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[Astramancer]

http://blog.makezine.com/archive/2010/09/impressive_and_slightly_scary_coilg.html

I know it's a bit higher tech level that one normally sees in DF, but, damn I want one!

[Mephansteras]

Huh. Cool.

[Ø]

Commenter of the video calculates no more than 37 joules of energy in the projectile, which sounds about right.

Jesus, he was shooting metal stakes out of that. It's like a futuristic Vampire killing weapon.

[DJ]

Those do look like silver jacket bullets.

[ToonyMan]

That some is some sweet homemade stuff.

[Astramancer]

Yeah, it seems about as powerful as a weak BB Gun.  Still friggin' sweet, though.

[Trekkin]

If it were a railgun that kind of energy input would make for a fairly terrifying muzzle velocity. I suppose one could cut down on the coil and use it as the injector into a railgun mechanism, or use the coils to counter the repulsive effect on the rails.

I've been meaning for years to spend a summer building a coil-injected railgun that doesn't tear itself apart every few shots after my first camera coilgun...disappointed me.
http://www.instructables.com/id/Disposable-camera-coilgun/ only with a shoebox, eight camera caps and a lantern battery.

[Ø]

If it were a railgun...

He'd have to keep replacing the rails.

[nbonaparte]

wait, so why do railguns use the energy more efficiently?

[Ø]

wait, so why do railguns use the energy more efficiently?

A coilgun uses magnetic fields much more indirectly.

[Astramancer]

Essentially, in a coilgun, the coil draws the projectile towards the center of the coil.  The trick is to cut off the power right before the projectile reaches the critical point near the center of the coil where it starts slowing.  You're essentially turning on a big ol' electromagnet and turning it off at juuust the right time so that the metal slug you're throwing doesn't stick to it.

In a railgun, however, the projectile is actually bridging the circuit along the rails (or, rather, the armature connected to the projectile is), and thanks to the funkiness of parallel rotating magnetic fields (that are rotating counter to each other), the projectile gets pushed.

The upside of a coilgun is that nothing has to actually touch the coil.  The projectile passes through the middle, and you get no more wear and tear on the fragile conductors than you'd get in generator (i.e. we can make them last 50+ years).  The downside is that your power->force ratios suck, because you're using less than half the possible magnetic force that you can generate (because the coil has to turn off before the projectile is halfway through the coil).

The upside of a rail gun is that you can use 100% of your magnetic force, all the way down the end of the rail (and it turns off by default once the projectile is out, because the armature is no longer conducting between the rails).  This isn't to say that 1 kJ of electricity turns into 1 kJ of force, but you actually get to use much more of the potential magnetic force.  The downside?  Bridging the circuit like that isn't exactly friendly to the metal, you'll evaporate some of your rail material with each shot.  It's worse if you're aren't using a plasma armature (basically you use a really thin piece of aluminum which vaporizes into plasma), as then you have more drag from the armature which you have to overcome, in addition to the actual dragging of the armature along the rail.  Oh yeah, and your rails really, really, hate each other and want to move away, but only when your projectile is screaming down them at high speed.  So if you don't have those rails really solidly mounted, bending them into uselessness.

Long story short: coilguns will require significantly less maintenance, at the cost of performance.

edit: rails don't attract, they repulse

[Ampersand]

Could you use a series of coils activating one after the other, as the previous coil shuts off to increase the velocity of the projectile? I imagine the gain would drop after each coil eventually becoming negligible, but there might still be some benefit.

[Medicine Man]

Do you think it could just be an air rifle that has a lot of cool parts on it?

[Trekkin]

Could you use a series of coils activating one after the other, as the previous coil shuts off to increase the velocity of the projectile? I imagine the gain would drop after each coil eventually becoming negligible, but there might still be some benefit.

This is the essence of most of the more powerful coilguns; typically sequences of MOSFETs and optical gates turn on the coils in sequence. The problem is that the projectile rapidly gets saturated, so it becomes very inefficient after more than a few.

I wonder if using multiple pairs of rails in series with attached coils to push them together as they fired would help with bending.

[mendonca]

Very, very cool.

Still, the size off it goes to show why gunpowder* is still the energy source of choice.

*or whatever chemicals are used in modern firearms