The gear decrease in a right-angle worm drive is Planetary Wheel Drive dependent on the amount 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 provides 50 the teeth, the resulting equipment ratio is 25:1 (50 / 2 = 25).
Calculating the apparatus ratio in a planetary gear reducer is less intuitive as it is dependent on the amount of teeth of sunlight and band gears. The planet gears become idlers , nor affect the gear ratio. The planetary equipment ratio equals the sum of the number of teeth on the sun and ring gear divided by the number of teeth on the sun gear. For instance, 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 units can achieve ratios from about 3:1 to about 11:1. If more equipment 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 gear is named an idler and its principal function is to improve the direction of rotation instead of decrease the speed or increase the torque.
Parallel shaft gearboxes often contain multiple gear sets thereby increasing the gear reduction. The total gear decrease (ratio) depends upon multiplying each individual equipment ratio from each equipment set stage. If a gearbox consists of 3:1, 4:1 and 5:1 gear units, the total ratio is 60:1 (3 x 4 x 5 = 60). Inside our example above, the 3,450 rpm electric electric motor would have its speed decreased to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric motor torque would be risen to 600 lb-in (before effectiveness losses).