Page 271 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

In the prototype, the gearbox is set to the 1000:1 ratio. You can use
any gearbox that can fit and rotate inside the 5 / 2" transparent
sphere. Choose one with a high gear ratio that delivers low revolu-
tions per minute (7 rpm). 1
Robot construction
The shell is the first component for consideration. It must be trans-
parent and large enough to hold the gearbox and electronics. The
shell used in my prototype has a diameter of 5 / 2". Snap-together
1
transparent spheres are available in many hobby and craft stores.
Hobbyists use them to enclose holiday ornaments, If you cannot
find a suitable shell locally, you can purchase one from Images SI
(see the parts list at the end of this chapter). The plastic shell is
fragile. Do not have your robot try to climb or fall down stairs; it
is sure to crack and break.

Separate the two halves of the shell. The first job is to locate the
center of each half sphere.This is where the shafts of the gearbox
will be connected. Locating the center at first appears much easier
than it actually is. To find the center, I was forced to trace the diam-
eter of the shell on white paper, then draw a box around the drawn
250 circle that touched the circle on four sides (see Fig. 12.4). Drawing

12.4 Layout for finding circle center

Team LRN
Chapter twelve