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# planetary wheel drive

The gear reduction in a right-angle worm drive would depend on the number of threads or “starts” on the worm and the number of teeth on the mating worm wheel. If the worm has two starts and the mating worm wheel offers 50 tooth, the resulting gear ratio is 25:1 (50 / 2 = 25).

Calculating the gear ratio in a planetary equipment reducer is less intuitive as it is dependent upon the amount of teeth of sunlight and ring gears. The planet gears act as idlers and do not affect the gear ratio. The planetary gear ratio equals the sum of the amount of teeth on the sun and ring equipment divided by the amount of teeth on sunlight gear. For example, a planetary set with a 12-tooth sun gear and 72-tooth ring gear has a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear models can perform ratios from about 3:1 to about 11:1. If more equipment reduction is needed, additional planetary stages can be used.

If a pinion gear and its mating equipment have the same number of teeth, no decrease occurs and the apparatus ratio is 1:1. The gear is called an idler and its major function is to improve the direction of rotation rather than reduce the speed or increase the torque.

Planetary Wheel Drive Parallel shaft gearboxes many times contain multiple gear models thereby increasing the gear reduction. The total gear reduction (ratio) is determined by multiplying each individual equipment ratio from each gear established stage. If a gearbox contains 3:1, 4:1 and 5:1 gear pieces, the total ratio is 60:1 (3 x 4 x 5 = 60). Inside our example above, the 3,450 rpm electric engine would have its speed reduced to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric motor torque would be risen to 600 lb-in (before performance losses).

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