Page 16 - LEGO MINDSTORMS - Robotics Invention System-2 Projects

Robot 1 • The Bug

The Bug is a simple, differential-drive robot that was originally built to com-
pete in a MINDSTORMS robot competition. The goal for the competition was
to create a two-wheeled vehicle capable of navigating a figure-eight-shaped
course. That original Bug was quite different from the one shown on the pre-
vious page. It didn’t have a bumper, and the light sensor was mounted on a
spar that extended from the front of the robot. The sensor was used to track a
wide black line that ran down the center of the path the robots were to follow.
Unfortunately, the Bug was disqualified when the contest director decided to
allow only robots with a “bicycle-style” wheel configuration to enter the compe-
tition. As is the fate of most LEGO robots, the Bug was disassembled, its pieces
returned to the parts bin.
The Bug was reincarnated almost a year later as part of a MINDSTORMS
presentation given to generate interest in the FIRST LEGO League (FLL). I had
purchased some Robotics Discovery Sets (RDSs) and wanted to use them as
part of the demonstration. The RDS includes a blue programmable brick called
the Scout. The Scout is programmed using the LCD and four buttons mounted
on its faceplate; no external computer is required, and it only takes about five
minutes of instruction before children can start writing their own robot control
programs for it. A common Scout program for the Bug required it to wander
around seeking light or darkness using the Scout’s built-in light sensor. I added
a forward-facing bumper to help the Bug navigate around obstacles, which you
see in this version of the robot.
When doing presentations like the one at the FLL, I usually bring between
eight and 10 robots: a variety of two-, four-, and six-legged walkers, Killough
platforms, synchro drives, photo copiers, pick-and-place robots, and so on. But
most people zoom right in on the Bug, perhaps because of the combination of
its cute appearance, wobbly gait, and unusually inclined wheels. It’s very
common to hear the question, “Why did you put the wheels on that way?”
A two-wheeled robot like Bug is only stable if its center of gravity (COG) is
lower than the axis of rotation of the wheels. If the COG is too high, the robot

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