Page 274 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

mark as a guide. Cut a small length of / 2"-diameter solid rod. Check
1
to make sure the shaft fits easily into the / 8" tubing. If not, obtain a
5
1
small piece of 100-grit sandpaper. Wrap the sandpaper around a / 2"
length on the end of the shaft. Twist the sandpaper around on the
shaft to sand the end. Continue sanding until the end of the shaft
fits easily into and out of the tubing. Next, drill a hole down the
center that will fit the shaft from the gearbox.
We want the gearbox to be positioned in the center of the sphere.
Place the shaft of the gearbox in the plastic rod. Place the rod in
the tubing on half the sphere of the globe.
Position the gearbox so that it will lie in the center. Mark the depth
the gearbox shaft must go into the plastic rod on the gearbox
shaft. Remove the gearbox shaft. Mix a small amount of two-part
epoxy glue. Coat the gearbox shaft with the epoxy glue and insert
it into the plastic rod. Let the glue set before proceeding.

Once the glue has dried on the first shaft, we must glue the other
plastic rod on the opposite side of the shaft. Position the glued rod
into the half sphere. Place the other plastic rod on the opposite
shaft. Place the other half sphere together with the first. Gauge
the depth the gearbox shaft must be inserted in the plastic rod,
1
and then add another / 8" of depth for error. Glue and let set. Check 253
your work while the glue is setting on the second shaft to ensure
that you can close the sphere properly.

Electronics

The electronic circuit is a light-activated on/off switch. When the
ambient light level is low (user adjustable), the circuit shuts off
power to the gearbox. The user adjusts the sensitivity of the cir-
cuit using potentiometer V1.
There is nothing crucial about the circuit. If you do not wish to
purchase or make the printed circuit board (PCB), the circuit may
be wired and assembled on a standard breadboard.

How it works
The circuit configures a complementary metal-oxide semiconduc-
tor (CMOS) operational amplifier (op-amp) as a voltage compara-
tor. A comparator monitors two input voltages. One voltage is set
up as a reference voltage called “Vref.” The other voltage is the in-
put voltage called “Vin,” which is the voltage to be compared.
When the Vin voltage falls above or below the Vref, the output of
the comparator (pin 6) changes states.
Team LRN Solar-ball robot