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My 12v cluster launch controller build

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Joshua F Thomas

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I'm looking to get into clustered rockets. I knew from discussions with others, and The Handbook of Model Rocketry, that I was going to need a 12v launch controller capable of delivering large amperage quickly. Having some electronic skill, I decided to build my own.

I have to give appreciation to forum user Micromeister for sharing his own controller build in this thread, as I used it as a general starting point, and for various Radioshack parts numbers. Yes, you can still order them! The Igniter Continuity Tests by J. R. Brohm was also helpful for me to determine safe ranges of current for continuity tests. I ended up doing my own tests to find that limit, but having a source that agreed was quite helpful.

My build uses a power delivery box positioned close to the pad, drawing from a 12V sealed lead-acid battery of motorcycle size (any high-drain 12V source should work in theory), and a hand-held box with extension wires for launch activation. Power is delivered via a 12V relay. 14 AWG wire is used everywhere except for where LEDs are used, and there I used 22g just for ease of wiring. Wire from power delivery box to hand-held is 50 feet of 18g lamp cord. Microclips are used for the igniter leads. I'm building clip whips whips that can handle up to 4 igniters each, which should be enough for all my needs for quite a while.

The power delivery box has an on/off switch with indicator LED and continuity test switch with LED. I used a regular on-off and not a momentary for the continuity simply because I got multiple of the same switch when ordering, and it keeps the look clean. Having the continuity stay "on" even for prolonged periods is a low risk; total current draw is approx 10 mA via the LED. At that draw the igniters do not ever go off. I let several different ones run for hours, and they never even got warm. Brohm's testing also confirms this - you need closer to 100 mA for any of the igniter types in common use to go off. With both LEDs on the box draws about 20 mA, only 1/2 of that through the igniter.

The hand-held box has a tube-key arming switch. I paid a bunch for this switch - almost $15 - but I really like the way it looks and acts. It has a solid positive feel, and can not be removed in the armed position. It gives a highly authentic "I'm about to launch a rocket" feel. Another indicator LED is used to indicate the hand-held is receiving power and that the switch is in the armed position. Launch is a standard momentary pushbutton.

I have not had a chance to test this in the field yet; hoping for this tomorrow! About 3/4 of the way through this build I also realized that high-powered rechargeable batteries may also work and fit into the 7" x 4" x 2" power box. I would need close to or slightly better than 12 volts, and high-drain. After some research, it looks like 26650 sized Lithium Iron Phosphate (LFP) batteries will work. They are 3.3v each (x4 = 13.2v) and can handle large current delivery for short periods. Standard 3.7v lithium batteries don't add up well, you either get 11.1v or 14.8v. If I go this route I'm going to wire another switch to allow me to choose between external or internal batteries.

Photos below; any feedback or questions welcome. This was a fun build.

launch_controller_2.jpg


launch_controller_3.jpg


launch_controller_4.jpg


launch_controller_5.jpg


launch_controller_7.jpg
 

j.a.duke

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Joshua,

Looks pretty awesome. That battery box with the display looks very functional. Can you post some pictures of it “in use” as I’d like to see how visible those LEDs might be in daylight.

I’ve been looking to re-build, or more likely, build a new controller. I’ve read all the threads and circuit diagrams both here, on YORF and on the rest of the ‘net.

Would you care to share yours? I’m curious about where that meter can be obtained (I have something similar, but only voltage) and to see how it relates to my current attempt at wiring up something, which until now has been a mash-up of diagrams/plans.

Thanks.

Cheers,
Jon
 

rharshberger

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The late Micromeister provided us all with many bits of modelling wisdom during his time amongst us, hard to believe he has only been gone a little over a year.
 

Joshua F Thomas

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Would you care to share yours? I’m curious about where that meter can be obtained (I have something similar, but only voltage) and to see how it relates to my current attempt at wiring up something, which until now has been a mash-up of diagrams/plans.
I'm not the best at schematics, but I've managed to copy my rough one to something cleaner, see below. The scale has been exaggerated for readability.

Very important note about this design: You must use a 12v source that provides high amperage! The 12v source is used for both the relay coil and to fire the igniters. If your source does not have enough amps, the coil voltage will drop once the relay switches from open (NO) to closed (NC). This will then cause the relay to revert to open; and the coil voltage will rise; and the entire process will repeat. You will get "coil flutter" where it will open and close rapidly, and this will kill your relay. It may also cause failure of igniter.

