Page 309 - Robot Builder's Bonanza

278 MOUNTING MOTORS AND WHEELS

Idler Wheels
Idler wheels (also called idler pulleys or idlers) take up slack in belt- and
chain- driven mechanisms. The idler is placed along the length of the belt or

chain and is positioned so that any slack is pulled away from the belt or chain
loop. Not only does this allow more latitude in design, it also quiets the
mechanism.
Couplers
Couplers come in two basic styles: rigid and flexible. They are used to directly
connect two shafts together, so you don’t need a gear or belt to transfer the
power. Couplers are common when connecting wheels and motors that aren’t
otherwise designed for one another.
Bearings
Bearings are used to reduce the friction of a spinning component, such as a
wheel or idler, around a shaft. There are lots of types of bearings, but ball
bearings are the most common. The ball bearing is composed of two concentric
rings; between each ring is a row of metal balls. The rings— and the ball
bearings— are held in place by a flange.
Bushings
Bushings and bearings serve the same general purpose, except a bushing has
no moving parts. (Note: Some people call these dry bearings.) The bushing is
made of metal or plastic and is engineered to be self- lubricating. Bushings are
used instead of bearings to reduce cost, size, and weight, and are adequate
when friction between the moving parts can be kept relatively low.

Using Rigid and Flexible Couplers

Couplers are used to connect two drive shafts together end to end. A common application is
to use a coupler to connect the drive shaft of a motor with the axle of a wheel. Couplers can
be rigid or flexible.
Rigid couplers are best used when the torque of the motor is low, as it would be in a small
tabletop robot. Conversely, flexible couplers are advised for higher- torque applications, as
they are more forgiving of errors in alignment. Why is this? A rigid coupler may shear off or
damage the motors or shafts when misaligned.

PURCHASING READY- MADE COUPLERS
There are many types of commercially available rigid and flexible couplers, and cost varies
from a few dollars to well over $50, depending on materials and sizes. Common flexible cou-
plers include helical, universal joint (similar to the U- joint in the driveshafts in older cars), and
three- piece jaw.
The couplers attach to the shafts either with a press fit, by a clamping action, by setscrews,
or by keyway. Press fit and clamp are common on smaller couplers for low- torque applica-
tions; setscrews and keyways are used on larger couplers.
Three- piece jaw couplers (Figure 24- 12; see- through and partially disassembled), like
those made by Lovejoy, consist of two metal or plastic pieces that fit over the shafts. These

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