NAR Compliant Homemade Launch Control

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

tooth

Well-Known Member
TRF Supporter
Joined
Aug 19, 2022
Messages
72
Reaction score
90
Location
Kansas
Nothing here is completely original, but I had a ton of fun building my own launch control box. Wiring diagram from one place, saw someone who put theirs in a box which I thought was cool, decided to use a 12v battery so I could recharge it in the box so that led to screened vents on two sides and a set of charging terminals mounted through the box.

Activate with the key, power on with first switch, check launch area clear with second, continuity check with third – then countdown and hit the button!

01.jpg
02.jpg
03.jpg

View attachment PXL_20220927_032705738.TS.mp4
 

Attachments

  • PXL_20220927_032705738.TS.mp4
    20.7 MB
Last edited:
I’ve been smiling all day like I was a 12 year old. Today I used my home designed launch pad that I posted build directions for here in this forum, and the controller I built posted above to do 3 launches. First time I’ve sent anything up in more than 50 years if you can imagine. Everything worked flawlessly and I had a riot of a time. Thanks to everyone here on the forum who has helped me get started again.

Probably the biggest smile came watching the Squirrel Works X-RV tumble its way back. Clearly I did something wrong with that build, lol.
 
Ok in order for it to be NAR compliant. What does he got to have ?im actually having a friend build me a 4 pad control Box it’s almost complete
 

Attachments

  • 7FEB649F-D4F5-40B0-8255-59402399A63F.jpeg
    7FEB649F-D4F5-40B0-8255-59402399A63F.jpeg
    401.5 KB · Views: 2
I'm converting an 18v. Cordless drill as a launch controller. Having trouble figuring out how to Include a continuity circuit. Any ideas out there.
It works great. I can launch all day on one 18v. battery.
 
An LED uses about 20 mA of current to light. This is below the fire current for all igniters that I'm aware of. In order to limit current to 20 mA when using 18VDC, you would need a 900 Ohm resister in series with a LED. When the continuity button is pressed, the resister, LED, and igniter would be connected between the + & - of the battery. If the igniter is good, the current will flow and the LED will light.
 
Ok in order for it to be NAR compliant. What does he got to have?
in case anyone else is having trouble finding it:
Must use an electrical launch system and electrical motor igniters. Launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the “off” position when released. Ignition leads will be 15 feet long for rockets with D motors or smaller, and 30 feet for larger rockets
 
An LED uses about 20 mA of current to light. This is below the fire current for all igniters that I'm aware of. In order to limit current to 20 mA when using 18VDC, you would need a 900 Ohm resister in series with a LED. When the continuity button is pressed, the resister, LED, and igniter would be connected between the + & - of the battery. If the igniter is good, the current will flow and the LED will light.
Thank you for the information. I will be looking into doing just that.
 
Thank you for the information. I will be looking into doing just that.
I bought let's, resistors, and switches. Have tried wiring this thing up 5 different ways. I just can't get it right.
I'm starting with a wire from the + post,( the + post on the trigger), to the push button switch. On the opposite switch post, I soldered the resistor. To which I soldered the + pin of the led. Then into the + wire, going out to the clip.
The issue I'm having, is where do I bring the - back into the system?
I either just complete a circuit that lights the led, even with no ignitor. Or cause a short, that burns something up. Maybe it's not doable? Or I've got the wrong components.
Any thoughts?
 
Here's my basic single pad launch controller circuit I build 20 years ago and use with a 12V 350A car starter. It's been working fine all these years.
You can modify the component values for the battery voltage you use. This is set up so it has an independent continuity LED activated with a switch. The ARM and LAUNCH switches both have to be activated to actually launch the rocket.
Schematic.png
0701161216.jpg
 
This really helps. Thank you.
I've got 2 built in safety devices already. The directional toggle built into the drill. And im using guitar plug-ins to connect the fifty feet of wire. Male end on drill, and male end on the cord. I've got a double female adapter that I keep in my pocket, that connects the two together. Without it, nobody can accidentally launch. Do I really need an arm switch? I've only got so much room to work with.
 
This really helps. Thank you.
I've got 2 built in safety devices already. The directional toggle built into the drill. And im using guitar plug-ins to connect the fifty feet of wire. Male end on drill, and male end on the cord. I've got a double female adapter that I keep in my pocket, that connects the two together. Without it, nobody can accidentally launch. Do I really need an arm switch? I've only got so much room to work with.
You don't need an ARM switch. I just use it as an additional safety measure. With the ARM switch needing to be toggled forward, just something falling on, landing on, or accidently pressing the LAUNCH button won't launch the rocket. Of course, putting the Safety Key on a wrist coil and the LCO taking it with them, prevents any accidental launch.
 
