Page 76 - Build Your Own Combat Robot

FIGURE 3-10 Chapter 3: Robot Locomotion 57
A weapon hinge
mechanism using
pillow block
bearings.
(courtesyof
Andrew Lindsey)

Wheel Drive Types
Another important consideration is what method of wheel driving you’ll choose
for your robot: passive wheel drive or powered axle drive.

Passive Wheel Drive

Many of the wheels you might find in surplus markets and catalogs are of the
“passive” type, which means that they are not powered but provide only a rolling
support. They are not designed for the attachment of a powered shaft and might
have two sets of ball bearings inserted into each side of the rim. A non-rotating
axle is inserted through both holes; and a nut, or washer and cotter pin, keeps the
wheel on the axle. The wheel on a wheelbarrow is an example of a passive wheel.
Many robot builders have used these types of wheels as powered wheels by adding
a large sprocket on the inside of the rim. In some cases, the center of the sprocket is
bored out with a lathe to accommodate the non-powered axle.
A chain drive is connected from this wheel sprocket to another sprocket on the
drive motor or gearmotor’s shaft protruding out of the robot’s shell. This method
provides a simple way to power a wheel, but it exposes the drive chain and power
system to damage. Figure 3-11 illustrates this type of arrangement.

Powered Axle Drive

The powered axle drive system requires the robot designer to provide a way to fas-
ten a wheel assembly securely to a powered shaft. Figure 3-12 illustrates a method
to power a shaft.