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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!"
. . . about 'Gauss Guns' can be found here
Your hair look like poop, Bob! - Wanker.
What makes the monitor degauss is just a coil of wire around the edge of the screen, that has an alternating current put through it to create an alternating magnetic field. The field it creates doesn't need to extend very far, since it's wound directly around the screen.
If you hooked up a stronger power supply to the degauss coil, you could probably degauss a couple monitors at once, but the coil would burn out quickly.
Interesting trick though, if you ever have a monitor or tv that needs to be degaussed, that doesn't have it's own degauss coil. Hold it face to face with a monitor with a degausser, and hit the button, it will degauss them both at once.
Strictly speaking, this is not a gauss gun. A real gauss gun would use the Lentz (sp?) effect or something similar to accelerate the ball down the rails; this weapon, however, is built entirely out of plain old permanent magnets and kinetic energy. Actually, I suppose that maglev trains could be considered as gigantic gauss guns also, though they do not use the Lentz effect.
>|<*:=
Here's a coil gun I found on google.
Instead of using fixed magnets to release the energy of the balls hitting each magnet in sccuession, this coil gun uses a series of timed pulses to accellerate the projectile down the length of a tube. That's a block of concrete in the photo, and I think the black spike in the top left corner is the projectile.
http://www.resonanceresearch.com/prod06.htm
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.
2000ms over a 3m barrel is not "hundreds of thousands of G's" its about 66G. Your average 24" (less than a .5m) rifle barrel acclerates a lead slug to about 1100m/s. This is about 220g. Air does not become concrete, the rifle does not explode. BTY 1G is 9.98m/s per sec.
As for 5000v, I thought you wanted lots of amps for a solenoid, but it is a small matter to ramp up/down a voltage using a transformer (which is just two coils, one inside the other).
So while I'm sure making a rail gun isn't that simple your "science" is just as bad. Might want to read a 1st year phyics book.
Anarchists never rule
Back in high-school for Honors/Advanced Physics I took it upon myself to build a rail-gun, you know - something that could be cool (everyone in high-school thought Quake/Doom was the shiz) and somewhat useful (provided you needed to drive a projectile at 2 to 3 km/sec). The other students were building oh I don't know weird tinker-toys like reverse-osmosis water filtration and a electrolysis something-or-other (a guy the semester before built a tesla-coil using IBC root-beer bottles as capacitors - turned out he had wayyy more capacitance than needed and not enough current) but I wanted to make something that blew stuff up.
:) So a couple hundred dollars later and I have some copper rails fixed to a base (some wood ;)), a whole lot of 2ga. wire (friend's dad worked for the electric company), and some .9F of capacitors hooked up to provide the juice.
.9F of capacitance (after working out the numbers) proved to be far too few amps to do anything but make a whole lot of sparks. Actually I managed to vaporize some of the smaller projectiles with only a small scrap of what was left pitifully dribbled out of the end of the gun. In any rate, after researching further, I found some 5 and 10F capacitors which would've done the job nicely could I have afforded the several thousand dollars it required to buy one.
:)
So I went to work assembling materials for the gun.. I didn't worry about the math behind why rail guns worked, all I knew is that it did plenty of damage in Quake.
Two things I learned:
1) You need a fuckton of capacitance to really achieve massive current (talking hundreds of thousands of Amps needed)
2) You also need an electronic switch instead of a mechanical switch so you don't lose said Amps to welding the switch to itself.
So I guess the moral of the story is if you don't have $10M in defense contracts you're not going to get a good rail-gun built since it requires MASSIVE amperage to create a plasma to launch your armature out of the weapon. And Capacitors are not tiny objects, so the likelihood of a 'Eraser'-style railgun are slim to none unless someone magically comes up with a much more compact and higher-capacity capacitor (which can still discharge at 1/1000th or better of a second).
The problem with a coil gun is that you need massive voltage plus some sizeable amps, which is generally very hard to come by. Your local mains circuit won't provide enough voltage. Although you could push it through a transformer you would need a very large and bulky one, and then you still probably would wind up with not enough amps to do the job. Most capacitors work at low enough voltages that a commodity (e.g. plugs into your regular wall socket) transformer could easily provide it, but achieving enough capacitance is both cost and size prohibitive (ignoring the rail mass loss due to vaporization).
Stupid Quake.
Thanks,
--
Matt
If you want to know how to build a REAL railgun, try this. Admittedly, its a bit harder to build.