From bench testing, you want a minimum of 5A of instant current if your relay coil is rated for 160 ohms of resistance. If you can get a relay with [edit] more resistance, that's even better, because you'll have less voltage drop. A 12V sealed lead-acid motorcycle battery will provide enough current for this. If you're going to use other batteries - NiMH, lithium batteries - bench test this with an igniter first to make sure it can deliver enough current!

Regarding LED visibility, in full summer sun they're bright enough for me to tell when they're on, but I'll try to get some pictures the next time I use it.



 
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Joshua F Thomas

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I’m curious about where that meter can be obtained (I have something similar, but only voltage) and to see how it relates to my current attempt at wiring up something, which until now has been a mash-up of diagrams/plans.
If you mean in the second and third pictures, that's a DIY kit for a bench-top power supply. They can be ordered from china for not much money if you're willing to wait the month for arrival. You need some basic soldering skills to put it together, but it delivers constant current or constant voltage from a DC 6-40 V input. I hacked a DC plug jack into mine and use a laptop charger to power it.

For the head unit: https://www.banggood.com/RIDEN-DPS3...upply-Integrated-Meter-Ammeter-p-1062474.html

For the case: https://www.banggood.com/RIDEN-DP-A...-Voltage-Current-Casing-Module-p-1218785.html
 

Joshua F Thomas

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Correction: Coil with more resistance, not less resistance. The higher the coil resistance the less amperage it will pass at the same voltage.
 

Greg Furtman

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@Joshua F Thomas I built a launch controller based upon this thread.
https://www.rocketryforum.com/threads/next-launch-controller.34774/ There's a link to James Flenner's PDF.

I am using a 12v 7AH gel lead acid battery like the kind used in uninterruptible computer power supplies. I mounted all the relays, switches, battery, and LEDs inside of a tool box. I'm using 50' of low temp Cat5e to connect the power box to the hand controller . Since I live in WI I fly in the winter so flexible wire is a necessity so I went with finely stranded silicone jacketed wire.

20200705_090534.jpg
This is the base/power unit and the hand controller

20200705_090550.jpg
This is a closeup of the hand controller. I have both LEDs & buzzers for the continuity check as I wasn't sure how bright the LEDs would be outside. They are plenty bright so if I did it again I'd leave out the buzzers.

20200705_090610.jpg
These are the RJ 45 jacks I used. Weatherproof and they have a cap to cover them when not in use.

20200705_090628.jpg
This is the top of the main controller box which stays near the launch pad. I can check continuity at the pad & then double check it at the hand controller. Another nice thing with this circuit is that if someone has left the safety interlock switch in the hand controller on a buzzer notifies me.

20200705_090648.jpg
This is inside the box. You can see the 12v battery in the lower right with most of the wiring over it. One of the things is that the relays you use need to have internal diodes so the LEDs & buzzers don't get any back voltage. I used these and if you look at the diagram on the outside you can see the diagram of the internal diode. And the flexible silicone jacketed wire make it possible to cram all these in the box.

20200705_090734.jpg
I have safety covers on the main power switches.

20200705_090422.jpg
And it all fits into a small SterLite gasketed container for storage and transport.
 

Greg Furtman

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Nice build! I particularly like the Cat5 use.
@Joshua F Thomas Thanks! Every mid-February a bunch of us have RocketBoy Weekend at a friends cabin a few miles from me. We launch off of a frozen lake & as we've gotten older use snowmobiles to retrieve. In 2019 we were using an Estes controller that had 4 AA alkalines. Well after being out in the cold for 30 minutes it didn't have enough juice to heat up an igniter so I decided to build this. This February we used it and every single igniter worked, even the new Estes ones. I do have ethafoam under and on the sides of the battery to kind of insulate it & keep it in place. You can buy one of these 12v 7AH batteries for around $25. I bought those weatherproof RJ45 jacks from Digi-Key.
 

Joshua F Thomas

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I've upgraded my launch controller to use a more portable and less heavy power source: Lithium Iron Phosphate (LiFePO4) rechargeable batteries. I wanted a source that was going to be able to deliver close to 12 volts and high instant amperage.

The regular Lithium Ion batteries are 3.7 volts, which x4 is 14.8 volts. The LiFePO4s are 3.2 volts each which x4 provide 13.2 volts, much closer to the nominal 12 volts. In addition LiFePO4s are better for high-drain uses. I ended up using four of the 26650 size. They fit comfortably inside my case, along with the holder, and had no issues at all with those three Estees igniters.

