Launch controller

[user 35280]

When I do all fire testing I use a 100ms current pulse. (Q2G2 came out as 333mA)

A 2Ah capacity battery is more than enough. Assume that on average the load pulls 10A for 5 seconds. 2Amp-hour * 3600 seconds/hour/50 Amp-seconds = 144 launches.

Capacity is only loosely related to internal resistance. I have a 1 Ohm 25W resistor that is very handy for testing. Connect in place of igniter and measure the voltage across it. A good 12V system should manage 10V or better.

I have a 4.5Ah SLA battery that I use but I am on the lookout for a 4 cell LiFe battery of around 1Ah capacity.

Does a LiFe battery look like a LiPo?

 

[UhClem]

Does a LiFe battery look like a LiPo?

Similar but less likely to be an incendiary device.

 

[Collan Fraser]

when i built my controller i went down tom the hardware store and bought a CHEAP 12v cordless drill, cut the handle off as it contains the battery connector which i glued into the side of my case. came with 2 battery's and a charger... will launch rockets ALL day long and no miss fires on Estes igniters.

 

[MidOH]

Similar but less likely to be an incendiary device.

But less powerful, less durable, and sometimes a pita to charge well.

Stick with lipos. Dont charge them under your drapes or on a pile of hay, and you'll be fine.

 

[bjphoenix]

when i built my controller i went down tom the hardware store and bought a CHEAP 12v cordless drill, cut the handle off as it contains the battery connector which i glued into the side of my case. came with 2 battery's and a charger... will launch rockets ALL day long and no miss fires on Estes igniters.

That's interesting- I was experimenting yesterday and could not get a 20V lithium drill battery to fire 35gage steel wire (not nichrome).

 

[ep29030]

Here's a generic simple launch controller circuit I found here:
View attachment 473800

For simple single-pad duty, this is all you need. The continuity light should be a bright LED in series with a 1K resistor, roughly.

Here is a diagram I created for my launch system. Left side comes from 12V power source, right side goes to launch pad. If you want
continuity light to stay ON continuously, omit the Continuity pushbutton.

 

[ep29030]

I like to run a 50ft cord from launcher to my car battery for power.

 

[icyclops]

Here is what your circuit should look like. I include an electronic schematic and a simple drawing of the circuit:

View attachment 473828

The idea here is that, when the "launch" push button is NOT pressed, the 1K ohm resistor and the LED are in series with the igniter. The 1K ohm resistor limits the current through the circuit to just a few milliamps. That is enough current to light up the LED, showing you that the igniter clips are connected correctly, but it is not enough current to actually heat up the igniter and set off the rocket motor.

When you press the push button, you create a "short" circuit through the push button, bypassing the resistor and the LED. Now the full current of the battery pack(s) is sent to the igniter (through the push button). This is enough current to cause the igniter to get hot. When the igniter gets hot, it sets off the rocket motor.

The LED will stop glowing when you press the push button because now the vast majority of the current in the circuit is bypassing the LED and flowing through the push button.

When you stop pressing the push button, the only way for current to flow is once again through the resistor and the LED. Again, only a small amount of current can flow. Since it is no longer bypassed, the LED comes back on.

The toggle switch in the circuit is just a simple "on/off" switch for the entire circuit. It serves the same role as the "safety key" in the Estes launch controller. Without the toggle switch in the "ON" position, the circuit is cut off and cannot operate at all.

On your 4th sentence below….once the igniter is spent/broken, shouldn’t there be no LED light on because the entire circuit is cut? So after you press the launch button with an igniter in place and the rocket is launch, the continuity light should be dead as the circuit is now cut?

 

[BEC]

I know it's based upon the impulse of the motor. To me, it's the altitude. 1000 to 5000 ft is MPR. I say this knowing that at 5000ft, my rockets might land on Midway.

BTW, here's the battery that @BEC uses in his PSII controller. I'm not sure if that's a JST connector or what.

View attachment 474054

Well, since I got dragged into this: the connector nearest that battery is a 2-pin polarized mini Deans connector, which is what I was using in my small electric RC models when rockets took over my life again. I just made a short adapter from mini-Deans to the orange 2-pin JST so I could use this battery in my PSII controller. This battery, by the way, will fire models from this controller for the whole flying season on one charge, which for me is typically more than 200 flights. It can and has lit even the infamous Aerotech copperhead igniters.

The connector in an Estes PSII controller is a JST RCY type:
https://www.amazon.com/gp/product/B071XN7C43/

Yup! And, at least to me, this is the weakest link in the whole controller as those things can’t handle much current. Fortunately, as noted elsewhere in this thread, firing a rocket only takes a fraction of a second of relatively high current. The continuity indication in the PSII controller is an LED (41ma) when the key is inserted then a tone from a piezo buzzer type device when the yellow button is held down, which adds another 20 ma. But compared to powering an electric motor or something (as this particular battery was originally intended to do) the duty cycle is very short and not much current. So, that wimpy little JST connector doesn’t melt, fortunately.

(added: updated current values based on measurements just made with that controller and that battery.)

Also added: to the OP: Unless you want to build yourself a launch controller for the fun of it, by far the simplest and most effective thing to do is get an Estes PSII controller from your favorite source (AC Supply carries it, and I’ve seen it in HobbyTown USA stores, and even Amazon has it: https://smile.amazon.com/Estes-PS-II-Launch-Controller/dp/B00FU4AX44/) and just use it as designed on six alkaline C-cells. It has 30 feet of adequate wiring so you can use it for up to G power, is simple to use, and with no external battery is easy to set up and put away.

