Gear Ratios Review

1. Review Important Information--
-In a gear train, the gear connected to the motor is called the driver.
-The driver turns the other gear(s) which are called the follower(s).
-Small gears are fast, but weak.
-Large gears are strong, but slow.
-When a small gear drives a large gear, you have a mechanical advantage of power.
-When a large gear drives a small gear, you have a mechanical advantage of speed.

2. Calculate Mechanical Advantages

To calculate the mechanical advantage of a gear train, you must create a fraction.


-The number of teeth on the follower is the numerator (top number)
-The number of teeth on the driver is the denominator (bottom number)
-Divide your numerator by your denominator to determine your mechanical advantage

Example--If you have a 32-tooth gear as the follower and an 8-tooth gear as the driver, your fraction is 32/8.

32 / 8 = 4, so you have a mechanical advantage of 4. Any mechanical advantage greater than one, produces a larger force than it starts with. So, this gear train would produce a mechanical advantage of power!

BUT, if the 8-tooth gear is the follower and the 32-tooth gear is the driver, the fraction would be 8/32.

8 /32 = .25 Here the gear train is moving with much less force, but the output gear (follower) is moving with greater speed—it is spinning around four times each time the 32 tooth gear goes around once.