This piece of engineering is so simple and elegant, you’ll want to build a pretty serious water rocket just so you can try it out. It’s an automatic parachute deployment system that you build into the nose-cone of your rocket. The main portion of the build is made out of plastic soda bottles (2 liter size) to end up with a chamber to store the chute, as well as a friction joint that holds the thing together.
The video after the break shows a complete tutorial on how to build one of these. It starts by tracing out a sine-wave-like pattern on the wall of the bottle. The staggered tongues that are left after cutting along this line make up the friction joint. After gluing a cone (the blue thing) to the bottom of the bottle, it receives the parachute and is then slipped over another bottle that makes up the body of the rocket. The rubber band wraps around the outside of the chassis, holding those plastic tongues in place. The loose end of the rubber band is hooked around the horn of a servo motor, which can then be triggered remotely, or by using a sensor of your choosing. There is even a spring made out of a loop of plastic bottle — you can see it just on top of the chute in the image above.
Need a launching system that is as fancy as the parachute system? Here you go.