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Homemade Gauss Gun
bonzoesc writes: "I'm sure we all remember getting owned by some railgun-wielding kid in Quake2. Ever wanted a way to get back? Enter the Homemade Gauss Rifle. Requires wooden ruler with groove down the middle to serve as the rail, steel balls that can roll down the groove to use as projectiles, and magnets to store and redirect energy. Physics is fun!"
I knew this would happen. First you had Physics for Game Developers Now you have Game Weapons for Physicists.
Sigh, what's next, perpetual motion?
(At least this isn't a homemade BFG -- I'd be really scared then)
Eh.. i'm disappointed. I initially misread that as "degauss rifle"..
After discovering in computer labs that hitting the "deguass" button on a monitor will cause the monitors nearby to trip out very slightly for an instant, i had these vague daydreams of rewiring whatever it is in the monitor that makes it deguass to be unreasonably strong, so that hitting "deguass" would cause the monitors of all the computers in the lab or whatever else is in a 40-foot radius to be degaussed at once, Matrix EMP-blast style. This would probably break stuff, but then that's the point, i suppose.
I dunno.. i guess having instructions on how to build a mini-rail-gun really is much cooler, but still, i wonder if the guass-blast idea is possible.. and if it were, modifying the idea to create a gun you could stick at a monitor and pull the trigger to deguass it would be really funny. Alas, there's no practical use for such a thing as far as i can tell, and it isn't really *that* interesting, so i don't really care enough to do any research on the subject, so for now, it looks like i'm going to have to limit myself to putting an electric pencil sharpener next to the monitor, sticking in pencils, and giggling.
Irritable, left-wing and possibly humorous bumper stickers and t-shirts
. . . about 'Gauss Guns' can be found here
Your hair look like poop, Bob! - Wanker.
you didn't just give a bunch of undersexed, over hormonal, arrogant teenagers instructions on how to build a DANGEROUS WEAPON, now, did you?
-ugh-
:)
Well, it's a "gauss gun." Gauss = magnetic flux density. It's true that this isn't a railgun, which accelerates a projectile by means of the Lorentz force on the projectile which arises from the interaction of the current through the projectile and the magnetic field created by the passage of that current. But "gauss gun" is something of a catch-all phrase which comprises railguns, coilguns, and so forth. I guess if you wanted to you could even refer to linear induction motors as gauss guns.
"Nice little website ya have here. Be a shame if it got slashdotted, ya know?"
Chris Mattern
I've spotted multiple errors in this person's page. It looks like he was cribbing notes from a more informed paper.
Problems I've found:
The authour claims that coilgun coils attract the projectiles. This is not correct. They work by repulson (by Lenz's Law, the induced field in the conducting slug repels the coil's field).
The authour does handwaving towards the 3-body problem to support his claim that you can't figure out what the best configuration of a coilgun is. These are completely unrelated problems. The 3-body problem is hard because the system a) has no general closed-form solution and b) is chaotic, so you can't even approximate a closed-form solution for many configurations.
A coilgun, on the other hand, just has more variables than you need. You don't have one optimal coilgun - you have an infinite number of optimal coilguns. Pick some of your parameters to be convenient, and solve for the others.
It's not hard to calculate how strong the induced field will be in a coilgun, or the force transferred to the projectile. It's also not hard to calculate how a capacitor-driven system will behave (hint: consider the coil's inductance with and without the slug inside it, and you can figure out how the energy transfer works).
If you're building a tabletop coilgun, you don't have to worry about energy storage. Just get a good DC supply, set up the coils in parallel with capacitors to get a nice LC tank circuit, and set up a transistor on each coil driven off an extra turn of the coil (or a secondary coil) just as you'd set up an RF signal generator. You're going to put at most a few hundred joules into your projectile (and that's if you're heaving aluminum pipe segments across the street). Exotic solutions are only needed if you're trying to shell a neighbouring city.
As driving frequency goes up (or pulse length shortens), inductive effects become important. This is how a real coilgun works - it's driven by inductive repulsion of a conducting slug. If you have an iron slug, a) attractive and repulsive forces will fight each other (or you can think of it as induced currents shielding the slug from your applied magnetic field).
Magnetic slugs only work for tabletop devices with slow firing speeds.
He's using a metal pipe as a guide for the projectile. A closed pipe would shield the inside of the tube just as a conducting projectile shields itself. He cuts a slot through the length of the pipe to avoid this, but you still have very high induced voltages around the pipe. A coilgun that switches at any decent speed with a strong magnetic field will induce currents that arc across this gap.
If you want a projectile guide, use rails.
If you want an elegant solution, let the slug move through open air and use secondary coils to adjust the geometry of the magnetic field as the projectile passes through to nudge it back into line if you notice it drifting. But this is not trivial to implement.