Page 247 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 7 Bearings, Couplers, Gears, Screws, and Springs 225

FIGURE 7-37 Final laser-cut gear assembly

Idler Gears
When you have two gears that mesh, they both turn in opposite directions when they
spin. If you want to make two gears spin in the same direction, you can space them
out with another gear between them. This is called an idler gear. It doesn’t change
the gear ratio of the system. It just allows you to get the input and output gears
moving in the same direction (see Figure 7-38).
Idler gears are also handy when your input and output gear shafts are far apart. They
don’t need to form a straight line between your input and output gears, but can be
offset, which allows you to vary your input and output shaft distance almost infinitely.

Compound Gears

Compound gears are formed when you have more than one gear on the same axle
(see Figure 7-39). A compound gear system has multiple gear pairs. Each pair has its
own gear ratio, but since a shared axle connects the pairs to each other, you multiply
the gear ratios together to get the gear ratio of the system.

Compound gears are a very efficient way to gear up a weak motor to increase torque
and decrease speed.