Electromagnets

Discussion in 'General Science & Technology' started by einsteinium bro, Oct 18, 2015.

  1. Q-reeus Valued Senior Member

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    Right then. Getting back to intent of OP re coil gun. A 'serious' coil gun will actually be a rail-gun and won't be using magnetic media but typically capacitor discharge through a net single-turn circuit. Quite some years back I got talking to a lecturer at a local Uni who had been asked by a government funded rail-gun researcher whether to use the standard Biot-Savart expression, or a long discarded alternative owing to variously Weber and Ampere and Neumann being championed at the time by a Peter Graneau & co.
    I was surprised there was any real uncertainty. Pointed out that Weber/Ampere/Neumann formula that predicted longitudinal stresses in a current carrying wire was easily discounted just on a simple scaling argument. Not sure if that ever got back to the researcher, or whether that particular project ever went anywhere useful. Apparently courtesy of BAE the US navy now has a useful 'killer' version.
     
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  3. danshawen Valued Senior Member

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    You may need to align the azimuths of individual electromagnet stages here as well.

    And this may be difficult to do at extreme muzzle velocities. Electrostatic projectile drive might be a better technological choice.
     
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  5. Q-reeus Valued Senior Member

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    The technology details are no doubt highly classified, but I'd say the premise of multistages will be correct. Required power/current densities will be so great a single-stage system would likely burn up trying. Hard to see hypersonic rail-gun lifetime being anything like that of a conventional cannon. But who knows. 'Defense' industries are such great money makers - for the industry players that is. Not the taxpayers.
    Well if you have a workable idea there, my suggestion is patent first, then try and chat up likely interested military-industrial-complex players. On second thoughts, try doing a patent search beforehand - on the off chance initial research by others has not been gagged/muzzled owing to 'national security' concerns. Somehow though I'd say magnetics is picked for good reasons.
     
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  7. danshawen Valued Senior Member

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    This idea would be unpatentable due to its extreme simplicity. The projectile is the dielectric, and the opposing plates of a capacitor are inside the barrel where the riflings would be (and you can also "twist" the plates along the barrel in order to impart spin). For as long as the dielectric is between the plates, there is a force pushing it out. No alignment of anything dynamic, like a magnet, would be required and this simplifies the design greatly. You could even ramp up the voltage to higher levels near the end of the muzzle to achieve extreme muzzle velocities.

    Anyone who has worked with reversing polarity of a tantalum electrolytic is familiar with the force with which the core (usually ferrite) is ejected, but this is due as much to a buildup of gasses inside the capacitor that have to be vented, more than the effect of the expulsion of the wrong polarity dielectric material between the plates, a smaller effect in this case. The direction it explodes is unpredictable (it could also eject from the side of the device), so please don't try this at home. Those of us who have seen this have done so accidentally. Reversing polarity is an easy mistake to make in electronics, but it is usually a catastrophic one.
     
    Last edited: Oct 25, 2015
  8. Q-reeus Valued Senior Member

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    Hmmm....There are a few things to carefully consider there. Number one would be the force densities possible before catastrophic dielectric breakdown spoils things. You have done some simple back-of-envelope calculations for that? Actually, an even greater limitation will be air breakdown. To avoid the latter, extremely high vacuum throughout the barrel length would be needed. So how long between shots are we talking about? Is this starting to look a little impractical?
    Agreed. And yes can be risky.
     

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