Launch Controller Parts Help

The Rocketry Forum

Help Support The Rocketry Forum:

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

Kruegon

Well-Known Member
Joined
May 20, 2014
Messages
1,885
Reaction score
5
I posted about building some launch controllers a while back. I got a ton of help with schematics and explanations. And I've been reading and learning. I think I'm ready to try building one. Ok, two actually. One relay based system and one more traditional system. Both will be four pads per bank. The first (relay) will be two banks, eight pads total. The second (non-relay) will be three or four banks (depending on available selector switch) for 12 or 16 pads, respectively.

I am having a hard time locating the proper parts. Where do you guys get your parts?
So here are the parts I still need:

Toggle switch (on-off) capable of 12v with the silver "stick" style lever. Does Amp rating matter here?

Rotary selector switch capable of 12v, with a hand knob, with one input and two output, and a second one with the same specs but one input and 4 output. (three is acceptable, but four is prefered). Again, appropriate amp rating?

Red LED lights with a built in resistor, to use for continuity, the is made to be panel mounted. And I'm not sure what the resistance should be on this.

The rest I think I have figured out. Although I'm not counting my chickens just yet. Thanks guys.
 
I posted about building some launch controllers a while back. I got a ton of help with schematics and explanations. And I've been reading and learning. I think I'm ready to try building one. Ok, two actually. One relay based system and one more traditional system. Both will be four pads per bank. The first (relay) will be two banks, eight pads total. The second (non-relay) will be three or four banks (depending on available selector switch) for 12 or 16 pads, respectively.

I am having a hard time locating the proper parts. Where do you guys get your parts?
So here are the parts I still need:

Toggle switch (on-off) capable of 12v with the silver "stick" style lever. Does Amp rating matter here?

Rotary selector switch capable of 12v, with a hand knob, with one input and two output, and a second one with the same specs but one input and 4 output. (three is acceptable, but four is prefered). Again, appropriate amp rating?

Red LED lights with a built in resistor, to use for continuity, the is made to be panel mounted. And I'm not sure what the resistance should be on this.

The rest I think I have figured out. Although I'm not counting my chickens just yet. Thanks guys.

I don't know exact part numbers for switches, etc., but picking resistors isn't that complicated. Voltage = current * resistance, and LEDs always have a 2- to 3-volt "drop", so with a 12V battery (13V fully charged) you're looking at a 10-11V effective voltage. Most normal LEDs can take up to about 30mA, so that gives you 11V <= 0.03A * resistance. That tells me 366 ohms- if you wanted to be safe you could go 500 or 1K, I have a 330 ohm resistor with no problems. LEDs on the bluer end of the spectrum will have bigger voltage drops and therefore need less resistance.

Does that make sense?
 
I don't know exact part numbers for switches, etc., but picking resistors isn't that complicated. Voltage = current * resistance, and LEDs always have a 2- to 3-volt "drop", so with a 12V battery (13V fully charged) you're looking at a 10-11V effective voltage. Most normal LEDs can take up to about 30mA, so that gives you 11V <= 0.03A * resistance. That tells me 366 ohms- if you wanted to be safe you could go 500 or 1K, I have a 330 ohm resistor with no problems. LEDs on the bluer end of the spectrum will have bigger voltage drops and therefore need less resistance.

Does that make sense?

Makes perfect sense. I've heard of some that have resistors built in, but adding one isn't an issue. My soldering skills may not be Eggtimer level yet, but they've gotten dang good since I started building so many a/v bays. So I guess I'll jumper the LED and test it's voltage to determine the best resistor. Needs to be high enough to light it up, but low enough to not fire the igniter.
 
I've ordered some components from Digi-Key in the past. They have a very large selection.

https://www.digikey.com/products/en
Thank you. I will check them out. Once I understand the parts (by working with them), thus should be a breeze to repeat. I've actually considered looking into a professional PCB design for this. But I think I'd need to offer both wired and wireless options. I'm not ready for wireless yet.
 
