"Preventing those hard landings"

I have tried a number of deployment systems. However my track history so far is not so great!

Having said that, the 'no-parachute' rockets always seem to go higher! Simple rockets are quick and easy to make, so often a parachute is not worth the effort.

It's a different story for multi-bottle rockets or when a camera is aboard!

Supposedly the simplest. The nosecone just falls off at the top of the flight. However for me it usually doesn't fall off at all, or comes off at take-off. Occasionally it works, but this is rare!

This system was a full controller with altimeter data logging, accelerometers, IrDA interface (for data extraction and setup using a PDA) and a deployment system using a catch activated by muscle wire.

Documentation is here.    Electronic circuit is here.

Worked on the bench, but in a real launch the nosecone was forced off at take-off

The most promising so far. A cheap ($10) RC car was used to release the nosecone on command.

The RC car was disassembled. This gave two geared motors that could be controller to run in either direction, and a receiver PCB with battery. Twin-wall plastic sheet was used to make the mounts. The rear axial and motor plus the receiver were glued to this (hot-melt glue). A length of nylon line was tied to the wheel such that when operated it wound up on the motor axial. This line was set up to pull out the pin which held the nosecone in place. Once released the nosecone was pulled off by a rubberband, thus freeing the parachute.

The system was designed to also allow a camera to be mounted - once reliable operation was proven. 

The second channel of the RC was not used. The motor was removed, and replaced with a dual-colour LED. This provides a radio-check function on the other RC channel.

The RC range was increased by extending the receiver wire. This gave a range of approximately 50 metres. It may be possible to improve this by also extending the transmitter antenna length.

It worked, eventually! After moments of terror with the rocket rapidly falling to the ground the chute popped about 4m from the ground, allowing the rocket to gracefully land ... in the stream! The electronics did not survive the dunking!

I used a clockwork toy to release the door holding the chute in the nosecone. It would have worked if the chute had been lose enough to come out! Too many hard landings have broken the timer, but with some work this looks promising. Next version needs a chute deployment spring to actually push the chute out of the rocket.