A launch controller design for idiots???

Discussion in 'Ground Support' started by ThreeJsDad, Feb 13, 2020.

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  1. Feb 13, 2020 #1

    ThreeJsDad

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    I am great with composites and mechanical stuff but electronic symbols might as well be Egyptian Hieroglyphics to me.

    My wife and I are planning a rocket program for her 4th grade class. I can easily build a 4-6 launch pad system but a launch controller for that launch pad could be beyond my reach without some help from you folks.

    I don't need any drag race functions so it may be simpler than I think but I am at a loss right now for how to build one. When I look up plans they are those Egyptian Symbols.

    Could I build a simple box that has individual circuits but power is drawn from one source. Just separate buttons for each pad?

    Thanks in advance for helping an electronics idiot. The sad thing is I solder really well....LOL

    Paul
     
  2. Feb 13, 2020 #2

    samb

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  3. Feb 13, 2020 #3

    samb

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  4. Feb 13, 2020 #4

    jrap330

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    I graduated with my Engineering degree over 35 years ago, so my circuit analysis is rusty, but you can just use one Estes Controller or two and move the clips around since you are not doing drag races. But more important, they are Electrical Schematic Symbols. Now Hieroglyphics are all those emojis created for texting on a smart phone. If it looks like a door it is a switch, if it looks like a push close door, a button switch and anything with like a light build is a bulb or LED bulb. Google electrical symbols.
     
  5. Feb 13, 2020 #5

    ThreeJsDad

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    I am learning the emjoi thing.... Thanks I will see what I can figure out...
     
  6. Feb 13, 2020 #6

    Kelly

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    All of these seem overkill, if we're talking about LPR. Relays? for a 15 foot lead?
    A simple 6-pad system (without dragrace capability) can be built with a rotary selector switch, a couple more switches for arming and launch, and a continuity indicator light. An old estes publication talks about the basics, and shows such a system:
    https://estesrockets.com/wp-content/uploads/Educator/2811_Estes_Model_Rocket_Launch_Systems.pdf
    Old Centauri catalog showed a simple setup:
    http://www.ninfinger.org/rockets/catalogs/centuri71d/71dcen72.html

    You could probably add dragrace with a couple additional switches, if that were necessary.
     
  7. Feb 13, 2020 #7

    ThreeJsDad

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    You are awesome, thanks so much !! We talking about just that, a simple little LPR pad.

    PS that first link to Estes was perfect, that is a great PDF and a sweet little pad system.
     
  8. Feb 13, 2020 #8

    Kelly

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    One thing that makes the Estes link a little dated, is that LEDs (with a current-limiting resistor) have pretty much replaced incandescent bulbs for these applications, due to lower cost, lower current raw, longer life, etc. This is an easy substitution to make.
     
  9. Feb 15, 2020 #9

    kweaver

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    This complete launch controller system may be worth considering.
    https://www.rocketryworks.com/houston-6-pad-launch-controller/
    It ships as complete package with cabling and pad connectors, carrying case and an optional 12v battery and charger can be included.
    All you would need to add would be, your launch pads and rockets.
    Ken Weaver
     
  10. Feb 29, 2020 #10

    ThreeJsDad

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    I got together with the fella who built our clubs launch system. He had some great ideas and thought the rotary switch was a great idea for a simple system like I need. I am going to use Cat 6 wire out to the pads.

    I am going to use a 3S Lipo for my power supply because I have three of them. I believe they have a high enough C rating to even do some drag races if we go that route.

    My question that I really need help with is with the continuity light. I may go with an LED designed for 12v. Do I still need a resistor and if so what size. Should I simply go with a small buzzer instead of a light?
     
  11. Feb 29, 2020 #11

    Voyager1

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    The 12V LEDs usually have a resistor installed in one of the leads. It’s probably about 500-600 Ohms, but no more than 1k. You could also have a 12V beeping buzzer to alert everyone that you’re about to launch.
     
  12. Feb 29, 2020 #12

    ThreeJsDad

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    I got together with the fella who built our clubs launch system. He had some great ideas and thought the rotary switch was a great idea for a simple system like I need. I am going to use Cat 6 wire out to the pads.

    I am going to use a 3S Lipo for my power supply because I have three of them. I believe they have a high enough C rating to even do some drag races if we go that route.

    My question that I really need help with is with the continuity light. I may go with an LED designed for 12v. Do I still need a resistor and if so what size. Should I simply go with a small buzzer instead of a light?
    I mentioned the buzzer because my little hand held has one and I have found some. Could I just skip the lights and use the beeper as my continuity check and an indicator that the pad is live? Will it absorb enough voltage to keep the igniter from firing?
     
  13. Feb 29, 2020 #13

    Kelly

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    Basically, the current through your buzzer needs to be less than the 'no-fire' current of your igniters. No-fire current depends on what brand you're using, but I think the lowest tend to come in around 150 mA or so. Estes igniters probably 2-3X that.
    So, find a buzzer that has well under 100mA current - like, 30-50mA max. Should be able to find one that meets that spec; if you have a buzzer and don't know what it is then test using the max voltage you expect to use, and an ammeter.
     
  14. Feb 29, 2020 #14

    Voyager1

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    Yes, the buzzer shouldn't use much current to function, depending on the type you use. Be careful how you wire it in to your circuit. You want to make sure you don't have a continuity check current higher than 10-20 mA for safety. Hopefully, that should be enough to drive the buzzer.
    Here is a simple implementation. The "R" is to adjust the continuity current to no more than 20mA, if necessary. You can use a higher current, but lower is better if possible. Whatever buzzer you get, check its current requirement, either from a spec sheet or by measuring it.
     

