, yet still transmit torque smoothly.</li>
<li>The speed ratios of <a href="/facts/Chain_drive/exQgpatc">chain</a> and <a href="/facts/Belt_(mechanical)/k2zQ5tGv">belt drives</a> are computed in the same way as gear ratios. See <a href="/facts/Bicycle_gearing/rWCu742d">bicycle gearing</a>.</li></ul>
The transmission of rotation between contacting toothed wheels can be traced back to the <a href="/facts/Antikythera_mechanism/GHqvxCwR">Antikythera mechanism</a> of Greece and the <a href="/facts/South-pointing_chariot/WV0sqhoH">south-pointing chariot</a> of China. Illustrations by the Renaissance scientist <a href="/facts/Georgius_Agricola/FXprFXAK">Georgius Agricola</a> show gear trains with cylindrical teeth. The implementation of the <a href="/facts/Involute_gear/3kawpyMv">involute tooth</a> yielded a standard gear design that provides a constant speed ratio.

Gear train open-in-new

Gear train