Induction/repulsion coilgun / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Induction/repulsion coilgun

1 2 next

Move Thread

LAN_403

pulslaser

Sun Feb 12 2006, 08:19PM

Registered Member #156 Joined: Sun Feb 12 2006, 07:04PM
Location:
Posts: 23

Hi,
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 40ÂµF 2.5kV) are spark gap switched and the injector (680ÂµF 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)

...

Sun Feb 12 2006, 08:26PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

well the burning question these days seems to be...
What is the efficiency?

Nice looking coilgun though :)

pulslaser

Sun Feb 12 2006, 08:38PM

Registered Member #156 Joined: Sun Feb 12 2006, 07:04PM
Location:
Posts: 23

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

Eric

Sun Feb 12 2006, 09:13PM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116

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.

pulslaser

Mon Feb 13 2006, 10:31PM

Registered Member #156 Joined: Sun Feb 12 2006, 07:04PM
Location:
Posts: 23

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.

Madgyver

Wed Feb 15 2006, 02:27PM

Registered Member #177 Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214

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?

pulslaser

Sun Feb 19 2006, 09:29AM

Registered Member #156 Joined: Sun Feb 12 2006, 07:04PM
Location:
Posts: 23

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.

Plasmaniac

Sun Feb 19 2006, 06:08PM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

Nice work pulslaser! Where did you got the caps? I got one on ebay.de and an other 125ÂµF 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:

Cap New

btw: I payed 20â‚¬ for the tiny cap and 5â‚¬ for the big one

Dr. Shark

Sun Feb 19 2006, 07:36PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

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!

pulslaser

Sun Feb 19 2006, 08:38PM

Registered Member #156 Joined: Sun Feb 12 2006, 07:04PM
Location:
Posts: 23

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

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob