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Inspired mostly by the guy from Powerlabs, I've decided to build a railgun. In the appendix (pdf), I've made a sketch of my plan. I am not sure if somebody has already tried this, but I'll make it to test my engineering skills anyway.
The images basically speak for themselves. Regarding the working principle: I want to use an MPD-thruster schematic (from myelectricengine.com) and couple this to a railgun design. The idea is that a high voltage secondary source creates arcs over the two electrodes, hereby closing the primary circuit (the cap bank). At this point, the expansion of the air and the Lorenz force on the plasma will cause the projectile to be accelerated. The benefit would be that the gun only requires some non-conducting projectile and no gunpowder or similar.
My concern is that the plasma pressure may not be sufficient, and that a vacuum is created behind the projectile, slowing it down.
I am planning to build this device anyway, but I'm curious if anyone has tried it and/or can state why it would (not) work.
Thanks in advance for your input. ]v0.2.pdf[/file]
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
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Posts: 117
Why do you need the conducting rails if you want your projectile to be non-conducting? The rails are usually there to conduct electricity into and through the projectile. If you want it to be accelerated by the expanding air, then I think it would be much easier to build if you omit the two rails.
That would yield an ETG, where the expansion due to plasmafication (is that the right word?) of some metal causes the excess pressure that propels the projectile. This design will probably have much lower plasma pressure, but since the lorentz force acting on the plasma will also act on the projectile, the projectile will be accelerated (i hope). Actually it's quite similar to a normal plasma armature railgun, but now the armature is made of air
Registered Member #3950
Joined: Wed Jun 15 2011, 12:45AM
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Posts: 51
The lorentz force is when a current flows through a conductive projectile. A non-conductive projectile will have no forces acting on it other than that of the expanding gases behind it. And if that is the case, why not just use gunpowder?
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
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Posts: 600
You are creating an arc, and then using the power in the rails to accelerate that arc down barrel behind a nonconductive armature? That sounds terribly inefficient... but if you are still stuck on using plasma pressure/movement to accelerate a projectile, why not use this force as an "injector" system. Of course if you want a really efficient gun, just stick with a copper/aluminum armature and rails. You will be surprised how much energy is wasted in plasma.
Although it would look very cool to have a thick glass/plexi barrel so you can see the plasma!
The lorentz force is when a current flows through a conductive projectile. A non-conductive projectile will have no forces acting on it other than that of the expanding gases behind it. And if that is the case, why not just use gunpowder?
Actually it's the reactive force on a moving charged particle through a magnetic field, so the arc (moving charged particles) pushes the projectile forward. You could call this force an additional pressure.
ben123324 wrote ...
You are creating an arc, and then using the power in the rails to accelerate that arc down barrel behind a nonconductive armature? That sounds terribly inefficient... but if you are still stuck on using plasma pressure/movement to accelerate a projectile, why not use this force as an "injector" system. Of course if you want a really efficient gun, just stick with a copper/aluminum armature and rails. You will be surprised how much energy is wasted in plasma.
Although it would look very cool to have a thick glass/plexi barrel so you can see the plasma!
Haha I agree it would look cool. I might reconsider using garolite :D. I can imagine it is quite inefficient if ohmic losses through the plasma are much higher in an 'arc'-armature compared to a metal armature. Especially since a plasma contains both positive and negative charges which yields about half the charges wanting to go the other way :(. Unfortunately, my knowledge on plasma's is quite limited.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
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The conductivity of plasma isn't as good as a nice chunk of copper, but it's still very low(relative). Most of the wasted power is in creating/maintaining the arc. All plasma is after all is superheated gas. Imagine how much heat and noise are produced, then see if you can calculate the amount of energy required to generate that heat. If efficiency isn't the objective the I for one would strongly support this idea. But a combination of the two systems together as mentioned above- plasmatic(real word?) expansion/acceleration used to inject a conductive armature into the classic railgun- would yield both impressive results and a very cool looking system. But try using a seperate bank for each subsystem. You wouldn't want to inadvertantly waste the whole banks energy on just the injector. Anyways- goods luck!
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529
Hey, What you're describing is called a plasma armature. They can work well, but will take effort. You will see heavy corrosion on the rails. Typically instead of creating a high voltage arc, you use an injector that pushes your non-conducting projectile into the bore backed with a thin material. The material is vaporized and forms a plasma channel. I have used aluminum foil and magnesium (loud and fun :p). They look cooler (plasma!), but they won't work as well as a solid projectile. If you are using low powers, plasma is better as the pressure will be the primary propellant. In higher power designs, plasma simply wastes energy and corrodes the rails and projectiles. Alot of the times when using a solid projectile, you still get plasma. Small ohmic contacts vaporize and create a sort of hybrid: Rail->plasma->projectile->plasma->rail. My project is here: Never got around to finishing it, contact me if you have specific questions (contact form on the site)!
Hey, What you're describing is called a plasma armature. They can work well, but will take effort. You will see heavy corrosion on the rails. Typically instead of creating a high voltage arc, you use an injector that pushes your non-conducting projectile into the bore backed with a thin material. The material is vaporized and forms a plasma channel. I have used aluminum foil and magnesium (loud and fun :p). They look cooler (plasma!), but they won't work as well as a solid projectile. If you are using low powers, plasma is better as the pressure will be the primary propellant. In higher power designs, plasma simply wastes energy and corrodes the rails and projectiles. Alot of the times when using a solid projectile, you still get plasma. Small ohmic contacts vaporize and create a sort of hybrid: Rail->plasma->projectile->plasma->rail. My project is here: Never got around to finishing it, contact me if you have specific questions (contact form on the site)!
Are you sure conventional plasma armatures do not work as well as a solid projectile? I thought that navy uber shot was done with a plasma armature? Anyway does this rail erosion happen from using a plasma armature or a solid projectile? And how are you sure it is caused by the plasma (in the former case)? Can it be caused by misalignment of the projectile, leaving some sort of skidmark?
Cool site btw, too bad you haven't got more time. Did you make this drawing ( or where does it originate from? Maybe i can borrow some fabrication ideas, since I'm also going for this approach.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529
Nope, the navy uses solid armatures. The projectiles are pushed in with hydraulics to maximize contact. That erosion is from a solid projectile. I have to make it loose enough that the injector can push it in the rails, and that allows for wobble. It is not a skid mark- not there is physical erosion and aluminum deposits on the copper. That link isn't pointing to anything! I'm guessing you mean the dimensioned drawings, those are mine. Feel free to use them!
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ETRG: (hybrid) electrothermal railgun
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