This creates segments of 8 centimetres (3. 1 in), 3. 5 centimetres (1. 4 in), 8 centimetres (3. 1 in), 3. 2 centimetres (1. 3 in), and 7. 7 centimetres (3. 0 in). Do not cut these segments.
The metal shaft does not have to be anything in particular. Any piece of metal that will fit through the hole and come all the way out the other side of the frame is acceptable. The nail you use to make the hole will work perfectly.
For best results, use 1x2x5 cm ceramic magnets (these can be found online for a reasonable price). Glue them so that two magnets are facing the coil with their north side, and two are facing the coil with their south side.
You could improve the power output by putting a pinwheel on the end of the shaft and connecting it to an electric fan to turn the wheel. Keep in mind that this is only good to demonstrate the operation of the generator since you use more electricity turning it than you create.
