Induction/repulsion coilgun
pulslaser, Sun Feb 12 2006, 08:19PMHi,
I just finished my first induction coilgun which works by repulsion of an aluminium projectil by eddy currents. The injector works with a normal coilgun which accelerate a iron core which in turn preaccelerate the aluminium projectil. The gun has five stages including the injector, the four main stages (4 x 40µF 2.5kV) are spark gap switched and the injector (680µF 400V) is thyristor switched. The projectil reach a speed of about 100m/s, which I think is not too bad for a coilgun.
More detailed information is found on my page http://www.rapp-instruments.de (german langue)
Re: Induction/repulsion coilgun
..., Sun Feb 12 2006, 08:26PM
well the burning question these days seems to be...
What is the efficiency?
Nice looking coilgun though :)
..., Sun Feb 12 2006, 08:26PM
well the burning question these days seems to be...
What is the efficiency?
Nice looking coilgun though :)
Re: Induction/repulsion coilgun
pulslaser, Sun Feb 12 2006, 08:38PM
Hi,
the stored energy is 800 Joule and the kinetic energy of the projectil is 10 Joule so the efficiency is only 1.25% but at the end I prefer high speed but high efficiency
pulslaser, Sun Feb 12 2006, 08:38PM
Hi,
the stored energy is 800 Joule and the kinetic energy of the projectil is 10 Joule so the efficiency is only 1.25% but at the end I prefer high speed but high efficiency
Re: Induction/repulsion coilgun
Eric, Sun Feb 12 2006, 09:13PM
That's a really beautiful peice of work. Do you think you have it optimized in terms of number of turns on the coils, guage wire, timing, etc.? I would guess you could get even better efficiency. Especially if you count recovered energy in the caps.
Eric, Sun Feb 12 2006, 09:13PM
That's a really beautiful peice of work. Do you think you have it optimized in terms of number of turns on the coils, guage wire, timing, etc.? I would guess you could get even better efficiency. Especially if you count recovered energy in the caps.
Re: Induction/repulsion coilgun
pulslaser, Mon Feb 13 2006, 10:31PM
I didn't really optimize the coils, because it would be very time consuming. Starting with 60 turns, I reduced to 20 turns and doubled the speed, further reducing to 10 turns showed difficulties with reliable triggering of the spark gaps because the accelerating coils works as it's own trigger transformer. I used 1mm CuL wire because thinner wire didn't stand the high currents and thicker wire increase the size of the coils which in turn reduce the magnetic field density. Timing is not that problem in repulsion mode, as long as the current puls is short compared with projectils speed.
pulslaser, Mon Feb 13 2006, 10:31PM
I didn't really optimize the coils, because it would be very time consuming. Starting with 60 turns, I reduced to 20 turns and doubled the speed, further reducing to 10 turns showed difficulties with reliable triggering of the spark gaps because the accelerating coils works as it's own trigger transformer. I used 1mm CuL wire because thinner wire didn't stand the high currents and thicker wire increase the size of the coils which in turn reduce the magnetic field density. Timing is not that problem in repulsion mode, as long as the current puls is short compared with projectils speed.
Re: Induction/repulsion coilgun
Madgyver, Wed Feb 15 2006, 02:27PM
Nice to see that you are up to something again. I am still waiting to see your railgun ideas though. That would be enormous exciting. Any work done yet?
Madgyver, Wed Feb 15 2006, 02:27PM
Nice to see that you are up to something again. I am still waiting to see your railgun ideas though. That would be enormous exciting. Any work done yet?
Re: Induction/repulsion coilgun
pulslaser, Sun Feb 19 2006, 09:29AM
Hi Mad Gyver,
are You still in Munic, I think there are semester holidays quite now, and maybe You're at home. I know working with a 8 stage repulsion coil gun, and I'm hopping to strike the sound barrier. I think I will do first test shots next week. If You like to have a look to the gun, You're invited.
