Build Your own LAW Rocket Launcher - Cheap, Portable and Simple Author: Nick
*Caution assemble and use at own risk
This article is for everyone who has been kicking ass on the field only to have it all go to hell as soon as that enemy tank creeps up the hill. Scattering the rest of your soldiers into the tree lines. Where is that guy with his LAW rocket? Well ill show you how to make a small, portable rocket launcher for cheap so you can take out that tank or clear a room when YOU need it.
First of all what is a LAW rocket launcher anyway? Well this is also know as an Air Cannon, RPG, Rocket Launcher but most of the time you will just hear people scream "LAW"! LAWS are used to destroy tanks, take out a single room in a bunker or just kill everyone within 10 feet of impact depending on the fields rules. These LAWS work buy using air pressure to shoot out Nerf Footballs (with the fins).
So enough talking about LAWS lets get to work making one!
Materials
So in my design all of your parts can be purchased at Home Depot except for one. The only part your going to need to order I found at ActionVillage.com its called a "Brass Eagle 12 Gram CO2 Quick Change Adapter" all of the other parts are found at Home Depot pretty much on the plumbing isle. And the total cost will something around $30.00 - 40.00.
First lay out all the pieces you bought and try to think through the construction for the LAW. The 2" diameter PVC pipe will need to be no shorter than 12 inches or so. Of course the longer the pipe the greater the accuracy but also brings down your mobility. Honestly you don't want a long barrel, about 15 - 16 inches should be the perfect balance. The barrel will be a low pressure area It will not need PVC glue on the cap but it wouldn't hurt, a good bashing on the cement should seat the cap firmly on the barrel.
Drill a hole into the barrel near the end with the cap. I used I think a .5 inch drill piece and slowly filed it larger to fit the 90 deg elbow. When it came time to insert the 90deg elbow I heated it up using a blow torch so when I screwed it in it would "melt" the PVC around the threads. It worked pretty well.
Assemble the high pressure steel tubing area. Now the Quick Change adapter will screw into the steel pipe reducer. The reducer will be mounted to the long piece of steel pipe and then to the ball valve. Don't try anything smaller than a 5" long pipe you can go longer but not shorter. The pipe will act as an expansion chamber for the 12grams CO2. When connecting these pipes I tried to use LocTite (Red) but this didn't seal all the air leaks. So USE Plumbers tape for all the steel tubing to keep them form leaking. Assemble the steel tubing together using the photos for reference it should be pretty strait forward. You have to really secure these HARD CORE! I used my bench mounted vice and screwed them in as hard as I could. This steel tubing is good for up to about 2000 psi so make sure they are on there really good. When the tubing is charged it will be holding around 500 psi. You'll notice the Ball valve is only rated up to 600 psi so this is why you don't go shorter than 5" pipe.
After assembling all the high pressure areas (steel tubing) all you have to do is screw the 90deg elbow back into the barrel and your almost finished. To finish up the LAW I used a spare piece of wood with some holes drilled into it. I mounted this in the center between the steel tubing and barrel, and secured it with some zip ties I had laying around. This makes the LAW a little more durable and sturdy.
Testing
When you first pressurize the system take safety precautions. Wrap it up in a heavy towel or something so if something does explode it wont be that bad ;) Use soapy water (normal dish washer soap is fine) from a squirt bottle and spray the steel tubing looking for leaks ( you will see a ton of bubbles if there's a leak). It will be hard to make it 100% leak proof. I would settle for 98% leak proof and be happy. Only charge the system up with a 12gram right before your about to shoot the LAW. I wouldn't leave charged for long since you can never be sure if its 100% leak proof or not.
Depending on the arc when you shoot it should travel about 2-3 houses yards. This LAW wont set and distance records but it will be enough to make it into a buildings window or hit a tank almost as far as your gun can shoot. This LAW also wont shoot past 250fps either. I have made larger more powerful LAWS but none have been this portable.
Check out the video below to see it in action!
Video was shot outside my house with a Northern 8-13mph wind at 69F. The arch was around a 35-40deg angle. Total distance was 124 feet (see update below It can go 220+ feet) directly into the wind. It went about 5 feet past the stop sign and I almost hit the car driving past in the video. One second sooner and that car would have been waving a white flag. :) If distance is really a concern making the expansion chamber tube longer will add some distance but lowers the portability.
Photo of the Nerf footballs used for LAWS
Brass Eagle 12 Gram CO2 Quick Change Adapter
Drill a hole for the 90deg elbow
Here is the barrel with the hole drilled
Using a blow torch I heated the pipe up before inserting into the pipe. This will melt the pvc around the threads to seal it in. Careful its hot!
Here is the elbow inserted into the barrel.
Here is the plumbing for the expansion chamber and valve. You can see the 90deg elbow on the end that inserts into the barrel.
The Quick change adapter holds a single 12 gram CO2 to power the LAW.
Final assembly of the LAW rocket launcher before painting. Wood block in center is for support with zip ties to secure it.
(click picture for a larger view)
!UPDATES!
April 28, 2008 - Hi everyone I have officially tested it out on its first 24-hr senerio battle and I can say im very pleased. First of all I have no leaks! Walked around for about 20 min with it charged up and when I went to shoot wham! Strait as an arrow. Some upgrades since I wrote the article were I extened the handle on the ball valve so it takes less force to open it up. The faster you can open it up = more distance it will fire. I extened the handle buy just using some force and a 1/2"? pvc pipe till I got the lenght I wanted. I attatched a Sling onto some of the zip-ties and It worked fine the whole game even while crawling. After the game I tested it on the Camp sites field which had camp spaces with poles every 21-22 feet. So I stood at one and rounded down the math to 20ft spaces and shot down the lane. After two test firings its max distance is right around 220+ft. I think the handle helps alot since microseconds count when opening the ball valve. Next upgrade is I want the handle to be spring loaded somehow to achieve Max. distance and speed. But this is still a top-dawg LAW performance wise.
One Con must be mentioned as I have had this problem and multiple people who build this run into the same thing. When loading a new 12gram in the Quick Change CO2 adapter, If it starts leaking where its screws together this is common. See the Quick Change adapter has a needle and oring that are replaceable. You can see them easily if you just look at the asa end when the top is screwed off. This unscrews itself when you unscrew the top to replace the CO2 12gram. So be sure its all the way screwed in or it will leak. Just use a finger nail or screw driver to twist it down (righty tighty). Maybe some Blue (NOT RED) Loc-tite? Ill have to try it out next game.
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