You don't need an ARM switch. I just use it as an additional safety measure. With the ARM switch needing to be toggled forward, just something falling on, landing on, or accidently pressing the LAUNCH button won't launch the rocket. Of course, putting the Safety Key on a wrist coil and the LCO taking it with them, prevents any accidental launch.
After alot of trial and error, I finally decided to visit an electronic guy. Seems what I'm wanting to do isn't possible with the trigger mechanism in cordless drills. Something about it being a rheostat. SO, I gutted the trigger system. Ran jumpers. Hollowed out the trigger. Now I'm just gonna use a mini-switch. I'm kinda bummed. But I'll still have my 18v drill launch controller.
 
I’ve been smiling all day like I was a 12 year old. Today I used my home designed launch pad that I posted build directions for here in this forum, and the controller I built posted above to do 3 launches. First time I’ve sent anything up in more than 50 years if you can imagine. Everything worked flawlessly and I had a riot of a time. Thanks to everyone here on the forum who has helped me get started again.

Probably the biggest smile came watching the Squirrel Works X-RV tumble its way back. Clearly I did something wrong with that build, lol.


Tooth,

Your Controller looks very nice ! Isn't it a great feeling to build one and have it all work .....
I built mine with a fellow Electrician & friend who passed away couple years ago from Cancer (RIP Joe)



IMG_3620.JPGIMG_3626.JPG
 
Here’s the diagram that Stine included in his Handbook of Model Rocketry.

IMG_9374.jpeg

The continuity and ignition circuits can be duplicated and connected to additional switches to select between multiple racks and pads. A lot of high-power clubs have their controllers wired up so that having a pad selected and the safety key inserted activates an audible buzzer regardless of continuity.

DART has their ignition leads connected to the controller with 1/4-inch TS plugs that you’ll see with electric guitar cables, so that bad cables and clips can be swapped out quickly.

ROC also has a neat setup where continuity checks can happen at the pad; pushing a button a few feet to the side of the rack or pad will activate a buzzer if the circuit is complete.

None of these additional features are required for NAR compliance, they just improve convenience and safety, especially if you’re going to be handling a lot of pads from one controller.
 
Here’s the diagram that Stine included in his Handbook of Model Rocketry.

View attachment 589625

The continuity and ignition circuits can be duplicated and connected to additional switches to select between multiple racks and pads. A lot of high-power clubs have their controllers wired up so that having a pad selected and the safety key inserted activates an audible buzzer regardless of continuity.

DART has their ignition leads connected to the controller with 1/4-inch TS plugs that you’ll see with electric guitar cables, so that bad cables and clips can be swapped out quickly.

ROC also has a neat setup where continuity checks can happen at the pad; pushing a button a few feet to the side of the rack or pad will activate a buzzer if the circuit is complete.

None of these additional features are required for NAR compliance, they just improve convenience and safety, especially if you’re going to be handling a lot of pads from one controller.

That is not safe for some of today's modern ignitors, many used for clusters.

Any continuity "lamp" is dangerous today. Our club's systems do not do continuity checks, they are not needed; it either ignites or it doesn't. As you are not going to allow someone to run out to the pad and fix it if it does not light up with a busy rack or stack of pads so why bother?

There are firewire safe or known as flash bulb safe systems in the old days using solid state checks with current under what firewire type ignitors state as max non-fire current. Generally using a transistor and a Piezo buzzer or LED for the notification.

PS: in the old days where people were using flash bulbs and Centuri sure shot dot wicks for cluster ignitors, many LCO would set them off by mistake with a continuity test, even with the flight card saying launch fires on Continuity test.

Count Annuity
 
That is not safe for some of today's modern ignitors, many used for clusters.

Any continuity "lamp" is dangerous today. Our club's systems do not do continuity checks, they are not needed; it either ignites or it doesn't. As you are not going to allow someone to run out to the pad and fix it if it does not light up with a busy rack or stack of pads so why bother?

I do not know the specifics of the DART or ROC systems but I know they use LED lights, presumably very low current draw. The book is from 2004 and the diagram may date from editions earlier than that.

But I may ask about that the next time I’m flying with either. DART flies again on the 9th but I won’t be able to make ROC until like November.
 
I do not know the specifics of the DART or ROC systems but I know they use LED lights, presumably very low current draw. The book is from 2004 and the diagram may date from editions earlier than that.