I’ve shopped for components from Allied Electronics, Digikey, Mouser, and even sometimes the local automotive parts stores where 12 volt DC is the norm.
It’s pretty important to learn and understand the meaning of the different ratings and to understand Ohm’s law. It’s also important to read the data sheets for components you are considering. A course in basic electricity, accompanied by a course in basic electronics might really increase your satisfaction. It’s obvious you’ve got the necessary interest and it certainly appears that you have an aptitude; taking a few courses could even lead you to a new career.


Steve Shannon
 
Makes perfect sense. I've heard of some that have resistors built in, but adding one isn't an issue. My soldering skills may not be Eggtimer level yet, but they've gotten dang good since I started building so many a/v bays. So I guess I'll jumper the LED and test it's voltage to determine the best resistor. Needs to be high enough to light it up, but low enough to not fire the igniter.

I can't really add to the places to order parts from. The folks here have listed the ones I use already.

You mentioned testing the LED to find the resistor, but don't want to fire the igniter. Remember, the resistor sets the amount of current that flows through the LED, that is the same current that will flow through the igniter. While you test resistors for the LED, remember that it will also affect the current through the igniter.
Older style LED usually use 0.020 A, or 20 milliamp (ma). The super bright LED, which are much easier to see in bright sun light, tend to run in the 30 ma range.

Either one should work for standard rocket igniters, including the ematch type used in CTI motors with the BP pellet. good luck
 
Hi, we used Eaton toggles for the new 2016 DART launch controller for both the arming and pad selectors, and an Eaton key switch. They have been very good through two seasons of heavy use already. Things are connected internally with 0.25" automotive "quick-disconnect" terminals, which provide the desired high current and relatively low resistance needed. Ultimately we were able to keep the total resistance inside the panel to slightly over 1 Ohm, giving an ultimate capacity of about 10 A at the clips from a 3S 20C 3000mAh LiPo battery. I did put an automotive relay inside the panel since the fire button looked to be a weakness in current/resistance; using the relay takes the pushbutton out of the picture. The system reliably fires 3-motor clusters through 40' of 16-gauge wire.

I did not use any rotary selectors in the design; if you look at how they work, they become the limiting factor in current carrying and resistance. Also the toggles let you set up "drag race" simultaneous launches. I don't have any good recommendations for you on 12V LEDs. The ones we have draw about 15mA and are safe with all modern ignitors, but are too dim in sunlight.
 
Hi, we used Eaton toggles for the new 2016 DART launch controller for both the arming and pad selectors, and an Eaton key switch. They have been very good through two seasons of heavy use already. Things are connected internally with 0.25" automotive "quick-disconnect" terminals, which provide the desired high current and relatively low resistance needed. Ultimately we were able to keep the total resistance inside the panel to slightly over 1 Ohm, giving an ultimate capacity of about 10 A at the clips from a 3S 20C 3000mAh LiPo battery. I did put an automotive relay inside the panel since the fire button looked to be a weakness in current/resistance; using the relay takes the pushbutton out of the picture. The system reliably fires 3-motor clusters through 40' of 16-gauge wire.

I did not use any rotary selectors in the design; if you look at how they work, they become the limiting factor in current carrying and resistance. Also the toggles let you set up "drag race" simultaneous launches. I don't have any good recommendations for you on 12V LEDs. The ones we have draw about 15mA and are safe with all modern ignitors, but are too dim in sunlight.
The toggles are a good idea, but have one major weakness. Human error. While they may work nice, arm bank A, fire, range cold and load. Come back, arm bank B, ID10T error, forget to disarm bank A, and you have a drag race you never intended.

With a rotary selector, you can only arm one bank at a time, this limits the chances of accidental launch across banks. This is very important for outreach, where kids get very upset about someone else launching their rocket.
 
The toggles are a good idea, but have one major weakness. Human error. While they may work nice, arm bank A, fire, range cold and load. Come back, arm bank B, ID10T error, forget to disarm bank A, and you have a drag race you never intended.

With a rotary selector, you can only arm one bank at a time, this limits the chances of accidental launch across banks. This is very important for outreach, where kids get very upset about someone else launching their rocket.

