SpudFiles

(Skip to next paragraph to get to the details) As the title indicates this is my first step into hybrid cannons, and it took a while to actually get just right, but I love this thing so far (even though I only shot one shot). I got the bulk of the design from using HGDT, but I also took a look at similar cannons made by wyz2285, MrCrowley, and airpress to get a general idea of what I wanted to make. Another thanks to noname, D_Hall, DYI, SpudBlaster15, and MrCrowley for answering all of my stupid questions and helping me out. Any how, I've only dry fired this thing once at 3x mix (I attempted a 2x mix before but my fuel didn't seem to mix well in the chamber) and never having fired a hybrid I had no idea what to expect, yet even loaded down under blankets and pillows it still made an earsplitting bang (hearing protection is the next investment)
The barrel is a piece of 3/4'' x 5' EMT pipe but I haven't gotten to connect it to the gun yet, I was going to epoxy it into a 3/4'' coupling and then thread that onto the gun, but the store ran out of couplings and ever since I've been wondering if that'll actually hold up.

Finally, specifications:
Materials: Galvanized and some brass fittings
Chamber volume: 350 mL (measured with water)
Valve: 3/4'' modified union
Barrel: 3/4''x5' EMT (I want to pick up another one that's 1/2'' as well)
Ignition: Homemade spark plug and 3million volt stun gun (that's what's advertised, at least)
Fuel: Butane
Metering: Volumetric
I'm not sure what else to say about it, it only cost about 30$ (45$ with the stun gun and syringe), and I think it turned out quite well so far. I'm not yet sure if I want to make a stand for it with some sort of recoil reducer or just try and fire it handheld. I modified the union using a dremel, to grind it down, a file to even it out, and a sander to smooth it (it took a good 1 and a half hours) but I think it turned out well

Any questions or complaints are welcome

Looks good! Nice simple launcher with plenty of room for reconfiguration and modifications.

What, no video?

Good to see you got this working, especially considering the awkward ignition placement. I've used regular 600 WOG ball valves on hybrids up to 10X air/propane with no major problems, so you should be fine here.

As regards your question on the barrel: J-B Weld claims a tensile lap shear strength of about 1000psi, and 3/4" EMT conduit has an outer diameter of roughly 0.92". If you want to use this gun up to 10X it should be designed for an operating pressure of 1000psi, which gives a minimum length of 0.23" for the epoxy connection. As such, I would recommend a length of at least 1" for the joint, assuming that you rough up the outside of the pipe for the epoxy to grab and operate the gun such that you won't be harmed if the connection fails on firing. This setup will be prone to breakage from rough handling and heavy recoil, of course. I have used a similar setup, but they can be a hassle in the long run, and there's are better solutions.

The obvious solution is to just use 3/4" type L copper tube - it has a burst pressure on the order of 5-6kpsi, and is rated for use up to nearly 1000psi at room temperature. I've used it (with solder joints, albeit exaggeratedly long ones) up to 4.5kpsi (remotely) without any failures. If you're dead-set on using the 3/4" EMT conduit, you could use something similar to the barrel arrangement on ME20H-41. The barrel is centered in the outer shell using tape, and the gap is lightly filled with loose glass fiber (NOT mat or any other directional product), then poured full of resin.

DYI wrote:What, no video?

I really should've set up the camera XD; the one shot I made so far was beautiful, worked the first time and even shot out sparks from the aluminum foil burst disk (looked more impressive than it sounds).

UPDATE: I tried to get some footage/shoot it more today, it didn't go so well. I spent about an hour running around trying to get it to work but there was always something that went wrong, the first couple of tries I don't think succeeded due to leaks around the union (aluminum foil is very annoying) and then the latter portion of tries was probably due to my horrible stun gun running out of juice or completely breaking down. I tested my stun gun at about 40PSI and it turns out it didn't have enough juice to create a spark. Oh well, I guess I'll have to put it up for another day.

DYI wrote:Good to see you got this working, especially considering the awkward ignition placement. I've used regular 600 WOG ball valves on hybrids up to 10X air/propane with no major problems, so you should be fine here.

At first I was pretty worried that the spark plug would be the gun's downfall and had ideas of lengthening the wire so that it could extend into the main chamber, then trying to glue it down at a certain point, but it would have made it quite hard to actually modify the spark gap or replace the thing all together.

As far as the ball valve goes, I believe it should hold well enough, I also got the smallest one they had to try and reduce the amount of force exerted on it (am I wrong to believe that this would actually help btw?).

And finally I wanted to try and use the EMT since it was cheap and seemed quite safe. As far as that goes I will try to find something to attach it safely, but if no such thing can do so easily then I might invest in a new copper barrel (nearly 4x the price) or use some length of pipe I've scavenged (I don't know of it's type, and may not be able to measure it's wall thickness for a while, plus it's a hair shorter at 3 1/2 or 4 feet).

Thanks! And thank you too, noname; I tried to keep it somewhat simple and sufficiently cost effective. That and I like the ability to easily modify it.

~NooooooB~ wrote:Metering: Volumetric

Splitter!

Just kidding! Nice job and a good introduction to hybrid cannons. Troubleshooting can be an issue, just rule out each problem one by one. Use water and detergent to test for leaks, once that's solved work on testing your stungun at higher pressures (with no fuel mixture), and if that's working start fiddling with sparkplug placement.

Thanks! I'm pretty sure at first it was that the fueling, I have yet to completely seal the threads to the union, and after I had tightened that up it was just an issue of the stun gun being crappy. I want to try and get a BBQ igniter, since they don't take batteries (the stun gun has an internal battery that only lasts a few bursts before needing up to 5 hours of charging )
And it all that fails then I might switch the places of the spark plug and ball valve, and if THAT doesn't work then I'll try and make some sort of extension onto the spark plug so the wires extend into the chamber itself.
Hope to have videos up soon.

Update: It was giving me trouble so I extended the spark plug so it now reaches to the middle of the chamber, although I don't believe it will last, I need to get it all epoxied yet. But so far it works wonders at 1x mix (I haven't found the volume of the dead space of my pump so I can't very well shoot at higher mixes )

We started off allmoust the same time. Nice to see you allready have a spud ready. Keep up the work with this project.

D3vil5ro53 wrote:We started off allmoust the same time. Nice to see you allready have a spud ready. Keep up the work with this project.

I noticed that, although your project sounds like it should look a lot nicer

I finally got everything pretty much sorted out (kind of), I pretty much just redid the spark plug and measured the volume of dead space to my pump. The stun gun is somewhat restricting though, so my next step will be making a nicer ignition circuit and implementing some sort of remote firing. Once again nicer photos and videos to come when I get a new camera (my old one took a dump on me)