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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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M41 SPNKr Halo Rocket Launcher dual barrel spud gun

Unread postAuthor: kwhee07 » Thu Jul 12, 2007 11:40 am

This is my first post but I'm about to start a pretty big project(in my book at least) and figured its a good time to post about it and ask any questions.

The idea is to build a 1:1 scale replica of the halo/halo2 rocket launcher that has 2 barrels and 2 chambers and fires 2 spuds(or whatever else i determine makes a better rocket) either simultaneously or separately.

I've built 2 combustions and I'm pretty new to this whole concept,although a few years ago i built a mini and didn't even realize it was just a mini spud gun, i always called it the q-tip gun. So far I've built a BL series classic spud gun, and an over/under redesign of the BL with dual ignition.

I started getting any render of the M41 i could find a few days ago, and I've broken it down as far as i can before i actually start the build. To get the dimensions right i first looked in the halo manual, and found that the rockets it fires in game are just over 4 inches. Perfect! I'm going to use 4 inch ABS for the barrels.
Using that information, and a perfect profile render along with some basic trig and geometry i started finding the dimensions. Its going to be just over 60 inches long, with 2 60 inch barrels.
I'm going to use a stun gun for the ignition, although i haven't figured out how to rig that up where i can fire them separately. For the main body and back "fat part" I'm going to use 8 inch concrete filler tubes, inside 10inch ones.
The majority of the cosmetic work will be out of cardboard or thin plastic,something cheap and easily workable,and then most likely filled with foam once its done for a bit more durability.
The front grip will be a modified bike pump, the middle/trigger grip will be the stun gun,and the rear one(which is really just a shoulder rest) is probably going to be raw material(steel?) with a foam pad on the back.
The support part of the body will likely be built out of steel or aluminum, although I'm not ruling out wood.
I've never done a propane metered gun, but this might be my first. If i decide not to initially, will it be hard to go back later and convert it?

The original plan was to use a 4 inch diameter chamber with a 2 inch barrel. The rear part of the tube would be the chamber, and inside the concrete tube in the middle, i would reduce it down to 2 inches, but keep the 4 inch tube on the outside for aesthetic reasons, and just have the 2 inch barrel come up to the front of the 4 inch(with some support inside to keep it from wobbling around. i started to realize how difficult it is going to be to reload this, which is what makes me want to make it propane metered. If i do decide to do propane metered, would it be easy to rig up one can(hidden inside the center of the body) and fill both chambers with it?


Does anyone by chance know what size the nerf footballs with the tails are? If they would fit in the 4 inch barrel without the 2 inch in there, would that cause problems with the chamber not being the right proportion, or would it just make it not fire optimally?
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Unread postAuthor: PVC Arsenal 17 » Thu Jul 12, 2007 12:12 pm

You know, I was just looking the Halo Wikia yesterday and that I think that idea must've crossed my mind as well.

The "block" that MC loads the rockets into would probably end up being your chamber. You'd need to think of a way to divide in half if you want the fire separately. Are you planning on having them rotate like the it does in Halo?

Also, the big Nerf rockets aren't going to be a very good projectile. They're too heavy and large to be realistic. But the Mini Nerfs fit almost perfectly in 2" PVC. And they'll fly real well...
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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 12:20 pm

hmm, maybe ill use mini nerfs. the advantage to that(especially if i also did propane metering) is that i don't have to keep the inner barrel flush with the front so i can keep the good look of huge barrels, where as if i have to use potatoes,the inner barrels have to be just as long as the outer barrels.

Your suggesting that the big center block would make the best chamber? i wasn't planning on making that sturdy at all,mostly just aesthetic. my big mental struggle right now is how to reduce the inner barrel size, but keep the front end of the outer barrels sturdy because there going to be heavy
i guess i could use a steel frame lower body and just bolt them on to it because the front portion of the outer barrel wont have any pressure in it, just its own weight.

I didn't plan on having it rotate. I thought about it initially, and as sweet as it would be,its just not practical. Theres no realistic way to get the loading and firing accurate to the game without ALOT more work, so i figured if i can make it look right as a model, ill be content, and its just a bonus that it shoots. I think i might just make both barrels fire one one trigger pull. Its alot easier plus whatever i rain havoc down on will get twice the ownage.
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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 12:32 pm

Heres a labeled picture so you might be able to have a better idea on what im trying to do
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Unread postAuthor: Flying_Salt » Thu Jul 12, 2007 12:32 pm

I can see a coaxial made out of that...

