Building a launcher

The launcher we will build here is made from a few pieces of PVC pipe and some “Gardena” parts.

Release mechanism

First we will modify the Quick connect coupling so we are able to mount two pieces of nylon cord to it. To do this we have made two small incisions into the opposite sides of the Quick connect coupling. Next take the nylon cord and put one of the ends into a flame so it will start melting. Then press the molten end of the nylon cord to for example a piece of wood. This will flatten the end of the nylon cord. Repeat this step for the other end of the cord. The flattened ends should now be made to fit into the incisions that are made into the coupling. On the left you can see the finished product in action.

To make the coupling fit into the launch pipe we will mount it into a 40 mm PVC socket. The nut from the Quick connect coupling fits almost perfectly in a 40 mm PVC socket as shown in the picture below. Before we do any mounting we will first connect the coupling to a piece of garden hose. Make sure you use a garden hose that can take a lot of pressure, about 10 bar (145 psi). Also make sure that the hose is long enough, at least 1 meter.

After mounting the hose to the Quick connect coupling, it can be glued into the PVC socket. Let it dry for a few hours.

In the meanwhile we need cut up a piece of PVC pipe which has a diameter of 40 mm. What we need is the following:

To get accurate measurement and straight cuts, you should use a pipe cutter instead of a saw. Once you have cut all pieces to the right lengths, it’s time to glue them together. Before you start gluing things together make sure you have to follwing parts:

Well all we need to do now is glue the pieces together. Click this link to see how the launchers base should be assembled.
 

Fitting the quick connect  nozzle to the bottle

Before I came up with this solution I went to a lot of effort trying to fix the nozzle to the bottle. Even after all the effort it took to fit the nozzle it kept coming off the bottle between 8 (116 psi) and 10 bar (145 psi) of pressure. One of the goals of the Gardena Launcher is that it should be able to pressurize the bottle to at least 12 bar (174 psi) or better to the maximum specs (17 bar / 250 psi) of the compressor that I use, that is if the PET bottle can take it. Anyway, the nozzle should stick to bottle even if it explodes. I now have found a better way to fix the nozzle to bottle. Regretfully I have not yet been able to test the solution I came up with. Don't worry though I will test it ... soon.

First thing I did was modifying the Gardena quick connect nozzle so it would fit in the bottles screw cap. To make it fit in the bottles screw cap I also had to modify the screw cap. First things first; I first sawed off the nozzles helix and flattened it. Then I made the outside diameter of the nozzle fit the inside diameter of the bottles screw cap. The last modification I made was reducing the thickness of the nozzle. I have to do this becaues the nozzle is made to make an exact fit to the quick connect coupling. To make the bottles screw cap fit between the nozzle and the quick connect coupling I have to reduce the nozzles thickness from 2 mm to about 1 mm to make it fit again. Make sure you reduce the side that will go into the quick connect coupling. The best tool to do these kinds of modifications is by using a lathe. Regretfully I don't own a lathe ... yet, so I improvised one using an old electric motor, a battery and a Stanley knife; it works like a charm.

After modifying the nozzle I had to drill a hole into the bottles screw cap. The hole is about 20 mm in diameter. I used a cone cutter drill and drill press to drill the hole. These tools are in my possession, so that was easy. The tighter the nozzle fits into the hole the better. Below on the left a picture of the modified nozzle, in the middle the modified screw cap, and on the right a picture of the finished product. The O-rings you see on the bottle don’t have any function; they are leftovers from another experiment.

The rest of this workshop will folow shortly.
In the meanwhile take a look at the finished product in action. The movie on the left shows the launcher in action. The first test was done at 8 bar (116 psi). The movie on the right shows how all the stuff fits in my wife’s car.