[freyguy]

having looked through the threads i've seen alot of people making their own rocket launchers. I spent some time seeing what was out there, and did some research on parts and pieces and designed what I thought would be a compact, safe, field legal alternative to the prefabricated launchers.

basic launcher set up is as follows:
3000 PSI high pressure tank with remote line (the one i play ball with)
remote feeds into vertical regulator
vert. reg. adapter with pressure gauge, blow off valve, and braided hose leading to trigger
trigger is push button valve i found on mcmaster
braided hose leading to pvc end cap attached to 2" pvc pipe (barrel)

when the system is regulated to 200psi i'm lucky to get a 10 foot launch

My thinking is that the standard macro lines and braided hose i'm using is restricting the air flow too much to get the push I need.

any suggestions or solutions?

P.S. I've seen the sprinkler valves used for spud launchers but i'm trying to keep this thing compact. my ultimate goal is to attach it to a marker, much like an m203. If i can build a model that works I'd be more then willing to share the design

[voodoo27909]

You are correct. You are not getting enough volume to launch with the absence of an air storage tank. A larger and faster escape route is needed for your air source to reach the firing chamber. Your hose, and even the regulator on your air tank, are not capable of moving the neccessary amount of air in the time frame needed to "hammer" the rocket in the firing chamber.

[beakerman]

voodoo has this surrounded. You need a dump chamber. The launcher is like a paint ball gun on steroids...it has to have the same basic functional parts: barrel, valve, trigger for valve, regulated supply of some sort and dump chamber. Everything else is cosmetic.

200 PSI is too high for schedule 40 PVC. You need to back that down a bit. I know 2 inch schedule 40 PVC is rated to 280psi but most folk like around a 2X safety factor. Most fields require a 150 PSI pop off max. You want to keep that in mind also.

If you are looking for an m203 style launcher then well I wish you luck on that. The best I've been able to achieve is about 18 inches long and 3.5 inches in diameter. I've tinkered with aluminum and can get shorter (10 inches) but I seem to be stuck with that diameter. Even though I was using aluminum the head ref said that the 150psi pop off rule still applied--so I stopped working on that particular project.

I did however see one guy take a very short piece of PVC (about 10 inches or so and he made a little blooper. It was only good to about 15 yards but it was enough to take out a helo because they did not expect him to literally pull this thing out of his pocket and pop them with it.

[freyguy]

Thanks very much for the responses. Firstly I just want to make a clarification. THERE IS NO PVC UNDER PRESSURE IN THIS DESIGN. I'm only using pvc for the barrel assembly. there is no PVC used backwards from the release valve. I don't want to take any chances. I'm using still pipe, brass fittings and gun parts for any pieces that are under pressure.

After spending about two hours in home depot today ther design has been modified. the barrel remains basically the same, however now it leads to a half inch ball valve. behind the ball valve is a 1/2" x 5" long steal pipe which is acting as the dump chamber. directly behind that is the paintball regulator and high pressure air tank run off a remote line.

I'm achieving a launch of about 20 feet now. here are my questions. is there an ideal ration of barrel length and diameter as compared to the size of the air chamber?

Is there a minimum length of barrel needed to get atleast 150feet out of this thing?

[voodoo27909]

Barrel length has nothing to do with it. Its all about the dump chamber.


Your current design would work with a 12gram Co2 fuel source. the 1/2" x 5" steel pipe would allow good expansion for the Co2 to enable a decent launch. That is about the only way you are going to get the amount of pressure you need both safely and effectively, and still allow for the very compact design which you desire. Volume is the key to air operated cannons....and that translates into SIZE when it comes to dump chambers. The larger the dump chamber...the less pressure you will need to use with air. 12 grams of Co2 only needs about a 1/2" inside diameter x 8" (or so) long steel chamber to allow it to expand, and become an effective fuel source for distance. If you are looking to scale down the launcher, that is the route I would go with it.

Good luck with the project.

[noah harper]

hey Dave, do you think I can launch waterbottles at my mechanics with your toy?


KEEP UP THE GOOD WORK!

WE NEED THIS BY FEB. 7TH and did you get the email about the jerseys?

[beakerman]

Originally Posted by freyguy

Thanks very much for the responses. Firstly I just want to make a clarification. THERE IS NO PVC UNDER PRESSURE IN THIS DESIGN. I'm only using pvc for the barrel assembly. there is no PVC used backwards from the release valve. I don't want to take any chances. I'm using still pipe, brass fittings and gun parts for any pieces that are under pressure.

After spending about two hours in home depot today ther design has been modified. the barrel remains basically the same, however now it leads to a half inch ball valve. behind the ball valve is a 1/2" x 5" long steal pipe which is acting as the dump chamber. directly behind that is the paintball regulator and high pressure air tank run off a remote line.

I'm achieving a launch of about 20 feet now. here are my questions. is there an ideal ration of barrel length and diameter as compared to the size of the air chamber?

Is there a minimum length of barrel needed to get atleast 150feet out of this thing?

ok it will work but not at the pressures that you are trying to work at. Like the dude above says it will work with 12 grams.