I was working with a plasma armatured rail gun, but it was extremly loud and I can't do this experiments without frightening my neighbarhood. So I first have to constuct a envelop which dimmish the exlosion noise.
pulslaser, Sun Feb 19 2006, 09:29AM
Hi Mad Gyver,
are You still in Munic, I think there are semester holidays quite now, and maybe You're at home. I know working with a 8 stage repulsion coil gun, and I'm hopping to strike the sound barrier. I think I will do first test shots next week. If You like to have a look to the gun, You're invited.
I was working with a plasma armatured rail gun, but it was extremly loud and I can't do this experiments without frightening my neighbarhood. So I first have to constuct a envelop which dimmish the exlosion noise.
Re: Induction/repulsion coilgun
Plasmaniac, Sun Feb 19 2006, 06:08PM
Nice work pulslaser! Where did you got the caps? I got one on ebay.de and an other 125µF one from an radio amateur flea market (translated correctly?).
I never archieved good results with "normal" projectiles, but around 5% with pancake coils and flat projectiles. I'm going to wire both caps in parallel and try to shoot a little aluminium pipe projectile. I hope aluminium pipe will fly better than the piece of aluminium that I used last time.
EDIT: A pic of my old crappy induction coilgun (cap similar to one of yours) and my new capacitor:
btw: I payed 20€ for the tiny cap and 5€ for the big one
Plasmaniac, Sun Feb 19 2006, 06:08PM
Nice work pulslaser! Where did you got the caps? I got one on ebay.de and an other 125µF one from an radio amateur flea market (translated correctly?).
I never archieved good results with "normal" projectiles, but around 5% with pancake coils and flat projectiles. I'm going to wire both caps in parallel and try to shoot a little aluminium pipe projectile. I hope aluminium pipe will fly better than the piece of aluminium that I used last time.
EDIT: A pic of my old crappy induction coilgun (cap similar to one of yours) and my new capacitor:
btw: I payed 20€ for the tiny cap and 5€ for the big one
Re: Induction/repulsion coilgun
Dr. Shark, Sun Feb 19 2006, 07:36PM
Thomas sold a bunch of 30 of those caps to me a couple of years ago, but I cant really use them now since I am now in Helsinki. So if you need some, I guess I could part with a few. I will pass them on for the same low price Thomas asked, since we are all friends here
Thomas, can I also come and visit you? I think a tour of your lab would be well worth the price for a flight!
Dr. Shark, Sun Feb 19 2006, 07:36PM
Thomas sold a bunch of 30 of those caps to me a couple of years ago, but I cant really use them now since I am now in Helsinki. So if you need some, I guess I could part with a few. I will pass them on for the same low price Thomas asked, since we are all friends here
Thomas, can I also come and visit you? I think a tour of your lab would be well worth the price for a flight!
Re: Induction/repulsion coilgun
pulslaser, Sun Feb 19 2006, 08:38PM
Hi Plasmaniac,
I got the capacitors from the junk yard of a university, they have been used in a ruby laser. like You I got much better efficiency with a flat coil and a alu disk where you have a very strong coupling between the coil ad the disk( have a look to my "Wirbelstrom Beschleuniger"). I easily got speeds over 200m/s and some 500 m/s seems possible (The TUM/LRT electromagnetic launchers von Igenbergs, E. Aigner, S. Hudepohl, A. Rott, M. Weishaupt, U. Kuczera, H.). But of course this will not work in a multistage device. I found that the current puls has to be as short as possible( low capacitance, high voltage), because the length of acceleration is very short and the time of the projectil pass is short. So I don't know if it is a good idea to wire the capacitors parallel. Perhaps better way is to use to stages the larger capacitor for the first stage and the smaller for the second
pulslaser, Sun Feb 19 2006, 08:38PM
Hi Plasmaniac,
I got the capacitors from the junk yard of a university, they have been used in a ruby laser. like You I got much better efficiency with a flat coil and a alu disk where you have a very strong coupling between the coil ad the disk( have a look to my "Wirbelstrom Beschleuniger"). I easily got speeds over 200m/s and some 500 m/s seems possible (The TUM/LRT electromagnetic launchers von Igenbergs, E. Aigner, S. Hudepohl, A. Rott, M. Weishaupt, U. Kuczera, H.). But of course this will not work in a multistage device. I found that the current puls has to be as short as possible( low capacitance, high voltage), because the length of acceleration is very short and the time of the projectil pass is short. So I don't know if it is a good idea to wire the capacitors parallel. Perhaps better way is to use to stages the larger capacitor for the first stage and the smaller for the second
Re: Induction/repulsion coilgun
Plasmaniac, Sun Feb 19 2006, 09:48PM
What about shoothing a ring(or short piece of aluminium tube), just like the thomson's ringtosser? The triggering and winding of the coils would be hard, but the coupling would be much better.
