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Induction AL coin launcher Help

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Forty

Tue Feb 28 2012, 05:16PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

I think gluing any conductive ring in the center of the coil is gonna rob a lot of your energy. You're using eddy currents to repel the projectile but you've essentially got a second projectile "in series" with it but fixed in place. (i understand you were only using it as a spacer)

If you want to try out flux concentrating materials with the coil I'd make sure they were non conductive or at least highly resistive (like powdered iron or ferrite) so that you don't generate a bunch of eddy currents in them as well.

A magnet might work fine as a projectile because the pulse is fast enough that it might not be flipped over. i imagine it might shoot off at an angle though if it begins to flip. neodymium earth magnets tend to shatter when they hit stuff too, so be careful of that.

Another neat thing to try out with the small scale induction launcher would be making a reconnection coilgun

that's something i've been meaning to try out myself.

pauleddy

Wed Feb 29 2012, 02:28AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

well this thing has quit a kick, it will lanch my little AL disk clear across a room and make dents in my ceiling from the floor so i dont think that it will make that much of a differance. i might try putting a a ferrite in the middle, but the object of the pancake coil is to have the flux spread out over the the disk for uniform force, you can see the how the field looks from the short video i made in the link with the pics.

Forty

Wed Feb 29 2012, 03:14AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

Yea I'm sure it still works just fine with the Al ring in there, I was just clarifying for Ben that Al in the flux path isn't necessary and would probably use up energy. It's impressive how much of a kick you can get out of just a few camera capacitors isn't it? I recently had several small SCRs that I thought I broke so i made up a test circuit for them. To make the testing more fun I discharged a 450uf 350v camera cap into a little coil to launch stuff. Turned out that only 1 out of 7 of them were broken.

Anyways, to be more on topic: for such a small scale induction launcher, you could probably use up to 20awg wire for the coil (to answer ljfa321's question) because the energy levels are pretty small (<100J), the repetition rate is low (limited by charging speed) and your projectile is small so your coil area should be small.
since you've got the camera parts already, you could use the flash tube as a triggered spark gap. just find the connections where the camera flash was originally triggered and use them for your fire switch. when closed the switch will send a signal to a small pulse transformer, which sends hv to the outside of the xenon bulb and ionizes the gas inside, allowing the capacitor to discharge through the bulb. your coil would go in series with the bulb. surround the bulb with something to cover up the flash and shield it in case it pops.

klugesmith

Wed Feb 29 2012, 04:37AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Forty: how about leaving the flashlamp exposed, where it can illuminate the projectile?
When you fire the launcher in the dark, it will be evident how far the projectile moves while current flows in the coil.

I expect the coil inductance will reduce the peak current and increase the pulse duration, compared to the coil-less flash with extra capacitors. You could substitute a larger flashlamp to safely switch the circuit with extra capacitors.

ljfa321

Thu Mar 01 2012, 06:33AM

Registered Member #4455 Joined: Sun Feb 26 2012, 12:49AM
Location:
Posts: 14

Thanks, I end up adding 4 more capacitor into the bank :p

I will go find some thicker wire to make my coil, since the thing wire i'm using right now give out some really weird result and terrible performance.

ljfa321

Thu Mar 01 2012, 06:48AM

Registered Member #4455 Joined: Sun Feb 26 2012, 12:49AM
Location:
Posts: 14

This one I made is made out of 22 gauge wire, but terrible performance.
2mm lift :S

ljfa321

Thu Mar 01 2012, 06:53AM

Registered Member #4455 Joined: Sun Feb 26 2012, 12:49AM
Location:
Posts: 14

This is a coil I found in my junk yard.
Not sure what is this coil's original use.
32~35 gauge wire.
Probably really high on resistance. (Don't make a spark like the coil I made myself when connect to capacitor)
With one capacitor, 15cm lift.
With five capacitor, 15cm lift.
:S

Forty

Thu Mar 01 2012, 06:16PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

So that nice looking coil with many turns works better than the pancake coil with fewer turns? hmm.
I always thought low inductance coils were better for launchers because of the faster rise time.
The projectile is only near the coil for a couple ms so any current flowing in the coil after that is unnecessary (<- wow, spelled that right the first time)
Well keep trying out coil geometries, it'll be interesting to see what you come up with. The two I've been experimenting with are double layer pancake coils (nice because the leads are on the outside and not one protruding from the center) for launching whatever and heatshrink covered copper strip rolled up into a tight spiral (lots of conductor but little surface area) for use with coins.

@klugesmith that's a very clever idea with the flashlamp! I'd be worried about them exploding though. I originally used the flashlamps as a spark gap switch for a coilgun (so even higher inductance in that case) and they'd progressively melt on the inside until the whole bulb just crumbled. They're definitely a temporary switching device when over powered.
A voltage divider and an LED might accomplish the same illumination idea however. I'm not sure if it would help optimizing the coil/capacitor though. You want the current to peak very quickly so that the projectile is still in range to be affected, but no matter what, the projectile is going to leave the surface of the coil while current is still flowing.

pauleddy

Fri Mar 02 2012, 01:25AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

you need a lower gauge wire, lower the R the smaller your time constant. the pulse must be quick enough to put as much energy into the disk before it leaves the field. less the field it self will drag the disk. basicly you want the EMP there and gone before the disk has had a chance to move. keep your wire short as possible as well. lenth of wire also efect the R. when your rise time is in >ms the smallest resistance will greatly effect your energy transfer from EM to kenetic.
try too keep the resistance below 2 ohms the lower the better. I once made a coil out of ribbon cable, for my lange cap bank, i might have an old video on you tube i think it was my first, here it is, just skip to about 2:00

ljfa321

Fri Mar 02 2012, 08:15AM

Registered Member #4455 Joined: Sun Feb 26 2012, 12:49AM
Location:
Posts: 14

pauleddy wrote ...

you need a lower gauge wire........

Thanks pauleddy!

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