The gear Planetary Wheel Drive decrease in a right-angle worm drive is dependent 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 has 50 teeth, the resulting gear ratio is 25:1 (50 / 2 = 25).

Calculating the gear ratio in a planetary equipment reducer is much less intuitive as it is dependent upon the number of teeth of the sun and ring gears. The planet gears act as idlers and don’t affect the gear 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 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 sets can perform 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 number of teeth, no decrease occurs and the gear ratio is 1:1. The apparatus is called an idler and its own primary function is to change the direction of rotation rather than decrease the speed or raise 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 gear 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). In our example above, the 3,450 rpm electric electric motor would have its swiftness reduced to 57.5 rpm by utilizing a 60:1 gearbox. The 10 lb-in electric electric motor torque would be increased to 600 lb-in (before performance losses).