This is a pretty impressive induction coilgun that you have! The only way I can measure the projectiles speed is through the height that it travels in total, so I can just calculate the efficiency for shots at around 400V. On such low voltages, much of the caps' energy gets lost due to sparkgap losses. I made a shot at 2500V... It can't be "just" 5% efficiency telling by the time it tooks until the projectile to hit the floor again...
I'll try a shot with both of them parallel. The capacistace isn't _that_ high (160µF) and the current rises to some 1000A, so the pulse can be short enough. We'll se. I'll compare both efficiencys. If they are nearly equal the pulse is short enough, if the efficiency without the big cap is less, the pulse is too long and if the efficiency with the big cap is even higher (which wont happen...) the internal resistance of my tiny 40µF cap also get worse, when the charger charged the cap to 3kV, blew my dmm and took away around 5µF of the cap's old total capacistance some month ago.
Plasmaniac, Sun Feb 19 2006, 09:48PM
What about shoothing a ring(or short piece of aluminium tube), just like the thomson's ringtosser? The triggering and winding of the coils would be hard, but the coupling would be much better.
This is a pretty impressive induction coilgun that you have! The only way I can measure the projectiles speed is through the height that it travels in total, so I can just calculate the efficiency for shots at around 400V. On such low voltages, much of the caps' energy gets lost due to sparkgap losses. I made a shot at 2500V... It can't be "just" 5% efficiency telling by the time it tooks until the projectile to hit the floor again...
I'll try a shot with both of them parallel. The capacistace isn't _that_ high (160µF) and the current rises to some 1000A, so the pulse can be short enough. We'll se. I'll compare both efficiencys. If they are nearly equal the pulse is short enough, if the efficiency without the big cap is less, the pulse is too long and if the efficiency with the big cap is even higher (which wont happen...) the internal resistance of my tiny 40µF cap also get worse, when the charger charged the cap to 3kV, blew my dmm and took away around 5µF of the cap's old total capacistance some month ago.
Re: Induction/repulsion coilgun
Madgyver, Sun Feb 19 2006, 10:05PM
Yes, your right, just finished a nasty chemistry exam and heading for my Praktikum tomorrow. Well, don't mind if a come around an visit you when I'am back then. That gun looks realy exciting.
Cheers, Minh
Madgyver, Sun Feb 19 2006, 10:05PM
pulslaser wrote ...
Hi Mad Gyver,
are You still in Munic, I think there are semester holidays quite now, and maybe You're at home. I know working with a 8 stage repulsion coil gun, and I'm hopping to strike the sound barrier. I think I will do first test shots next week. If You like to have a look to the gun, You're invited.
I was working with a plasma armatured rail gun, but it was extremly loud and I can't do this experiments without frightening my neighbarhood. So I first have to constuct a envelop which dimmish the exlosion noise.
Hi Mad Gyver,
are You still in Munic, I think there are semester holidays quite now, and maybe You're at home. I know working with a 8 stage repulsion coil gun, and I'm hopping to strike the sound barrier. I think I will do first test shots next week. If You like to have a look to the gun, You're invited.
I was working with a plasma armatured rail gun, but it was extremly loud and I can't do this experiments without frightening my neighbarhood. So I first have to constuct a envelop which dimmish the exlosion noise.
Yes, your right, just finished a nasty chemistry exam and heading for my Praktikum tomorrow. Well, don't mind if a come around an visit you when I'am back then. That gun looks realy exciting.
Cheers, Minh
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