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Simple disposable camera coilgun

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Alfons

Fri Jun 23 2006, 05:39PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

Hi,

I just finished a very simple disposable camera coilgun. You can find the details about the construction etc... here:

I didn't tune it or anything, since I just didn't know what to do and decided to build one

It works, and performs quite well, so I'm pleased with it.

Tell me what you think!

GimpyJoe

Fri Jun 23 2006, 06:46PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Cool, Alfons! I like the way it's nicely put together instead of just being a jumble of camera junk the way most simple CG's are. Does it penetrate a can?

Alfons

Fri Jun 23 2006, 07:13PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

Funky wrote ...

Cool, Alfons! I like the way it's nicely put together instead of just being a jumble of camera junk the way most simple CG's are. Does it penetrate a can?

Thanks! It allmost penetrates a can, but not quite. I guess it's the coil, since I do have quite a lot of energy stored in these 5 caps... But, as mentioned, I didn't tune it or anything so I guess I shouldn't count on it penetrating a can. I don't really mind. Maybe I'll try to upgrade it when I'm into it

Alfons

Sat Jun 24 2006, 10:48AM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

I just measured the projectile's speed using the Horizontal Ballistic Speed Trap Method and the speed is about 7,437 m/s (about 26,775 km/h, that is).

That isn't really fast, is it? Would winding a better coil help?

Bjørn

Sat Jun 24 2006, 12:08PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Find the weight of your projectile and calculate the energy at 7,437 m/s. Then calculate your efficiency. 1% is not too bad for a small coil gun, 3% is good, 10% is brilliant.

Alfons

Sat Jun 24 2006, 12:45PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

BjÃ¸rn BÃ¦verfjord wrote ...

Find the weight of your projectile and calculate the energy at 7,437 m/s. Then calculate your efficiency. 1% is not too bad for a small coil gun, 3% is good, 10% is brilliant.

Ok; my projectile weigs 1,2g; so if my calculations are correct, the Ek=(0,0012*7,437^2)/2=0,033J

There's one cap in my circuit on which no capacity nor voltage are printed; it only says 9(2) and 3e. Does anyone know about the capacitance / voltage of this cap?
Since it's about as big as the other caps, I'll assume it's a 80ÂµF, 330V cap.

The other caps are all rated 330V and wired in parallel; so the total capacitance is 120ÂµF+100ÂµF+80ÂµF+80ÂµF+80ÂµF=460ÂµF.

To calculate the stored energy; should I just do ((1/2)*0,000460F)*(330V^2)=25,047J?

So my efficiency is... 0,033J/25,047J=0,13%

Too bad...

Alfons

Sat Jun 24 2006, 01:40PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

Oops... I just blew up a cap...

I'm going to fetch some used disposable camera's in the local photostore to make another cg.

I do have a question: if I test the working of the coilgun, most of the time I get a huge ZAP between one wire of the coil and the wire I touch it with (which was connected to the flash-tube before I removed it). I thought to put a resistor in between but of course the resistor went up in smoke...
Does anyone know how to prevent a zap, but still get a decent result from the coilgun?

GimpyJoe

Sat Jun 24 2006, 03:30PM

Registered Member #316 Joined: Mon Mar 13 2006, 01:30PM
Location: Marietta, GA
Posts: 212

Find an SCR! You can read up on them on the wiki, using an SCR will reduce your switching losses enormously and maybe get you to .5% efficiency. From there, try winding a better coil and remember this is a magnet; you want the windings as close to the projectile as possible. Use the thinnest barrel material you can find.

Electroholic

Sat Jun 24 2006, 03:45PM

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

does the huge zap discharge the cap?
whats the problem?

and as stated, SCRs will also improve the performance A LOT.

Alfons

Sat Jun 24 2006, 04:18PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

Electroholic wrote ...

does the huge zap discharge the cap?
whats the problem?

and as stated, SCRs will also improve the performance A LOT.

Yes, it does discharge it into the coil.

I just got some *new* used disposable camera's, and I made an array using 10(!) photoflash caps; thus giving 1000ÂµF at 330V.
I think that the standard flash circuit will not be good enough to charge these, would it? Any suggestions which kind of charging circuit I could use instead?

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