Homemade launch controller plans available

I'm looking forward to build a homemade launch controller for lpr and mpr. I want it to be secure (requiring a key and button press to launch) made of thin 1/4 plywood and to be able to hook different batteries to it (9V 4x1.5v 12V...).

The searching engine for TRF is plain awful plus I use my phone most of the time to browse so I couldn't find any of the probably numerous good threads on the subject.

I think the Stine book offers some electronic schematics but does anybody know of other good sources to get inspiration?

https://www.oldrocketplans.com/centuri/cen1654/cen1654.pdf

Go to page 7.

The plans are old. You need 15 feet minimum for the length of wires from controller to pad and 30 feet minimum for anything with 30 N-s or more total impulse.

And Radio Shack is useless. Look elsewhere, like Home Depot, Lowes or online.

shreadvector said:

https://www.oldrocketplans.com/centuri/cen1654/cen1654.pdf

Go to page 7.

The plans are old. You need 15 feet minimum for the length of wires from controller to pad and 30 feet minimum for anything with 30 N-s or more total impulse.

And Radio Shack is useless. Look elsewhere, like Home Depot, Lowes or online.

Click to expand...

Thanks. These are dead simple plans! Anyone can comment on needs to adjust any resistance values for 12V for example?

An incandescent continuity lamp will probably conduct enough current to fire something like a Quest starter. People are using an LED with a resistor these days...

The basic design is good and can be adapted to almost anything. Change the momentary switch, the insert key, continuity lamp, etc. Put the components in a box/container and use a shorted speaker/mic plug as your key. Your choices are varied while using the same simple electronic schematic.

If you plan to use it on a 12V system only, I would change the continuity lamp to a LED and 470 ohm resistor in series. That will keep the continuity current low enough so you won't fire the Quest ignitors or CTI ematches as soon as you plug in the key.

Standard LEDs draw/drop/use 2.2 volts DC while drawing 20 milliAmps, or .020 Amperes. That means if your source is 12 VDC and the LED is using 2.2 VDC, then your resistor needs to drop/use 9.8 VDC. Ohm's law is Voltage = Current x Resistance or E = I * R. Change that to E/I = R or 9.8 VDC/0.02 Amps = 490 Ohms. Standard resistor sizes come in 470 ohm or 510 ohm. I would use the 470 ohm resistor. The LED will work with a little higher current (resistor values are usually +- 20%) and won't dim as quick if the voltage drops a little while using the battery.

Here's a slightly more complicated schematic. R1 and R2 would be 470 ohm for a 12 VDC system. The launch and continuity switches are momentary switches.

Handeman's circuit is the basic LED launcher circuit. You can't go wrong with it. It will work with 6 V, 9 V or 12 V without changing anything. I suggest using the superbright versions of the LEDs which are much brighter for the same current draw, and using 1 K resistors to lower the current drain if you use 9 volt batteries. This modification will double the battery life if you leave it on as the current would be reduced from ~14 ma to 7 ma.

Bob

Good suggestions. Thanks.

Also, what is the maximum current that it is safe to push throug small Estes or Aerotech igniters for 10 seconds without risking to ignite them?