can be left bare, but the generator will work a little better if it is made fatter by wrapping tape around it, or (better) putting a plastic rod with a hole in the center onto the shaft to act as a pulley for the rubber band.
Next, we drill a small hole in the side of the PVC "T" connector, just under the makeshift pulley on the motor. This hole will be used to hold the lower "brush", which is simply a bit of stranded wire frayed at the end, that is almost touching the rubber band on the pulley.
As the photo shows, the stranded wire is held in place with some electrical tape, or some other tape or glue.
The rubber band is now placed on the pulley, and allowed to hang out the top of the "T" connector.
Next, cut another 3 or 4 inch piece of 3/4 inch PVC plumbing pipe. This will go into the top of the "T" connector, with the rubber band going up through it. Use the small nail to hold the rubber band in place, as in the photo below. The length of the PVC pipe should be just enough to fit the rubber band. The rubber band should not be stretched too tightly, since the resulting friction would prevent the motor from turning properly, and increase wear on the parts.
Cut the styrofoam cup about an inch from the bottom, and carefully cut a 3/4 inch diameter hole in the center of the bottom of the cup. This hole should fit snugly onto the 3/4 inch PVC pipe.
Now drill three holes near the top of the PVC union coupling. Two of these holes need to be diametrically opposite one another, since they will hold the small nail which will act as an axle for the rubber band. The third hole is between the other two, and it will hold the top "brush", which, like the bottom brush, will almost touch the rubber band.
The top brush is taped to the PVC union coupler, and the coupler is placed on the 3/4 inch pipe, above the styrofoam cup collar. The rubber band is threaded through the coupler, and held in place with the small nail, as before.
Bare the top brush (so it has no insulation) and twist it to keep the individual wires from coming apart. You can solder the free end if you like, but it is not necessary.
The free end of the top brush will be curled up inside the empty soda can when we are done, and thus electrically connect the soda can to the top brush.
We need a small glass tube to act as both a low-friction top pulley, and as a "triboelectric" complement to the rubber band, to generate static electricity by rubbing. Glass is one of the best materials to rub against rubber to create electricity.
We get the tube by taking apart a small electrical fuse. The metal ends of the fuse come off easily if heated with a soldering iron or a match. The solder inside them drips out when they come off, so be careful. The glass, the metal cap, and the molten solder are all quite hot, and will blister the skin if you touch them before they cool.
Save the metal caps � we will use them in a future project!
The resulting glass tube has nice straight, even edges, which are "fire polished" for you, so there is no sharp glass, and no uneven edges to catch on the PVC and break the glass.
The next step is a little tricky. The small nail is placed through one of the two holes in the PVC union coupler, and the small glass tube is placed on the nail. Then the rubber band is placed on the glass tube, and the nail is then placed in the second hole. The rubber band is on the glass tube, which is free to rotate around the nail.
Now we glue the styrofoam collar in place on the PVC pipe. I like to use a hot glue gun for this, since the glue can be laid on thickly to stabilize the collar, and it sets quickly and does not dissolve the styrofoam.
At this point we are ready for the empty soda can. Aluminum pop-top cans are good for high voltage because they have nice rounded edges, which minimizes "corona discharge".
With a sharp knife, carefully cut out the top of the soda can. Leave the nice crimped edge, and cut close to the side of the can so as to leave very little in the way of sharp edges. You can smooth the cut edge by "stirring" the can with a metal tool like a screwdriver, pressing outward as you stir, to flatten the sharp edge.
Tuck the free end of the top brush wire into the can, and invert the can over the top of the device, until it rests snugly on the styrofoam collar.
The last step is to attach the batteries. I like to solder a battery clip to the motor terminals, and then clip this onto either a nine-volt battery, or a battery holder for two AA size batteries. The nine-volt battery works, but it runs the
