Build Your Own Combat Robot

286 Build Your Own Combat Robot
left or right, an elevon/v-tail mixer can be placed between the R/C receiver and the
R/C servos. The mixer can be obtained at most hobby stores.
At this point, you will be ready to compete in any remote-control mini sumo
contest. An interesting thing to note: the bot you’ve just built is functionally the
same as a two-wheeled BattleBots-type machine. The mini sumo is just a micro
version of a two-wheeled BattleBot, and it will drive the same way.
Autonomous Mini Sumo
Edge Detector
Autonomous mini sumos are probably the most exciting ones to make. The primary
difference between the autonomous mini sumo and the remote-control mini
sumo is that the autonomous mini sumo runs completely on its own. How well it
performs depends on how well the software is written, how well the sensors work,
and how well your opponent’s autonomous bot works.
The main component of an autonomous mini sumo is the microcontroller
that is used for the bot’s “brain.” The next question that comes up is which
microcontroller to use. The fastest way to start a microcontroller holy war is to
ask a room full of bot builders, “What’s the best microcontroller?” You will get
as many different answers as there are people in the room. There really is no best
microcontroller, because they will all work. They all have their advantages and
disadvantages. In our opinion, the best microcontroller is the one that you are
most comfortable with. The examples in the following sections will use a Basic
Stamp 1 from Parallax, Inc. (www.parallaxinc.com). The Basic Stamp 1 was selected
because it’s a good microcontroller; it is relatively easy to learn how to
use; and, most of all, it has been proven to be an effective microcontroller on
champion mini sumos.
The absolute minimum capability that an autonomous mini sumo needs is the
ability to detect the edge of the sumo ring so that it doesn’t run out of the ring on its
own. There are many different ways to detect the edge of the sumo ring. The two
more common ways are to use either mechanical contact switches or optical
color-detection switches. If the switches and software work correctly, there really
is no advantage to using one or the other. Some mini sumos use a combination of
both mechanical and optical switches. This section will talk about how to implement
an optical-edge-detection switch.
One method that can be used to detect the edge of a sumo ring is to use an infrared
detector pair. This consists of using an infrared phototransistor and an infrared
light emitting diode (LED). Because the edge of the sumo ring has a white band
around the perimeter, the infrared detector pair can be used to detect the color
change as the sensor passes over from the black surface to the white surface.
The basic theory behind this approach is that the amount of current that flows
through an infrared phototransistor is a function of how much infrared light it