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Simple electrothermal gun

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Simple electrothermal gun

Unread postAuthor: jon_89 » Thu Mar 20, 2008 11:39 pm

Check this out.http://www.instructables.com/id/How-to-build-a-simple-Plasma-Rifle-aka-Electrother/. This is just a super simplified version of this right?http://www.spudfiles.com/forums/28-8kj-electrothermal-gun-with-videos-and-damage-pics-t13449.html. In the instructions it says low an high velocity anybody know or do something like this?
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Unread postAuthor: Hotwired » Fri Mar 21, 2008 3:15 am

Well it's the easiest capacitor source anywhere ^_^

I'm doing something vaguely like that right now. Currently at the "build a large capacitor bank" stage.

3300V and 100uf for 544J is the aim :)

In camera circuit terms thats at least 100 disposables. If my wierd design works I'll move to real capacitors :wink:
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Unread postAuthor: Antonio » Fri Mar 21, 2008 3:48 am

I like this one
You know we should actually combine electro and pneumatic valve guns. Like my moving barrel gun> it could be actuated using a coil. I did some calculations on how many coils I need, and it was allot. Are there any instructions for making coils, or do you guys buy ehm?
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Unread postAuthor: Hotwired » Fri Mar 21, 2008 8:49 am

For BB guns a coil is feasible.

I don't think anyone making a hobby coilgun buys their coil, especially if it's a camera circuit based one. It's just enamelled wire tediously wound round a coil forming cylinder or the barrel itself (I personally just unwound a small motors coils for my wire)

After doing that its a good thing to have the ends held tight and cover the coil in a glue, epoxy or shrink wrap tubing so it doesnt try to unwind.

As to how strong the magnetic field is from a coil made of X wire of X dimensions and with X voltage... you'd need to do some research. Or forget research and experiment ^_^
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Unread postAuthor: Fnord » Fri Mar 21, 2008 9:06 am

I think we're going to need a new showcase section with the upgrade to bb3.
There seems to be a lot of interest in non-traditional launchers lately.

I may make a small electrothermal gun after the railgun... with 312 joules in each 2.5 x 5 capacitor I could easily make a handheld.
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Unread postAuthor: Antonio » Fri Mar 21, 2008 9:08 am

Hotwired wrote:For BB guns a coil is feasible.

I don't think anyone making a hobby coilgun buys their coil, especially if it's a camera circuit based one. It's just enamelled wire tediously wound round a coil forming cylinder or the barrel itself (I personally just unwound a small motors coils for my wire)

After doing that its a good thing to have the ends held tight and cover the coil in a glue, epoxy or shrink wrap tubing so it doesnt try to unwind.

As to how strong the magnetic field is from a coil made of X wire of X dimensions and with X voltage... you'd need to do some research. Or forget research and experiment ^_^


Yeah I had done some calculations before, but i needed something like 6million coils lol. As in this case the acceleration wasnt that important, rather the force that it could exert. But yeah ill check it out again and post it here, c what other ppl think. Btw how many coils(turns) do u use for your strongest gun? Also over how many cm of length is it coiled?
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Unread postAuthor: TurboSuper » Fri Mar 21, 2008 9:45 am

Generally speaking, building a coilgun to have performance comparable to most pneumatic or chemical launchers is quite a stretch. However, that electrothermal gun seems somewhat simpler, especially since it doesn't need precise timing like a coilgun does.

Better start collecting them capacitors :D
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Unread postAuthor: Hotwired » Fri Mar 21, 2008 4:22 pm

I've got a pile of 54 circuit boards sitting on my desk this very moment :wink:

Another 50-odd should have me set for the capacitor bank given that not all the capacitors will be useful for it.

Just that lot required visiting five different shops where I was given anything from 0 to 28 camera shells. I'll probably try the unhelpful ones again when different staff are in :)

TurboSuper to be honest I'd rank both a single stage coilgun and a electrothermal gun as the same difficulty. A single stage coil requires zero timing and they both need pretty much the same charging circuits and switching gear.
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Unread postAuthor: TurboSuper » Fri Mar 21, 2008 4:37 pm

Hotwired wrote:TurboSuper to be honest I'd rank both a single stage coilgun and a electrothermal gun as the same difficulty. A single stage coil requires zero timing and they both need pretty much the same charging circuits and switching gear.


Definitely true, I suppose I didn't word my opinion correctly:

The way I see it, it would be easier to scale up an electrothermal gun since all you're really doing is dumping more and more current through more and more material to be vapourized. I think after a certain point, dumping current through a coil doesn't do very much for the coilgun as much as multistaging it does, so you end up with a bit of a brick wall.

Now I'm sure there's also the situation of efficiency (I.E: How much electrical energy is converted into kinetic energy within the projectile), but unfortunately, I'm not really much of an expert when it comes to that.

And man, you guys sure seem to have an easy time getting camera flashes. I always have found it rather difficult; I need a better supplier. I have, however, had good luck finding old CRTs which have beefy caps on their circuit boards (not to mention the CRT itself).
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Unread postAuthor: jon_89 » Fri Mar 21, 2008 7:51 pm

what is the biggest cap a camera flash could charge? i have thought about coil guns and willmost likely build one.
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Unread postAuthor: Hotwired » Fri Mar 21, 2008 8:28 pm

jon_89 wrote:what is the biggest cap a camera flash could charge?


There is no limit aside from charging time on how large a capacitor you charge with it. Even then you can add more batteries and more circuits to decrease the charge time.
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Unread postAuthor: jon_89 » Fri Mar 21, 2008 11:25 pm

As of now I am leaning towards the coilgun. I got some steel wool and touched it to my capacitor and it just caught on fire. To me this doesn't seem like it would create much if any at all. Coilgun here I come. :twisted:
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Unread postAuthor: Daegurth » Sat Mar 22, 2008 4:47 am

Hotwired wrote:Just that lot required visiting five different shops where I was given anything from 0 to 28 camera shells. I'll probably try the unhelpful ones again when different staff are in :)


which photo shops did you go to? i went to a click 1hr place, and they yold me that they have to send the cases back to the maufacturer. :?

i'd have thought that would work out much more expensive in the long run, but it was probably just the guy being unhelpful.
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Unread postAuthor: Hotwired » Sat Mar 22, 2008 9:06 am

They're talking bollocks ^_^

What happens in all photo development shops is that they take in dozens of differently manufactured disposable cameras, rip out the film (and sometimes the battery) then toss the assorted cases into a sack or box for disposal.

I've taken hundreds apart and the possibilities of recycling them without manual labour are slim.

Too many different plastics, little bits of metal etc...

Anyway.

I've obtained cameras from Boots (four branches of), a Jessops, a photo developing department in Sainsburys and a little privately owned place I forget the name of.

Anywhere with a photo department will do.

Boots can be erratic, you have to make sure someone is physically at the photo desk because asking other people tends to end you up with the manager who is more likely than junior staff to play it safe and say they don't think they can give them out etc...
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