Planetary Gear Train Analysis

The planetary gear train is an important, but complex mechanism.  When it comes to analyzing rotation directions and gear speeds, intuition is not enough.  We’ll look at the superposition method to determine speeds and rotation directions. For a planetary (a.k.a. epicyclic) gear train there are three possible inputs/outputs: two gears and the planetary gear carrier.  …

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Helical Gear Forces

In this article we’ll look at helical gear forces that result from gear mesh. These forces are important to determine the loads on shafts and bearings.  Unlike spur gears, single helical gears generate an axial force.  This thrust can be canceled by using a double helical gear (herringbone). This article focuses on single helical gears. …

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Spur Gear Forces

In this article we’ll look at spur gear forces that result from gear mesh.  These forces are important to determine the loads on shafts and bearings. Gear Mesh When two spur gears mesh, their pitch circles touch as shown below. Looking at the free body diagrams for each gear, there is a normal force acting …

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Worm Gear Forces

Calculating worm gear forces is necessary to determine bearing reactions and shaft loads.  Because of the sliding action between the worm and gear, friction plays a major role in a worm gear set’s efficiency. For this discussion, we assume the worm and gear shafts are 90 degrees apart and that the worm is driving the …

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Worm Gear Efficiency

Most gear types have efficiencies in a fairly tight range.  On the other hand, worm gear efficiency can vary greatly.  A large portion of losses in a worm gear set is due to the sliding friction between the worm and gear. The sliding friction is dependent on the worm lead angle, λ and the coefficient …

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