Homemade Gauss Gun 243
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!"
Re:Why can't we advance things like this? (Score:2, Informative)
Background information . . . (Score:5, Informative)
In case of /. effect (Score:3, Informative)
Experimenting with magnetorheological fluids.
Suspending a magnet in mid-air.
Levitating pyrolytic graphite.
A Gauss Rifle: A Magnetic Linear Accelerator.
Building a Curie-effect heat engine.
Going further:
Superconductors.
The Gauss Rifle:
A Magnetic Linear Accelerator
This very simple toy uses a magnetic chain reaction to launch a steel marble at a target at high speed. The toy is very simple to build, going together in minutes, and is very simple to understand and explain, and yet fascinating to watch and to use.
The photo above shows six frames of video showing this toy in action. Each frame shows 1/30th of a second. In the first frame, a steel ball starts rolling towards a magnet taped to a wooden ruler. In the second frame, a second ball can be seen speeding between the rightmost two magnets. By the third frame, the accelerator has sped up so much that the ball that is seen leaving the left side of the device is just a blur as it smashes into the target. One ball, starting at rest, has caused another ball to leave the device at a very high speed.
The materials are simple. We need a wooden ruler that has a groove in the top in which a steel ball can roll easily. Any piece of wood or aluminum or brass with a groove will work. We chose the ruler because they are easy to find around the house or at school or at a local stationery store.
We need some sticky tape. Again, almost any kind will do. Here we use Scotch brand transparent tape, but vinyl electrical tape works just as well.
We need four magnets. Most any type will do, but the stronger the magnets are, the faster the balls will go. Here we use the super strong gold-plated neodymium-iron-boron magnets we have made available in our catalog for the other projects. They work great.
We will also need nine steel balls, with a diameter that is a close match to the height of the magnets. We use 5/8 inch diameter nickel plated steel balls from our catalog.
The only tool we will need is a sharp knife for trimming the tape.
We start by taping the first magnet to the ruler at the 2.5 inch mark. The distance is somewhat arbitrary -- we wanted to get all four magnets on a one foot ruler. Feel free to experiment with the spacing later.
With the sharp knife, trim off any excess tape. Be careful, since the knife will be strongly attracted to the magnet.
It is very important that you keep the magnets from jumping together. They are made of a brittle sintered material that shatters like a ceramic. Tape the ruler to the table temporarily, so that it doesn't jump up to the next magnet as you tape the second magnet to the ruler.
Continue taping the magnets to the ruler, leaving 2.5 inches between the magnets.
When all four magnets are taped to the ruler, it is time to load the device with the balls.
To the right of each magnet, place two steel balls. Arrange a target to the right of the device, so the ball does not roll down the street and get lost.
To fire the gun, set a steel ball in the groove to the left of the leftmost magnet. Let the ball go. If it is close enough to the magnet, it will start rolling by itself, and hit the magnet.
When the gun fires, it will happen too fast to see. The ball on the right will shoot away from the gun, and hit the target with considerable force. Our one foot long version is designed so the speed is not enough to hurt someone, and you can use your hand or foot as a target.
How does it do that?
When you release the first ball, it is attracted to the first magnet. It hits the magnet with a respectable amount of force, and a kinetic energy we will call "1 unit".
The kinetic energy of the ball is transfered to the magnet, and then to the ball that is touching it on the right, and then to the ball that is touching that one. This transfer of kinetic energy is familiar to billiards players -- when the cue ball hits another ball, the cue ball stops and the other ball speeds off.
The third ball is now moving with a kinetic energy of 1 unit. But it is moving towards the second magnet. It picks up speed as the second magnet pulls it closer. When it hits the second magnet, it is moving nearly twice as fast as the first ball.
The third ball hits the magnet, and the fifth ball starts to move with a kinetic energy of 2 units. It speeds up as it nears the third magnet, and hits with of 3 units of kinetic energy. This causes the seventh ball to speed off towards the last magnet. As it gets drawn to the last magnet, it speeds up to 4 units of kinetic energy.
The kinetic energy is now transfered to the last ball, which speeds off at 4 units, to hit the target.
When the device is all set up and ready to be triggered, we can see that there are four balls that are touching their magnets. These balls are at what physicists call the "ground state". It takes energy to move them away from the magnets.
But each of these balls has another ball touching it. These second balls are not at the ground state. They are each 5/8ths of an inch from a magnet. They are easier to move than the balls that are touching the magnet.
If we were to take a ball that was touching a magnet, and pull it away from the magnet until it was 5/8ths of an inch away, we would be adding energy to the ball. The ball would be pulling towards the magnet with some considerable force. We could get the energy back by letting the ball go.
After the gun has fired, the situation is different. Now each of the balls is touching a magnet. There is one ball on each side of each magnet. Each ball is in its ground state, and has given up the energy that was stored by being 5/8ths of an inch from a magnet. That energy has gone into the last ball, which uses it to destroy the target.
