When chall2009 was a kid, he loved playing with Estes Rockets:

So I decided to get back into the hobby but using all of my maker skizzls. So here’s a really cool Arduino Rocket Launcher launching 3D Printed rockets from my MakerBot Rep2! Enjoy! Fully Open Source for anyone to make!

Full Assembly and Launch Instructions are on Instructables, Arduino code is on Github and the 3d files for the rockets are downloadable from Thingiverse!