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Spray n pray hybrid

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Spray n pray hybrid

Unread postAuthor: daccel » Sat May 30, 2009 1:01 am

Current project is still under development, and I wanted something to take camping this weekend, so I threw this together.

It has .75" chamber, .569" barrel, and the ammo is .55" sinkers. Fueling is just a quick spray on the schrader, then attach pump and fill.

My question is am I safe with the 3/4" parts if I do a 25x mix and best (worst?) case scenario it happens to be fueled perfectly to reach the peak theoretical pressure?

I can't track down the thread where, I think it was Gippetto, pressure tested some (1/2"?) fittings?

Oh yeah, here is a preview of the early stages of what will hopefully be running the same caliber and fuel.
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Unread postAuthor: daccel » Mon Jun 01, 2009 8:43 pm

Lesson learned - pressure test before heading out.. or bring tools. The chamber had a leak so I wasn't able to make it over 4x.

On the bright side we found an abandoned truck which was just begging to be used as a target!

[youtube]http://www.youtube.com/watch?v=NGa8nZRdL_Y[/youtube]

At 4x it didn't quite make it all the way through the door, just dented the inside.

A can of V8 also got sacrificed in the name of science, at 2x.

[youtube]http://www.youtube.com/watch?v=OUDvnsEjGaU[/youtube]
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Unread postAuthor: MountainousDew » Wed Jun 03, 2009 9:41 am

My Truck!
I was just gone for a few minutes...
It was you! You did this! Why?! ¿Por qué?

Sweet gun, I'm surprised that no one had commented yet...
And where did you get those awesome fishing weights?
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<a href="http://s709.photobucket.com/albums/ww95/JKazkid/?action=view&current=MDSig.jpg" target="_blank"><img src="http://i709.photobucket.com/albums/ww95/JKazkid/MDSig.jpg" border="0" alt="Photobucket"></a>
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Unread postAuthor: Carlman » Wed Jun 03, 2009 9:46 am

sweet mate! i would not try 25x in copper though...
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Aussie spudders unite!!
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Unread postAuthor: MountainousDew » Wed Jun 03, 2009 10:03 am

Yeah, definitely don't take it tom 25x...
When I first read it, I thought it was 2-5x, was I right? Was it a typo? Please can I be right?!
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<a href="http://s709.photobucket.com/albums/ww95/JKazkid/?action=view&current=MDSig.jpg" target="_blank"><img src="http://i709.photobucket.com/albums/ww95/JKazkid/MDSig.jpg" border="0" alt="Photobucket"></a>
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Unread postAuthor: daccel » Wed Jun 03, 2009 2:26 pm

Thanks. Just to clarify, in my original post it is the second picture that is the cannon in the videos (the other is a work in progress). So as you can see it has a steel chamber, and yes I meant 25x.

I believe the burst pressure of the copper is about double that, so while not a huge safety margin, it doesn't seem unreasonable? I probably won't end up running it that high, but while on the subject..

The sinkers I got from Canadian Tire, but I can't find them on the website. Here they are on another site though.

They are .55" which is a good fit with .569" ID of type m copper pipe. As are 1/4" sch 40 nipples.
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Unread postAuthor: Ragnarok » Wed Jun 03, 2009 6:39 pm

daccel wrote:I believe the burst pressure of the copper is about double that, so while not a huge safety margin, it doesn't seem unreasonable?

Do not mistake burst and yield pressures for one another. The yield pressure is around a third of the burst pressure in copper (although the exact results may vary depending on copper purity), and this is when the pipe will start to permanently stretch and deform.

So, although the pipe may not burst at your pressures, it will likely deform.

EDIT: Spelling.
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Last edited by Ragnarok on Thu Jun 04, 2009 6:01 am, edited 1 time in total.
Does that thing kinda look like a big cat to you?
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Unread postAuthor: daccel » Wed Jun 03, 2009 11:07 pm

Hmm.. I hadn't considered that. Thanks for the heads up. I will adjust working pressure accordingly.
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Unread postAuthor: starman » Wed Jun 03, 2009 11:25 pm

Even though you made it only to 4X, pretty cool little hybrid there. How are you measuring your fuel volume with this setup?
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Unread postAuthor: daccel » Wed Jun 03, 2009 11:59 pm

Thanks. It was a pretty easy build though, just threading fittings together really. Everyone should make one of these! :)

For fuel measurement, I first tried just filling the hole in the back of the schrader like I had on my mini, but it was too hot out I guess because it just evaporated. So I resorted to unscrewing the schrader, giving a quick spray of starter fluid, and quickly rescrewing it on. Could have gone through the union, but I was using tape/aluminum foil for a disk to enhance the seal and thought it might dissolve the glue on the tape.

So, in short, not a whole lot (hence the title), other than trying to use as short a burst as possible, because it was likely running rich already, given how little liquid fuel is needed.

Ignition was surprisingly reliable, though, with just a piezo - the electric ignitor soldering fell apart. The only time it wouldn't fire was when I fueled, pressurized to check seal @ schrader, then depressurized and repressurized without fueling. I imagine it was understandably too lean at that point.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 04, 2009 1:08 am

For science!

Sweet, and that ali furniture looks very promising :D
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