A high voltage motor in 5 minutes

This toy is so simple to build, it goes together in 5 minutes from a few things found around the house.


Click on the photo to see an animated picture
The toy is a high voltage motor that acts like a bell, with a clapper that bangs furiously from one can to the other and back again, sometimes several times per second.
Occasionaly, the big blue spark snaps between the cans, to add interest to frenetic activity.
To build the toy, you need:

• Two empty soda cans.
• A plastic rod such as a ball-point pen.
• 5 inches of sewing thread.
• A couple square feet of aluminum foil.
• Cellophane tape.
• Two wires (alligator test leads work great).

The photo may be all you need to get the toy working.
Remove the pull-tops from both cans, and discard one of the pull-tops.
Tie the thread to the other pull-top. Tape the other end of the thread to the center of the plastic rod.
Place the two cans side-by-side two or three inches apart.
Place the plastic rod on top of the two cans, so the pull-tab dangles freely about an inch from the table.
Tape the bare end of one wire to the left can. This is the ground wire, and the free end should be connected to an electrical ground, such as a cold water pipe, or the metal frame of a computer. If a good electrical ground is not convenient, you can just hold onto the free end, since your body is a good enough ground for this device.
Tape the other wire to the can on the right. It's free end will be connected to a source of high voltage. This is easier than it sounds, since a safe source of high voltage is right in front of you when you watch television or use a computer with a CRT monitor.



In the photo above, you can see that the toy is sitting on top of a television. About two square feet of aluminum foil is pressed onto the face of the TV screen. It sticks there because the TV screen is highly charged with electricity. The free end of the right can's wire is attached to the aluminum foil.
You start the toy by turning on the TV. The pull-top gets pulled to one can, but when it hits it, it gets pulled to the other can, and then repeats.

How does it do that?

Inside a television, a high voltage is used to send electrons to the screen at high speed, to create the picture. By placing a large conductor on the front of the screen, we can make a capacitor, to tap into some of that high voltage and put it to use outside of the television. The voltage is high, but the current is very small, so that touching the foil or the toy is no more harmful than touching a doorknob after scuffing your feet on the carpet.
The can on the right is connected to the high voltage. The can on the left is connected to the ground, which can absorb all of the voltage we can send it, and still be ready for more.
The pull-tab and the can on the left starts out without any electrical charge. We say they are at "ground potential".
The can on the right is charged with a lot of free electrons, from the foil on the TV screen. These electrons repel the electrons in the pull-tab, and attract the positive nuclei in the pull-tab.
The electrons in the pull-tab move to the side farthest from the high voltage can on the right. This leaves the right side of the pull-tab more positive than the left side. The positive side of the pull-tab is attracted to the highly negative can on the right, and the pull-tab jumps over to touch the can on the right.
Once it touches the can, the electrons from the can rush onto the pull-tab, until it has the same high voltage charge as the can it is touching. The pull-tab and the can now have the same charge, and like charges repel. The charged pull-tab is now repelled by the can on the right, and moves to the left.
The electrons in the can on the left are repelled by the pull-tab, and they move to the left side of the can, leaving the right side somewhat positive. This positive side attracts the negatively charged pull-tab, and draws it up to touch the can.
Now the excess electrons on the pull-tab move onto the left can, and into the ground. The pull-tab is now at ground potential again. It swings back towards the can on the right, and the whole process starts over again.

A fancier version

The device we have just built is called "Franklin's Bells", after a description of the device given by Benjamin Franklin, who used it to detect the approach lightning storms. He connected one end to his lightning rod on top of the house, and the other end to an iron water pump well connected to the ground.
Of course Ben didn't use soda cans. He used bells.


Click on the photo to see an animated picture
I built a pretty version with bells and set it up on top of the TV just like our first version.
Click on the photo to see a larger picture
I left the clappers on the bells, even though they no longer serve any purpose. The bells are connected to the aluminum foil and the ground by thin copper wires you can just barely see in the photo.
The bells are from a craft store. The clapper is one of the small round bells called "jingle bells".

