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Crazy 10kJ coilgun in youtube

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LAN_403

Wizzup

Sun Feb 24 2013, 04:52PM

Registered Member #3302 Joined: Sun Oct 10 2010, 02:21PM
Location: Finland
Posts: 42

I found this video in youtube:

In the end of the video I understand that it says that it has 4% effiency, 4% out of 10kJ is 400J of kinetic energy! It also seems like it is just one coil and it mentions aluminum in the text so I would guess that this is induction based, but in the schematic in the video the coil looks very much like "normal" coil so what do you think? Is there any people here from Poland that could translate the texts for us who dont speak Polish? I would like to know more about the coil's structure and what kind of capacitors they use. There is also some footage of it firing, it goes through those wooden plates like its nothing.

EDIT: I just noticed that if you look at the coil before the shooting you can actually see the projectile there, so it is for sure inductance based. Would be interesting to know the velocity of the projectile and how much it weights.

Maxwell

Tue Feb 26 2013, 02:25AM

Registered Member #8497 Joined: Tue Dec 04 2012, 06:24PM
Location:
Posts: 74

I noticed they're using what looks to be a thyratron - which I believe is regulated (in the U.S.) much as nuclear weapons are - as they can be used to detonate nuclear explosions.

Electroholic

Tue Feb 26 2013, 04:39AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

That's a trigatron, a triggered sparkgap in other words. Pressurized with argon I think he mentioned.
Quite impressive I must say.

...

Tue Feb 26 2013, 04:42AM

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

It looks like a trigatron (which admittedly is very similar to a thyratron), most likely built in house by the looks of it.

I think you are right that it is induction based, although the coil geometry seems odd for a normal induction launcher, but I do not think there would be any way to get that class of performance from a single stage 'normal' coilgun.

DerAlbi

Tue Feb 26 2013, 02:14PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

May i ask what you think is the limiting factor?

and... Maxwell... seriously...

Adrenaline

Tue Feb 26 2013, 04:05PM

Registered Member #235 Joined: Wed Feb 22 2006, 04:59PM
Location:
Posts: 80

Maxwell wrote ...

I noticed they're using what looks to be a thyratron - which I believe is regulated (in the U.S.) much as nuclear weapons are - as they can be used to detonate nuclear explosions.

I believe you are thinking of the Krytron.

The coil 'geometry' is odd, I wonder if it is just showing the position of the projectile WRT the center of the solenoid coil. The coil just being a regular solenoid.

...

Tue Feb 26 2013, 05:18PM

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

DerAlbi wrote ...

May i ask what you think is the limiting factor?

Assume a 100g projectile, means it is accelerated to 100m/s (projectile probably weighs less than that)

Acceleration length looks to be about .02 meters, assuming constant acceleration the projectile is in the coil for 400us.

This means that all 10kj of energy needs to be dissipated in well under 1ms, which is in agreement with their claim of a having on the order of 10^6 amps of current.

Assume the caps are 10kv, 200uf (wild guess, but I see some maxwell pulse caps under the table), the series inductance of the whole mess has to on the order of 10uH, which would be consistent with an air core coil about the size of theirs, but if you put a lump of metal in it the inductance is going to go up significantly, making it hard to keep the pulse width short enough while still generating a large B-field in the coil. This is why there are few successful single stage coil guns with more than a few KJ of energy.

So- I conclude that either they are purposefully running the projectile in the 'very' saturated regime to keep the inductance down (which is hard to believe given their decent 4% efficiency), or they are using a non-ferrous projectile which they are accelerating purely using induction.

MrFlatox

Tue Feb 26 2013, 10:37PM

Registered Member #9349 Joined: Mon Jan 07 2013, 08:50AM
Location: France
Posts: 102

You can use non-ferrous material in a coilgun ??

DerAlbi

Wed Feb 27 2013, 12:03AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

... May i ask why smaller coil guns work then? they suffer from the same effects - these scale with the projectile size.
Or can you explain why the mentioned things dont effect smaller guns?

Current rise time can be influenced by voltage - not only by inductance - and Amps*turns matter sooo... decreasing inductance is not the best thing.

Where would you set the theoretical limits and why? Sry, i realy dont see your point

Yandersen

Wed Feb 27 2013, 12:06AM

Registered Member #6944 Joined: Fri Sept 28 2012, 04:54PM
Location: Canada
Posts: 340

Surely it is an induction launcher - regular coilguns are not for such energies (at least single staged ones) and that's why thyrasmg is used - no semiconductor exists that can handle megaamps.
The efficiency of regular coilgun drops after saturation, but induction launcher increases efficiency with power. The explanation is following: before saturation force is proportional to the square of the current (for both coilgun types) - the same as heat losses. So increasing energy lowers the time it takes for projectile to leave the coil, so the higher the energy, the less the pulse time, so efficiency rises. But regular coilgun experiences saturation after some energy limit and force becomes proportional to the current almost linearly (while induction launcher always has force proportional to the square of the current), and as result efficiency starts to lower with increase of energy. At some point low initial efficiency of induction launcher becomes larger than a regular coilgun's efficiency. In addition, with very short pulse times repulsion from eddy currents in a regular coilgun with solid iron projectile may decrease the force dramatically.

I was thinking about making an induction launcher shooting pennys - two flat spiral coils on top of each other and a penny in the gap between those coils, slightly pushed out of center of those coils. But so far my experiments with induction give me the way too low initial efficiencies, and I'm not a fan of high power.

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