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Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
The revision 2 Railgun will incorporate several major changes, and several minor changes. Major updates: -The capacitor bank will be expanded by 22 capacitors, giving a increase from 5616 joules to 12480 joules, at 400 volts. Peak energy, with capacitors set aside for coilgun and surge voltage, will be 16980 joules. -The bus bars are reconfigured to use minimal material, and have minimal resistance. They will be 1/2" thick aluminium (due to cost restrictions). Total bus bar length will 8 feet, versus the 11 feet for the current much smaller bank. -8x 2"x2"x1" NdFeB magnets (grade N50) will be used for a permanent magnet augmented railgun. The field strength of these is large enough to be beneficial even with 100,000A current. Minor changes: -The injection valve was retrofitted with a solenoid, which will allow for remote triggering -The rails will be silver plated, with the cool-amp silver plating powder. -In an effort to minimise resistance, the cables have been eliminated. -a analog pressure sensor was connected, and a comparator circuit (point to point solder) is set to trigger at 50 PSI. -The charging will be a HF transformer with a flyback core, for better voltage level control. Some things I plan on trying out: - 3" square pieces of bullet proof glass (thanks Jimmy) will be shot, hopefully getting fractal patterns. This will be useful for comparing power, and seeing the orientation of the projectile when impacted. -self-augmented rails -Switching power into the rails with a triggered sparkgap, built into the back of the railgun. Pictures can be seen at:
Registered Member #1917
Joined: Fri Jan 09 2009, 02:38AM
Location:
Posts: 62
That's interesting, because I've never even seen the test results of the original railgun posted anywhere yet. How fast were the projectiles going? What different projectile types did you compare? Was the rail erosion study conducted?
As far as the second design goes, it sounds good. You really need to aim for tolerances as close as possible between the projectile and the rails. Unless you're using plasma armatures, you shouldn't be able to load it without a hammer. Keeping it down to 400V will also work in your favour. I'm also interested in how you plan to implement the triggered spark gap switching to coincide with the projectile entering the rails - wouldn't it be simpler to do away with the injection altogether? You're not gaining a whole lot of kinetic energy through it anyway.
As for seeing which way the projectile was oriented on impact: You'd be better of having it hit a lead block, assuming the speeds are low enough. At higher speeds, anything you shoot will tend to develop craters and the projectile just kind of disappears.
Good luck with this project. If you manage to avoid smashing the ends off of several fingers with those magnets during construction, you can consider it mostly successful
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
I already managed to get the magnets in a block. A railgun enclosure makes a great tool to seperate magnets. I can machine the projectiles with close tolerances, but they will not work. They have to be kept fairly loose for the injector to work. That is why I want to use a two brush projectile, it allows both to work. Research papers have also shown these to work best. The first one was based on visual observations, I will make an attempt to make speed measurments on this one, with sound based ,as well as a break wire. Also used will be a serpintine B-dot probe, as well as up to 12 B-dot probes, 4 in each axis. Frankly, revision 1 sucked. Every single shot with that was done with the same rails. I did, however, find that a lubricant does help, as does a V tail.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
rp181 wrote ...
I already managed to get the magnets in a block. A railgun enclosure makes a great tool to seperate magnets. I want to do away with the injector, send me a SCR stack, and I would be happy too. I can machine the projectiles with close tolerances, but they will not work. They have to be kept fairly loose for the injector to work. That is why I want to use a two brush projectile, it allows both to work. Research papers have also shown these to work best. The first one was based on visual observations, I will make an attempt to make speed measurments on this one, with sound based ,as well as a break wire. Also used will be a serpintine B-dot probe, as well as up to 12 B-dot probes, 4 in each axis. Frankly, revision 1 sucked. Every single shot with that was done with the same rails. I did, however, find that a lubricant does help, as does a V tail.
Where did you see the triggered spark gap switch? My plans for that invlolve the projectile starting in the rails, the TSG is built in the back to contribute its pressure.
the triggered gap is listed under minor changes in the OP, but as long as the injection system works you shouldn't need it as the Projectile will act as the Switch.
and just remember, that glass is Bullet Resistant, not Bullet Proof - and while it is level III (rated for up to a .44 three times in a small triangle), your projectile may be VERY hot! - I still expect it to hold up, as you are doing single shots per piece of glass, but make sure you post to YouTube with the results!
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Thats embarrassing.... When I talked about the TSG, the plan for that was to get rid of the injection system, and start the projectile in the rails. It would basically be the same as badastronauts railgun, but instead of a SCR, I use a TSG.
I also expect the glass to holdup, But it wouldn't be bad if it didn't =)
I am determined to get velocity readings on this, a break wire chrono with a serpintine b-dot probe, and normal B-dot probes almost gaurentee's a velocity reading.
I started measuring the RC time constant of each capacitor. Its looking like the capacitance will be equivilant to about 38 spec capacitors.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
rp181 wrote ...
Thats embarrassing.... When I talked about the TSG, the plan for that was to get rid of the injection system, and start the projectile in the rails. It would basically be the same as badastronauts railgun, but instead of a SCR, I use a TSG.
I also expect the glass to holdup, But it wouldn't be bad if it didn't =)
I am determined to get velocity readings on this, a break wire chrono with a serpintine b-dot probe, and normal B-dot probes almost gaurentee's a velocity reading.
I started measuring the RC time constant of each capacitor. Its looking like the capacitance will be equivilant to about 38 spec capacitors.
if I remember, you mentioned in a PM a high speed camera being involved? - if one is, you could use a reference board in the background of its view (yellow/black strips of a known and equal length, alternating) and by using the camera frame rate, and the number of frames it takes the projectile to cross the reference board, you can determine velocity without having to affect your results by using a break wire... just a thought, but I use the same method since I have a high speed camera (Casio EX-FH20), any camera will work but the lower the frame rate the less accurate the results.
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Yes, But I expect the camera to be blinded by the plasma. a break wires affect will be negligible with this amount of power. I will try it anyway, I already printed a reference background.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042
rp181 wrote ...
Yes, But I expect the camera to be blinded by the plasma. a break wires affect will be negligible with this amount of power. I will try it anyway, I already printed a reference background.
"break wire's effect" - just getting an English compulsion out of the way
and remember, these cameras take an enormous amount of light, I would be shocked to see the plasma blind the camera unless you used bizarre settings or unless your lighting conditions are already extremely bright
I'll put it this way, when I was using the camera on fire crackers to get photos of the explosion in progress, I had to ADD light to the scene and do it in broad daylight, and the image is just right.
also, I fotgot to say good luck with your new railgun!
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Railgun V2
