SpudFiles

Hey everybody!! hope you're enjoying your time as christmas comes!! Today was a great day (at the exception that i caught a bad cold...) as i drove to "leroy merlin" something like home depot . I needed a 1/2" union to pre-complete my hybrid. By that i mean that i now only have to figure a simple and yet reliable way of ignition.

I know a post without pics isn't that much fun, but they'll come later this evening or tomorow.
To give you all a taste here are the specs :
-chamber is 1" by 1' steel pipe
-onboard butane/propane/mapp
-overall pressure rating : bursts at 1300 psi
-ignition is made by a plasma globe circuit, that send 10kv at 60hz.

i have now found a safe brust disc that holds the pressure...i actualy get it to fire 2 times out of 10...i know the correct mix for butane is around 3% , my chamber is 247 ml ...(247 cm^3) so i guess for a 2x mix i need 6% of butane that makes 14 cm3 of butane...when i does work, it's loud as a gun though...

Edit: okay, i tried adding the very least i can, as my hamber volume is small. So did i. internal pressure was very small, then i added air, at 30psi (3x mix) i added the barrel (1/2" galvanized steel for 2' long) and went in my guests room, opened the velux, and sho outside (blank shot) ...first clik, weak. Second clik....instant CRRAAAAKK!!! slight recoil, even with no projectile, that is kinda weird; my ear is still ringing and it was 10 minutes ago. here is a pic of the new design of burst discs. (plactic foil (2 layer) and alluminium (2 layer) for a burst at 130 psi.)
hybrid is now handheld, BBQ igniter, insulated. extreme fun with that, but i have no doubt it will be supersonic with light projectiles.




To avoid tripple posting, i'm now adding one more pic...a damage one.
This is simply the most powerfull gun i've ever made. took it to 3.5x and my gosh...i learned a lesson, i'm now wearing earing protections. This, was done with only one shot at 3.5x. The projectile was (it is now lost) a 1.5 gram plastic cap, and went completely through, shredding the coca cola bottle...


The next shot i do will be filmed. So that you get an idea of what a small hybrid can do. (out runs my 15 bars pneumatic...) Oh, and i almost forgot, the barrel i used to make this is a 15cm 1/2" barrel....

drill two holes along the length of it and use rubber grommets to mount a spark strip inside the chamber. tighten the whole deal down with machine screws and those rubber grommets should seal your chamber and insulate the spark strip from the wall of the chamber allowing you to use the bbq igniter. i'll draw up a picture here in a few if you dont understand it

CpTn_lAw iv been waiting for this for a good time now and im very happy to see that you are "allmost" done. cant wait to see it in the end.

well actually, i don't want to drill holes in the chamber, i want to screw the electrode in the back of the design....

Lol, you've been expecting this??? thanks! that's pretty motivating! i hope you will like this!

hmmm, I would go with a spark plug then, you could power a spark plug with a bbq ignitor in theory. i mean heck you wouldn't have to worry about the gap or anything. you could even find one that will screw into a plumbing fitting reducer. that'd be awesome

Yea a new hybrid i always love it when a new one comes out they are so amazing this one sounds really awsome

a hybrid really is something impressive...i plan on running this one at 6x max. but standard use will be around 3x.

That's kind of a waste, isn't it? If the overall pressure rating is 1300 psi, you could use it at about 12x without exceeding the rating, and there isn't enough run up distance for a detonation to occur.

I've started spudguns when i was 14, without knowing that there were other people doing that. So i basicly "invented" the concept from looking around the parts lying in my garage. Since then i've had my part of good times, and my part of bad ones. Bad one were really bad ones, like when the spudgun i ha designed for my little brother blew up near him, sending pieces of plastic at his hands and face, cutting him (fortunately, it was superficiel).
I don't recall when it was that my copper pneumatic blew up besides me, making me a deaf man for two days lol.
So, i'll get this cannon to 6x mix by small increments and then i'll see...but i like to be careful.

here i join three pics of the early stage of developpement. Note: the burst discs are from 2 layer of aluminium foil, and were tested at 5 bars. (6x mix) juste with air. guess i need to put some more foil. i'm surprised with the noise of just the air getting out with the burst disc. it is really fast and really loud.

looks good so far I like it a lot

I just built a really ghetto spare parts 400 psi handheld burst disk gun yesterday, which happens to have a 1" union. 16 layers bursts after 300 psi, and before 400, which is as far as I can tell from a rather nervewracking test I did this afternoon (300... fire! *tssss* aw crap. *PHHHHHHHHHH* sh*t, the filling system's leaking! *gets out big wrench, tightens flare fitting* *turns reg to 400* fire! *tsssssssss CRAAACK!!!*).

For a 12x mix (which I absolutely insist you do ) a good burst disk in a 1" union would probably be 32 - 48 layers of foil. For 4x mixes, 12 layers, possibly 16, should be about right.

don't forget it is only a 1/2" union i have, thus needing more pressure to operate and more : accelerating the gases with venturi effect. (if there is something i've learnt over the past few years..."Venturi is your friend" )

And LOL for your little story DYI!!

I was thinkin of something, i have a 6L empty fireextinguisher that i used to fill up my BB piston rifle when it was the low pressure style, i could use it to store a perfect 2x mix to start and just fill the hybrid with it. but i'm to afraid f it going boom accidentaly (the F.E.)

Oh, I had assumed you had a 1" union. It seems as though different union sizes and disk thicknesses don't scale linearly like one would expect. For example, a 16 layer alu. foil disk holds about 140 psi in a 1.5" union before bursting, however a 32 layer disk in the same union will easily survive 350 psi continually, sometimes 400 if it's made well. A 1" burst disk has about 1/2 the surface area of a 1.5" one, so you could expect it to hold twice as much pressure, i.e. ~280psi. However, it survived 300 for several minutes, even after an extremely rapid pressurisation to 300 (about 1 second).

You can make rough estimates of bursting pressure, but the only way to know for sure is to test it (of course, most people here don't have the equipment to test pneumatically to 500 psi). 16 layers of alu. foil in a 1/2" union should hold over 600 psi easily in a 1/2" union, so it should be good for mixes of about 8x - 10x or so. For the higher mixes, just build up slowly, and keep a safe distance until you're sure it's safe.

Larger diameter chambers provide greater safety, as the detonation run up distance increases for larger diameter cylinders. The 30x (no typo) hybrid I'm planning for the summer will have a 3" ID chamber, only 1' long (SCH 160 of course). The online EVBEC really, really sucks. It keeps saying that barrel length is too long for model.

My short opinion. I use spark plugs on all my guns including the stainless steel one. I just double the gap on the plug from the factory setting. You can get a metric tap from places like NAPA. It works every time with a cheap bbq ignitor. I think the tap is 17 mm for the plugs I use. Hope this helps. I also found that placing the spark near the middle of the chamber works best.

ok today i'm starting the testing...i have to make my butane meter to directly inject the mix in the hybrid. spark is in the rear of the gun, at normal combustion mixes, it is already loud. i'll let you know the progress!

first 2x and 3x done!!! works great, still, as i didn't do any calculation for the butane volume, i did it to the intuition lol. i guess a Blue flame is good. without a barrel that is freakin loud!

I can't shoot that thing even blank cause it's too loud and the neighnors won't like it....pretty happy my hybrid works (my second one actually: the first wasn't posted, was a 14mm mini that worked at 2x et 3 x)