I'm helping a friend with a physics high school project and we are thinking about doing some rockets fueled with chemicals and a chain reaction for launching.
The general idea is: the first rocket will be launched manually, but when it starts to fall (velocity reaches 0 and acceleration becomes negative on the y-axis) an Arduino will release a lock to the second rocket, and so on. In order to do that, we would need some way to measure the acceleration of the rockets on air. Googling it a little, I've found some stuff about XBee devices, but it would make the project quite expensive.
Can you guys suggest me any other techniques?