So... I'm going to build a launcher.

Hey all,

I've been looking for some more projects to keep me busy. The first is going to be a pump-pneuMag for which I'm sourcing parts now. However, having played mostly scenario for a year or so, the merits of anti-artillery firepower are becoming clear. I know that there are some pre-fab, very nice options out there. However, they are generally VERY expensive (considering the limited utility) and tend toward the cumbersome.

Just to preface this, I know this isn't the easy way to get a launcher. I know I could just buy one, or make one of those awful hack-jobs with plumbing fixtures and PVC. I'm a tinkerer. I like to figure things out, take things apart and make them into something else, and so on. I'm posting this to get some collaborative insight on this project. Constructive criticism is humbly and anxiously welcome. Unconstructive criticism is not.

So... I'm really just at the drawing board so far. I'm pooling all the ideas as they come into this and a few other threads. There are a few things that I definitely want included:

• Relatively small (akin to the Metadyne launcher, perhaps the m79 Thumper [see "stock"])
  
• Regulated air: Going to use a reg. Period. I'd like the flexibility of using 12g CO2, CA CO2, and HPA. The only way to do this is to build with CO2 in mind and regulate pressure to the dump chamber so that shot pressure is consistent regardless of input.
  
• CO2 compatible: Obvious, but important to keep in mind when choosing components.
  
• Portability: I don't expect to carry this as a primary, and I don't want it to be so cumbersome that it sits in my gearbag as a show piece.
  
• Stock: I definitely want a stock, but with weight/size concerns, a traditional wooden stock is impractical. I know there are paintball-specific options available and may go with one for cost concerns. However, I really like the top-folding stock on the SPAS-12 (See Robert Muldoon in Jurassic Park), which is unfortunately not made anymore and costs around $1000 if you can find one. Similar top-folding shotgun stocks are available for around $60, still more than I want to spend for that component. WWII Paratrooper folding wire stocks are also interesting. (ATI makes a glass-fiber composite top-folding shotgun stock that I really like. $50 for that may be worth it, versus the cost of fabbing something similar.)

Question marks: These are the things I'm still working out and really would like some input on.

• Actuation: Mechanical actuation (trigger) is the simpler in terms of operation, but electronic actuation opens a lot more doors of possibility, not the least of which is that the trigger/frame components do not have to be located in any exact physical proximity to the valve assembly/firing mechanism. Which brings us to...
  
• Firing mechanism: So, existing gun platforms have been ruled out as too limiting in flow capacity. Remaining options are the standard sprinkler valve setup (which I don't like much at all), similar QE valves (I like more than sprinklers, but not perfect), some Clippard mini toggle valves (limited selection, but some in 300psi, small, and cheap), and a 100% scratch-made valve system. As things progress, the last option is becoming more and more attractive.
  
• Materials: The barrel, in particular, is the first materials question. I believe the Nerf rockets are 2"OD, so I need a tube that's 2"ID. I'd like to go metal. Aluminum is probably best for weight/durability balance, but I don't know where I'd source 2" aluminum pipe and what that'll cost me. [Note: Found Al online for about $7-20/ft depending on the wall thickness.] Update: I'm definitely going with an aluminum barrel. I'm absolutely not doing PVC. I don't mean to disparage anyone who has used PVC for their build, it's perfetly fine for most designs. I'm looking to push operating pressure up around 300. PVC just isn't safe at that range.
  
• Dump chamber/valve operation: This largely falls under the "firing mechanism" discussion. If I'm fabricating, I'll need to figure out the logistics and dimensions of the dump chamber and valve setup. If I'm using a sprinkler/QE valve, I'm going to need a substantial, integrated dump chamber (such as the fire extinguishers used on some models seen in these threads). If I can up the pressure, such as with the Clippard toggle valves, the chamber can be significantly smaller. If I go 100% from scratch, I'll integrate the dump chamber into the valve body, eliminating flow issues entirely.

That's all I've got at the moment. For the record, I'll be trying to scavenge as many parts as I can from PBN and other classifieds and ebay. Building something awesome from stuff other people don't want is part of the thrill. Thanks in advance for all of your help.

John
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Valve Roundup!
Seeing as the valve is the primary issue thus far in all of the discussion going on, I thught I would try to keep everything re: valves up front here for anyone who's trying to reference or contribute. Here goes:

Existing Marker Systems
I'm sending this one to the idea graveyard. I'm still not convinced that it can't be done, but I've concluded that it's beyond the realm of what I want to do. I will be keeping existing systems in mind if I decide to go the route of having a valve system fabricated from scratch.

Sprinkler Valves
These are the current standard in DIY rocket launchers. Pros are that they are relatively inexpensive, readily available, exist in easy-to-accommodate threads, and have relatively high flow rate capability. Cons are that they're plastic, rated to 150psi or less, open slowly, and are generally unattractive.

I'm simply not going to use a sprinkler valve. I put it here just so everyone knows that I'm aware of sprinkler valves and have evaluated the merits of using them in my build. They're just not what I'm looking for.

Quick Exhaust Valves (QEVs)
These are not terribly unlike sprinkler valves in their general operation. They're a bit like the sprinkler valve's tougher, older brother. Pros are that they are metal, reasonably inexpensive, reasonably easy to find, open faster than sprinkler valves, (sometimes) flow higher than sprinkler valves, and are also available in common pipe threading. Cons are that they can get a bit heavy (~1/2-2 1/2#), are generally rated to 150psi, and are still a bit unsightly.

Some of these are looking very, very promising. They're cheap enough to buy one or two for prototyping and not cry if they don't work out. The real big issue with these (and sprinkler valves) is that the pressure restriction (150psi) demands very, very huge air flow and volume, which in turn requires a large dump chamber and big valve/pipe openings. This means that the convenience of a small, inexpensive valve is offset by the inconvenience and cost of a secondary air chamber and the associated plumbing.

Other Valves
So far, this is including only Clippard's valves. They are small industrial valves typically used for industrial pneumatic controlling. Pros include being VERY small, inexpensive, mechanically (not pneumatically) actuated, rated to 300psi (sometimes), and available in 1/8"npt threading. Cons include limited flow (per 1/8"npt threading) and limited selection beyond 150psi.

So far these are the prefabricated option that has me most hopeful in terms of staying within the logistics I set out at the beginning of the post. The 300psi flow rate should mitigate the need for a huge air chamber (athough time will tell how much) and the nature of the valves' functioning should remedy the slow-opening problem of sprinkler valves (which is part of the reason they need such huge flow consideration).