The gear decrease in a right-angle worm drive would depend on the amount of threads or “starts” on the worm and the amount 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 apparatus ratio in a planetary gear reducer is much less intuitive since it is dependent upon the number of teeth of sunlight and ring gears. The earth gears act as idlers and do not affect the gear ratio. The planetary gear ratio equals the sum of the amount of teeth on sunlight and ring gear divided by the number of teeth on the sun gear. For instance, a planetary established with a 12-tooth sun gear and 72-tooth ring gear has a gear ratio of 7:1 ([12 + 72]/12 = 7). Planetary gear pieces can achieve ratios from about 3:1 to about 11:1. If more gear reduction is necessary, additional planetary stages can be used.
If a pinion equipment and its mating gear have the same quantity of teeth, no decrease occurs and the gear ratio is 1:1. The gear is named an idler and its principal function is to change the path of rotation instead of reduce the speed or boost the torque.
Parallel shaft gearboxes many times contain Planetary Wheel Drive multiple gear units thereby increasing the gear reduction. The total gear decrease (ratio) is determined by multiplying each individual equipment ratio from each equipment arranged stage. If a gearbox contains 3:1, 4:1 and 5:1 gear models, the total ratio is 60:1 (3 x 4 x 5 = 60). In our example above, the 3,450 rpm electric engine 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).