I started with designing the launchpad and release mechanism.
The launcher needs to do the following things:
- Hold the rocket in place
- Allow presurising of the rocket reliably
- Provide a quick release launch mechanism
I spend a good few days reading various websites and looking at numerous designs. One of my goals for the design was to be as cheap as possible, so I settled on a system based on some PVC pipe, an old shelf that I’d recently take down and a couple of extras from B&Q. Total cost for the launcher is probably about £10.
- 21.5mm PVC overflow pipe
- 2 x 22mm PVC push-fit end caps
- 1 21.5mm PVC pipe t-connector
- PVC Pipe Weld glue
- Evostik Serious Glue
- Schrader valve from a bike innertube
- PTFE tape
- 2 x 21.5mm PVC pipe clips
- 4 lengths of Mecanno
- a bunch of screws
- 4 tent pegs
- a bit of coathanger wire
- various bits of coloured insulating tape and spray paint for decoration
Using a hack saw I cut a lengh of pipe that was the length of the inside of a 2-litre bottle + the height of the upright on the launchpad. I wraped some PTFE tape around one end and used the Pipe Weld glue to secure it into the centre of the t-piece. On each end of the t-piece I did the same fitting process with two short lengths (about 4 inches long), and left it all to cure for 24 hours.
Next day I drilled a hole in one of the end caps the same diameter as the Schrader valve. I managed to blag a burst bike innertube from the service desk in Halfords, and set about cutting the valve and the small sourounding circle of rubber from the tube. Using the Serious Glue I fitted this from the inside of the end cap before welding both end caps onto the arms of the t-piece. Once this is set the plumbing for the launcher is complete. The final part of the tubing is to wrap some PTFE tape around the section of the upright pipe where the neck of the bottle will sit to make for a better quality seal.