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High School Science Fair Railgun

  1. Jan 28, 2010 #1
    Hello, I posted a thread over a month ago asking some basic questions on railguns for my high school science fair project. Since then, I've built a working railgun that fires both cyndrilical and square projectiles. Unfortunately those projectiles consist of compressed aluminum foil, so it doesn't have much mass (around .1g). My goal was more along the lines of .25X.25X.25 inch cube of solid aluminum. The aluminum cubes I have put through my rails have stuck. Any help with figuring out my problem would be greatly appreciated.

    My problem, as I stated before, is that my aluminum cube (about 1g) is getting stuck in the middle of my rails. The odd thing is, that when I use my injector alone, it goes all the way through. Somehow when I apply current through my rails, the projectile slows down. On the other hand, I got my al. foil projectile to work by using less psi in my injector (I got it so the projectile would get stuck in the rails when only using compressed air). What could be happening to make my projectile get stuck?

    I have more details on some of my test firing if they are needed to understand the problem better. If anyone is interested, I'll post pictures and the essay I have to turn in for science fair.
     
  2. jcsd
  3. Jan 28, 2010 #2

    berkeman

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    Staff: Mentor

    I think posting the pictures would be great. I'm not sure we should see the essay until after the Fair. There would be too much temptation to give you feedback, and that would be unfair to the other Fair competitors.
     
  4. Jan 28, 2010 #3
    Congrats!,

    You've gone a long way. Now, it sounds as though your having problems with your projectile / armature welding to the rails. This wasn't a problem with the big ones, because the armature was blasted to plasma before it began to move ( very liquid thing, plasma ) and the projectile was ceramic.

    You may experiment with ways to inhibit the welding. For example welding requires hot spot + material that will melt at that temp + adhesion. Hot spots will happen when you have a tiny surface area with a lot of current. Then you're material must have a low enough melting point to flow (copper melts at a higher temp than aluminum). And finally, your materials must have the right conditions to alloy. Some metals don't alloy well with others and some materials, such as graphite, simply shed.

    Hmmm, I wonder what would happen with a motor brush....

    Once again, I'd like to put in that you've done very well, and I'm impressed. I wasn't overly encouraged about this project to start. You're a testament to enthusiasm over experience and that's good lesson for us all.

    - Mike
     
  5. Feb 1, 2010 #4
    Just wanted to post that I finished second (physical science) in my school's science fair. I'll be moving on to regionals in two months. Unfortunately my railgun didn't work any of the three times I fired it for the judges, all three times it welded. I'll be working on improving the design and attempting to make it more consistent.
     
  6. Feb 1, 2010 #5

    berkeman

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    Staff: Mentor

    Congrats BC! Good luck in the next round.

    I don't know if it's been mentioned before, but you might look into conductive grease to see if that helps to avoid the sticking and welding problem. We use it in radio antenna connections that are outdoors to help maintain weather-resistant, conductive connections. You can find it at HAM radio stores like HAM Radio Outlet. It uses silver in the grease, I believe to give it good conduction.

    http://www.google.com/search?source...US301US302&q=conductive+grease+silver+antenna

    .
     
  7. Feb 2, 2010 #6

    taylaron

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    Gold Member

    May I suggest aluminum spheres as ammunition. When the cube is shot through the nozzle, it may tend to turn and get wedged in there from the force of the EM fields. Also, the speed in which your coils activate may be too fast for the mass of your ammo if they stop mid way.

    (isn't using compressed air cheating??)

    -Tay
     
  8. Feb 5, 2010 #7

    turin

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    Homework Helper

    You might try scraping a pencil (or lead holder) along the rails to coat them with graphite as a cheap solution. (That's how we used to "lube" pine wood derby axles. Does anyone make those anymore?) However, the reduced conductivity might be intolerable.
     
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