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Post by goduranus on Dec 14, 2016 14:01:37 GMT
Yeah, but bleach won't jump out of the bottle and fly at you at high speeds.
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Post by shurugal on Dec 14, 2016 17:43:15 GMT
Yeah, but bleach won't jump out of the bottle and fly at you at high speeds. Is that so?
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Post by lawson on Dec 14, 2016 19:34:04 GMT
I actually found the places to buy a rare earth magnet and a copper pipe for cheap, but decided against it since I often get careless and might injure people. Thanks for the math, I haven't done the math, but although forces from eddie current may be much weaker than force from the coils on the aperture, wouldn't that still be a very strong? Say if the coilgun accelerates the slug to 8km/s with 4meters of coils, that's zero to 8km/s in 0.001 seconds, so the acceleration is 8000km/s^2, which for a 5kg projectile is 40 million newtons, even a fraction of that is still a hefty amount of force. Wouldn't this be strong enough to crush propellant cans/warheads? Also, let's say that eddie currents is not strong enough, how about the mechanical forces from 8000km/s^2 of acceleration? The rare earth magnet and copper pipe demo works just fine with smaller magnets and pipes. Get a 10-15mm cube magnet and a length of 3/4inch copper pipe if you're concerned about safety. You can also easily show eddi currents with a flat copper sheet, but the magnet flips over if it starts sliding too fast.
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Post by dpidz0r on Dec 14, 2016 20:03:21 GMT
I wouldn't recommend having a 1kg rare-earth magnet "just laying around". If you get one you should have a special storage bin for it, and I'd recommend wrapping it in several layers (like, more than 10) of high visibility duct tape. The tape gives it some padding, helps keep it from sticking flush against the surface of things (magnetic field drops off rapidly by distance), and gives you something to grip in the event it sticks to something metallic.
Something closer to the 1cm cube range should be fairly safe though.
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Post by n2maniac on Dec 15, 2016 6:35:55 GMT
I actually found the places to buy a rare earth magnet and a copper pipe for cheap, but decided against it since I often get careless and might injure people. Thanks for the math, I haven't done the math, but although forces from eddie current may be much weaker than force from the coils on the aperture, wouldn't that still be a very strong? Say if the coilgun accelerates the slug to 8km/s with 4meters of coils, that's zero to 8km/s in 0.001 seconds, so the acceleration is 8000km/s^2, which for a 5kg projectile is 40 million newtons, even a fraction of that is still a hefty amount of force. Wouldn't this be strong enough to crush propellant cans/warheads? Also, let's say that eddie currents is not strong enough, how about the mechanical forces from 8000km/s^2 of acceleration? The eddy currents are probably not negligible, but they certainly aren't anywhere near coin crushing levels. You are very right to worry about acceleration. It is the same order of magnitude as seen in a rifle bullet being fired. People have made smart electronics and complicated fuzing schemes / cluster bombs to go into artillery shells before, so I would say it isn't out of the realm of possibility. That being said, reinforcement is typically mandatory, and artillery shells probably get 1 order of magnitude gentler acceleration. Your example with 800 kgee acceleration would require very sturdy structures. I suspect the ingame limits on propellant tanks are laughably far off from being able to withstand this. Pressurize the tank to ~50,000 psi (similar to the chamber pressure in a rifle) with a suitably strong wall (with the wall in tension, basically a balloon) and we might be talking workable, however. Admittedly, the rocket cannons (read: cannons that shoot rockets) probably would need sturdy enough structure that their delta-V would evaporate.
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Post by newageofpower on Dec 15, 2016 6:43:18 GMT
Hmm. In conventional cannon (and thus, jet assisted artillery) the greatest stress impulse is an instant or two after ignition. Coilguns might actually be gentler in the stress-loading deparment. May have effects on electronics, however.
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Post by goduranus on Dec 15, 2016 7:46:04 GMT
Hmm. In conventional cannon (and thus, jet assisted artillery) the greatest stress impulse is an instant or two after ignition. Coilguns might actually be gentler in the stress-loading deparment. May have effects on electronics, however. Agreed, although conventional modern day artillery with 800m/s muzzle velocity only experience 1/100th the average acceleration of a similarly lengthed coilgun with 8km/s muzzle velocity. So forces on the coilgun may still be much stronger.
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Post by shurugal on Dec 15, 2016 12:48:40 GMT
It is worth noting that in a coilgun, the stresses are also distributed evenly throughout the three-dimensional structure of the projectile. In a conventional gun, all the stress is focused onto the two-dimensional base of the projectile. This actually makes the square-cube law work in favor of a coilgun projectile with greater mass.
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Post by goduranus on Dec 15, 2016 14:53:01 GMT
Only true for near uniform projectiles or solid slugs though, if parts of the projectile don't have the same magnetic properties as the armature, stresses would still be concentrated at contact points.
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Post by thorneel on Dec 15, 2016 16:08:48 GMT
Layman question: can we put the sensitive parts of the projectile in a Faraday cage to protect them?
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Aron0621
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Post by Aron0621 on Dec 15, 2016 18:23:16 GMT
Layman question: can we put the sensitive parts of the projectile in a Faraday cage to protect them? ...from electromagnetic pulse thingy, yes. From mechanical stress caused by uneven magnetic property of the projectile, probably no.
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Post by shurugal on Dec 15, 2016 18:30:37 GMT
Only true for near uniform projectiles or solid slugs though, if parts of the projectile don't have the same magnetic properties as the armature, stresses would still be concentrated at contact points. True, but this is something that an armature could be engineered to take advantage of. Since the armature will experience a uniform force, the payload can be honeycombed through it to maximize the contact-area:mass ratio. One could even envision an alloying technique that would allow for making the explosive payload part of the armature itself, though this may reduce the mechanical properties of the armature beyond usable tolerances. Layman question: can we put the sensitive parts of the projectile in a Faraday cage to protect them? Short answer? No, not in a coilgun or railgun. Long answer: the magnetic field inside a coilgun or railgun is so strong that it induces powerful eddy currents in any conductor. These currents then cause the conductor to behave as an electromagnet. You would literally turn your Faraday cage into an electromagnet.
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Post by newageofpower on Dec 15, 2016 18:51:43 GMT
Long answer: the magnetic field inside a coilgun or railgun is so strong that it induces powerful eddy currents in any conductor. These currents then cause the conductor to behave as an electromagnet. You would literally turn your Faraday cage into an electromagnet. You are forgetting the properties of superconductors. While unviable for induction-type coilguns, a superconducting substrate is magnetically impermeable under the correct circumstances and could be used to prevent magnetic leakage to internal components (such as a Faraday cage holding the electronics).
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Post by amimai on Dec 15, 2016 19:54:14 GMT
Aren't superconductors impermeable BECAUSE they generate massive opposing eddiy currents?
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Post by newageofpower on Dec 15, 2016 22:13:40 GMT
Aren't superconductors impermeable BECAUSE they generate massive opposing eddiy currents? Not exactly but the concept is sufficiently correct (and I'm way too overworked right now to go into detailed explanation) that Induction coilguns do not use superconductors. However, there are types of coilgun that exploit the properties of superconductive projectiles.
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