Multi-channel rocket launcher

Description
This launch controller can be used with low voltage battery igniters, which fire rocket engines in model rockets such as the Estes range. These circuits are electrical, only switches and contacts are involved. First the circuit for a single rocket:

The only thing to note here is that this controller uses "C" cells, providing more current than "AA" batteries and that the push button switch has contacts rated 1 amp or higher. The wire to the igniter is isolated via a 3.5 inch jack plug and socket. Connect the igniter, then plug in to control box and then press button, making sure you are the recommended distance away. Below is an internal and external picture of my controller:-

Ok, does anyone think my grass needs cutting? Moving on to the multi launch controller:-

Once again, nothing too complicated. The single pole rotary switch has contacts rated 1 amp so can easily handle the 400 mA of current that the igniter takes. Here three rockets can be launched by rotating the switch. The Green LED provides continuity between battery,igniter and wiring. This extinguishes as the launch switch is pressed. Once again, observe safety precautions.

Mission Critical:
Heres a story about my own Estes space shuttle, on its one and only mission. This is what happens when you're too eager to get a rocket flying and don't pay attention to balance. It was a late November afternoon in 1998 when I first launched the shuttle. Lift off was perfect, no wind, clear skies (doesn't sound at all like England), and the rocket motor was a C6-5. At launch, the rocket motor fired, though lift off acceleration was not as good as I expected, I blame too much paint and excess weight). As my rocket reached apogee, (estimated height about 100 meters) and acceleration became zero there was no immediate separation between the shuttle and main fuel tank. There was of course a delay of 5 seconds between the rocket engine blowing its ejection charge. Five seconds is a long time too wait, especially when the forces excerted of gravity take hold. At 9.8 meters/second, the rocket plunged towards earth losing at least half its height. Then, thankfully the ejection charge blew, separation was achieved the the main fuel tank with SRB's drifted slowly down to earth on its parachute. However all was not well with the shuttle. It was only after separation that I realized there was too much nose weight (hence a heavy lift up and not enough height). The shuttle did glide, but only at about 45 degrees downward, picking up speed until eventually it crash landed in some soft mud. Luckily it survived the impact, I cleaned it up but have not yet removed the nose cone to balance the shuttle. I like it as an ornament anyway.

Here is another equally cool low voltage alarm circuit for your glider receiver battery that I've shamelessly stolen from George Steiner's book "A to Z--Radio Control Electronic Journal" (see below).  I've modified it to use with small battery packs in R/C gliders. This design has a trigger voltage at about 4.3 volts, and it draws 1mA or less when quiet and about 4mA when buzzing.  This can be constructed from parts fromt Radio Shack, though you may need to order a few through them.

The voltage of a receiver system is punctuated by low-voltage spikes every time the servo motors spin up, since the servos draw more than the battery can deliver.  With large receiver battery packs, this is not as much of an issue, and it may not be noticeable.  However with 270mA and smaller battery packs, particularly with more than two servos,  low voltage alarms can chirp constantly, every time a servo moves.  The challenge is to design in a little slack or delay, just enough so that you are not annoyed by constant chirping, but not too much so that the chirps can give you a warning before the battery is completely exhausted.  Here, this "hysteresis" is adjusted with the capacitor.  For large packs (600mA and above), no capacitor is probably needed, although I've been using a 1uF capacitor on my open class ship with 6 servos and a 600mA battery.   For 270 mA and two servos, I'd suggest trying a 1uF capacitor.  For 150mA or less,  a 2.2uF capacitor works well.  If you want to know only when the battery has finally reached the trigger voltage, try a 5uF (or 4.7uF) capacitor.  The actual type of capacitor is not critical, but tantalum capacitors are physically smaller.  If you want to worry about the polarity of  the capacitor, the negative side should be directed toward the negative pole of the battery, but at these relatively low voltages compared to the capacitor rating, the polarity probably does not matter.