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This is a question Darwin Awards

Bluffboy says: My mate cheated death and burned his eyebrows off looking down the barrel of a potato gun. Tell us about your brushes with the Grim Reaper through stupidity.

(, Thu 12 Feb 2009, 20:01)
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Just remembered (too late to win but hey)
The "Railgun incident" as it became known at my old alma mater.

I was a sciency type at school, I pestered our physics teacher to allow us to make a railgun "to demonstrate the power of electricity/magnetism" or some such bollocks. In truth we were teenage boys so any projectile hurling gizmo was ok by us (and after the "School pond incident" I was not allowed near any burny explody things) so we built one!

A railgun is a way of throwing ferrous projectiles using the power of electromagnets. Basically you get a series of magnets arranged along and around a tube, each switched by the previous one, to drag the projectile down to the end where it flies out at amazing speed. No propellant, no chemicals, just magnetism.

We decided to power it with mains electricity. Bad move.

The switching was simple, as the projectile reached a magnet it made a circuit to the next one and switched off the one it had just left and so on.

In hindsight perhaps we shouldn't have made so many magnets (25) or made them quite so strong. Perhaps a 50mm steel ballbearing was a bit big for our first projectile. Probably we should have taken heed of the law of motion " for every action there is an equal and opposite reaction".

However, we took some precautions. We placed the railgun, all 2 metres of it, outside on to the school playing field and set it up on a workmate. We neglected to strap it down.

Once the power was hooked up, we put the projectile in the breech end and took up our stations behind it, I mean, we were well behind the line of fire so what's the worst that could happen?

Imagine if you will our surprise when the switch was pressed. There was no noise as the railgun threw itself backwards at some speed into the throng of eagerly watching schoolboys. luckily it missed everyone but caught my blazer and tore it off me like a hen night strippers uniform.

Had it hit me it would have punched a hole through me big enough to put your head in. As it was, it only buried itself in the brick wall of the swimming pool.

50 yards away.

We never found the projectile.

I was banned from suggesting any science experiments after that.
(, Wed 18 Feb 2009, 10:24, 15 replies)
I need one for my car.
(, Wed 18 Feb 2009, 10:30, closed)

*clicks with the force of a railgun*
(, Wed 18 Feb 2009, 10:44, closed)
Extreme pedantry
Great story, but I don't think it was a railgun that you built.

A railgun uses two parallel rails which are connected one to each side of a power source. A conductive projectile, on contacting the rails, completes the circuit. The resulting interaction between the opposing magnetic fields in the rails and the current induced field in the projectile accelerates the bullet out of the railgun at silly speed.

What you wonderfully irresponsible louts built was more likely a Gauss gun, which uses electromagnets to fire ferrous projectiles.

(Of course neither one can be powered by mains electricity unless you rectify it to DC, which you definitely did otherwise the ball bearing would have stuck at the first magnet.)

Still, definitely worth a click.
(, Wed 18 Feb 2009, 11:20, closed)
Ah yes!
It WAS a gauss gun! Now I remember (I am old) the big yellow-painted DC gizmo that the teacher plugged into the mains.

Still scary though!
(, Wed 18 Feb 2009, 11:32, closed)
You are lucky for doing this at school! Great science lesson though, wasn't it? Electricity, magentism, Newton's laws and with your nice nylon uniform blazer probably a bit on materials as well. Well done sir.
(, Wed 18 Feb 2009, 11:36, closed)
Makes my university mass driver project story where I sent a cat into planetary orbit pale into insignificance*.

(, Wed 18 Feb 2009, 11:21, closed)
Lies about the cat, or false-modesty lies about the insignificance of the story?
(, Wed 18 Feb 2009, 11:34, closed)
I too...
...do not buy into this tale.

Hyper-velocity magneto-rail weapons (commonly called the Railgun) have been a Holy Grail project for the military for some years... yet you build one in school? Ahem. Yes. Ahem.

Also, Gauss Cannon and/or Coilguns are exactly the same thing....
(, Wed 18 Feb 2009, 12:22, closed)
He didn't build a railgun
Gauss cannon equals coilgun, but neither of those is remotely like a railgun. They are quite different. See above. They all sound all sci-fi but they're not really, it's simple tech.

The holy grail for the military is to make a railgun that's reliable enough to use again and again. The rails melt because of the current and friction from the projectile. The military has had prototypes for years that are ridiculously powerful but liquify after a couple of shots. They are easy to make at home as well (at lower powers obviously), probably easier than a Gauss gun.

That reliability problem is not an issue with a Gauss gun. The difficulty with a Gauss gun is making it powerful enough to bring the pain, something that involves supercooled magnets and liquid nitrogen. That isn't really battlefield-friendly technology. Hence why all the research at the moment is directed at railguns. Which isn't what the OP built.
(, Wed 18 Feb 2009, 13:07, closed)
Don't worry kids
It's all lies about the mass driver. However I did make a time machine in my garage and made a little money on the stock market*.

*I might be confusing my life with that of the protagonists in the movie 'Primer' again though...
(, Wed 18 Feb 2009, 13:06, closed)
If it knocked a heavy block of copper & iron
plus whatever else was inside it 50ft- and hard enough to embed itself in a wall- your projectile would have been accellerated at a huge speed. Though not THAT huge as its accelerator magnets would have repulsed the body as well, shortening the distance of track that was doing the accelerating.

I'm skeptical that a max of 3kW supply (230V @ 13A- and that'd need a hefty rectifier) could have provided the neccesary power to push a 2m long gauss gun that far with that distance- though it would certainly have quite a kick to it!

So "Pics or it didn't happen" and I'm off to the lab to try it out...

Edit: I just had a quick refresher look at the gauss gun principle- and a 2m long mains powered one- especially with a big-ass cap on each coil- one would be bloody powerful so I guess it's not utterly impossible. Are you sure of the distances involved though?
(, Wed 18 Feb 2009, 13:17, closed)
Other variables
230V, 13A and I'm guessing at least 30 years of retelling-induced exaggeration.
(, Wed 18 Feb 2009, 13:22, closed)
Great story,
Unfortunately, complete fiction.
(, Wed 18 Feb 2009, 15:28, closed)
I doubt it's complete fiction
Because I don't doubt he built a gauss cannon.

But I do seriously doubt the distances involved.

*Wanders off, looking for the bits to recreate experiment*
(, Wed 18 Feb 2009, 17:25, closed)
A few calculations show that if the projectile (which would weigh about 0.5kg) was lauched with enough force for the gun to hit the wall of the pool (it would have to travel at roughly 90mph, and even then it would hit the very bottom of the wall), it would have been accelerated to at least 550mph in 2 metres, with a force of roughly 10,000N.

In order for the gun to embed itself higher in the wall than ground level, the projectile would have to break the sound barrier by a fair bit.

(Calculations made on the assumption that the railgun weighed 25kg and a workmate is roughly 80cm high).
(, Wed 18 Feb 2009, 17:56, closed)

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