This!

I’ve seen many instances of multiple launches done as a result of crappy interface design and human error. Each of those instances could have led to an injury. Each of those did result in people being upset that their rockets were flown without an announcement.
 
The toggles are a good idea, but have one major weakness. Human error. While they may work nice, arm bank A, fire, range cold and load. Come back, arm bank B, ID10T error, forget to disarm bank A, and you have a drag race you never intended.

The DARS design uses toggles but includes an operator warning: Select one pad and it starts beeping at you. Select more than one and get double beeps. Arm and it switches to a continuous tone.

You have to switch to safe and disable all pads to make it shut up.

There is no warning for selecting the wrong pad. :)
 
The DARS design uses toggles but includes an operator warning: Select one pad and it starts beeping at you. Select more than one and get double beeps. Arm and it switches to a continuous tone.

You have to switch to safe and disable all pads to make it shut up.

There is no warning for selecting the wrong pad. :)

Great!
 
Can AC switches be used on a DC system? All of the SPST 12VDC switches I find are light up style.

Also, I'm trying to locate a dual SPST button. When released, one set of polls are on the other is off. When pressed they switch. And it needs to be a momentary switch.
 
Can AC switches be used on a DC system? All of the SPST 12VDC switches I find are light up style.

Also, I'm trying to locate a dual SPST button. When released, one set of polls are on the other is off. When pressed they switch. And it needs to be a momentary switch.

AC switches usually have a DC rating also, which is usually much lower voltage and current. Google “automotive switches” and you’ll be okay.
That two pole switch you’re looking for would be called a “momentary DPST switch”.
DP means double pole.
Here’s a switch selector tool at Mouser:
https://www.mouser.com/Mobile/Elect...ushbutton-Switches/_/N-5g30?P=1z0z2qgZ1z0z2y3
 
Last edited by a moderator:
We've not had too many issues with the toggle system...it's actually pretty essential as we can get long lines when lots of Scouts show up, and once in a while we do drag race competition. The kids in our neck of the woods actually like drag racing their Gnomes. We have to be hyper vigilant anyway with all the enthusiastic 10-12 year olds caroming about the place. I do like the idea of a multi-select beeper though but I don't see a good way to do it without active electronics.
 
We've not had too many issues with the toggle system...it's actually pretty essential as we can get long lines when lots of Scouts show up, and once in a while we do drag race competition. The kids in our neck of the woods actually like drag racing their Gnomes. We have to be hyper vigilant anyway with all the enthusiastic 10-12 year olds caroming about the place. I do like the idea of a multi-select beeper though but I don't see a good way to do it without active electronics.

When I built the controller for our club in 2002 I designed it with a rotary switch to select the pad, but I included one position (0) for use when drag racing. The way it works is, if flying any of the single pads I simply rotate it to select the pad. A red light shows which pad. If I would want to drag race I would rotate it all the way counterclockwise to position 0, then activate the race pads by flipping toggle switches. Those toggle switches would have no effect unless the rotary switch is in the drag race (0) position. Because the rotary switch has multiple gangs, I could easily wire it to sound a special chime or buzzer when placed in the drag race position. Confession: I never did finish wiring up the toggles for drag racing. It’s just never been a priority and after 16 years I might not.
 
I'm going to revive this thread, as I'm looking to build a 12V controller.

I've looked at a bunch of diagrams and they're starting to make some sense (I'm really not strong with electronic circuits), but I'm missing a bit of information. What is the minimum resistance needed for the continuity check so that the igniter doesn't ignite but the LED will light up?

This will be a simple, single motor launcher but I may want it to be capable of doing 3 motor clusters later.

Thanks in advance!
 
Also, if I'm reading correctly, minimum distance from the pad has to be 100' from hpr G up to L motors, so 100' for levels 1 and 2.

What gauge is usable for this kind of distance?
 
Also, if I'm reading correctly, minimum distance from the pad has to be 100' from hpr G up to L motors, so 100' for levels 1 and 2.