There is a relati0nship between barrel length and dump chamber and maximum velocity. Too long and the charge of air drops in pressure too much before the projectile leaves the barrel, too long and you don't have enough residence time to get up to speed.

I would suggest going here and downloading the program from this site:

http://www.thehalls-in-bfe.com/GGDT/

It does not explain things very well but it does give you a real good idea as to how your tater gun will perform. I use it all the time to predict my various ratios and I have found it to be pretty darned good at the numbers provided I put the correct dimensions in to begin with.

[beakerman]

Originally Posted by voodoo27909

Barrel length has nothing to do with it. Its all about the dump chamber.


Your current design would work with a 12gram Co2 fuel source. the 1/2" x 5" steel pipe would allow good expansion for the Co2 to enable a decent launch. That is about the only way you are going to get the amount of pressure you need both safely and effectively, and still allow for the very compact design which you desire. Volume is the key to air operated cannons....and that translates into SIZE when it comes to dump chambers. The larger the dump chamber...the less pressure you will need to use with air. 12 grams of Co2 only needs about a 1/2" inside diameter x 8" (or so) long steel chamber to allow it to expand, and become an effective fuel source for distance. If you are looking to scale down the launcher, that is the route I would go with it.

Good luck with the project.

Voodoo of course barrel length comes into play. If I have a ridiculously long barrel there is no way a 12 gram will do the job by the same token a very short barrel would not work either. The physics just don't work out at the extremes. There is an ideal ratio between barrel length, dump chamber volume and pressure.

[voodoo27909]

I was not anticipating him going for a ridicuously long barrel...since his intentions were to stay as small as possible, and even just 12.5 inches of a barrel works pretty well for launches as far as short goes. I did not want to go into alot of physics with him at this point. Even though it is "Rocket science" so to speak, it is not really that critical an issue when considering just a few more feet or less of effective range unless, like you stated, we begin to deal with extreme's. His current issue, and range failure, is due to his dump chamber Inadequacies. This was all I was concerned with addressing at the moment. We can deal with the barrel later through experimentation, yes?

[freyguy]

very good information; thank you once again for your input. Here's the other requirement I'm trying to stay with in. I want this cannon to operate on compressed air. in this manner when it is mounted to the gun, I can just run a splitter from my regular line and operate the cannon on the same tank my marker is using.

Would air necessarily need a larger dumb chamber to achieve the same affect as CO2, and if so, any thoughts on why?

[voodoo27909]

Here is a site explaining why Co2 does what it does in a smaller area than compressed air can, like the application you are shooting for. I hope this explaines the answer you are looking for better than I could.

http://www.doomlabs.com/science/CO2_Science.html

[freyguy]

Thanks the website was helpful. however I think I'm gonna keep working with compressed air as my fuel. it's tricky and with all the parts I've purchased my total for this project is starting to get up there. Although it's all in the name of paintball. I'm hoping that with just the right combo of valve size and sufficient dump chamber I will be able to achieve a launch of around 50 feet.

it's certainly not as impressive as laying a foam rocket into the side of a tank from 50 yards out, but lets be honest, how often do you get a clear shot at a tank from 50 yards in a woods ball game.

if anyone comes up with a ground breaking revelation let me know

[noah harper]

alot of the launchers that I've seen work off HPA... like the JCS launchers.

and remember the last tank mission we went on... we got shot out from around 50-60 feet from the top of a hill...

[voodoo27909]

50 ft should not be much of a problem to come up with using HPA. Sounds like you know exactly what you are after on this.

Good luck with the project.

[freyguy]

Thanks very much, from the looks of it, I'll need. I'm just about ready to scrap the m203 concept. If I had more time, patience and money I'm sure I could get it to work, However I'm running low on all three. I think for the time being, I'm just going to scale up, follow some online diagrams and make a shoulder mounted version.

[bruno v]

http://s69.photobucket.com/albums/i56/rbrunov/LAW/

Any plastic air chamber is dangerous don't use it!!!!

First I take no responsibility for what you are about to do.
I used a 1' X 2" aluminum pipe for the air chamber (rear) it needs to be thick enough to with stand 300psi and it needs to be tapped for the gauge, fill button and blow off valve I used a piece of aluminum pipe used for out riggers on a boat.
I threaded the back end and closed it with a black pipe cap (if you could it would be a lot lighter if you could close the end with a aluminum end and wield it. The black pipe cap is the heaviest part on my law.
On the pipe I tapped holes for the gauge, the adjustable blow off valve, and the fill button valve.

The front end of the pipe needs to have a 3/4" threaded hole. I had a friend of a friend do the wielding and I think he wielded a nut into the middle of an aluminum plug to give me a strong threaded end. (Do not try to use the reducers that are designed for aluminum pipe, you can't get them to seal properly).

I used a globe valve (rated 300psi) for the trigger you can get the globe valve, button valve and the adjustable blow off at Grainger and McMaster Carr they are catalogs and are on the web I forget where I got what but if your serious I will search and let you know the part numbers.

