the device works with a tilt sensor, when the rockets power tails of then it will tip forward as the front is heavier, this will (hopefully) trigger the tilt sensor which will turn the servo releasing the door .
What you'll need:
Arduino Pro mini (or a full sized one would work fine)
tilt sensor http://www.oomlout.co.uk/tilt-switch-p-243.html?zenid=b02b94c613289937d7d01f66b4264578
pliers and wire clippers
FTDI breakout board( to program the arduino)
Step 1: Making the frame
i cut out four cardboard triangles to support the circles and glued them in place. i made a flap that goes over the servo to protect it from the parachute and made two boxes of card for it to rest on and glued a bath sponge cut in half to the flap, this is so that when the door on the bottle opens then the parachute is pushed out.