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 begins and the mating worm wheel provides 50 tooth, the resulting gear ratio is 25:1 (50 / 2 = 25).
Calculating the apparatus ratio in a planetary equipment reducer is less intuitive as it is dependent upon the number of teeth of sunlight and ring gears. The earth gears become idlers and don’t affect the apparatus ratio. The planetary gear ratio equals the sum of the number of teeth on the sun and ring gear divided by the amount of teeth on the sun gear. For example, a planetary arranged with a 12-tooth sun gear and 72-tooth ring gear has a equipment ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear sets can achieve ratios from about 3:1 to about 11:1. If more gear reduction is needed, additional planetary stages may be used.
If a pinion gear and its mating gear have the same amount of teeth, no reduction occurs and the gear ratio is 1:1. The apparatus is called an idler and its primary function is to change the path of rotation instead of decrease the speed or boost the torque.
Parallel shaft gearboxes often contain multiple gear pieces thereby increasing the apparatus reduction. The full total gear reduction (ratio) depends upon multiplying each individual gear ratio from each equipment arranged stage. If a gearbox includes 3:1, 4:1 and 5:1 gear pieces, the full total ratio is 60:1 (3 x 4 x 5 = 60). Inside our example above, the 3,450 rpm electric motor would have its swiftness reduced to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric electric motor torque would be risen to 600 lb-in (before efficiency Planetary Wheel Drive losses).