Now I just need to work out a switch allowing me to choose between the internal batteries and an external source, and wire in a recharger lead. The project never ends....
 

jrap330

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I've upgraded my launch controller to use a more portable and less heavy power source: Lithium Iron Phosphate (LiFePO4) rechargeable batteries. I wanted a source that was going to be able to deliver close to 12 volts and high instant amperage.

The regular Lithium Ion batteries are 3.7 volts, which x4 is 14.8 volts. The LiFePO4s are 3.2 volts each which x4 provide 13.2 volts, much closer to the nominal 12 volts. In addition LiFePO4s are better for high-drain uses. I ended up using four of the 26650 size. They fit comfortably inside my case, along with the holder, and had no issues at all with those three Estees igniters.

Now I just need to work out a switch allowing me to choose between the internal batteries and an external source, and wire in a recharge lead. The project never ends....
Josh...looks great..you did a lot of work since starting this thread.
 

hermanjc

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I recently built a custom launch controller (inspired by a YouTube video) with the intent of firing Estes motor clusters. At first I just used a bank of 8AAs for 12v of power, but bench testing with 3 igniters proved that wouldn't work. So then I added external power jacks for my lawn mower battery, which worked great, except removing it from the mower and hauling it around was a pain. So most recently I modified an old Ryobi charger to provide 20v of power from my readily available power tool batteries (just needed to add some resistors to the LEDs) and today it worked great for 3 motors clusters. Far more convenient than the mower battery. I also use 50ft of 14awg speaker cable from the controller to the launch pad for clusters. I still have the AA battery bank inside, but I cut an access hole on the back to switch it off when using external power, the LEDs are a little dimmer now on the 12v, but still plenty bright in full sunlight.
IMG_20200801_134448590.jpg
IMG_20200801_134616570.jpg
IMG_20200801_135228889.jpg
IMG_20200801_113605835.jpg
Screenshot_20200801-113537.png
IMG_20200801_134705595.jpg
 

Joshua F Thomas

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Nice build! That looks like the same size project box I used, but you’ve added a coat of paint?

The voltmeter is also a nice touch and I wish I had added one.

Your voltage drop with 100 ft of wire (out and back at 50 ft) is probably mitigated by the 20 volt source. How rapidly did the igniters fire? I recall Stine saying in his book that over 18 volts the igniters burned so rapidly they might not be reliable.
 

arconhi

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I'm looking to get into clustered rockets. I knew from discussions with others, and The Handbook of Model Rocketry, that I was going to need a 12v launch controller capable of delivering large amperage quickly. Having some electronic skill, I decided to build my own.

I have to give appreciation to forum user Micromeister for sharing his own controller build in this thread, as I used it as a general starting point, and for various Radioshack parts numbers. Yes, you can still order them! The Igniter Continuity Tests by J. R. Brohm was also helpful for me to determine safe ranges of current for continuity tests. I ended up doing my own tests to find that limit, but having a source that agreed was quite helpful.

My build uses a power delivery box positioned close to the pad, drawing from a 12V sealed lead-acid battery of motorcycle size (any high-drain 12V source should work in theory), and a hand-held box with extension wires for launch activation. Power is delivered via a 12V relay. 14 AWG wire is used everywhere except for where LEDs are used, and there I used 22g just for ease of wiring. Wire from power delivery box to hand-held is 50 feet of 18g lamp cord. Microclips are used for the igniter leads. I'm building clip whips whips that can handle up to 4 igniters each, which should be enough for all my needs for quite a while.

The power delivery box has an on/off switch with indicator LED and continuity test switch with LED. I used a regular on-off and not a momentary for the continuity simply because I got multiple of the same switch when ordering, and it keeps the look clean. Having the continuity stay "on" even for prolonged periods is a low risk; total current draw is approx 10 mA via the LED. At that draw the igniters do not ever go off. I let several different ones run for hours, and they never even got warm. Brohm's testing also confirms this - you need closer to 100 mA for any of the igniter types in common use to go off. With both LEDs on the box draws about 20 mA, only 1/2 of that through the igniter.

The hand-held box has a tube-key arming switch. I paid a bunch for this switch - almost $15 - but I really like the way it looks and acts. It has a solid positive feel, and can not be removed in the armed position. It gives a highly authentic "I'm about to launch a rocket" feel. Another indicator LED is used to indicate the hand-held is receiving power and that the switch is in the armed position. Launch is a standard momentary pushbutton.