For the metering system, maybe you could put the propane can in the box, then have the ball valves and stuff on the bottom, out of the way but still in easy reach.
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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 12:41 pm

thats what i was thinking. if i do end up doing metering it will all be inside the box, and then the valves would be either on the back or hidden. that would completely eliminate the problem of fueling it,and that combined with nerf rockets would keep it looking great and highly functional without too much extra stuff, or having to take it apart every time to refuel.
Can u draw and ms paint picture or modify the blue and black render to show me what your suggesting with the coax? i know how and have seen coaxial guns but i don't understand how it will work in this application
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Unread postAuthor: Flying_Salt » Thu Jul 12, 2007 12:51 pm

MS Paint doesn't like me lately, so I'll try to explain it.
You could have the chamber be the 4'' pipe, then either have the piston thing in the box or way in the back, with a hose going to the trigger area for exhaust.
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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 1:06 pm

OK now I'm really confused. I didn't know i needed a piston or an exhaust hose.

are you referring a coax design or a propane metered system in relation to the piston and exhaust hose. i know i can hide the tank inside the center box/body and ill just run the hose in between the 2 barrels between the middle and the back, as well as the ignition the same way (of course heavily insulated. If i do propane could i possibly even route the hoses to fill it in the rear chamber, so you don't see hoses at all?

what about an electronic filling system. I'm guessing id have to use a solenoid and a regulator. which might not be so bad. if that would work i could have a flip cover missile switch to fill the chamber and red push button to fire. that would be sweet.

I'm also thinking about putting the stun gun internals hidden too and making a new grip and trigger, although the stun gun already has a pretty fitting grip,and will probably look better than anything i can make. hmm
guess well have to see. When i head over to my buddy's house after work were going to look over my drawings and start figuring costs. If all goes as planned ill start building this weekend. My biggest fear(and mark my words now) is that ill get hasty and want it to be done and fire-able so ill cut corners(not safety wise, those corners are not to be cut) and it will come out either being a pain in the ass to use, or looking like crap. i just need to take my time and put a good effort into this and it will turn out sweet. i was also thinking about using a looped back headphone jack as kind of a key for ignition. have it in line with the stun gun wires so that when the jacks not in there it cant spark, but if i put it in,that completes the circuit and its like a key. would that work?

EDIT: i just realized id have to use a huge jack or my spark gap would have to be less than 3.5mm so that idea probably doesn't work. Do you think that having dual ignition(but just one on each barrel) would be sufficent or do i need to try and get 4 sparks out of the stun gun and have it be a quad, or 2 on each?
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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 2:13 pm

alright more searching, i just searched the spudtech archives and I'm definitely not the first to do this. There were 2 threads there, as well as a youtube video shooting model rocket engines with TERRIBLE build quality and one barrel, a google one that was like half scale,but actually a spud gun,and a full scale replica that doesn't shoot.

If i complete this(which i realllllyyy want to) mine will be the first dual barrel, full scale, firing halo 2 rocket launcher to hit the internet(that I've found,and 8 hours of work a day at the computer lets you find a lot of stuff)

I'm pretty excited. i think I'm going to do an external metering system and a valve on each chamber to keep weight down, and keep it looking good.

I planned on using a bike pump for the front grip because it looks like one, and i was originally going to put a setscrew in it so you cant move it but i was wondering...if i kept it working and hooked up to the chambers, could i theoretically leave the back of the chamber permanently sealed, and just pump in fresh air with the bike pump and then add the propane? I guess it would be like a really low pressure hybrid, as i would be pressurizing it. although if i do that, then i don't think i can use abs. I'm not sure. would it be feasible to use the bike pump to either clear the chamber or ad oxygen from the air to the chamber so i never had to open it from the back once its done
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Unread postAuthor: sharpshooter » Thu Jul 12, 2007 2:20 pm

this is def coaxial gun. use 4" pvc with 2" running down the middle, supported buy altered bushings or reducers. Have a cleanout on the end for loading/venting. A propane meter system should fit nicely inside the middle box.

Really what you are gonna have here is 2 identical coaxials joined together in one sweet package.

Is a stun gun even necessary? Id just put 2 BBQ ignitors (one above the other) on the handle, running to a spark strip in the respective barrels.
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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 2:31 pm

i think thats a good idea to turn it into a coax gun. how far back should the barrels be? I'm really confused as to what pieces i can use the seal off the back as a chamber. its really boggling my mind. ive never seen a coax that uses the same pipe as the chamber and outer barrel. i guess ill have to look into it
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Unread postAuthor: robert23 » Thu Jul 12, 2007 3:34 pm

Just a quick thought, could you do this all with only one chamber? If so it would eliminate metering propane to two different ones. You could just use a ball valve to shut one barrel off and fire with the other one. Or, leave it open and fire both barrels. I've never built a propane combustion, so I don't even know if that would work, it's just the first thing that came to my head when I read your post. Seems like it might make construction a little simpler.
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Unread postAuthor: frankrede » Thu Jul 12, 2007 4:10 pm

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Unread postAuthor: kwhee07 » Thu Jul 12, 2007 11:18 pm

i dunno. i think making 1 chamber would not only decrease performance(just from reading about single chamber dual barrel setups on here) but also make it much more complicated. as it is now I'm basically building 2 super simple combustion cannons in a shell that looks like a halo 2 rocket launcher, that are propane metered, the difference being ill either split the meter with a t and use adjusted pressure, or ill fill them with an external setup and a nipple on the chamber
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Unread postAuthor: TwitchTheAussie » Thu Jul 12, 2007 11:45 pm

Just build it as a pneumatic I say but you seem pretty determined so Ill say this; a metal chamber will make a difference. That and two different ignitions in the same handle will solve a problem.
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