Inspired by an existing project I saw linked on Hackaday, I couldn’t resist having a go at building a compressed air rocket launcher. To keep the costs down, I tried to use commonly available plumbing fittings where possible (40mm solvent weld waste pipe). Originally I planned to use larger diameter pipe, but reducing fittings didn’t seem that easy to source locally.
Here’s my first prototype assembled, with the rocket (made of 15mm pipe insulation foam) in situ. The rocket is concealing a length of 15mm copper pipe which serves as the launch tube:
To get a reasonable volume of air in a small footprint, the pipework is folded into an S shape, rather than having one long length. The two parallel pipes at the left were intended to be closer together, but I accidentally welded in a longer pipe than I planned, and there was no going back 🙂
The 40mm pipe is solvent welded, and has two screw on access plugs at either end. These have been drilled through, and fitted with tank connectors, along with the various reducing fittings needed to connect the inlet and outlet valves.
This next shot shows a close-up of the outlet side which consists of a 12V solenoid valve (the black cylinder) which is normally closed, and fires a blast of compressed air when it opens. The other cylindrical component is an oil pressure sensor, which I plan to use to measure the air pressure. The pressure sensor has NPT thread, so an adaptor is needed for BSP thread. There’s also a 1/4 BSP female 3 way tee fitting used to connect the pressure sensor in circuit.
Various 1/4″ and 1/2″ brass hexagon bushes, hexagon nipples and other parts are needed to connect these together, with PTFE tape used on all joints. The final output is through a compression wallplate elbow, with a vertical 15mm copper pipe for the launch tube.
There was some guesswork in the design, because I didn’t bother to calculate what sort of volume of air was needed, and wasn’t sure if the solenoid valve would have a high enough flow rate (it has quite a narrow bore). I just decided to try it and see what happens.
Obligatory warning: if you build something like this, be aware that the plastic pipe could explode and shatter under pressure.
Having built it, I donned safety glasses, retired to a safe distance and pressurised it. At the first attempt I managed to get it up to 30psi, due to a slow air leak. The first launch was pretty impressive, and the foam rocket (lacking flights at this point) narrowly missed landing on the roof of the house! Adding some cardboard flights to the rocket improved the aim dramatically.
Some reassembly of the outlet joints cured the leak, and I’ve since had it up to 60psi. I’m going to box it up before pushing it to higher pressures. The compressor is rated for 100psi (just under 7 bar) so it will be interesting to see how high this thing can go 🙂
Next steps are to build a box for it, and to make the control unit. I’m planning to give it a mission control look with key switch, flip up covered toggle switch and big red button to launch… to be continued!