Having nearly completed a coilgun (Google it if you don't know what it is) I have a fair amount of experience with electromagnets and powering thereof. I think that this is a place where electromagnet application would work, but there are several things that you need to watch out for.
First, when making the electromagnet: Make sure you use thin but insulated wire. The more wire you have in the small space you're using, the stronger the magnetic field will be. It does, however, need to be insulated for various reasons. Something to watch out for is that after being "on" for any significant amount of time, the wire will get hot. The coilgun has to have its coils replaced after every shot because the wire gets hot enough to melt the insulation and thereby ruin that section of the coil. And we're talking split-second activation; it just gets that hot because of the amount of current going through it. Yours will heat up more slowly because you have less current, but the end result will be the same if the coil is "on" for too long. I don't know how you're planning to make your magnets, but keep all that in mind.
Second, power: You said you're powering the magnets off of a 9-volt, right? I would recommend using one 9-volt for EACH of the barrels. 4 circuits. You won't get enough power otherwise, at least I don't think so. The big danger here is that in the circuit you're going to be making, the 9-volt is going to get VERY hot VERY fast. If you have the circuit "on" for too long, the battery could damage itself and rupture or otherwise cause problems (leak, etc). If you do wind up using 9-volts, just make sure you don't keep the circuit "on" for more than 45-60 seconds at a time.
That's my advice. You can listen to me or not, doesn't matter to me. The coil overheating is probably a much smaller problem than the batteries overheating, so keep an eye on them.
Edit: Here is a picture of one of our prototype coils:
The purple thing it is wrapped around is a large straw. Yes, the wire is that thin. It has a red insulating coating on it. What I did there is I wrapped one very tight layer, wrapped e-tape around it, and then did another layer over it. That is the amount of wire you want to be present. That coil produced a strong enough field to suspend a nail in the air inside the straw - so you see the kind of thing you're going to need in order to be strong enough to hold a piece of pipe, right? That coil was powered off a 9-volt, incidentally. You might find you need more than one battery per electromagnet to hold the weight you're doing.
Edited by MithMorchaint, 16 June 2008 - 07:49 PM.