Speed and kinetic energy
The kinetic energy of an object is defined as its mass times the square of its velocity. As each magnet pulls on a ball, it adds kinetic energy to the ball linearly.
But the speed does not add up linearly. If we have 4 magnets, the kinetic energy is 4, but the speed goes up as the square root of the kinetic energy. As we add more magnets, the speed goes up by a smaller amount each time. But the distance the ball will roll, and the damage it causes to what it hits, is a function of the kinetic energy, and thus a function of how many magnets we use.
We can keep scaling up the gun until the kinetic energy gets so high that the last magnet is shattered by the impact. After that, adding more magnets will not do much good.
Why a circular track will not be a perpetual motion device
I have been getting a lot of mail asking what would happen if we made the track circular. Would we get free energy? Would the balls keep accelerating forever?
I have been tempted to reply with the famous quote: "There are two kinds of people in the world -- those who understand the second law of thermodynamics, and those who don't".
However, I am not the kind of person to leave an inquiring mind unsatisfied, and it is more productive (and kind) to explain in a little more depth what is going on.
Suppose you made a circular track, and put two balls after each magnet. When the last ball is released, it encounters a magnet that has two balls at the ground state. There is no energy to be had from this magnet. The ball just bounces back.
Now suppose you had placed three balls after each magnet. When the last ball is released, it hits a ball that is 5/8ths inch from the magnet. It has not gained much momentum, because most of the momentum gained is in the last half inch as the magnet pulls much stronger on things that are closer. But the ball has enough energy from previous accelerations to release the next ball. However, that ball has less energy than the ball that caused it to release. It may have enough energy to release another ball or two, but each ball that is released has less energy than before, and eventually the chain stops.
You can show by inductive logic that no matter how many balls you stack in front of each magnet, eventually the system stops.
To estimate the losses due to heating the balls as they compress when hit, consider a plastic tube standing upright on a table. Place one steel ball at the bottom of the tube. Now drop another ball into the tube, so it hits the ball at the bottom, and bounces back up.
Now measure how high the ball bounced. If it bounces halfway back up, the losses are 50%. Perform the experiment for yourself with the balls from the Gauss Rifle. How high does your ball bounce? Send me mail with your results.
Re:Degaussing gun (Score:2, Informative)
the will do a number on a monitor at about 5 feet.
It's nifty to look at if your into that kind of thing.
Re:Degaussing gun (Score:5, Informative)
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.
Well... (Score:4, Informative)
Something similar (Score:4, Informative)
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 [resonanceresearch.com]
Re:Something similar-military. (Score:1, Informative)
A few of the best pics.. (Score:3, Informative)
Neat, but not really a gauss gun (Score:2, Informative)
They may seem fun . . . (Score:3, Informative)
Re:Well... (Score:5, Informative)
Re:Why can't we advance things like this? (Score:2, Informative)
Several points look suspicious. (Score:5, Informative)
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.
Re:so, you people want to build a gun eh? (Score:4, Informative)
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.
syndicate (Score:2, Informative)
Old EA game made by Bullfrog. Lots of fun. The gauss gun in that game looked like an oversized pistol IIRC, and it made big explosions.
Large soldering iron for degaussing (Score:3, Informative)
You can also use a large soldering iron or an electric drill to degauss monitors. A soldering iron contains a coil that generates an oscillating magnetic field at 60 Hz. I use this technique to degauss my arcade video games.
Oh yeah, don't actually touch these things to your monitor! You're just using the magnetic fields from them, not the business ends.
Rail Guns are more fun! :D (Score:4, Informative)
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.
Trial results (Score:2, Informative)
I was able to get one of the balls off the board a few tiems, but never did it have enough force to knock over a tape dispenser. Maybe quality parts would yield better results.
Where to get those magnets (Score:2, Informative)
The link to the article is here [dansdata.com] The link for where to cool magnets on his page is here [wondermagnet.com]
Now we just have to wait for a slashdotter to build a large version of this and use it to smash some watermelons
Re:so, you people want to build a gun eh? (Score:3, Informative)
What you are forgetting is that modern projectile weapons trade mass for velocity. A standard 9mm pistol fires a bullet that has a mass of only 8 grams. By rifle standards, that is huge. Your standard 5.56mm round is only about 3.5-4 grams. It sounds as if this rail gun was much the same. I don't imagine that the magnet used weighed very much.
A Real Railgun (Score:4, Informative)
Re:Degaussing gun (Score:2, Informative)
Re:Full-size gun (Score:2, Informative)
However there is one more limiting factor-- reloading the darned thing. So you have BIG magnets-- how do you reseat the balls between the magnets which transfer the energy. If you don't do this, you don't get the energy changes necessary to project the projectile anywhere (and you have the explosive charge....)
This rail gun is human muscle powered and the magnets simply create a storage vessel for the energy.