What gauge is usable for this kind of distance?
It depends entirely on the design. For a relay based system where the high current is carried entirely at the pad box you can get away with very light cable. For instance, the system I designed, uses “Silver Satin”, telephone extension cable, which is a four conductor 22 ga. cable. It works reliably with the 12 volt relays to a distance of over 500 feet, allowing us to fly M motors. Because it’s a relay based system the number of motors ignited isn’t affected by the distance. I bought some 48 volt relays recently in order to extend the distance. That works because the current requirements for 48 volt relays are only a quarter of the current needed for 12 volt relays. When I mention 12 volt or 48 volt relays, that’s the voltage the coil of the relay is designed to accept, the controlling voltage. The controlled voltage can be anything the contacts are rated to handle.

I'm going to revive this thread, as I'm looking to build a 12V controller.

I've looked at a bunch of diagrams and they're starting to make some sense (I'm really not strong with electronic circuits), but I'm missing a bit of information. What is the minimum resistance needed for the continuity check so that the igniter doesn't ignite but the LED will light up?

This will be a simple, single motor launcher but I may want it to be capable of doing 3 motor clusters later.

Thanks in advance!
That depends on two things: the maximum test current rating of the initiators you use. Electric matches have a low rating, meaning they are very sensitive. For instance, the MJG FireWire has a max test current of 40 mA. https://electricmatch.com/pyrotechnics/see/6/5/mjg-firewire-initiator
The other factor is the forward voltage drop of the LED. In my launch controller I used two LEDs, one at the pad box and one at the controller. Each LED has a voltage drop of X volts. Two of those in series means a 2X drop. The ones I used have about 0.7 volts each or 1.4 volts total. So, with a 12 volt battery (which when brand new and freshly charged might actually be close to 13 volts) the voltage drop through the current limiting resistor would need to be about 11.6 volts. I assumed the initiator has a zero impedance. That’s unrealistic, but only leads to a more conservative result.
Ohm’s law applies of course, so voltage equals current x resistance. Or, rearranged, resistance equals voltage divided by current.
So, in order to limit the current to 40 mA, simply do the math:
11.6 volts/0.040 Amperes = 290 Ohms.
Resistors come in standard values. The next larger value is 300 Ohms.
 
So, I'm planning on using 3s LiPo packs. In theory, the voltage drop should be less than other traditional cells, as LiPos are known to be able to deliver more current with less voltage drop through their discharge cycle.

The packs in question are 16000mah 11.1V 15C. Again, in theory, these can deliver 240A for the length of their discharge cycle. I have two of them and also have made a parallel harness to use them as a 32000mah pack that I've used to power 35lb thrust trolling motor on my canoe.

Would you say it would make more sense to run a system such as you describe with a control box running to a pad box or could I keep it more simple with a direct run? A direct run will mean running heavier gauge for the whole length. I guess I can calculate the voltage drop by calculating the resistance per foot of the wire in question.

At this point, not even having my L1, but intending to progress to at least L2 over the next couple years, I think I'm okay with limiting this setup to the necessary 100'.

Given what I've seen here in this discussion, and with your help, it looks like a 300 Ohm resistor will suffice ahead of the LED. Now the decision is whether to build it with a relay setup or direct run.
 
Last edited:
So, I'm planning on using 3s LiPo packs. In theory, the voltage drop should be less than other traditional cells, as LiPos are known to be able to deliver more current with less voltage drop through their discharge cycle.

The packs in question are 16000mah 11.1V 15C. Again, in theory, these can deliver 240A for the length of their discharge cycle. I have two of them and also have made a parallel harness to use them as a 32000mah pack that I've used to power 35lb thrust trolling motor on my canoe.

Would you say it would make more sense to run a system such as you describe with a control box running to a pad box or could I keep it more simple with a direct run? A direct run will mean running heavier gauge for the whole length. I guess I can calculate the voltage drop by calculating the resistance per foot of the wire in question.

At this point, not even having my L1, but intending to progress to at least L2 over the next couple years, I think I'm okay with limiting this setup to the necessary 100'.

