Page 17 - LEGO MINDSTORMS - Robotics Invention System-2 Projects

Robot 1 • The Bug

will tip over. The farther below the axis of rotation the COG is, the more stable
the robot. The Bug is unusually stable for a two-wheeled robot. You can tip it
more than 45 degrees forward or backward and it will return to an upright
position. Adding off-center weight (such as the bumper and light sensor) has
little effect on its attitude. It’s even capable of climbing a gentle grade, or tra-
versing small obstacles. The secret to the Bug’s stability is the extreme camber
of its wheels. When you look at the Bug from the side, the wheels appear to be
elliptical (oval-shaped) instead of round. The flattened bottom of the ellipse
closely matches the curvature of a circle with a much larger radius then that of
the Bug’s wheels. In fact, the 63 degrees of camber make the axis of rotation
higher than that of a robot whose normal-oriented wheels (those oriented per-
pendicular to the ground) are twice the size of the Bug’s wheels.
In addition to the base robot design for the Bug that is shown within the
pages of this book, note that two alternative optimizations exist for the Bug: A
line-following version and a proximity sensor version. Building instructions and
programs for all versions of the bug are available for viewing and for download
at the Syngress Solutions Web site (www.syngress.com/solutions).

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