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Amateur coil gun approach sound barrier

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LAN_403

pulslaser

Thu Mar 02 2006, 09:19PM

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

hi,
I now finish my second induktion coil gun. It uses 8 stages including injector. Each stage has a 40ÂµF 2.5kV capacitor which is discharged through the coil by a trigger spark gap. The spark gap is by triggered by another gap which is triggered by the passing projectil. The projectile, a short piece (2.5 cm) of alu tube has reached a velocity of 270 m/s . So I hope to reach the magic 330 m/s by optimization during next days. More infos will follow at weekend when I will have enough time to do some work

Simon

Fri Mar 03 2006, 12:01AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

What's the mass of the projectile?

How does the triggering work? Is it optical? Inductive?

(That's serious amateur work, by the way.)

...

Fri Mar 03 2006, 12:27AM

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

looks nice!

looking at the first post he is using a mechanical trigger...

Liam

Fri Mar 03 2006, 06:36AM

Registered Member #113 Joined: Fri Feb 10 2006, 01:40AM
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Posts: 49

Pardon my ignorance (I've never built a coilgun). I understand this is a tremendous amount of power, but isn't the spark gap AWFUL in terms of power loss? I mean, it has to have one of the worst efficiencies of any switch. Could you not find a large enough SCR?

Desmogod

Fri Mar 03 2006, 08:08AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

Liam, I think the problem with finding a puck to transfer that amount of energy is going to be cost.
i.e. it'll be huge.

Plasmaniac

Fri Mar 03 2006, 01:12PM

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

I've blown an 10kA peak SCR with one similar cap @ just a little over 1kV. In my single stage induction coilgun, I use a mechanical triggered sparkgap, so the losses are a little lower, but it is too slow for multistage designs.

Pulslaser: Do you get higher efficiencys with pieces of aluminum tube than with solid aluminium?

pulslaser

Fri Mar 03 2006, 06:56PM

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

Simon: triggering is done by a spark gap across the barrel just behind each coil. This gap fires when the conduction projectil passes and discharge the red 6 kV capacitors over the trigger pin of the main switch gaps which in turn discharge the main capacitors through the coils
Liam: it would be very expensive to buy 8 high power thyristors, and there are not as robust than spark gaps which are easily homemade and in case of failure repaired. The losses at high voltages of 2.5 kV are not as serious as in low voltage applications.
Plasmaniac: I found solid projectil much slower (100 m/s) mayby because of higher weight or because in this case the projectil works like a piston and has to suck the air behind into the barrel and press it out infront.
I just made some shots on a 1cm strong piece of wood. It makes a very nice sharp entrance whole

rupidust

Fri Mar 03 2006, 08:09PM

Banned
Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

Nice setup. Is this 125 Joules per stage? That sounds like a reasonable energy level for puck SCRs. The pulse discharge is obviously shorter than most CGs. SCR need to be increadibly large but just need to cover the large current value. What is the current anyhow, coil resistance? An R-puk SCR will cover the voltage and current spec at 2500v to 4000v and surge current starting at 20,000A.

There are not big, but their price will choke you. Acquirement by distributor is out of the question, but might get lucky on ebay or a surplus source. Noise issue of triggered sparks is only reason I opt not for spark gap.

Tipp

Sat Mar 04 2006, 04:24PM

Registered Member #215 Joined: Sun Feb 19 2006, 09:14PM
Location:
Posts: 30

Thats incredable! Very sweet! I'm quite impressed, to say the least.

Best wishes in your efforts to reach 330

pulslaser

Sun Mar 05 2006, 07:50PM

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

Hi,
after some hours of working with the coil gun I have to admit that the sound barrier is still intact. Mostly I reached some 300 m/s. I think one or two more stages would fix the probleem, but it's not possible with the existing device. Anyway it was a great fun building the device.

To rapidust, I didn't measure current, but according to a pspice simulation it should be around 2..3 kA, the resistance of the coils is negible, 10 to 30 windings of 1mm CuL wire. With the the main spar gaps enclosed in plexiglastubes they don't make much noise. More noise is produced by the recoil forces on the coils. The very tight windings are repelled about 1mm on the barrel after some 50 shots. And of course most noise is made by the impact of the projectil in the target.
More information is found again on my webpage http://www.rapp-instruments.de (sorry in german language)

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