The gear reduction in a right-angle worm drive is 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 tooth, the resulting equipment ratio is 25:1 (50 / 2 = 25).

Calculating the gear ratio in a planetary gear reducer is much less intuitive since it is dependent on the amount 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 sunlight and ring gear divided by the number of teeth on sunlight gear. For example, a planetary arranged 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 perform ratios from about 3:1 to about 11:1. If more equipment reduction is needed, additional planetary stages may be used.

If a pinion equipment and its mating equipment have the same number of teeth, no reduction occurs and the gear ratio is 1:1. The apparatus is named an idler and its own major function is to change the path of rotation rather than decrease the speed or raise the torque.

Parallel shaft gearboxes often contain multiple gear sets thereby increasing the gear reduction. The full total gear decrease (ratio) is determined by multiplying each individual equipment ratio from each equipment established stage. If a gearbox includes 3:1, 4:1 and 5:1 gear units, the full total ratio is 60:1 (3 x 4 x 5 = 60). Inside our example above, the 3,450 rpm electric engine would have its acceleration reduced to 57.5 rpm by using a 60:1 gearbox. The 10 lb-in electric engine torque would be risen to 600 lb-in (Planetary Wheel Drive before efficiency losses).