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Small EML washer launcher

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Voltwad

Tue Aug 18 2009, 08:07PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

I just can't seem to finish one project without first deciding to start another. Kerr Drug gave me a pile of disposable cameras and I thought I'd make a washer launcher with the caps.
And here she is.

1250625233 1829 FT0 Eml2

The caps are charged with another of my homemade flybacks driven by an 2n3055. The switch is a spring loaded bolt with some transparency paper between the contacts. I'm going to try and build a better charger, get a meter to monitor the voltage and come up with a better switch, mechanical or silicon. I tried the thyristors from a microwave but they fried after a few launches. I might try to find a suitable scr.

Here's a Youtube vid of a launch. And here's a longer video showing the whole setup.

EDIT:

I just had a good idea for a little contest, 'Biggest disposable camera cap bank'.
Do with it what you will, launcher, gun, can crusher. The only rule should be all energy storage caps should be from disposable cameras.

UPDATE:

Here's a new version.

1251484190 1829 FT74569 New Eml

And here's a larger version.

I'm using a 555 + MOSFET driver now so the bank charges up to 2 kV in about ten or fifteen seconds. I reconfigured the bank to 2310 volts. I made a new coil, tightly wound, about 15 or 20 turns encased in epoxy. What I'm most proud of is the contactor I made. Spring loaded copper pipe caps with a spring loaded piece of polyethylene cutting board between them. A solenoid briefly pulls on one of the caps allowing one of the springs to pull the plastic out of the way, then the solenoid releases and the other spring slams the two caps into each other. The solenoid is isolated from the contacts with some nylon bits and pieces. I made a battery powered remote trigger for the solenoid too. I still need to get a meter to monitor the voltage, build a comparator circuit so's I don't overvolt the bank, get some more caps, maybe a more powerful charging supply in the future, and if I do that I guess I'll reconfigure the bank for an even higher voltage. Till then, here's some more vids...

Steel washer
Brass washer
Copper washer

These are all at 2 kV. You can hear the copper washer hit the ceiling.

CT2

Wed Aug 19 2009, 02:36PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

That's such an awsome little set up! I like that it can be built with just old re-used parts, although I bet the SCR would be nice. I think the contest is a sweet idea, I have probably one hundred or more disposable cameras, so I'm in! When we say biggest cap bank do we mean most caps? I wonder what the best way to hook them up is, high voltage less capacitance would probably be better for launching stuff. Hmmmm time to brainstorm!

Voltwad

Wed Aug 19 2009, 05:40PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

I should think 'most energy stored' would be better/more impressive. Especially since there's such a wide range of values used in these things. My bank has multiple parallel strings of four series caps for a total voltage rating of 1320 volts. I don't know what the capacitance is because half of them are unmarked and it's beyond the range of my only capacitance meter. I guess I'll need to do some time constant experiments to ballpark it. Also, AN IMPORTANT NOTE TO ANYONE... There's more often than not still a charge left in those things even after the flash has been discharged. So take a screwdriver you don't care about and short the caps before anyone goes sticking their fingers in to pry apart the case.

Myke

Wed Aug 19 2009, 07:09PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

I would like to participate in this but I can't because of time constraints. One thing is that the caps can build up some of their charge even after being shorted. I would use an alligator clip to short the bank and leave it on there when it is not in use.

I would think that the height of the washer would be determined by the material of it and also the number of caps used. If someone got 100 cameras, would do better than someone who got 50 (unless the person who used 50 wired it so he got a fast rise time).

Voltwad

Fri Aug 21 2009, 01:32PM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

the caps can build up some of their charge even after being shorted

This is true, a large cap bank needs a resistor or short across it when in storage. I have seen a difference in the way a washer jumps. The first time I tried it I used a regular galvanized steel washer of about the same diameter as the brass one and it just flipped off the coil without really going anywhere. What puzzles me is, the brass washer doesn't seem to weigh that much less than the steel one, maybe about half as much. Not enough to account for the tremendous difference in performance. I'm going to get more caps, build a better coil, and try some other metals as well. The number of caps isn't as important as the total capacitance simply because, in any given camera you can find a capacitor value anywhere in the range from 60 uF to 160 uF (in my experience thusfar). 50 160 uF capacitors will easily outperform 100 60 uF caps but there's no telling what you'll find when you open one up. tearing them apart can be time consuming but I went through about fifty in a few hours.

CT2

Tue Aug 25 2009, 01:39PM

Registered Member #180 Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187

I'd have to say the reason for the brass washer having so much better performance is because its made of brass, not the galvanized steel. Brass is a far better conductor for the eddy currents then the steel is, and therefore creates a much stronger repelling magnetic field and thus flies higher. When I get some time I will have to build mine too, but my co-op work term is just ending and school is starting so I'm a little busy.

Myke

Tue Aug 25 2009, 05:00PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

I'd think that aluminum and copper washers would do better than brass but I'm not completely sure. I know they are good at conducting eddy currents so they like to repel changing magnetic fields.

Voltwad

Wed Sept 02 2009, 04:50AM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

I just put a dent in my ceiling with a 1980 penny :) I'll have to find an aluminum coin or washer now.

Killa-X

Wed Sept 02 2009, 09:09PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Looks like it's going good Voltwad! I put mine in semi-delayed. Since my Last test I upgraded it from 16 to 32 camera caps..I've seen people on this forum have 2 banks of 50 camera capacitors for coilguns.

Anyways, Keep us updated with results :D

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