If you’re into RC models and have a charger for lithium polymer batteries that can do a good job on a small three-cell Li-Poly, then you can put that inside as shown in the picture Ron posted of mine for more kick. I use 3s li-polys in the PSII controller, for my personal three-pad system that I built based on my club’s 10-pad setup, and for the club’s 10-pad setup itself. But I have lots of chargers from my electric airplane days and so the batteries are easy for me to deal with.

 

[Grog6]

I'm working on my first 80/20 rail launchpad.
It's designed for safety;pad electronics are only operable by 24V, with a 12V gelcell supplies ignition power, and warning lights.

I'm upgrading from the launcher I built in 1985.


Old:

 

[Grog6]

BTW I found out years ago you Can hit an igniter too hard; If it explodes, it can propagate a detonation wave into the BP propellant, which explodes all at once. I use an inline resistor to set the max current to about5 amps.

 

[Ronz Rocketz]

I'm working on my first 80/20 rail launchpad.
It's designed for safety;pad electronics are only operable by 24V, with a 12V gelcell supplies ignition power, and warning lights.

I'm upgrading from the launcher I built in 1985.


Old:View attachment 474854View attachment 474854

 

[Rocketman19]

Dang! This post really blew up! Thanks everyone for the suggestions some will be disappointed that I did not do continuity a continuity light but it sounded rather complicated and so I stuck to the simple idea. I made it completely up to spec for the NAR code and had a spring button + 15 feet of wire between the clips and the box. Whoever said 6 volt battery, ( Neil W, I think) thank you. it provided just more than the 2 amps needed for the igniter to completely burn through and ignite. If you are wonder what took so long, I made the mistake of ordering a box on amazon without the Prime shipping. so instead of 2 days it was 2 months.When it all arrived, one side on each switch would shut off and the other on. So, I had to not only figure out how to wire it, as it came with no diagram, but also had to take it completely apart and I now have a reversed key. Other than that, smooth sailing all the way! Here is it a picture of it and a video of it. The multi meter is in volts just so you know.
View attachment VID_20210818_135503.mp4

 

[trialsguy]

BTW I found out years ago you Can hit an igniter too hard; If it explodes, it can propagate a detonation wave into the BP propellant, which explodes all at once. I use an inline resistor to set the max current to about5 amps.

-Don't try this at home, kids-

Way back when I was a model rocket kid (1969 or so), I used to launch BP estes rockets with a very high voltage (120 v AC). Yes the estes ignitor would explode. But I never had a bad launch. And I never had a mis-fire either. -Don't try this at home, kids-

 

[Ronz Rocketz]

-Don't try this at home, kids-

Way back when I was a model rocket kid (1969 or so), I used to launch BP estes rockets with a very high voltage (120 v AC). Yes the estes ignitor would explode. But I never had a bad launch. And I never had a mis-fire either. -Don't try this at home, kids-

Not to mention using firecracker fuses to ignite the motors...

 

[neil_w]

Dang! This post really blew up! Thanks everyone for the suggestions some will be disappointed that I did not do continuity a continuity light but it sounded rather complicated

I would instead say that a continuity light is the opposite of complicated. You should consider adding one.

Whoever said 6 volt battery, ( Neil W, I think) thank you.

Wasn't me, I definitely wouldn't have recommended 6V.

 

[Ronz Rocketz]

These work well, and they’re cheap.

https://www.amazon.com/gp/aw/d/B014YSFMXI?psc=1&ref=ppx_pop_mob_b_asin_title
Obviously 12v is twice as fun as 6v.

 

[user 35280]

Not to mention using firecracker fuses to ignite the motors...

Green canon fuse worked well

 

[Ronz Rocketz]

Green canon fuse worked well

In a don't do this at home, kids kinda way.

 

[teepot]

Dang! This post really blew up! Thanks everyone for the suggestions some will be disappointed that I did not do continuity a continuity light but it sounded rather complicated and so I stuck to the simple idea. I made it completely up to spec for the NAR code and had a spring button + 15 feet of wire between the clips and the box. Whoever said 6 volt battery, ( Neil W, I think) thank you. it provided just more than the 2 amps needed for the igniter to completely burn through and ignite. If you are wonder what took so long, I made the mistake of ordering a box on amazon without the Prime shipping. so instead of 2 days it was 2 months.When it all arrived, one side on each switch would shut off and the other on. So, I had to not only figure out how to wire it, as it came with no diagram, but also had to take it completely apart and I now have a reversed key. Other than that, smooth sailing all the way! Here is it a picture of it and a video of it. The multi meter is in volts just so you know.View attachment 478080
View attachment 478081

I got the same switch without instructions. I ended up taking it over to Bill at BMS. He was an electrical engineer. He told me how to wire it.

 

[Cape Byron]

I'm working on my first 80/20 rail launchpad.
It's designed for safety;pad electronics are only operable by 24V, with a 12V gelcell supplies ignition power, and warning lights.

I'm upgrading from the launcher I built in 1985.


Old:View attachment 474854View attachment 474854

You don't need a new controller! All this version needs is Dymo punch tape with Cyrillic script and it would be close to perfect, Comrade. В Советской России мы делаем лучшие авиадиспетчеры!

 

[Grog6]

Strangely enough, I have a dymo label maker, lol. But no Cyrillic I think it's from the 60's.

 

[Grog6]

A great source for 'slightly worn' 12V gel cells are broken toys: all these scooters, 4x2's etcetera for kids have two of them.
/////////////theyll work for us long after they lose capacity and won;t run toys.