You need to use 2"X 3/4" pipe nipples to connect the trigger (globe valve) to the air chamber and the barrel.
To make the barrel I used 2" PVC pipe that is used for under ground electrical wires, it is flared on one end and you need the flare to make a tight seal for the breach loader. (I think I cut some of the flare off I have a 1 1/2" long flare)
My barrel is 19" from end to end. You need to get the pvc fittings to reduce the flare end of the barrel down to a 3/4" threaded hole. (Make sure you check out the reducer fittings, some plumping store clerks will give you more than you need and it will not look good).
Attach the barrel and air chamber to the trigger using the nipples.
I had to cut the lever of the globe valve so it would make it pass the end of the air chamber (don't make it too short it takes a good pull to pull the trigger when it is filled with air).
I tapped a 1/4" hole on the top and towards the front of the air chamber for the gauge.
About 2" back from the gauge hole I tapped another 1/4 " hole for the fill button. (If I were to do it over I would of tapped the fill button hole for a 3/8" fitting it would be stronger). You need brass nipples to attach the fill button and adjustable regulator to the air chamber.
I bought a cheap adjustable low-pressure vertical regulator and 1/4" adapter that you attach the reg to the in put of the fill button.
The reg's intake is off set 90 degrees, I attached a 1/4" adapter to the reg in-take and use a remote to fill the Law air chamber (I use a remote with my marker and because where the reg is attached to the air chamber it is not strong enough to hold an air bottle).
Next to the reg and near the back of the air chamber I tapped a hole for the blow off valve. (Put the blow off valve away from where your head will be).
I drilled a 2" hole with a hole drill about 2 1/2" in front of the flare for the breach loader. I then slid a 2" fernco (it is a rubber sleeve that is used to connect two pipes together you can buy it at any plumbing supply house) over the barrel. This will seal the hole after you load the rocket into the barrel. I also cut a 1/2" off a 2" pvc coupler and glued it to the barrel about 5 1/2" in front of the breach hole so the fernco will not slide off the barrel. You get 2 hose clamps with the fernco slide them over each end of the fernco and tighten them down just enough to prevent the air from escaping out the breach hole but not too tight, you want to be able to slide it forward to load the law.

Now trust me the way I designed this is for safety.

The adjustable blow off is good in the way it releases air, if you fill the air chamber too much, it does not pop, it releases the air slowly (saving air if you fill it to much). Also you may have to adjust it for the field’s specifications. I set the blow off for 275psi and I fill the air chamber to 250psi.
The fill button (rated too 300psi) is used to fill the air chamber when your ready to shoot it, this way you are not running around with the chamber charged, you can charge it when you need it.
The aluminum pipe is light and will not explode like PVC, it will just split if some thing goes wrong.
I used a cheap low-pressure reg (Tippman that I bought on line for about $20.00). I had to take one of the washers out of the reg to get it to adjust properly to 250psi. (The reg adjuster was not sensitive enough).
The most expensive part is the globe valve and the aluminum pipe.
Also don't paint the fernco it will not dry.
If you are serious about this I will take better pics of my Law and post them on the site that I posted above.
With very little practice you can shoot reload and fire again in about 6 seconds.
At 250psi this thing will shoot a nerf over 100' straight at a slight angle it will go a lot further. You also don't need to cut the wings of the nerf.

[freyguy]

Hi bruno,

I've looked at your design before, and it's a beauty. How well does it opperate at around 120 psi. most fields now will not allow you to pressurize the cannon to more then 150 PSI. how does your design function within those constraints?

[bruno v]

I have used it only a couple of times but I charge the air chamber to 250psi
The last time I used it the rockets corked screwed a little I don't know if it happened because the Nerf fins were bent or if I was using too much air pressure, I will take it out soon to see if lowering the psi will help.
My experience with fields has not been a problem with using 250psi once I show them that the air chamber is metal.
I am also going to hone out the barrel so the Nerf is not such a tight fit I don't like cutting the fins because if they are not perfect the Nerf will not fly right.
Also with my design you have to make sure you hold the trigger down long enough to let all the air out I have a tendency of letting it go too soon.

[freyguy]

Well if you've looked over the rest of this thread you can see that this was my first launcher project and have been toying with several slight variations of the same design to achieve the best launch possible.

From the legitimate research I've done combined with what I've experienced first hand, there are a few things I might suggest.

The rockets cork screw as you said is probably due to the fins being bent. too much psi would result in one or both of too things, a longer shot, and waisted air pressure.

I would be careful boring out your barrel, although not clipping the rocket fins is a tempting gain, there is a very sensitive balance between barrel bore, rocket diameter and launch distance. Too tight and the friction will slow it down, too loose and the air will escape around the sides of the projectile, making a shorter launch.

If you were achieving 100 foot straight shots at 250 psi, it's very likely that you will only get about 50 or 60 foot straight shots at 120 psi. I'm curious to know how it does though.

I've found there is a lot involved in creating a working a launcher. namely a sensitive relationship between barrel size, dump chamber volume, psi and valve size and efficiency. roll that around in your head for a bit if you want to go crazy.

I'll be posting pictures of my launcher in progress shortly.

if you should come up with any break throughs, or launch it at 150 psi, let me know the results