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M41 SPNKr Halo Rocket Launcher dual barrel spud gun

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: kwhee07 » Fri Jul 13, 2007 3:16 pm

So can i glue the ABS to the PVC barrel, or should i bring back the PVC and just get ABS barrels?

I just realized I'm using almost exclusively ABS, but i bought PVC barrels. I didn't even think to check if they glue to each other. I cant really find a definitive answer online, other than you can use a special transition cement, but its still out of code for housing.
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Unread postAuthor: psycix » Fri Jul 13, 2007 3:20 pm

noname wrote:Psycix, you do know what a check valve is, right? They don't hold pressure on the side which would be connected to the meter. Therefore, the meter's pressure guage would never raise above 1 psi until the chamber was totally flooded, and wouldn't work.


Hmm your right. It would need check valves instead of the ball valves AND one ball valve in front of the check valves. Then you can load the chamers in the same time.

CHAMBER1
|
CHECK
|
------BALL---rest of propane metering
|
CHECK
|
CHAMBER2
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Unread postAuthor: kwhee07 » Fri Jul 13, 2007 8:16 pm

UPDATE: Construction has begun. The chambers and barrels are in place, as well as both of the big tubes that house them. Glue is drying as we speak. Tomorrow I add lower receiver, 3 grips, ignition, possibly propane injection, and the big box

ill try to get some pix up tonight. its pretty sweet already. the shadow looks awesome!
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Unread postAuthor: kwhee07 » Sat Jul 14, 2007 12:10 pm

Basic construction is complete! Details, paint,front grip,shoulder pads,and propane injection, as well as other small mods(chamber fan,spark strip,etc) are to come.

I do have one safety concern. I used all 3" fittings, and ground the little tabs(that are supposed to prevent you from doing this) off so i could fit them inside the 4" pipe. I did clean and glue the inside,as well as the fittings, but I'm concerned that its not a good enough seal, or possibly not enough glue. I cant get the pieces out as there already glued(possibly only partially) and I'm worried that it could cause problems during firing. I know the pieces hardly fit down the tube,and make a very good seal, but I'm not so sure that when i shoot it the barrel reducer isn't going to come out of the front. The back caps are glued much better as i can see it closely as I'm gluing, but i think ill add a couple screws through the 4" into the adapters so they dont slide around if somehow they become dislodged.

This has already gotten pretty expensive, but its really just 2 guns and a bunch of other stuff so its about right i guess. Ive already spent well over 100 on adapters, tools(that i didn't have or were worn out) and other parts.

without more delay, here are the pics as it lays right now
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Unread postAuthor: kwhee07 » Sat Jul 14, 2007 12:38 pm

heres a few more pix after a little more modification. I cut the wood inner lower receiver so you dont see it between tubes, and screwed it all together, so its all one, big, spud gun at this point. it still doesn't have propane injection or any ignition source(i have spark strips made, just not going to install until i have ignition ready)

Need to find a bike pump or something for the front grip, figure out how to build the big middle box. i was originally going to do it out of cardboard but im not sure now. i may not do it for a week or so. I gotta clean and paint it after i get the third grip and a few more parts. thats what will really get it looking right
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Unread postAuthor: Kufive » Sun Jul 15, 2007 12:38 pm

Man that is looking really good! Good Job!
Definitely keep us posted when you build more
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Unread postAuthor: kwhee07 » Sun Jul 15, 2007 1:31 pm

I'm working on the middle box. its turning out to be a real P.I.T.A.. Ive tried 5 different materials, but cardboard is the only thing that i can cut with the tools i have and to the right shapes. i think I'm building the middle square box out of a box just cut in 3d out to that shape.its a real challenge though.
once i get it done ill post some more pix.

I ran up and got 2 disposable cameras for their circuits but i blew a diode on one,so ill have to go get another later. I have a pcb board i want to use as a spark strip but i don't think the cameras will power that, guess ill have to see


back to building
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Unread postAuthor: kwhee07 » Mon Jul 16, 2007 8:30 am

Update: Central box is getting closer to done. I ran an ignition for one of the barrels, using a 15 spark gap(piece of a blank pcb) but for some reason it didn't work. so i had to redo it to just bare wires temporarily. also the cameras didn't work so i switched back to a bbq ignition. i fired the first shot yesterday... just used hairspray to try it out, and performance was pretty dismal, but i think with the fan installed, propane injection, and the spark gaps all right it will be better. Ill paint the whole thing when the middle box is done, and post more pix then
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Unread postAuthor: Fnord » Mon Jul 16, 2007 10:01 am

Here's a propane meter suggestion:
Instead of using three ball valves, could you just use 1 ball valve and two blowguns?
Each blowgun runs to a different chamber, so you: 1. open the ball valve. 2. tap the first blowgun 3. repeat for the other chamber.

Or if you can find a 3-way valve, you could probably make that work for you too.
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Unread postAuthor: anatov » Tue Jul 17, 2007 5:58 pm

I may try to make one, but I'm going to make it out of 2 inch pipe first, and after I have the design right, I think I'll try to make it out of 4 inch pipe. I'm not sure about you, but I'm going to try to make mine able to rotate the barrels the way they rotate around the center axis and also try to have it be reloadable. Anotehr difference is mine will be pneumatic.
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Unread postAuthor: spudgunnerwryyyyy » Thu Aug 02, 2007 1:25 pm

Over under combustion?
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Unread postAuthor: hi » Thu Aug 02, 2007 1:40 pm

spudgunnerwryyyyy wrote:Over under combustion?


it looks like its inline.

or are you asking what an over under is?

if so then it is where the barrel is on top of the chamber.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: psycix » Sat Aug 04, 2007 3:29 pm

could we get another update?
did you make further progress in the contruction?

we want to see more of this beautiful thing in construction!
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Unread postAuthor: dongfang » Sat Aug 04, 2007 4:18 pm

Hi,

Just skimmed over the suggestions,

Why not just keep it a combustion for construction simplicity, and make it a dual combustion coaxial? No pistons.

OK I see the problem: Getting the chambers vented.

OK here is a suggestion. It looks almost impossible in this form, but you will find another...

The two coaxial chamber/barrels are mounted in a rotating assembly. On the left is the "big box" which is getting hard to construct... There is a big flange, holding the barrel assembly. The barrel/chamber on top is getting vented by a fan and loaded (and fueled; find out something). The barrel/chamber in the bottom position is ready for firing.

I know there are 2 major problems: Constructing that box, and dealing with the pressure wanting to tear the barrel/chamber assembly off the box when firing. Well, and getting the barrel/chamber assembly to rotate smoothly. So it's just for inspiration; not refined to practicality.

You know, if you keep your eyes open for a solution for each problem everywhere you go, you will eventually find a solution for each problem. But maybe it will take some time.

EDIT: Oops I didn't see you decided on a design already and had started construction. What you are doing looks more realistic anyway so keep working on it ;)

Regards
Soren
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First idea; 2 barrel coaxial combustion
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Unread postAuthor: paintballninja » Tue Nov 27, 2007 1:40 am

i've got a design based on the SPNKr you might like, but it's only single barrel, works great though, i'll have pics & vids up soon, & i'll let ya know when i do if you're interested
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