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  15. Feb 29, 2020 #15

    ThreeJsDad

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    Thanks everyone. My understanding seems to be way off. I was thinking the continuity "checker" like a bulb or buzzer was intended to take up or absorb enough current so the igniter did not get enough current to fire.

    Our club system I know can even check e-matches and not fire them. I am normally very careful to make my igniters so they require a decent current to fire. My intended use for this system is basic LPR launches with Estes style igniters.

    I am looking at building something very much like the old Estes multipad launcher. They use a bulb though. I found small "lights" at an electronics supply and they are rated for 12v.

    Even with all my mechanical skills electrical stuff has always felt like a dark art to me....
     
  16. Feb 29, 2020 #16

    Kelly

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    Your understanding is maybe not off... the checker (bulb/buzzer/whatever) CAN act as the current limiting element. This is how the older systems worked, the bulb was basically the current-limiting element, you just needed to select a bulb with the right resistance. If you put a high-wattage (low R) bulb in, you're going to get too much current.
    When we switched from incandescents to LEDs, things were a bit different, because LED's don't act like resistors at all. They have virtually 0 resistance, and can pass all the current you want (until they burn out). So with an LED in the loop, you need a current limiting resistor. (If you're using something like a "12V LED", that means it already has a real resistor wired in.)
    A DC buzzer acts more or less like a resistor. If it's rated for, say 30mA at 12V, then that means you can use it directly (without a limiting resistor) in a 12V circuit, and it will limit the current to 30mA. You just need to look at the rating of the buzzer.
    The circuit Voyager1 showed might work, depending on the size of the resistor, the rating of the buzzer, and the voltage of the battery. But if you put a resistor in line with a 12V battery and a 12V buzzer, the buzzer won't get the voltage/current it needs, and will produce less amplitude, or maybe none at all.

    Do you have an ammeter? Do you have a buzzer? Tell us what you've got and we'll tell you how to make it work.
     
  17. Feb 29, 2020 #17

    BBowmaster

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    My 4H club uses the six-pack. It’s simple, sturdy, and professional looking. The last helps with skeptical parents that wonder if the hobby is safe.

    A rotary switch can sometimes induce a surge as you switch positions. I’ve seen them blow bulbs and fry printers. I’d be wary of an accidental launch if you switched with the master key in place.
     
  18. Feb 29, 2020 #18

    ThreeJsDad

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    We need to keep this low budget. I cannot afford to buy a nice launch system and I would not buy one for a one day event. If I had a local club I would look into acquiring something nicer. Making it look clean and professional is not the issue for me, it's what components to put where. I can even solder with the best of them, again a mechanical skill.
     
  19. Feb 29, 2020 #19

    ThreeJsDad

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    I have a multimeter and i have a nice soldering station. I have not had a need for buzzers or resistors until now. If you want to move this to Pm's that is fine. I realize we are getting down to the finer details and I am sure some folks are sick of my neophyte questions.
     
  20. Feb 29, 2020 #20

    Kelly

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    No worries :) If you have a multimeter bu not a buzzer, go ahead and buy a buzzer if that's what you want. Try and get a 12V one, and then you can measure the current through it with a multimeter. If the current is too high, drop in a resistor and you're good to go.
     
  21. Mar 8, 2020 #21

    boatgeek

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    I'm putting together a launch controller to replace our TARC team's PS2 unit. We mainly want to get a little more distance to the pad for the higher thrust F and G motors.

    I've got a simple design hacked together, but I've run into a rules question. NAR Model Rocket Safety Code says (end of rule 3):

    The second sentence is easy--a momentary on button switch. To meet the letter and spirit of the first sentence, do I need a pin key like the PS2 and Electron Beam controllers have? Would a simple momentary on push button work for that as well, as long as both buttons had to be pushed at the same time for the igniter to fire? If not, would a keyed switch work? I'm trying to do this mostly out of materials I can find at the local hardware store, and the pin key "switch" is eluding me so far.

    Thanks!
     
  22. Mar 8, 2020 #22

    UhClem

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    It must be removable. A key switch works well but make sure the key can only be removed in the off position. A phone jack works well too.

    Don't forget the misfire rule: "If my rocket does not launch when I press the button of my electrical launch system, I will remove the launcher’s safety interlock..."
     
  23. Mar 8, 2020 #23

    Greg Furtman

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    I'm mentoring a rocket team and we were supposed to launch a Quest rocket & shoot video & submit it. The kit came with a Quest motor & ignitor. We were using an old Estes launch controller that had a bulb instead of an LED like the newer ones. As soon as I inserted the safety key to check continuity the ignitor lit & the rocket took off. No one was looking & luckily no one was near the launch pad.
     
  24. Mar 8, 2020 #24

    Greg Furtman

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    Paul, here's your Rosetta Stone. :D

    https://www.electronicshub.org/symbols/
     
  25. Mar 8, 2020 #25

    ThreeJsDad

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    Funny, real funny !!!! Okay, so that was really was funny. I have been building a Quark and that has helped but I am sure your link will be even more useful, thanks.

    If you ever want some help with resins and additives let me know,.......I will find a Rosetta Stone for you...:D:D
     
  26. Mar 8, 2020 #26

    ThreeJsDad

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    many folks use the micro ones for the power switch in large RC airplanes. I will be using something similar but in reverse with my altimeter. Like I said I can solder the wings back on a fly but someone needs to tell me which one goes on which side.....LOL
     

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