When you create an electromagnet by coiling wire around, say, a piece of PVC, and then running current through it (9V batteries work well, but AAs are also possible), the magnetic field is actually directional. Meaning, if you were to place a piece of metal in it it will simply be suspended in the air in the middle of the coil (it's pretty cool, we've suspended finishing nails inside a straw), but if you place a magnet in it it will launch out one end. Since this force is constant, you would just need to figure out what direction the field goes, then attach a magnet to the bottom of the dart advancer. It would be pressed forward with a constant force, since it cannot accelerate and gain any momentum.
The only real trick with this would be making it move circularly. I have a design that I think would make this work (a variation on Fenixharth's design using the electromagnet/magnet idea instead of a spring) but it is hard to describe, a picture would work better. Will draw one up when I get home.
The only limit to the practical application of a magnetic feeder would be battery life - wouldn't want it to crap out in the middle of a battle and have to replace the (somewhat expensive, in quantity) batteries. Reloading, on the other hand, would be a snap. Reverse the current to draw the loader all the way to the back, then simply drop the darts in.
Edit: In thinking further about this, I realized a further benefit; no limit to how big the drum could be. It would work equally well with 10 or 100 darts.
Edited by MithMorchaint, 19 July 2007 - 11:10 AM.