This is a fairly simple launcher I came up with. I wanted it cheap,
sturdy and reliable. It is made from common pvc pipe and fittings.
The release mechanism is based on the ingenious “Clark
Cable” design. The materials list is:
Rocket on launcher |
|
| The hardest part in the building of this launcher was cutting the o-ring groove in the top pipe. I wanted just enough interference between the o-ring and the inside of the bottle to ensure a good seal, but not so tight that I would try to shear off part of the o-ring every time I loaded a rocket. What I came up with was to use a slightly under sized o-ring (13/16=.8125 OD, bottle neck ID=.850) in an o-ring groove that had a larger dia than the ID of the o-ring. The trick was to find the right diameter that would stretch the o-ring so it’s outside diameter, when installed, would give me the kind of fit I was looking for. I got what I wanted with some patients and my radial arm saw. | 
Cable ties hooked over bottle flange |
| I put a stop on the fence so the saw blade will cut the pipe about 2 inches from the end. Using about 1.5 feet of 1/2 in pipe, I lay the pipe along the fence and against the stop. I turn on the saw and pull the blade into the pipe until it looks like I'm cutting about .050 deep and lock the blade in place. Holding the pipe against the fence and stop, I slowly turn the pipe cutting a groove around the entire circumference. With the o-ring installed in this new groove, I test fit it into a bottle. | 
Release Mech. |
If it is too tight I remove the o-ring, put the pipe back on the saw and reposition the blade to take a few more mils (thousands of an inch) off the bottom of the groove, slowly rotate the pipe again, deepening the groove. Recheck the fit. I keep doing this until I get the fit I am looking for. Or, if I end up going too deep, pull the blade all the way through the pipe and start the process over again. When I get the groove I want I trim the end of the pipe so, when it is glued into the coupling, the o-ring groove is about .38 in above the coupling. The other end is trimmed to about 10 inches above o-ring groove. |
Close up of rocket on launcher |
The only other modification to a pipe or fitting is the hole in one of the pipe caps for the Schrader valve. These requirements depend on the particular valve you have. I have some valves that I got from an auto parts store for an earlier project (water balloon launcher, another story). They are metallic with a jam nut to hold them in place and work great. | 
Cable ties & Hose clamps |
Release mechanisum details |
One of the last things to do to complete the launcher is to position and secure the cable ties. I mount a bottle on the launcher, butting the mouth of the bottle against the ½ in coupling. I line up, and temporarily hold in place with duct tape, the cable ties hooked over the flange of the bottle. I then position and tighten the hose clamps. Trimming the cable ties leaving about .50 in past the bottom hose clamp is the last step. I like to locate the upper hose clamp close enough to the ½ in coupling so that the cable ties, when unrestrained, will naturally position themselves clear of the bottle flange. 12 cable ties seems a bit excessive since one could probably take the load (the area of the bottle throat is about ½ square inch, and with 100 psi in the bottle this translate into about 50 lbs of launching force). Having may of them will help center the trigger and looks cool. I would suggest using three at the minimum. |
| To finish up the launcher all that is needed is the trigger.
All this is, is a tube with an inside diameter that will keep the cable
ties hooked over the bottle flange. Any plastic tube with an inside
diameter around 1.50 inches and around 1.50 inches long will work fine.
A hole some where along the bottom edge for the trigger string will complete
the trigger, and the launcher!
Some extra precaution should be used during the first launch with a new launcher. Any substandard pipe joints will announce themselves during this first pressurization. |
Release Mech. |
Rocket on launcher |
Here is a drawing with some dimensions that might be some help (e size, will take a while).
