Page 65 - Build Your Own Combat Robot

Build Your Own Combat Robot
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Bot experimenters usually opt for the rubber tracks removed from a child’s toy
bulldozer, and then start piling batteries, extra motors, sensors, and arms onto
the new machine. When the first test run is started, the rubber tips of the tread
surface begin to bend as they push onto the floor. The robot chugs along just fine
until it has to make a turn. If the operator happens to be monitoring the current
drawn by the drive motors, he’ll see a sharp increase as the turn begins. This is one
of the major drawbacks of tank-style treads: they must skid while making a turn,
and energy is wasted in this skid. Only the center points of each “track” are not
skidding in a turn. For this reason, many robotics engineers opt not to use
tank-style treads in their machines.
However, the efficiency of the propulsion system is a less significant factor in
combat robots than in other types of bots. Because a combat robot’s “moment of
truth” is limited to a 3-to 5-minute match, builders can easily recharge or install
new batteries between matches, making the issue of wasted energy less of a con-
sideration. With this fact in mind, many builders opt for tank-style treads, so let’s
examine another feature of treads: they’re complex and hard to mount.
The toy rubber ring tank tread seems anything but complex. It’s just a toothy
rubber ring strung between two pulleys. The experimenter with his toy bulldozer
treads might be so preoccupied with the current draw of his drive motors or with
maneuvering the machine that he doesn’t notice one of the treads working its way
off the drive spindle. And if the tread slips off your heavyweight bot in a robot
combat match, chances are you’ll lose.

Building Tank Treads for a Robot
You’ve probably realized by now that even the largest toy tracks you can find are
too small for a combat robot or any other type of large robot. The smallest of the
real metal treads are ones you’ve seen on a garden tractor, and these are too big
for your machine. So, if you’re dead set on making your robot move with tank
treads, you’re probably wondering what to do next. You might start to look at
wide-toothed belts, which work much like the timing belt on your car. The only
trick to using these is that you need to make sure whatever belt you choose has
enough traction to stay competitive on the arena floor. Some successful builders
have used snow-blower tracks, which seem to be just the right size for many types
of combat robots. Flipping a large industrial belt with softer rubber teeth inside
out is another option for builders who want tank treads on their bots. These are
ready-made teeth to dig into the floor, flexible and cheap—what a way to go!
In this case, you go to a friend and have him machine two spindles out of alumi-
num that fit the width of the belt. After mounting one of the spindles on a
free-turning shaft and the other to a driven shaft, you try out one of your timing-
belt treads. Almost at once you notice the driving spindle spinning on the belt’s
surface when you apply a load to the bottom of the tread. You remember seeing
that the driving spindle on a real tractor has teeth that engage the back of the
tracks. You decide to machine two new drive spindles out of rubber. You’re back