Given what I've seen here in this discussion, and with your help, it looks like a 300 Ohm resistor will suffice ahead of the LED. Now the decision is whether to build it with a relay setup or direct run.

That 240 Amp figure is only if you introduce no impedance at all with your circuit, which is impossible. You’re going to need to calculate losses as you say, by figuring out the resistance of your leads. Keep in mind that for a lead that runs 100 feet you have a current loop of 200 feet.
 
That 240 Amp figure is only if you introduce no impedance at all with your circuit, which is impossible. You’re going to need to calculate losses as you say, by figuring out the resistance of your leads. Keep in mind that for a lead that runs 100 feet you have a current loop of 200 feet.

Yup, 200', but also the discharge rating actually goes up to 580A with the 32000mah configuration (theoretically, not including losses).

How tricky is the relay setup? The schematics definitely look more complicated. On one hand I'd like to keep it simple, but on the other hand the relay design sounds better in that you can really extend it out.
 
Go with the relay design for long distances. You won't regret it.

Have a good think about the cable you will be using. It is one of the high-maintenance items in the launch kit IMHO. Mishandling is the rule rather than the exception. :(.

I'm really leaning towards the relay setup, as it's a bit more future-proof. What I'm afraid of is that it's a bit over my head as far as wiring is concerned. I really need to get my head wrapped around the diagrams. It's not a super difficult concept but I've always struggled with it.

Thanks for all your input, especially Steve Shannon.:)
 
I'm really leaning towards the relay setup, as it's a bit more future-proof. What I'm afraid of is that it's a bit over my head as far as wiring is concerned. I really need to get my head wrapped around the diagrams. It's not a super difficult concept but I've always struggled with it.

Thanks for all your input, especially Steve Shannon.:)

You’re right; the relay setup is the way to go. Break it down into bite size pieces on paper and build it on the bench first. For instance, the control circuit controls the relay. It’s simply a push button, an arming switch, the battery, the relay coil, and a long run of two conductor wire. Don’t even think about how to do continuity check yet.
Another circuit is the ignition circuit. It consists of a battery, the contacts for the relay that are normally open, alligator clips and wire. It is all local to the pad.
Finally you build the continuity circuit that indicates continuity. It consists of the battery, LEDs (assuming you want one at the pad and one at the launch controller), another long run of two conductor wire, and the alligator clips and wire used previously.
If you use an SPDT relay you can use it to share the wires/alligator clips between the continuity and ignition circuits. One alligator clip lead connects to the the common terminal.
For the circuit I just described the two long two conductor wires can be replaced with a single four conductor lightweight cable. That’s where I used modular phone wire. It’s stranded, surprisingly resilient, and cheap. I think I bought a 2,000 foot roll for $87 when I first built my launch controller. I also used the modular connectors so I could just pick up phone extensions and plug them in. Any stranded four conductor wire will work though.
You can do this.
 
You’re right; the relay setup is the way to go. Break it down into bite size pieces on paper and build it on the bench first. For instance, the control circuit controls the relay. It’s simply a push button, an arming switch, the battery, the relay coil, and a long run of two conductor wire. Don’t even think about how to do continuity check yet.
Another circuit is the ignition circuit. It consists of a battery, the contacts for the relay that are normally open, alligator clips and wire. It is all local to the pad.
Finally you build the continuity circuit that indicates continuity. It consists of the battery, LEDs (assuming you want one at the pad and one at the launch controller), another long run of two conductor wire, and the alligator clips and wire used previously.
If you use an SPDT relay you can use it to share the wires/alligator clips between the continuity and ignition circuits. One alligator clip lead connects to the the common terminal.
For the circuit I just described the two long two conductor wires can be replaced with a single four conductor lightweight cable. That’s where I used modular phone wire. It’s stranded, surprisingly resilient, and cheap. I think I bought a 2,000 foot roll for $87 when I first built my launch controller. I also used the modular connectors so I could just pick up phone extensions and plug them in. Any stranded four conductor wire will work though.
You can do this.

Thanks so much, Steve! That definitely makes it seem a bit easier! Time to make a list of parts and go shopping!
 
Back
Top