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High School Rail Gun

  1. Dec 31, 2009 #1
    Hello, I am a high school senior making a railgun for my science fair project. I have been searching the internet and have finally come up with a plan for my railgun. I have some questions about my plan before I go out and buy materials. I have two questions currently, one about rails and one about projectiles.
    I have attached an image to show my plan for the rails and for the two projectiles.

    Rails: I plan on using 1/2" copper pipe (8-10" long) for my rails. I will surround and seperate the copper pipe with PVC pipe. Will a circular bore work instead of a rectangular one? All the railguns I've seen are rectangular and I wanted to know if it would be possible to make one circular.

    I also understand that 1/2" copper pipe is very big for a railgun(at least one that would be fairly inexspensive). I want to fire the projectile at roughly 100m/s. Approximately how much force would that take?

    Projectiles: My first projectile question is whether or not the round has to be magnetic. If it doesn't I was planning on using normal aluminum bought from a local hardware store. The dimensions I plan on using are in the attached image. The second projectile is more of an experimental round. I plan on buying several pistol cleaning brushes (for those who don't know what that looks like, I have a picture in the attached image). They will have a stainless steel body along with stainless steel bristles. I got the idea from RP181's nylon round with the wires inside. I hope the cleaning brush projectile will add a sabot like affect as well as reduce the mass of the projectile.

    Thank you for viewing the thread. I will be posting many more questions in the near future. All comments are greatly appreciated. Hopefully my questions make some sense, I'm sorry for my limited knowledge of electromagnetism and railguns, but I hope to gain some as I continue my science fair project.

    Attached Files:

    • rail.jpg
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  2. jcsd
  3. Dec 31, 2009 #2
    Hello BC,

    This is pretty inventive. Unfortunately, the actual currents you need to get significant propulsion are crazy high. When I was in college, they were working on the strategic defense initiative, and so we had a very short rail gun. The current it required was in the 100's of kilo amps.

    The force generated on what was left of the shorting bar (which promptly turned to plasma) was to the I^2 and so you started to get actual propulsion when you got into the 10's of KA.

    You may want to review the force equation on wikipedia: http://en.wikipedia.org/wiki/Railgun

    I do wonder if you could perform the same experiment with Neo magnets centered in the armature. Thus, the field which was normally supplied by current through the armature, would be supplied by the magnet, and the force would be proportional to I for all "sane" currents.

    - Mike
  4. Jan 1, 2010 #3


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    Staff: Mentor

    As Mike is expressing, your goals are about 1-2 orders of magnitude above what would be a reasonable science fair demo project. Has your HS advisor signed off on this? Probably not.

    Instead, consider still demonstrating the rail gun physics and concepts, but using more reasonable science fair levels of energy, voltage and current. Just shooting a small ball projectile reliably through a small basketball hoop at a meter distance would still be very impressive, and would demo the physics just as well.
  5. Jan 1, 2010 #4
    Hello BC2010,

    Above all else, put safety first when planning any project. Please consider the safety of other people as well as your own.

    There is an obvious danger from the intended projectiles flying at 200mph plus. Apart from this, attempting to generate anything like the necessary high energies and currents would be hazardous in itself. I believe it would also require resources very considerably beyond what is reasonable for a school student project, especially to tackle the job safely.

    Take the advice given in the other posts. It really is important to discuss this properly with your supervisor at School, so that they fully understand what you are planning.
  6. Jan 1, 2010 #5
    Thanks for the comments. I've started a new design for my railgun which I have scaled down. Before I post my new plan I would like to figure two things out.

    1) What can I use to insulate/cover the rails. I see many people use plexiglass, but its pretty expensive.

    2) I was hoping to figure how many amps I would need to power the railgun. I found a http://home.insightbb.com/~jmengel4/rail/rail-intro.html" , but didn't know if the formulas (specifically #7) were accurate. If anyone could verify that they're at least in the ballpark that would be fantastic.

    Thanks again for the comments. They are much appreciated.
    And this project was actually recommended to me by my physics teacher for science fair, so it has been approved. He doesn't expect too much from me because only one of his students has built a working railgun.
    Last edited by a moderator: Apr 24, 2017
  7. Jan 1, 2010 #6
    Plexiglas is pretty good for containing boo-boo's. When building motor drives, we would use 1/4" sheets as blast shields and nothing came close to getting through. McMaster Carr is a good place to buy this sort of stuff. Try mcmaster.com

    As for the bigger guns, nothing seemed entirely safe. We had a neighboring school that knocked a hole through a haydite wall when one of their buses broke loose. We did structural damage to a building with our early version that used a homopolar generator. It would create a great deal of mounting torque at firing. Later, we cleaned up, switched to capacitor banks and kept our buses close and tight.
  8. Jan 1, 2010 #7
    I know your going for a rail gun, but consider other possibilities as well. A rail gun does require a lot of current, as mentioned above, but is doable. A really cool project that get's people excited is the Jumping Ring which is really the Lenz Effect. It's not to difficult to explain to people, and with some liquid nitrogen you can have a lot of fun.

    Last edited by a moderator: Sep 25, 2014
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