Slashdot Mirror
World's Most Exciting Chemistry Movies
Michael Buckbee writes: "After Dan's page got too slashdotted to view, I ran a quick search on Google for more more fun Ferroliquid sites and stumbled into a collection of movies that I wish had been taken in my chemistry classes. Almost all of the experiment descriptions lean heavily on the phrase "EXTREME DANGER" and many contain other fun words like: "Explosion", "Toxic", "Detonation", and "Diazotization"."
Well You could have knocked me down with a feather.
Na Cl
Need a light, Salted
On the issue of controlling the solenoids, I would suggest you use logic gates run by a digital watch clock signal. Because most circuits allow you to set the time by sending the raw clock signal past the dividers (that slow it down) and straight into the counters. This has the effect of speeding up the clock and the digits change very fast.
(Remember when McGuyver was locked into a hazederous waste incinerator and the hot wast was about to pour into the chamber and the door had a time lock on it. He opened the back of the timer (not that it would have been accessible from the inside of the door) and shorted out the circuit (specific the divider circuit) and the timer started to run at like 1000 seconds per second. The door opened early and he an his female companions got out before the hazardous green sludge started to pore in. They also remembered to grab the folder containing the secret documents hidden behind a pipe to lure him inside the chamber). {rant}I am SOOOOOOO pissed that it was canceled. I learned so much clool stuff from that show.{/rant}
Take a look at this article, and search around for "half adders" and "full adders". Those are the kind of circuits you will be dealing with. Also, you could use a chain of flip-flops and capacitors attached to the coils to carry the signal down the length of the pipe.
I really like your idea and if you need additional advice or ideas, e-mail me. I'm not an expert on magnets or electronics, just a hobbiest I guess. :)
Tinfoil is a pretty poor choice for a projectile. Have you everpicked up a piece of tinfoil w/ a magnet? That's your problem.
Open an introductory physics text and look up the "motor principle". The projectile doesn't have to be magnetic - it has to be conducting.
Current flowing through a wire (or other conductor) in a magnetic field produces a force on the wire proportional to the magnetic field strength and the electric current, in a direction perpendicular to both.
That's why you can build a fountain with this effect in the first place (water certainly isn't magnetic).
The force is also proportional to the length of the wire, which gives interesting scaling effects but isn't direcly relevant.
Dude, F=BLI. There's no squaring at work here. You'll need 100's, if not K and M amps to do anything resembling a railgun.
:).
But, P=I^2R. Your Joule heating will be considerable. You'll need some good engineering so that your toy won't disintegrate itself.
And V=LdI/dT. You'll need city bus size capacitors and hydrogen thyratrons to switch massive currents quickly. For railguns we're talking mega-amps in 20 nanoseconds.
Depends on what you call a "railgun".
If you're trying to make a small water fountain, you can get away with a newton of force or less. You'd also be working in continuous mode, which means a capacitor bank isn't needed (just a DC or approximately DC power supply that can provide the needed current).
One-tesla magnets are easy to buy or build - about one tesla is the saturation point of most ferromagnetic materials, so a chunk of iron will turn a 0.01-T or 0.001-T solenoid into a 1T magnet in short order (depending on the permeability of garden-variety scrap iron).
Similarly, high-strength permanent magnets will be in the Tesla range (probably more like half a tesla, but still strong enough for our purposes).
At one tesla, for a force of 1N, and assuming a water tube 1 cm wide, a current of 100 amps is adequate. A step-down transformer, a bridge rectifier, and a wall plug, and you're there.
For a proof-of-concept tabletop railgun, you can similarly relax constraints. If I'm trying to fling, say, a 10g segment of copper plumbing pipe across a room, I don't need a capacitor bank - I need a marine battery. If I can fire the projectile at 10m/s, that gives me a good 5m or so before it hits the floor from tabletop height (10m if I fire it at an angle instead of level); more than enough for a party trick. At that low a speed, it's in the railgun for tens of milliseconds or longer - I don't need nanosecond discharge circuitry. My hypothetical 10g projectile would have a kinetic energy of about half a joule, which means that if my railgun is about a foot and a half long, I again need only 1N of force. A marine battery can supply the required 100 amps of current without any problems at all (in fact, I'd want to drop a resistor in series with it to make sure it doesn't supply much more than that when I short the railgun across it).
Preventing the slug from spot-welding itself to the rails is left as an exercise for the reader
In summary, while I'd need heftier electronics to build a military-grade weapon, tabletop railguns and similar motor-principle conversation pieces aren't that hard to build.
[Aside: I'd actually build a coilgun instead of a railgun if I wanted a military-grade weapon. Much, much easier to build at high power than an ultra-high-current railgun (it's just a series of high-power RF or IF coils repelling the slug with induced currents). Even here, millisecond-level timing is perfectly adequate.]