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Circular railgun?

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BigBad

Fri Jan 23 2015, 10:34PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

Not entirely sure we need high voltage.

The theoretical top speed of a railgun is apparently (

v = V/(BL)

where V is the voltage, B is the magnetic field (probably very low it's not even a full turn) and L is the width of the rails.

I plugged some numbers in, and got absurdly high speeds, which will never, ever be reached of course.

Even a NMh battery might be too much; probably not; but mains voltage could be scary, even with a current limiting resistor in there, like a kettle or something; you've got a few horsepower trying to push a teeny-tiny ballbearing along.

DerAlbi

Sat Jan 24 2015, 04:16PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

>> (probably very low it's not even a full turn)

there are no half turns.
I would suggest you start experiementing

Andy

Sat Jan 24 2015, 07:42PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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The final speed is set by E/B or the change of rail distance, you can increase the voltage buy dischargeing higher and higher voltage onto the rails or you can have more and mor resistance or you could change tje distance between electrodes, or maybe have a copper coating that gets vaporized then it becomes Al, or have the voltage quicly turned off with the shell change from 2H to 0.05ohm short.
Pics

1422128528 4266 FT168499 Img 20150125 083737

1422128528 4266 FT168499 Img 20150125 083723

BigBad

Sun Jan 25 2015, 01:22AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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DerAlbi wrote ...

>> (probably very low it's not even a full turn)

there are no half turns.

There kinda of is. I'm completely unconcerned about the part of the turn that isn't through the projectile, and is situated well away from the projectile

The flux from that is entirely non consequential.

DerAlbi

Sun Jan 25 2015, 04:26PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Now you talk about mutual- and stray inductance.
Thats not much arugment for fractional turns. If the current-loop is not completeley closed, its by definition not a loop and no current could ever flow. I dont want to go off-topic here. i just want to reduce "unphysical" concepts for understanding. Just google "fractional turn transformer" and learn how hard it is actually to get fractional turncounts. And maybe do some research about mutual and stray inductance in e-motors. It helps a lot to avoid such misconceptions.

Shrad

Sun Jan 25 2015, 06:50PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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has someone ever thought of segmented rails and projectile being switches in a switching converter where inductors/capacitors would be discharged mechanically?

would it be possible to achieve a kind of magnetic pulse compression so that the circuit accelerates exponentially, like with a kind of EMP generator where the projectile release rupture current would be used as a ETG "launch stage" discharge ?

just two ideas that come into my mind this late sunday after some beers and cakes ;)

hen918

Sun Jan 25 2015, 10:16PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Shrad wrote ...

has someone ever thought of segmented rails and projectile being switches in a switching converter where inductors/capacitors would be discharged mechanically?

would it be possible to achieve a kind of magnetic pulse compression so that the circuit accelerates exponentially, like with a kind of EMP generator where the projectile release rupture current would be used as a ETG "launch stage" discharge ?

just two ideas that come into my mind this late sunday after some beers and cakes ;)

The problem is that the projectile has to outrun the explosion. Which, as it accelerates pretty slowly, it won't.

BigBad

Tue Jan 27 2015, 01:54AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

DerAlbi wrote ...

Now you talk about mutual- and stray inductance.
Thats not much arugment for fractional turns. If the current-loop is not completeley closed, its by definition not a loop and no current could ever flow. I dont want to go off-topic here. i just want to reduce "unphysical" concepts for understanding. Just google "fractional turn transformer" and learn how hard it is actually to get fractional turncounts. And maybe do some research about mutual and stray inductance in e-motors. It helps a lot to avoid such misconceptions.

Sorry, but this isn't a transformer either, and Faraday's law (in the n dPhi/dt sense) does NOT apply to it!!!

Shrad

Tue Jan 27 2015, 08:27AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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I remember that battery and magnets thing inside a spiral copper wire moving along, and it mated in my mind with a story of pyrotechnic aided EMP generator where a fusing charge was, well, fusing an inductor to reduce its value as the magnetic field increased by shorting turns successively to generate a final EMP via the shorted end discharge

if we use a double set of conductors parallel to each other in a tubular barrel which would have spiraling carvings like a gun cannon, with way narrower turn spacing to achieve inductor effect, would it be possible to accelerate a conductive projectile using such magnetic pulse compression techniques?

I guess two parallel conductors would cancel each field out due to current direction being opposite... what about a single conductor surrounded by teflon or something, and a metallic casing which would act as iron to enhance the magnetic field as well as provide current return for the projectile?

this would, I think, provide projectile rotation as well as acceleration, and could even benefit of a ETG type initial launch

any thoughts about that?

BigBad

Tue Jan 27 2015, 10:02AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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That's just a spiral railgun. I'd thought about it, but I don't immediately see any major advantage. I'm not knocking it, it makes the railgun longer, but unless you turn the spin into motion somehow, what does it help?

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