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how many corners can you cut?

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LAN_403

splicer

Wed Oct 24 2007, 06:49PM

Registered Member #1077 Joined: Wed Oct 24 2007, 06:14PM
Location:
Posts: 1

I am making my first attempt at building a coilgun. So yeah, noob alert. I'm putting it together with whatever materials I have at hand, but I'm wondering how far I can deviate from the tutorials online and still get a working coilgun. This is actually my second attempt, my first attempt failed (the metal screw barely twitched), so I'd be glad if you could tell me whether I'm going in the right direction.

(I've done a bit of homework, but there doesn't seem to be a thread or a site telling you how many corners you can cut.)

Firstly, is it okay to ignore the fancy switching for a start, and just close the circuit by touching two wires together? There's a spark when I do that, and I'm wondering how much power is lost in that spark. I mean, will a proper switch make the difference between a small twitch and actually shooting stuff out of the coil?

Secondly, how important is it for the coil to be 'neat'? Is it okay if the wire isn't neatly divided into layers, but wire in the outer layers sink into the inner ones? And will it affect performance if the coil doesn't terminate neatly at the ends, but 'slopes' downwards?

Lastly, how important is the wire thickness? The wire I could get my hands on is 0.9mm thick, which is thicker than those I've seen in a few tutorials. (Also, does more turns of thinner wire give better results than less turns of thick wire? I mean for the same total coil length.)

uzzors2k

Wed Oct 24 2007, 07:47PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

This my friend, is as simple as they get.

As you can see a simple switch will work, at least for low powered coilguns. It can still transfer enough energy to move the projectile. If your coil is sloppy it will have have little impact on performance, unless you're running a high efficiency coilgun. Coil wire should be thick enough to have a negligible resistance and withstand the pulse current. Less turns of thicker wire is better than more turns of thinner.

Barry

Wed Oct 24 2007, 08:45PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

The simplest coilgun is still the Cadillac of simple circuits. You can toss things together more casually than the semi-professional construction techniques shown there. Just be sure to keep wires short and all connections well secured. Screw-down terminal strips will work, and soldered connections will work better.

The switch can be simple, but touching wires together will be relatively high resistance and its contact bounce results in wildly variable results. You'll be better off with a production switch; I recommend an ordinary light switch stolen from your bedroom wall.

Just put it back when you're done and nobody will be the wiser.

Heavier wire generally works better than thinner wire, but always plan on spending time tuning it up. We usually start with more turns than needed and tune it by removing 10% of the turns at a go.

Cheers, Barry

OZZY

Wed Oct 24 2007, 10:45PM

Registered Member #511 Joined: Sat Feb 10 2007, 11:36AM
Location: Somerset UK
Posts: 55

Actually the simple coilgun built by James Paul (Coilgun Systems) is a very clever design that uses closed loop control of the pulse length, and all without a single transistor to be seen! He used a 12V battery and two microswitches to drive the coil.

A similar design can be found here Coilgun with relay This guy used photoflash capacitors and a relay driven by switches.

Almost anything will work, a lightswitch is better than touching the wires together, an SCR is better than a lightswitch. A neat coil will not make a big difference but it will make a difference.

Wire thickness is one of the BIG questions, the best wire for your coilgun will depend on the components that you have used and the type of performance you are trying to achieve.

Simon

Thu Oct 25 2007, 12:45AM

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

My first coilgun was a large amount of magnet wire wrapped around a ballpoint pen tube with a nail inside. Touching the magnet wire ends to a capacitor from a disposable camera made the nail move somewhat.

It all went from there.

I like how with coilgunning you can tweak here and there, replacing the switching or improving the coil, and watch the efficiency creep up. That's the fun of the hobby.

Shaun

Thu Oct 25 2007, 12:45AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

SCRs are really great for these; they will always beat a contact switch or relay for high pulsed currents. They don't cost much either. You can get TO-220 sizes for under $3 that will handle a bunch of photoflash caps no questions asked.

My first coilgun (which I built before I knew coilguns existed) was a 1 lb. spool of 20ga wire that used an automotive rocker switch to discharge 9 parallel photoflash caps into it. A 3/4" ball bearing fit nicely in the center of the spool, and pointed straight upward it would launch them to about ceiling height.

Goes to show, don't expect 10% efficiency and super-high velocities with something like this, but you can get half-decent results with a 10-minute lash-up (for $0, BTW).

andy73

Fri Oct 26 2007, 04:13PM

Registered Member #926 Joined: Thu Jul 26 2007, 04:09PM
Location:
Posts: 9

hello splicer,

first good fun with you CG. now the simplest CG is a coil + battery = CG, the next step is normally photoflash hack + coil then on to the fun stuff.

1) battery
2) step-up transformer or HV source
3) cap bank
4) sensors (for multi stage)
5) switch (scr's are good but a simple microswitch will work for about 2 - 3 shots then inerds melt!)
6) coil + protective / communicating diode

thats about it really, i have found that keeping the J's to below 350 is the most efficent, bu that could be just my design, have a look at some of my very simple noob posts, there should be a few things that you might fing useful.

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