Solar Ball Robot Construction
While this particular robot doesn't incorporate the electronics for an on board power supply, it still uses a light trigger. The circuit shown in figure 1 controls the power from the batteries to the gear box motor. The circuit reads the level of illumination that the robot sees. If the light level is high enough it turns on the motor to the gear box. The trip level of the circuit is user adjustable using potentiometer V1.
Separate the two halves of the shell. The first job is to locate the center of the half sphere. This is where we will connect the shafts of the gear box. Locating the center at first appears much easier than it actually is. To find the center I was forced to trace the diameter of the shell on white paper. Then draw a box around the drawn circle that touched the circle on four sides, see figure 3. Drawing diagnal lines from the corners of the box I was able to locate the circle center. The half sphere is then position sphere you may be able to eyeball the center and mark it on the sphere with a magic marker. I tried once or twice with less than ideal results. Finally I taped the paper on a 1/2" 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 then the other.