A dynamo, short for dynamoelectric machine, is another name for an electric generator. Dynamos use moving magnets inside a closed circuit to convert mechanical energy into an electric current. A simple example of a dynamo is a bicycle light that uses the friction produced by a rotor against the rotating bike tire to move magnets inside a coil of wire and light a bulb. You can create an alternating current magnet dynamo that lights a small bulb with a safe current of less than 2 volts.
Place the strip vertically on a table. Measure and mark a line across the width of the strip 3 1/8 inches from the top. Continue marking lines at the following distances from the top of the strip: 4 1/2 inches, 7 5/8 inches and 9 1/8 inches.
Score the cardboard strip carefully on each line. Lightly press the knife through part of the top layer of cardboard. This will make it easier to fold the strip into a box shape.
Turn over the cardboard strip. Starting at the top line, fold each section in toward you on each scored line. Overlap the last section with the first section on the outside, to form a box with open ends. Tape the first and last sections together.
Turn the box so the overlapped side is away from you. On the side facing you, draw an “X” by connecting two diagonally opposite corners with the ruler and using the edge to draw a straight line. Repeat for the two remaining diagonally opposite corners.
Turn the box with the overlapped sides facing you. Repeat the procedure from Step 4 to make an “X” on this side.
Poke the nail through the cardboard strip at the center of the “X” on the overlapped side. Push the nail to the outside of the box through the center of the remaining “X.” Wiggle the nail in the holes a bit to make them larger, allowing the nail to rotate freely.
Stack two magnets together to make two stacks. Position the two stacks on opposite sides of the nail inside the box. Try to spin the nail to make sure it spins freely and the magnets don’t hit the inside of the box. Remove the magnets from the nail, pull the nail out of the box and set them aside.
Tape one end of the wire to the cardboard box. Wind the wire around the center section of the box tightly, but do not crush the box. When all the wire has been used except the last 4 inches, pull out the wire that was taped. Tape both ends to the box to keep the coil of wire from unwinding.
Remove 1 inch of the red insulation from each wire end to uncover the bare wire. Locate each nail hole, and move the wire away from the holes on both sides. Tape the wire to keep it from covering the holes.
Insert the nail through the two holes in the box. Attach the two stacks of magnets opposite each other on the nail. Spin the nail and try to balance the weights. Tape the weights in place on the nail when they are balanced.
Connect each free end of wire to one of the wires of the lamp. Twist the bare ends together two or three times. Do not let the two wire connections touch each other.
Turn off the room lights. Turn the nail between the thumb and index finger of your dominant hand as fast as you can, but at least eight revolutions per minute. The lamp will dimly light.
Connect the optional hand-crank drill to the dynamo by clamping the pointed end of the nail in the drill’s chuck. Crank the drill faster and faster until you see the lamp light more brightly. If you go too fast, the lamp may burn out or the magnets may fly off the nail.
Children should be supervised by an adult when using the knife.
Never connect the wires to an electrical outlet.