new EM gun, em slingshot
pulslaser, Sat Apr 01 2006, 05:25PMwhen I was working with last railgun I got the idea to use the enormous forces without the troublesome slide contact. So I made something which in german is called "armbrust" I don't know the english word. It is just a copperbar and a copper string infront of the bar, fixed to the bar are four guide rails for the projectil. With high current flowing through the string and back through the bar the magnetic field repells the string from the bar and the string accelerates the projectil like a string in bow. Better look the pictures than to try to understand my bad english. For the first trials a got a speed of about 40 m/s, which is not high, but not bad for beginning. There is a lot of power behind the string, after some shots the 5mm thick string was teared up. For excitation I used 34mF with 300V and my good old ignitron switch.
Re: new EM gun, em slingshot
Madgyver, Sat Apr 01 2006, 05:39PM
The english term would be "Crossbow".
Great! You finaly did it. Looks awesome, as always. When you told me about it, I didn't know you had a crossbow in mind, rather a catapult or something.
Where do you get that copperband anyway? I wanna try the "other Railgun" Idea you talked about. Cause I'm so bored right now.
I believe, that using a coil in series with the railgun, could improve results somewhat. You don't have timing issues anyway, don't you?
Madgyver, Sat Apr 01 2006, 05:39PM
The english term would be "Crossbow".
Great! You finaly did it. Looks awesome, as always. When you told me about it, I didn't know you had a crossbow in mind, rather a catapult or something.
Where do you get that copperband anyway? I wanna try the "other Railgun" Idea you talked about. Cause I'm so bored right now.
I believe, that using a coil in series with the railgun, could improve results somewhat. You don't have timing issues anyway, don't you?
Re: new EM gun, em slingshot
Quantum Singularity, Sat Apr 01 2006, 06:23PM
I have seen this concept in demonstrations before but never to launch a projectile, atleast if I understand this correctly. For example I have seen a car battery with a very low resistance load with two parallel wires feeding one terminal of the battery, or maybe it was opposite terminals, I cant remember. Anyhow, when the current flowed, the two wires sitting side by side would jump apart under repulsion.
For any star wars fans out there this kinda reminds me of chewie's bowcaster. I always tghought if its and energy weapon, why is it shaped like a crossbow? Well, maybe it was one of these types that pulslaser is building!
Quantum Singularity, Sat Apr 01 2006, 06:23PM
I have seen this concept in demonstrations before but never to launch a projectile, atleast if I understand this correctly. For example I have seen a car battery with a very low resistance load with two parallel wires feeding one terminal of the battery, or maybe it was opposite terminals, I cant remember. Anyhow, when the current flowed, the two wires sitting side by side would jump apart under repulsion.
For any star wars fans out there this kinda reminds me of chewie's bowcaster. I always tghought if its and energy weapon, why is it shaped like a crossbow? Well, maybe it was one of these types that pulslaser is building!
Re: new EM gun, em slingshot
pulslaser, Sun Apr 02 2006, 08:38AM
Hi Madgyver,
the copperband you will find at electric shops, it's sold as "Erdungsband", if you need only some meters you can get it from me.
I think it's a good idea to stretch the puls until it compare with the transittime of the projectil in the rails using a inductivity. I think the best way is to build the inductivity as serial augmentation windings beside the rails.
Meantime I'm trying to realize a railgun with a car battery. The battery has a capaticity of 64Ah, and a "Kälteprüfstrom" of 600A, I think the shortcurrent should be around 1000A or higher. So I can get high current pulses at least for 0.5 second.
pulslaser, Sun Apr 02 2006, 08:38AM
Hi Madgyver,
the copperband you will find at electric shops, it's sold as "Erdungsband", if you need only some meters you can get it from me.
I think it's a good idea to stretch the puls until it compare with the transittime of the projectil in the rails using a inductivity. I think the best way is to build the inductivity as serial augmentation windings beside the rails.
Meantime I'm trying to realize a railgun with a car battery. The battery has a capaticity of 64Ah, and a "Kälteprüfstrom" of 600A, I think the shortcurrent should be around 1000A or higher. So I can get high current pulses at least for 0.5 second.
Re: new EM gun, em slingshot
Electroholic, Sun Apr 02 2006, 06:51PM
34mf at 300v that is ~1.5kJ right?
whats the peak current?
I think it's the greatest em design ever!
Gota rig up one when i am done with my finals
Electroholic, Sun Apr 02 2006, 06:51PM
34mf at 300v that is ~1.5kJ right?
whats the peak current?
I think it's the greatest em design ever!
Gota rig up one when i am done with my finals
Re: new EM gun, em slingshot
Bjørn, Sun Apr 02 2006, 07:04PM
Some car batteries have been measured to 10 kA pulse current. A good quality car battery can deliver very large currents for some time so they should be fairly suitable for rail guns. Just make sure you don't get continuous arcs and hydrogen explosions.
Bjørn, Sun Apr 02 2006, 07:04PM
Some car batteries have been measured to 10 kA pulse current. A good quality car battery can deliver very large currents for some time so they should be fairly suitable for rail guns. Just make sure you don't get continuous arcs and hydrogen explosions.
Re: new EM gun, em slingshot
pulslaser, Sun Apr 02 2006, 08:54PM
Hi Jimmy,
I didn't had possibility to measure the current. I'm just building a rogowski coil for measuring high currents, but it's not finnished yet.
Hi Bjoern,
some ten's of kiloamps sounds good. I'm not shure about the switch to use. I have left a large igbt from oltc teslacoil which switch 2400A , but I'm afraid about the voltage drop, 12 V isn't too much to spend. Perhaps better way would be to charge a inductor coil for some hundred miliseconds and than release the stored energy into the rails. But there's of course the problem to build a opening switch for high currents.
pulslaser, Sun Apr 02 2006, 08:54PM
Hi Jimmy,
I didn't had possibility to measure the current. I'm just building a rogowski coil for measuring high currents, but it's not finnished yet.
Hi Bjoern,
some ten's of kiloamps sounds good. I'm not shure about the switch to use. I have left a large igbt from oltc teslacoil which switch 2400A , but I'm afraid about the voltage drop, 12 V isn't too much to spend. Perhaps better way would be to charge a inductor coil for some hundred miliseconds and than release the stored energy into the rails. But there's of course the problem to build a opening switch for high currents.
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