A hobby I've been meaning to publicise for quite some time is mine and my friends Water Rocketry! We have gained many idea's from Air Command http://www.aircommandrockets.com/ (Thanks Guys!). However are no where near as far advance as they are yet as we have really only just started to get serious with the hobby.
We went though all the basic little designs with single bottles.
We have made a series of rockets using Robinson couplings we have called Nexus(meaning join) which consists of 5 rockets ranging from 4l capacity up to 12l none of which have flown as of yet. We have also made a remotely controlled parachute deploying system, which we adapted from Air Commands instructions on how to make a system using their flight computer (thanks again =] ).
We have started making fins out of corriflute, another idea borrowed.
We are also currently building a more substantial launcher, of which i shall start to document on here soon followed by a back log of all our previous endeavours.
This will however take some time.