Page 272 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

12.5 Transparent sphere drive components
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the diagonal lines from the corners of the box, I was able to locate
the circle center. The half sphere is then positioned over the drawn
circle. If you hold your head directly over the half sphere, you may
be able to eyeball the center and mark it on the sphere with a magic
marker. I tried this once or twice with less than ideal results. Finally,
1
I taped the paper on a / 2" piece of wood and drilled a small hole at
dead center. Then I placed a small dowel, about 2.5" long, in the
hole, making sure it was perpendicular to the wood. Place the half
sphere over the fixture, lining up its diameter with the drawn circle;
the dowel locates the center of the sphere fairly accurately. Mark
the center of one half sphere, and then the other.
The next step is to make a drive-locking fixture in the sphere that
prevents the gearbox shaft from rotating freely inside. With the
shaft locked, it forces the gearbox itself to rotate inside the sphere,
changing the center of gravity and moving the robot along. The
drive fixture must at the same time allow the sphere to be assem-
bled or unassembled at will. The system I devised is illustrated in
Figs. 12.5 and 12.6. Although I built all the drive components out of
transparent plastic on the prototype, you can fabricate the parts
out of other materials like brass and wood.

Team LRN Solar-ball robot