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sensors, and processor board to be.
Keep the heavy battery low for
You’ll want the sensors and
microcontroller on top so the
switches, connectors, and buttons can
be easily reached. I also advise the use
of nuts, bolts, and screws instead of
welding to fasten metal pieces as
good welds are hard to make and
welded structures are hard to modify.
Use aluminum or steel angles or
brackets to join surfaces, or bend the
edges in a brake.
If you’re building a small robot,
you might want to use continuously-rotating modified servos. When I say
‘small,’ I mean a pound or under. The
typical model airplane servo is not
designed to have side loads on the
servo’s shaft. Most have a single
plastic or bronze bushing that is not
made to have bending moment that a
robot’s weight causes upon a wheel.
If at all possible, always try to
have at least two bushings. Or better
still, have two ball bearings on a
wheel’s shaft — whether the motor is
a small servo or a large gearmotor.
With the wheels and motors selected
and mounting locations laid out,
placement of the other large
components should be easy.
A larger robot base like the
Parallax ARLO (shown in Figure 11)
made from HDPE shows a popular
style with a wheel mounted directly to
a two-bushing gearmotor. (Check out
the August 2014 issue for a review of
the ARLO platform.) We’ll talk about
other wheel mounting techniques
Most small robot bases are
usually differentially steered in that
one side’s wheels can be sped up or
slowed in relation to the other side’s
wheels to cause the robot to go
straight or turn one way or another.
Differential steering is sometimes
called ‘tank style’ or ‘skid’ steering, as
the two treads move at different
speeds to turn the tank.
For robot R/C operation,
differential steering transmitters are
usually two sets of joysticks that
control each of the two side wheels of
the robot. There is no steering knob
since the steering is accomplished via
different speeds on each of the side
The other type used in some
robots is Ackermann steering
(Figure 12). This is similar to a car’s
steering. The robots that frequently
use this type of maneuvering have
been built from small radio controlled
off-road or racing car bodies that have
been modified to add robot
If you intend to control your robot
via a radio control system, many
people find the Ackermann steering
easier to control — especially at higher
speeds. Read more about Ackermann
steering on the Internet to learn about
the unique angles of the steering
linkages. If you look at the R/C
transmitters used for these type of
cars, you’ll notice that most use a
‘gun style’ transmitter with a trigger
for the car’s speed and a knob for the
Figure 11. Parallax ARLO robot base prototype.
Figure 13. Dagu Wild
Thumper robot base.