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dixie43

Wed Mar 28 2007, 12:08AM

Registered Member #608 Joined: Wed Mar 28 2007, 12:01AM
Location: Canada
Posts: 17

I used a disposable camera to charge up five capaciters (60v and 80 micro faradays each) connected in parallel to two steel rails. The steel rails are parallel side besdie sandwhiched in between two pieces of plexiglass and bolted together. The metal rails are 16 inches long each. The end of the rails where the projectile is supposed to shoot out are parallel however the other end connected to the capaciters is not completely parallel. I was able to charge the capaciter bank however, when i turn on the switch to connect the capaciters to the rails i only get a large spark in between the rails where my projectile is (piece of tin foil in a U shape). I can't figure out why the tin foil won't shoot through the rails and only spark at the area of the projectile. This is my first time making a railgun and i am a high school student working on an electromagnetic physics project and have only done about 5 hours of research on railguns, so please forgive me if i ask dumb questions. I have to have the railgun finished by april 16.

Michael W.

Wed Mar 28 2007, 12:23AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Either the tin foil could have vaporized or the capacitors don't provide near enough power to get the results your looking for...

dixie43

Wed Mar 28 2007, 12:28AM

Registered Member #608 Joined: Wed Mar 28 2007, 12:01AM
Location: Canada
Posts: 17

I have a total of 400 micro farads and 300 volts in the capaciters and the tin foil was still intact. Do you have any suggestions to how i can make this work.

Bjørn

Wed Mar 28 2007, 12:37AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Sparks means heat, heat means high resistance. Steel rails also means high resistance so your current is possibly too low.

You should put a lot of work into getting a very cood connection to the rails, maybe even use a spring mechanism to make sure the connection is close to perfect.

Connecting the capacitors in series to increase the voltage might increase the current, it depends on the ESR of the capacitors.

dixie43

Wed Mar 28 2007, 12:47AM

Registered Member #608 Joined: Wed Mar 28 2007, 12:01AM
Location: Canada
Posts: 17

Connecting the capacitors in series will definetely increase the voltage but, it will decrease the amount of energy i can store. Could you please explain the spring mechanism to me.

Billybobjoe

Wed Mar 28 2007, 01:18AM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

300 volts and 400uf isn't possible with your current setup of five 60v, 80 uf capacitors. Which is it? Even with 300v, 400 uf, thats only 18 joules. I'm not an expert with railguns, however most people use energies in the KILOjoule range. Yours could still work, but will probably have to be more efficient than larger models to yield appreciable results.

I think what Bjorn means by spring mechanism is something that will give your projectile (which currently is probably the worst possible thing to fire) constant mechanical contact and therefore the least amount of resistance to your rails. I don't really know how to make that much clearer.

Electroholic

Wed Mar 28 2007, 01:59AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

it doesn't matter how you connect the caps, maximum energy capacity would not change.

You might have too much friction on the rail/projectile contact.
also steel is not ideal rail material, and they are way too long for a 18J cap bank.

with that amount of energy, you can try to seal the end and let the explosion propel the projectile. make it an ETC gun.

dixie43

Wed Mar 28 2007, 02:21AM

Registered Member #608 Joined: Wed Mar 28 2007, 12:01AM
Location: Canada
Posts: 17

What material would you suggest that is better than steel for the rails.

What would you suggest for a projectile. I only need to fire the projectile approximately one to two meters.

[Edit: Fixed double post]

...

Wed Mar 28 2007, 02:55AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

For the rails, copper is best.

For the projectile, I have seen aluminum, copper, brass, and graphite used.

For your case, I would recommend changing the topology a little:
1. Seal one end of the gun (preferably the end that the caps are connected to)
2. Make a projectile by taking some plastic (whatever kind will work) and glue a little aluminum to the back.

Muzzle load, and when you fire the aluminum will vaporise, creating a lot of hot gas, launching out the plastic. You will probably also get a small amount of force from the railgun action (actually most big guns use this, it is called a plasma armature)} but you will get a decent amount of the energy you put in into that projectile.

And you can still call it a railgun, powerlabs style!

dixie43

Wed Mar 28 2007, 03:02AM

Registered Member #608 Joined: Wed Mar 28 2007, 12:01AM
Location: Canada
Posts: 17

thanx, for the idea, and anyone else who has an idea to make my railgun more effecient, please add them.

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