I have not had a chance to test this in the field yet; hoping for this tomorrow! About 3/4 of the way through this build I also realized that high-powered rechargeable batteries may also work and fit into the 7" x 4" x 2" power box. I would need close to or slightly better than 12 volts, and high-drain. After some research, it looks like 26650 sized Lithium Iron Phosphate (LFP) batteries will work. They are 3.3v each (x4 = 13.2v) and can handle large current delivery for short periods. Standard 3.7v lithium batteries don't add up well, you either get 11.1v or 14.8v. If I go this route I'm going to wire another switch to allow me to choose between external or internal batteries.

Photos below; any feedback or questions welcome. This was a fun build.

View attachment 421638

View attachment 421639

View attachment 421640

View attachment 421641

View attachment 421642
You can't get it any better than this. This is a nice system. Well done.
 

Joshua F Thomas

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Well, after having built my system, I would do a few things differently:

1) Use 16g wire instead of 14g wire for the internal connections. It’s less stiff and the voltage drop isn’t significant for the short lengths.

2) Add a voltage indicator for the batteries.

3) Find a way to hold the relay stationary instead of it just being loose on the inside.

4) Use spade terminals for more of the connections.

They aren’t deal breakers and in total this setup works well.
 

hermanjc

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Nice build! That looks like the same size project box I used, but you’ve added a coat of paint?

The voltmeter is also a nice touch and I wish I had added one.

Your voltage drop with 100 ft of wire (out and back at 50 ft) is probably mitigated by the 20 volt source. How rapidly did the igniters fire? I recall Stine saying in his book that over 18 volts the igniters burned so rapidly they might not be reliable.
Yup just added yellow paint to the black project box. I really like your idea of having the power box near the Launch tower with relays and the ignition switch be remote.

The igniters lit very fast (couldn't take my finger off the launch button fast enough to prevent total burnout of all 3). The video below is a slomo of my test.

I made a couple "triple whips" using alligator clips to attach to the main clip leads coming from the controller. I always make sure to do individual continuity checks for each igniter before connecting all 3.



IMG_20200801_123303019.jpg
 

Joshua F Thomas

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Yup just added yellow paint to the black project box. I really like your idea of having the power box near the Launch tower with relays and the ignition switch be remote.
I can’t take credit for the idea, that was originally from Harry Stine’s Handbook of Model Rocketry, as well as other builds here on the site.
 

Joshua F Thomas

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Update: Two months on and the LFP 26650 batteries have done very well. I have done about a dozen launches and they still read 13.4 volts. This is excellent performance - I have not charged them at all so far. Highly recommend these for portable launch controller use.
 

Greg Furtman

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I recently built a custom launch controller (inspired by a YouTube video) with the intent of firing Estes motor clusters. At first I just used a bank of 8AAs for 12v of power, but bench testing with 3 igniters proved that wouldn't work. So then I added external power jacks for my lawn mower battery, which worked great, except removing it from the mower and hauling it around was a pain. So most recently I modified an old Ryobi charger to provide 20v of power from my readily available power tool batteries (just needed to add some resistors to the LEDs) and today it worked great for 3 motors clusters. Far more convenient than the mower battery. I also use 50ft of 14awg speaker cable from the controller to the launch pad for clusters. I still have the AA battery bank inside, but I cut an access hole on the back to switch it off when using external power, the LEDs are a little dimmer now on the 12v, but still plenty bright in full sunlight.

View attachment 426673
Nice voltmeter! Who makes or sells them?
 

hermanjc

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Nice voltmeter! Who makes or sells them?
I got mine from Amazon (https://www.amazon.com/gp/product/B06Y3YS189/). They have lots of options if you search and you should find one to suit whatever your needs are.

Update: Two months on and the LFP 26650 batteries have done very well. I have done about a dozen launches and they still read 13.4 volts. This is excellent performance - I have not charged them at all so far. Highly recommend these for portable launch controller use.
That's excellent. Perhaps I will swap my AA battery pack out for those same batteries. Would certainly make it simpler to not need to bring a hobby battery or a drill battery with me.
 

jrap330

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Update: Two months on and the LFP 26650 batteries have done very well. I have done about a dozen launches and they still read 13.4 volts. This is excellent performance - I have not charged them at all so far. Highly recommend these for portable launch controller use.
great, not surprise .
 

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