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MOUNTING WHEELS TO DC GEAR MOTORS 273

can drill holes for attaching things to the horns. This is one of the primary ways of securing
wheels to a servo. You can also glue parts to the horns, though this works best when bonding
plastic pieces to plastic horns. Hot- melt glue and epoxy are good choices.

ADHESIVES

Some motor shafts, wheels, and other drivetrain components can be bonded with an adhesive.
This technique works best for plastic parts— don’t try to glue a metal shaft to a plastic wheel.
An example of using adhesives is to cement a LEGO axle into a non- LEGO plastic wheel.
You can then use the axle/wheel combo in a LEGO creation. Drill out the hub of the wheel
so it’s just smaller than the axle. Then gently tap the axle into the hole using a small hammer.
You may set the axle in place using epoxy or household adhesive.

Mounting Wheels to DC Gear Motors

In the world of amateur robotics, you can now find motors that match the wheels made for
them. Those are the easiest to use when building a bot, but there are many other options, too.
With some effort, you can adapt a wheel to most any kind of motor, using either a direct
connection— as described in this section— or a coupler, as detailed later in the chapter.

USING MATCHING MOTORS AND WHEELS
When I first started in robotics I used to spend an inordinate amount of time combing through
various surplus catalogs, looking for motors and wheels that could go together. It wasn’t
always easy to find matches. Today there are numerous specialty online robotics retailers that
offer low- cost DC motors and wheels that are designed to complement one another.
And when I say low- cost, I do mean low- cost— it’s easy to find a motor- and- wheel set that’s
priced under $10 each. You need two for a basic bot. Add some batteries, wire, some simple
electronics (or even a microcontroller like the PICAXE), and you have a fully functional auton-
omous robot for under $30. Not bad.

BUILDING CUSTOM WHEELS
While matching motors and wheels are handy, selection isn’t always great. You may want a
smaller or larger wheel than what’s offered, or you may not like the width of the rubber treads
on the wheel. That’s when you need to come up with your own motor- to- wheel solution.

Be sure to also see the section “Using Rigid and Flexible Couplers” for more ideas on how to
FYI match wheels to motor shafts. Using couplers requires a bit more work than the methods
outlined here, but sometimes you have no other choice.
Wheels with Setscrews
If your wheel already has a hub with a setscrew, you’re in business . . . assuming the wheel
hub is the right size for the motor shaft. If it is, you’re ready to go. But if it’s not, there are a
couple of things you can do to solve the problem:
• If the wheel hub is too small, drill it out to fit the shaft. Obviously, this works only if the hole
you drill isn’t so large that it destroys the wheel hub.

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