FIGURE 3. Cutting circular bases takes skill and patience. You can
create “circle-ish” bases with just straight cuts by lopping off the
corners of a square.
are engineered to fit specific types of motors or motor shafts.
That’s the case with the BeginnerBot which uses commonly
available Tamiya parts for both the wheels and the motors.
The motors come as a kit; construction time is under 15
minutes per motor, and requires only a small screwdriver and
pair of needle-nose pliers.
The arrangement of two drive wheels on each side of
the robot is commonly termed differential steering. The name
comes from how the robot is steered by changing the speed
and direction (“difference”) between the two wheels, as
shown in Figure 2. One of the key benefits of differential
steering is that the robot can spin in place by reversing one
wheel relative to the other.
A feature of most differentially steered robots is that
they use one or two casters (or skids) placed in the front
and/or back to provide support for the base. The first version
of the BeginnerBot uses a simple static skid which is nothing
more than the head of a metal machine screw. This works
because the BeginnerBot isn’t very heavy, so there’s not much
weight placed on the skid. The robot glides over the skid with
its rounded shape providing only modest friction.
In a more enhanced version of the BeginnerBot that will
be described in a later installment of this series, you’ll see
how to flip over the robot’s base and attach a metal or
plastic ball caster.
FIGURE 2. With differential steering, the
rotation of the two wheels on either side
of the base dictate the direction of the robot.
FIGURE 4. After cutting out the
basic square shape of the base,
remove each corner by sawing.
The Basics: Cutting
Things to Size
You don’t need special tools or techniques to cut wood
or plastic for a robot platform like the BeginnerBot. Basic
shop cutting tools suffice: a handsaw, a backsaw, and/or a
coping saw. When cutting plywood or soft plastics (like
expanded PVC), use a wood handsaw or backsaw with
medium teeth, or a motorized table saw. You’ll get the
straightest cuts with the table saw. When cutting hard
plastics (like acrylic), use a saw with fine teeth, or a
motorized scroll saw. You can use a table saw if you outfit it
with a blade suitable for cutting plastic. Make sure the blade
is made for cutting the particular material. Wood blades have
coarser teeth than blades for plastic. If using a power saw,
use a plywood-paneling or crosscut blade. These have more
teeth per inch and produce a smoother cut.
The easiest shape of all is square, and that’s what you’ll
begin with, even if you plan on a more elaborate base. After
all, what’s a circle than a square with lots and lots of corners!
Start with a square or rectangle that’s the size of the finished
robot base. If you have them, you can use power tools to
make short work out of cutting the material. Problem is,
square is not the ideal shape for a robot base because the
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