The gear decrease 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 provides 50 tooth, the resulting gear ratio is 25:1 (50 / 2 = 25).
Calculating the apparatus ratio in a planetary gear reducer is less intuitive since it is dependent upon the amount of teeth of sunlight and band gears. The earth gears become idlers and do not affect the apparatus ratio. The planetary gear ratio equals the sum of the amount of teeth on the sun and ring equipment divided by the number of teeth on sunlight gear. For instance, a planetary established with a 12-tooth sun gear and 72-tooth ring gear includes 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 equipment reduction is necessary, additional planetary stages may be used.
If a pinion equipment and its mating equipment have the same quantity of teeth, no reduction occurs and the apparatus ratio is 1:1. The gear is called an idler and its own major function is to change the direction of rotation rather than decrease the speed or boost the torque.
Parallel shaft gearboxes many times contain multiple gear sets thereby increasing the apparatus reduction. The total gear decrease (ratio) depends upon multiplying each individual equipment ratio from each gear established stage. If a gearbox consists of 3:1, 4:1 and 5:1 gear pieces, 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 rate decreased to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric motor Planetary Wheel Drive torque would be increased to 600 lb-in (before performance losses).