Launch Controller Idea

Hey guys, been in and out of the Model Rocketry scene for a few years. I built my own launch pad a couple years ago and I wanted to build a launch control box to go with it. I'm not launching anything crazy (LPR and maybe in the future MPR) but I kinda want to build something to say, hey, I built it myself!

I've got an idea for how it might look. I'm an engineer (student) but not an electrician. I may need some help on the schematics to get this up and running, or maybe someone to tell me just to buy a GO-Box. Anyway, here's the idea. When the 12V battery is connected, a POWER LED lights up. Arming the device will be accomplished by flipping a safety toggle switch. This will light up an ARMED LED, which also serves as the continuity light. To launch, a simple push button would be used.

What do you guys think? Thanks in advance for any help, this is a really great forum for rocketry!!!

Perfect. I built one very much like thet but used a buzzer instead of a light.

You need to incorporate a removable safety interlock device that is in series with the launch button.

Mark K.

You may find more ideas here https://principialabs.com/electronic-launch-control-system/

Would this schematic be close to what I'd need? Thanks for the help, guys!

View attachment Launcher Schematic.bmp

Two things:

1.) You need to use resistors in series with LEDs. I would make sure that no more than 1mA goes through your continuity circuit, otherwise, you could set off e-matches and Quest Q2G2s.

2.) Make sure your safety interlock is a key/pin/something removable from the launch system. A speaker jack wired to itself works great for this.

Re: the safety interlock. The idea is that if you walk away from the launch controller, there will be no way to activate the launch button and supply power to the igniter clips because you are carrying with you a key piece that is required in order to complete the circuit. This feature is required under NFPA 1124 and 1127 and is part of every Safety Code.

Mark K.

OK, so to review, a speaker jack makes a good key. I assume you can find the female plug easily enough at Radioshack? What other things make good safety keys?
A sizeable resistor is needed in the continuity circuit. In the schematic, would I put this right in front of the LED? How many ohms are we talking here?
Again, thank you so much for your help.

RadMax8 said:

Would this schematic be close to what I'd need? Thanks for the help, guys!

Click to expand...

NO! That would not work.

There is a red lamp bypassing the safety switch. Even if that is an LED and would prevent too much current from getting to the igniter, it's wrong. The safety switch has to be able to remove ALL electrical power from getting to the igniter.

The attached schematic would be better.

View attachment Basic Controller.bmp

Here's a component diagram and an 'interior view' of an Estes controller I drew showing modifications I made to my Estes controllers to make them into what they should be from the factory The interior view will show you how everything comes together compared to the component circuit diagram.

I've gotten a mess of parts to make a relay controller using off-the-shelf electrical boxes and receptacles and stuff from the hardware store and switches and LED indicators from Radio Shack. Tip: get your relays at the auto-supply store; they're much cheaper than RS or hardware stores. I plan on using a regular 110 volt two-prong electrical plug with a small jumper wire installed between the two blades inside the connector (one of those cheap 99cent lamp cord plug end replacements available at Home Depot, etc. as a 'safety key'.

Just need to get it all together. The modded Estes controllers work so well I haven't really had the need or motivation for the new controller yet...

Later and good luck! OL JR

PS... the Radio Shack "LED indicators" are excellent for this use-- they come in a pre-made housing with a threaded shank, with an LED with the resistor pre-installed and ready to go... just plug and play... OL JR

Agree with all that's been said so far.
Easiest Safety Disconnect i've found over the years has been a 1/8" phono jack and short piece of old 1/8" launch rod. or an 1/8" phono plug with both leads shorted to complete the circuit.

Simple or complex controllers pretty much all do the same thing. but it's sometimes fun to make all the bells and whistles come together for an interesting launch

TheAviator said:

Two things:

1.) You need to use resistors in series with LEDs. I would make sure that no more than 1mA goes through your continuity circuit, otherwise, you could set off e-matches and Quest Q2G2s.

2.) Make sure your safety interlock is a key/pin/something removable from the launch system. A speaker jack wired to itself works great for this.

Click to expand...

I would suggest a slightly higher condinuity current of ~10 ma instead of 1 ma. This won't activate ay commercial igniters, but will allow enough current through a led so that you can see it in sunlight. A ~1,000 ohm resistor is what you need to pass 10 ma in a 12 volt system.

Bob