Term - Gear Ratio
From VEX Wiki
The driving torque applies some force at a distance of “D” from the center of rotation. This force then applies some torque at distance “3D” (this diameter is three times as large as the small gear). If we simplify things, we see the new torque is equal to the original torque multiplied by (3X).
A torque increase is not the only result of this gear ratio. You can see in the diagram below that the smaller gear has half the circumference of the larger gear (the circumference is shown “unrolled”).
This means that the smaller gear must revolve three times in order for the large gear to revolve once; this results in the larger gear having (1/3) the rotational speed (RPM). Notice this is the inverse of the torque increase.
For each increase in torque, there is an equivalent speed reduction; for each decrease in torque, there is an equivalent speed increase.
Since the number of teeth a gear has is proportional to its radius, you can use tooth-count as a method for determining gear ratios. (For example, a 36-tooth gear is three times as big as a 12-tooth gear, so a 12:36-tooth gear would yield a 3:1 ratio.)
You can think of a gear ratio as a “multiplier” on torque and a “divider” on speed. If you have a gear ratio of 3:1, you have three times as much torque as you would if you had a gear ratio of 1:1, but only 1/3 as much speed.
Calculating the gear ratio between a pair of gears is simple. First, identify which gear is the driving gear, and which is the driven gear. The driving gear is the one that is providing the torque to turn the other one. This gear is typically the one on the motor side of the reduction, or even directly attached to the motor. The other gear, the one that the driving gear is turning, is called the driven gear. To find gear ratio, simply count the number of teeth on the driven gear and divide it by the number of teeth on the driving gear.