A rotary high voltage motor

Click on the photo to see an animated picture
At one company I once worked for, we had a contest for "The most creative use of office supplies". This toy would clearly be a contender. It is based on a wonderful design by Bill Beaty, but this version uses only things found around the typical office coffee room.
Using the safe high voltage power we get by placing a sheet of aluminum foil on the face of a television or computer CRT screen, it spins a styrofoam cup around at a respectable speed.
To build the toy, you need:

• Two empty soda cans.
• A styrofoam cup (a paper cup will also work).
• A ball-point pen (the simple non-clicking type).
• A couple square feet of aluminum foil.
• Two paper clips
• A hot glue gun (or regular glue if you don't mind waiting).
• Cellophane tape.
• Two wires (alligator test leads work great).

We start by spreading glue over the ouside of the styrofoam cup. Put just a thin layer on, so it dries quickly. Before it dries, cover the cup with aluminum foil. Press the foil flat against the cup, so any wrinkles are pressed down.
With a sharp knife, neatly cut a half inch strip out of the foil on both sides, so you have two patches of foil, one on each side of the cup, that do not touch one another.
The cup is going to be spinning upside down on the point of a ball-point pen. To keep the cup centered on the pen-point, and to provide a low friction bearing, we need to glue something hard to the center of the bottom of the cup, something that has a little dimple in it to sit on the pen-point.
I chose to sacrifice the end of another ball-point pen.


The photo shows the end of the pen, cut off with a sharp knife. The side of the cut end that is facing down has a little dimple that is perfect as a place to accept the point of the other ball-point pen.
The end of the pen is glued in the exact center of the bottom of the cup, as shown below. Note the little dimple.


Next we make the stand for the motor. Start with a paper plate, and glue the bottom of a ball point pen to the exact center of the plate, so the point stands straight up.
Glue the two soda cans upside-down onto the plate, leaving enough room between them for the strofoam cup to rotate easily without touching either can. There should ba about a half of an inch gap between the cup and either can.
Straighten two of the bends of a paper clip (leaving one end bent as in the photo below) and tape them to the cans as shown. Bend the wires into an S shape, leaving enough room to place the cup on top of the pen.


Now put the cup upside-down onto the pen-point. Make sure the dimple fits onto the pen-point. The wires should be about a half inch away from the cup, with the point being closest to the cup. Nothing should be touching the cup except the point of the pen.




Now connect a wire from the can on the right to a large sheet of aluminum foil pressed against the screen of a TV (or a computer with a CRT screen).
Connect another wire to the left can, and connect the free end to a good ground connection, such as a cold water pipe, or the metal frame of a computer. In a pinch, you can just hold onto the free end, since your body is a good enough ground for this little motor.
When you turn on the television, the foil will pick up a high voltage, and the little motor will start spinning. As it slows down, turn the television off, and the motor will get another kick, and spin faster. You can keep this up as long as you feel like turning the TV on and off.

How does it do that?

The can on the right is charged with high voltage from the face of the TV. This means that the electrons are pushed onto the can with a lot of electrical "pressure". The electrons all have the same negative charge, and so they repel one another.
At the point of the wire the electrone are most crowded, and so there is the highest pressure. It is so high that the electrons can get pushed right off the wire, landing on the air molecules near the wire. These air molecules are now also negative, so they are repelled by the extra electrons in the wire. They move away from the wire, and hit the aluminum foil, where the electrons leave the air molecules and collect on the foil.
The electrons on the foil are repelled by the can on the right, which still has an excess of electrons. The electrons in the can on the left are repelled by the electrons in the foil, so they move away from it, leaving behind the positively charged nucleus, which attracts the electrons in the foil.
With the right can repelling, and the left can attracting, the foil is pulled to the left, and the cup rotates.
Half a revolution later, the charged foil is next to the wire that is attached to the ground. The electrons from the foil charge the air around the wire, and the electrons can move from the foil through the air and the wire, to the ground. This leaves the foil uncharged, so it is not repelled by the can on the right as it moves by.
At this point we are back to where we started, and the process starts over again.