Page 78 - Build Your Own Combat Robot

FIGURE 3-13 Chapter 3: Robot Locomotion 59
Illustrations of a
shaft with “key”
slot, “D” flat, and
pin hole.

You may be lucky enough to obtain a wheel assembly with a pre-cut slot; then
you can cut a corresponding slot in your shaft in which to place a “key” to lock
your wheel in place. The wheel is retained on the axle with a nut and washer that
allow easy removal. Go-kart and off-road suppliers may be able to furnish you
with many wheel/shaft/sprocket assemblies for your robot.
Another way to remove a wheel quickly for fast repairs is to have the wheel per-
manently mounted to the powered axle. Rather than removing the wheel, you
simply flip the robot over and loosen the set screws in your pillow block bearings,
remove any retaining shaft collars you may have used and the drive sprocket, and
slide the complete wheel/axle assembly out. This obviously has its negative aspects,
especially with a heavy robot. It also may create a bit of a problem in reassembly
when you have to locate the drive sprocket and chain, and slide the shaft back
through. You’ll have to locate the flattened part of the shaft you place your
set-screws against or the holes through which you must insert pins, and then realign
all the bearings and collars before retightening the whole thing.

Protecting Your Robot’s Wheels
You might have hard rubber tires with large-diameter axles and heavy rims, but
continued pounding by another robot can take its toll on your machine’s wheels in
nothing flat. An easy way to protect the tires is to have them enclosed within a
heavy part of the body’s shell, or you can mount a rim around the outside at the
tire’s most vulnerable parts. You must make this outer shell structure or rim
strong so that denting caused by a hazard or opponent’s weapon will not cause
any part of the metal structure to come in contact with the tire, in which case it
could act like a brake or cut the tire.
There are more ways to provide power to wheels than we could ever print in
this book. Belt drives have been used successfully, as well as friction drives on the
wheels. Canted wheel drives have been used on several robots to provide a wide
wheelbase in a smaller-sized robot. Your best approach is to look at what’s been
done, what bot designs have consistently won over a period of time, and what de-
signs seem to have been problematic. As we mentioned in the beginning, we will
never attempt to tell you what is the best design—with a bit of experimenting, you
might be able to produce something better than any of today’s champion bots.