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ramses

Tue Apr 08 2008, 07:43PM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

I would seriously recommend building one almost exactly like the one TDU uses. his site should have details...

Barry

Tue Apr 08 2008, 09:26PM

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

I would highly recommend any sort of rugged mechanical switch with a reasonably fast closing time. The mechanical contactor provides lower resistance than any silicon or air-gap switch, and resistance is an extremely important factor in all coilguns of all types.

Not to mention, diagnosis and repair of mechanical switches will be very easy compared to semiconductors. The fabrication cost is expected to be much lower than semiconductors as well.

Cheers, Barry
Second Life is four times better than Half Life

Travlax1

Wed Apr 09 2008, 02:37AM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Barry, do you a website that has one of the mechanical switches for sale? Also, what about arcing and the contacts welding shut?

I've looked on the TDU site and see the section on coil guns but I dont see anything about a switch design, does anyone have the link to it?

teslacoolguy

Wed Apr 09 2008, 04:53AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

All it is is 2 pieces of heavy aluminum one piece connected to some strong springs and the other piece stationary and there is like a block of wood im between and when he pulls the block of wood out the switch snaps closed and the more surface area that is conducting the less chance of the electrodes welding shut.

Travlax1

Wed Apr 09 2008, 05:18AM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

I understand and like the simplicity of that design, however, is there a safe way to build that or a casing that could be put around it? any pics or drawings? Anything I use has to be extremely foolproof and safe as its being used in a high school where there are a lot of liability issues.

Andyman

Wed Apr 09 2008, 05:19AM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

Aluminum is not good for that kind of contact. Brass and/or copper are better. Aluminum vaporizes and melts at a relatively low temp.
The switch is under the can crushing section, and if you still can't find it then:

Also, heres another type of switch that is isolated from human contact:

The builder says that the contacts never touch, but come close. This way there is no chance of welding

Travlax1

Wed Apr 09 2008, 03:42PM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Those ideas look great and if I built one, it would probably be the trampoline spring idea, however, I'm looking to buy one premade as i'm coming up on the deadline for my project and want to spend time testing rather than building a switch. Would a heavy duty knife switch like

be able to withstand the capacitor spike without welding? thanks

ramses

Wed Apr 09 2008, 07:40PM

Registered Member #1208 Joined: Thu Jan 03 2008, 05:30PM
Location: Chesterland, OH
Posts: 154

i really don't think so. this is what I use:

I use pennies for contacts. they're disposable and dirt cheap. attach each to a 2x4 with a .5" groove with screws and washers, and your done.

if you do decide to go this route, make sure you get pennies made before 1982, so they are copper and not zinc (zinc burns rather well). I just prod a penny duct taped to a stick between them. BOOM!

and with my switch or the bedspring switch, make sure you have a hammer and chisel ready ;)

BTW, when is the deadline
ramses

Andyman

Wed Apr 09 2008, 09:28PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

If you use any pre-made switch, its going to cost ALOT. Check out

. My current switch is a few posts down. Works GREAT, but could use a fatter spring. Took me an afternoon or two to put together.

Travlax1

Mon Apr 14 2008, 04:33AM

Registered Member #1388 Joined: Wed Mar 12 2008, 04:42PM
Location:
Posts: 23

Ok I'll be making a pretty simple switch like the ones u guys have recommended. Now for the wire, I came across some 4 gauge audio wire at a store and I just got it but I'm not sure if it'll work. It just says High Quality Speaker Cable. It has a very thick insulation and then the actual wire is the strands of thin wire within the insulation. Will this work?

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