The increasing reduction of Planetary Gears

Planet gears, for their size, engage a lot of teeth as they circle the sun gear – therefore they can easily accommodate numerous turns of the driver for each output shaft revolution. To perform a comparable reduction between a standard pinion and gear, a sizable gear will need to mesh with a rather small pinion.

Simple planetary gears generally offer reductions as high as 10:1. Compound planetary systems, which are far more elaborate than the simple versions, can provide reductions many times higher. There are obvious ways to further reduce (or as the case may be, increase) speed, such as connecting planetary stages in series. The rotational output of the first stage is linked to the input of the next, and the multiple of the individual ratios represents the final reduction.

Another option is to introduce standard gear reducers into a planetary train. For instance, the high-speed power might pass through an ordinary fixedaxis pinion-and-gear set before the planetary reducer. Such a configuration, called a hybrid, is sometimes preferred as a simplistic alternative to additional planetary stages, or to lower input speeds that are too high for some planetary units to handle. It also provides an offset between the input and output. If a right angle is needed, bevel or hypoid gears are sometimes attached to an inline planetary system. Worm and planetary combinations are rare because the worm reducer by itself delivers such high changes in speed.

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