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The gear decrease in a right-angle worm drive is dependent on the number of threads or “starts” on the worm and the Planetary Wheel Drive amount of teeth on the mating worm wheel. If the worm has two starts and the mating worm wheel provides 50 the teeth, the resulting gear ratio is 25:1 (50 / 2 = 25).

Calculating the apparatus ratio in a planetary equipment reducer is much less intuitive as it is dependent on the number of teeth of the sun and band gears. The earth gears become idlers and don’t affect the gear ratio. The planetary gear ratio equals the sum of the amount of teeth on the sun and ring gear divided by the number of teeth on the sun gear. For example, a planetary arranged with a 12-tooth sun gear and 72-tooth ring gear includes a equipment ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear units can perform ratios from about 3:1 to about 11:1. If more equipment reduction is needed, additional planetary stages may be used.

If a pinion equipment and its mating equipment have the same number of teeth, no reduction occurs and the gear ratio is 1:1. The gear is called an idler and its own primary function is to change the direction of rotation instead of reduce the speed or increase the torque.

Parallel shaft gearboxes often contain multiple gear pieces thereby increasing the apparatus reduction. The total gear reduction (ratio) is determined by multiplying each individual equipment ratio from each equipment set stage. If a gearbox consists of 3:1, 4:1 and 5:1 gear sets, the full total ratio is 60:1 (3 x 4 x 5 = 60). In our example above, the 3,450 rpm electric electric motor would have its swiftness 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 effectiveness losses).