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Lorentz force, Rail Gun

  1. Jun 4, 2009 #1
    For my Final Project for my AP Physics class is a rail gun. But I am having trouble getting it to fire anything or even move it. I have no trouble charging the bank but when it is discharged into the rails the projectile doesn't move.

    I am using 11, 330v disposable camera capacitors in parallel. I am using a thick piece of graphite as my projectile, but have also tested aluminum foil and brass. The best I have gotten was placing aluminum foil across the top of the rails instead of between them, when I discharged the bank into the rails the foil pops into the air but thats it.

    The rails are the width of pencil lead apart about 5 inches long 1 inch wide, Bolted to a block of between 2 sheets of plexiglass and bolted to a block of wood.

    I have tested with 11 capacitors and with 4 caps since most of the ones i have seen online only used 3-5 caps. Still only got a spark. The current seems to jump straight through the graphite and sparks but never moves. Ive tested with the caps charged from 150 up to 310 but never get any movement.

    I am not sure what I am doing wrong, I am sure I may have left out some important detail but cant think of anything else right now, any questions lmk. Does anyone have any idea what could possibly be wrong with it? Thanks for any help.
  2. jcsd
  3. Jun 4, 2009 #2
    Why does everyone assume that rail guns are easy to build. You will need much more than a hand full of flash capacitors to produce the desired current. Usually the projectiles melt or fuse to the rails before acquiring any appreciable speed. You need .1 Farad just to melt 1g of Aluminum at 300V and we haven't even moved the target or heated the rest of the rail. Any setup for a railgun that even shoots a short distance will kill you on contact. Build a gauss gun like everyone else those can be made at home.
  4. Jun 4, 2009 #3


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    This is a high current low voltage device.
    Try just powering it with a car battery. Put a 12 volt lamp in series to limit the current.

    I've seen one work well like this and it just used a small cart with wheels that had no tyres on them so the current flowed across the axle between the rails. Tended to spark a lot at the contact point with the rails so you had to keep cleaning the rails, but it was OK for a few runs.

    Our one had a horse shoe magnet over and under the moving part. The effect is weaker without the magnet.
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