But I may ask about that the next time I’m flying with either. DART flies again on the 9th but I won’t be able to make ROC until like November.

I am SURE DART and ROC have flashbulb and firewire safe systems.

But again, why the point? It is either going to go or not. Have you seen a full rack and pad assignments where if the continuity did not check they allowed someone to run out there and fix it if it did not show continuity?

Or do they like the rest of the launches I have attended and continuity fails they say check that on the next rack go round and move to the next rocket to launch.

Now if say only 2 or three rockets are racked they might , but why? It will either launch or it won't and they can go back and fix it. Most No-goes at our club is ignitor burned in two but rocket did not ignite.
 
I am SURE DART and ROC have flashbulb and firewire safe systems.

But again, why the point? It is either going to go or not. Have you seen a full rack and pad assignments where if the continuity did not check they allowed someone to run out there and fix it if it did not show continuity?

Or do they like the rest of the launches I have attended and continuity fails they say check that on the next rack go round and move to the next rocket to launch.

Now if say only 2 or three rockets are racked they might , but why? It will either launch or it won't and they can go back and fix it. Most No-goes at our club is ignitor burned in two but rocket did not ignite.
There are different maximum SAFE currents for different ignitors. In general terms, Estes ignitors are one of the safest as they have very little pyrogen on them and use mainly the fusible link wire with a little amount of ignitable compound rather than a true pyrogen with either a thermite base or oxidiser/ fuel base. They require a high current to ignite with an all-fire current of 2A and a max safe current of 0.5A which is massive in comparison to a normal pyrogen igniter. This is what the circuit in Harry Stines book was designed for. And the old battery powered estes firing controller used this method albeit at a lower battery voltage. It's not really suited other than as a generalised model for a modern firing system as it does not explicitly specify the test current.
The more sensitive the pyrogen is, generally the less energy is required and the more likely it is to ignite with lower energy.
As we generally use a limited range of igniter types, all that we would use are safe with 10mA going through them for a test.
True flashbulbs(and I'm not sure who exactly would be using those today) are a magnesium swarf in a pure oxygen environment. They are considered to be safe up to 15mA. They are static sensitive.
The short version is to make sure the LCO knows what the flyer has got connected to the controller. If the flyer has manufactured an igniter themselves and cannot provide safe no-fire current test data, safer to not test it, and if it fails wait the 30 seconds required.

Norm
 
Last edited:
There are two very good reasons to have a continuity circuit readable from the pad-box as well as from the controller, built into a launch system. And just in case you were wondering, I happen to know that ROC has a Wilson F/X launch system.

WFX launch systems incorporate a flashbulb safe continuity circuit into each pad on each bank. Continuity can be tested at the pad as well as from the controller on the LCO table. We specifically have the continuity check at the pads so that the flier can test their own igniter. If its bad, then they can replace it before they go back to the flight line to await their launch. That's why we have the continuity check for the flier to use at the pad.

The continuity check at the controller on the LCO table is there so that the LCO almost always knows the status of the igniter at the pad. If the pad shows good continuity before the LCO hits the ignition switch and bad continuity after they pushed the ignition button, but the rocket did not fly, then 99.9% of the time that shows that the igniter fired without lighting the motor. If it shows continuity after the ignition switch was pushed, then it might be that the flier left the alligator clips touching at the pad.

Our system also over-rides a no-continuity signal and sends the impulse to ignite the motor regardless of the continuity status. We do that because there are some igniters out there that do not use a bridge wire. They might not ever show continuity good or bad.

So those are the reasons that we here at Wilson F/X have built in continuity circuits.

Brad
 
Here’s the diagram that Stine included in his Handbook of Model Rocketry.

View attachment 589625

The continuity and ignition circuits can be duplicated and connected to additional switches to select between multiple racks and pads. A lot of high-power clubs have their controllers wired up so that having a pad selected and the safety key inserted activates an audible buzzer regardless of continuity.

DART has their ignition leads connected to the controller with 1/4-inch TS plugs that you’ll see with electric guitar cables, so that bad cables and clips can be swapped out quickly.

ROC also has a neat setup where continuity checks can happen at the pad; pushing a button a few feet to the side of the rack or pad will activate a buzzer if the circuit is complete.

None of these additional features are required for NAR compliance, they just improve convenience and safety, especially if you’re going to be handling a lot of pads from one controller.

Replace the continuity light (bulb) with an appropriately selected resistor in series with an LED (limiting current to ~10mAh with the planned operating voltage) and this should be safe with non-Estes ignitors, AFAIK.
 
Back
Top