Timers for Rocket Ejection

Posted on Feb 4, 2014

This can be a thin strand of wire, like one of the copper `hairs` from a section of lamp cord, which is wired to the altimeter by terminals somewhere on the rocket body and anchored to the launch stand at some point. Rocket takes off, stand holds the wire back. Wire breaks, circuit is interrupted, and timer starts timing. Possible downside: Too

Timers for Rocket Ejection
Click here to download the full size of the above Circuit.

strong a wire could hold a small rocket back. Dangling wires could contact each other in flight, restarting the countdown and making for late ejection. b. I`ve heard of those that ran the current through a section of solder which went under the rocket nozzle. Exhaust heat melts solder, provided that the solder stayed in place. Actually that much heat could melt copper almost as easily. c. Another is to put a reed switch in the rocket, and have a magnet on the launch rod hold it closed. Rocket leaves rod, switch opens, timer starts timing. d. Some folks mount an audio-type earphone jack in the tail end of the rocket, facing down. A tethered plug is inserted in the jack, keeping the circuit closed. The plug is tied to the launch stand, so that when the rocket takes off, the plug is jerked out, the circuit broken, and the timer starts counting down. Possible downside: these jacks are not designed for high acceleration, so their reliability under rocket conditions must be monitored. Also, exhaust products are corrosive, and may cause flaky connections with any electrical connector mounted near the motor. e. Terminals on the side of the rocket are connected with a strong wire by small alligator clips, like those used for Estes ignitors. Wire is mounted firmly to test stand, so that when rocket takes off, the wire stays behind - clips slip off the terminals, breaking connection and starting the timer. Obviously, the rocket needs...

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