Build Your Own Combat Robot

Performance Improvements
Chapter 13: Robot Sumo 297
In sumo, two of the most important factors that make a winning bot are strength
and technique. Simply having the strongest bot doesn’t mean that you will have a
winning bot; and having the smartest bot doesn’t mean that you will have a winning
bot, either. Your bot needs both of these skills.
Strength is related to pushing power. From physics, we know that pushing
force is equal to the coefficient of friction between the bot wheels multiplied by the
weight of the bot. This simple relationship pretty much tells you what you need to
have in a strong bot: weight and traction. The higher the coefficient of friction, the
better the traction the bot will have. The heavier the bot is, the greater the amount
of force required to move it. It is best to make your bot as heavy as possible for it’s
weight class. For a mini sumo, this is 500 grams. As for traction, soft wheels usually
have better traction than hard wheels. Some bots have placed rubber O-rings
or rubber bands on the outside diameter of the wheel to improve traction, and others
have used foam wheels like you see on model airplanes.
Weight and traction are the two most common ways to improve the performance
of mini sumos. The other way to win is to use better strategy during the actual
contest. This really comes down to the type of programs you use in your bot.
Some bots spin more than they move in straight lines. Some bots use more sensors
to improve vision capabilities, where others use a stealth approach to keep from
being seen. Some bots even use arms to try to capture or corral their opponent.
This is what makes robot sumo exciting, because it allows for many different types
of bots to enter the competition. In fact, biped and hexapod bots have competed
and have even won some matches. The Basic Stamp 1 microcontroller used in this
example doesn’t have the memory space for advanced software control. You will
need to use a different microcontroller such as the Basic Stamp 2 or the BasicX-24
from NetMedia (www.basicx.com).
Various Mini Sumo Robots
Figure 13-13 shows a mini sumo named Minimum Capacity built by Pete Miles,
one of this book’s authors. This mini sumo uses the circuit shown in Figure 13-11
and the logic shown in Figure 13-12. The actual source code is shown at the end of
this chapter. Although this mini sumo is not the best-looking bot on the block, it
has placed in the top three positions in tournaments in Seattle, San Francisco, and
Los Angeles, and the All Japan Robot Sumo Tournament in Tokyo.
One of the most exciting aspects of robot sumo is that any type of robot can be entered
into the contests. Pete has also built biped and hexapod walking robots that are
fully functional and have won several matches. These robots were built to demonstrate
that walking robots can compete in robotic sumo contests. Figure 13-14 shows
two photographs of these walking bots.