Launch controller

I drew up a design I would like to build as my launch controller. I had a few things in mind when designing:

• 12 volt
• 10 amp capable
• Must have safty plug and secondary arm switch
• Continuity should be momentary
• No launch amps across switches except main
• Cannot test continuity while armed
• Igniter leads should be to ground when not testing or firing

I tested on a breadboard and it seems to work well but have question about the cont amps. This should work fine for lowpower but I don't know the amp limit for ignition for low resistance igniters for high power. What is the max cont amps that canbe used when testing low resistance igniters?

Any other thoughts about the design will also be appreciated.

TP1 - 4.2v
TP2 - .7v
Cont circuit - 2.4 mA

Also, I thought about moving the safety plug to allow the cont circuit to be powered without the plug inserted but didnt know how a RSO would like that. Cant find anything saying I cant and found a few designs that have it that way. Any thoughts?

Not quite sure what's going on in that diagram - is your battery at the pad end with a relay?
You might take a look at my design. (The "Launch Controller Build" thread.) I don't bother with continuity for the reasons you mention - don't want the risk...

What type of wire/length do you have in mind going out to the pad?

I didn't want to draw a ground bus loop as this would complicate the drawing so used a ground symbol instead. I know this is the symbol for earth ground not chassis ground but didn't think anyone would care. I drew the connector as an XLR, sorry for the confusion. I changed it to a terminal block in the new drawing I just posted.

I am planning on using 12/2 x 50'. This will only be used for low and mid power flights to test the design then I plan on converting this to a controller / pad box . In other words, pushing 12v 10 amps 250 feet is out of my budget. I already bought 300' of 2 gauge this year.

I wanted the internals to be able to handle 10 amps, I don't expect the wire. I have limited it to 5 amp fast blow for my actual build.

You like using relays! Looks good - the arm switch will see launch current also do you realise - you indicated you only wanted the main switch to be exposed to this....

You are right Lee. Guess I didnt consider the plug as a switch. Maybe I will add another relay.

But good point, I didnt spec the 1/4 phono for its amp rating. I have no clue what those things can actually take. As an audio engineer I have pushed some serious watts through them and always worried. Personaly I hate them as they fail all the time. Maybe I will use a Speakon. They look cooler anyway and never had one fail at the connector.

Tacocat said:

You are right Lee. Guess I didnt consider the plug as a switch. Maybe I will add another relay.

But good point, I didnt spec the 1/4 phono for its amp rating. I have no clue what those things can actually take. As an audio engineer I have pushed some serious watts through them and always worried. Personaly I hate them as they fail all the time. Maybe I will use a Speakon. They look cooler anyway and never had one fail at the connector.

Click to expand...

I wouldn't be too concerned - I've measured the current flow in an igniter with an oscilloscope (Estes Solar) - current only flows for 140ms before it burns through....
I don't use a phono plug, I use a keyswitch that isolates my firing transistor as the removable safety (I like transistors more than relays!).

Continuity check current of 2.4 ma will be fine. I researched before building our club launch controller (search through the threads here and you will find many discussions) and designed it for 10 ma continuity check, which still has a good margin for what was considered safe. I measured the actual current and tried copper heads, first fires, various Quest and Estes starters, e-matches etc and they all were safe.

I just used the minimum current I could use and still see the LED shining in the sunlight, turned out about 5mA from memory...

As or continuity when the controller is in safe, our club has that on all our pads. We can check continuity at the rail with a push button, and the controller will show continuity if it is powered on regardless of safety switch.

Good design but only need one relay. I made a few mods if you don't mind. The 12 volts for the igniter is connected to the main power switch thru RL1. This way the Safety Plug and the Arm switch can be a low current switch.

Steve G

My stuff is about a braindead as we could make it. Simple as it could be and still drive two lines. Two switches on the box, a momentary and a center off DPDT spring loaded switch that returns to center when released so you have to do two things for a rocket to launch, not just one button. The deal is the launch cord is common 3 conductor extension cord. When we did this we got 5 100 foot extension cords and split the positive for 1 channel and the negative side for #2 with the ground lug for common. 12 volts at 9 amp SLA battery at the controller and a cord 25' long for the close low power stuff then for more out come the long extensions and away relay packs that also have 12 v 9 amp SLA batterys. I just got new relays that carry more amperage so I'll be swapping out the old relays for the new.

I reuploaded the drawing with corrections as Lee pointed out the launch relay tap was incorrectly placed.

I like the simplicity sghioto. I think from a functionality standpoint yours meets most the requirements anyone could need.

Sometimes I get carried away and like to tinker with stuff to the edge of over complexity. I spent the last few days building an Arduino digital launch controller with 4 buttons, 5 LEDs and a relay to launch a single rocket for no reason other than could I do it. Next step getting two Arduinos talking to each other over serial. Why should I squint to look at an LED 250 feet away when I could see it in the palm of my hand?