What do we need to reliably and safely fire our model rockets? Well, the minimalist approach is simple enough as presented by G. Harry Stine in the Handbook of Model Rocketry (excerped here) and available through the basic Estes Electron Beam® launch controller. A small step up is a simple launch controller using an external 12v battery such as the AeroTech Interlock™ launch controller.
Things which might be desired beyond this are:
There is a nice home-brew launch controller system, designed by Michael Moncur. This seems very close to what is mentioned above. He uses relays instead of a transistor circuit for the continuity check, but otherwise the systems are very similar. Another interesting one-piece system by Robert Bright supports three ignitors at once.
There are some commercial controllers listed below which already address some of these problems.
Ideas for a Better Launch Controller
Higher Power Battery
Apparently NiCd batteries are also good for this use since they will put a lot of current into a short. A large NiCd pack might be the best answer. Motorcycle batteries have also been regularly used for starting R/C airplane motors and have never presented problems doing so.
Of course, if you have a source of A/C power, you could use a standard A/C brick to get a quick 12VDC (or 6, 9, 15, 18V) power source, however if you want to keep your setup totally portable, A/C power and car batteries aren't options. Lantern batteries apparently can't source the necessary current, have short lives at high current levels, and aren't rechargable.
Removal of the Continuity Lamp
Of course, the battery and controller base could stay near the rocket (presumably in a small field box) and only the handheld unit would need to have a long connection to the controller base. This means one could use a low-current signal to trigger a relay in the controller base allowing a more convenient physical connection. Low current, low voltage (12V) signalling like used in telephone lines are perfect for this. Telephone cords come in many flavors, coiled and with built-in retractors. And, it's much easier to handle than lamp cord.
Also, since telephone cord comes in 1-, 2- or 3-pair conductors (and data cable in 4-pair) you could have additional communication channels. The most interesting one is to drive a continuity indicator on the handset. A handset could control up to 7 ignitors (without handset continuity indicators) with a 4-pair wire (using a common ground). A trade-off between continuity indicators and number of ignitors could be made here. For example, using 4-pair wire, one connection could control 3 ignitors, including continuity indicators. Or 2-pair could control one ignitor and continuity indicator.
Note that using telephone wire and direct signalling such as described above requires no special tools or knowlege and should be 100% reliable. Noise won't affect the signal. RF won't create a strong enough current to switch a relay. You can't launch someone elses rocket without the physical connection.
Of course, there are real reasons to have computer control as an option:
There are several obvious approaches to computer integration:
The first step up seems to be the Aerotech Interlock™ launch controller. This unit connects to a motorcycle or car battery for power with large aligator clips and provides higher power than the penlight battery-type controllers.
Submitted by John Coker