FIrst, Get a tube, it doesn't matter what material, and get some wire. Take some black wire tape, and tape an end of the wire onto one of the ends of the tube. Start wrapping the wire around the tube, and keep the wire close together and very tightly wound. Once you get to the other end, start wrapping the other way, and stop about two-thirds down the tube. Move down the tube about one third of the way down the tube and wrap the wire until the end of the tube. Now cut the end of the wire, leaving about 5 inches of wire off the tube-coil. Now tape the end of the coil, so it doesn't go loose. Make sure your finished result looks like the picture below.
but how to rolling direction of the cord, whether clockwise or opposite the clock?
can i use magnet wire
can i use a pizeoignitor as a power source
and can i use a pentube
the electromagnet is only polarized when electricity flows through it
a piezoelectric source only produces a single electrical discharge, rather than a continuous current
your piezoelectric electromagnet (piezomagnet?) would only last as long as the electrical discharge. you probably would not even notice it.
http://en.wikipedia.org/wiki/Electromagnet
http://en.wikipedia.org/wiki/Solenoid
The material actually does have an effect actually in a sense some materials "amplify" a magnetic field. So a iron tube may produce a stronger magnet .
however since its hollow i'm not to sure.
Anyway nice instructable
http://en.wikipedia.org/wiki/Electromagnet
http://en.wikipedia.org/wiki/Solenoid
I think you're right. I don't know all of the specifics, but I am pretty sure that the one layer that you wrap the oppisite way will provide an electromagnetic force in the direction opposite that of the other two layers, canceling out some of the power. If, when you finished your first layer you went back to the end you started wrapping and then wrapped in the same direction, then repeated for the third wrapping, you should get the optimum force
http://www.instructables.com/id/E4AOEVXT79ES9J5P69/