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Railgun begginings and questions

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phil

Sun Jun 08 2008, 02:29AM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

Hello all, well now that summer is here i have a little time to work on a project before school starts again. I decided to make my first gun a railgun rather then a CG. here are two renders of my initial design for the rails.

From the front (the hole for the projectile is 1/2"

And a perspective view.

My first question is: Will placing the capacitors that close to the rails cause any interference that may damage the capacitors?
My second question: I modeled a boost converter (simple one) and the voltage just continues to rise in the simulation and never levels off, it reaches about 650 volts. Do i need to make a circuit to regulate the boost converter to keep it at the desired voltage level?

And my last question: I know the rails on the railgun will corrode, does that corrosion only occur in the first 2-4 inches? or is it along the entire length of the rails.

If it is only the first 2-4 inches i think i can make a "sacrificial" section of rails a few inches long so that they can be easily replaced. Just and idea of course.

Thanks for any help in advance =)

[Edit: Image size]

...

Sun Jun 08 2008, 03:54AM

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

I do not think the design will work with the caps arranges as so, because of the way the megnetic fields work.

There is a field inuced by the projectile, which opposes the field produced by the rais. But in order for the field from the rails to be produced, you need to have current flowing toward the end of the gun--which won't happen if you have the caps distrubuted across the rails like that. You could make it work by splitting the rails so that each cap has its own section of rail, and it is conneted at the back of the rail... That might actually do a really decent job of increasing efficiency since it would give just about the absolute lowest possible ESR--but rail errosion would be horrible (maybe plasma armature would help let the gun fire with pitted rails?) since there are so many connections being made and broken... It is certinly woth a try...

phil

Sun Jun 08 2008, 02:38PM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

I think there might be a bit of confusion. Those capacitors will all be connected to the rear of the rails, the housing holding them is plastic, it's kind of hard to tell from those renders i should have mentioned it. The capacitors are arranged like that to conserve space.

EDIT: Each bank (capacitors on the same side of the rail) will be wired in parallel, and then both banks will be wired together in series. The caps i plan on using are 160V 3300uF capacitors.

rp181

Sun Jun 08 2008, 03:57PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

2 things :
after looking at some capacitor charts, i found caps with high capacitance have lower ESR. When caps are put in parrallel, does ESR lower?

Are you actually going to use a round projectile instead of cube?

phil

Sun Jun 08 2008, 05:11PM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
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Posts: 52

I don't know the answer to the ESR question, the only reason I'm using caps with such a high capacitance is because i have a box of 60 of these sitting under my desk.

And yes i plan on using a round projectile with a spiral machined into the side so it will spin once it leaves the end of the rails.

rp181

Sun Jun 08 2008, 10:24PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

high capacitance is good, wont round projectile do things to the magnetic field? how are you going to do the rails?

Electroholic

Mon Jun 09 2008, 12:06AM

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

ball nose end mill?

phil

Mon Jun 09 2008, 01:09AM

Registered Member #314 Joined: Mon Mar 13 2006, 03:12AM
Location:
Posts: 52

Exactly Electroholic, I have Access to basicly every CNC machine known to man. I didn't think of that rp181, hopefully someone knows.... i just thought of making it round because then the projectile can spin and be more accurate.

Something like this:

[Edit: Image size, use the "img:width=400" tag or someone will get mad.]

Electroholic

Mon Jun 09 2008, 05:59AM

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

Isn't that too high a twist for a bullet?

and you probably want more land, too, to maximize contact area.

ea6b607

Mon Jun 09 2008, 06:23AM

Registered Member #1320 Joined: Sat Feb 16 2008, 01:31AM
Location:
Posts: 67

Ya way to high of a twist and to be honest for the amount of power you will get out of it rifling will be fairly insignificant. Even assuming a generous efficiency you will probably only get about 100 joules of projectile energy out of 14 of such capacitors. Which is still a fair amount, but no where in the range where rifling would help.

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