Questions about my DIY Launch Controller

Discussion in 'Ground Support' started by BrainlordMesomorph, Apr 8, 2018.

  1. Jul 5, 2018 #81

    BrainlordMesomorph

    BrainlordMesomorph

    BrainlordMesomorph

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    Thanks but;
    1. My first step in "googling" was asking my friends here on the Rocketry Forum.

    B. I'm really quite surprised that you guys haven't already done a scientific study on this. Am I the first guy to ask to ask this question? (I'm sorry, I just came here from years of playing Kerbal Space Program, and on the KSP forums they would have already digested this information into 3 spreadsheets; cross referenced by manufacturer, price, and ignition temperature.)

    So I'll go hunting on the big, wild, www. But isn't this part of an FAQ for this subforum?
     
  2. Jul 5, 2018 #82

    Steve Shannon

    Steve Shannon

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    Actually there is an excellent paper out there; that’s why I suggested googling. I could google it for you, but I’d prefer you do the work. I think you can find a link to it from one of the build your own igniter companies. Which I think you can find from Public Missiles. Search for “maximum current through Estes igniters.”

    Edit: https://publicmissiles.com/IgnitersWhitePaperbyG-Wiz.pdf
     
  3. Jul 5, 2018 #83

    BrainlordMesomorph

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    I tried to read that. I have no idea what he's talking about

    This page was more to my understanding:
    http://home.earthlink.net/~david.schultz/rnd/igniter/neyer.html

    He says the Estes igniters had an all fire at 4 amps
    and the Quests (which fire at 1/3 of an amp) had a no fire at 130mA.

    So (I think that means) I want an ignition current of 4 amps (or more), and a test current less than 100 mA.

    Since you get the math, maybe you can help me figure out what's the actual maximum current I can get from these batteries.

    I have 2 12 volt 7 Amp Hour lead acid gel batteries (in parallel)

    And they say these numbers that I don't understand:
    Cycle Use: 14.4~15.0 V
    Standby Use: 13.5~13.8 V
    Initial current: 2.1A MAX

    Does that mean between the two batteries I have a 4.2 amps max??
     
  4. Jul 5, 2018 #84

    Steve Shannon

    Steve Shannon

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    I would not design a controller around a single type of igniter. If the igniter manufacturer decides to change their igniter (which Estes recently did) your system may have to be redone. You might want to fly a rocket on a CTI motor someday. Some of them use electric matches that have a low no-fire current, meaning that a continuity test using the numbers you quote for Estes no-fire could light a motor; obviously that’s a bad thing.
    Instead, design it to have as little built in resistance as possible when firing and as low of continuity current as possible.
    The last three lines that you copied describe the charging requirements of the battery. They are meaningless when it comes to how the battery works under load.
    Those 12 volt, 7 amp hour SLA batteries can dump a pretty large current, well over 20 amps direct short terminal to terminal. The limiting factor is the internal resistance of the battery. You certainly don’t need to put two in parallel. I use a single one of those at each pad box in my system.
    I’d be happy to help with the math.
     
    Ted Cochran likes this.
  5. Jul 6, 2018 #85

    Voyager1

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    You can't use Piezo #2 in either of those configurations. It has to be wired between +12V (output side of ignition push button) and ground (-).
     
  6. Jul 6, 2018 #86

    Ted Cochran

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    Also remember that it is easy to short an igniter at the pad by mistake and your system needs to be able to handle that without melting or otherwise destroying itself. (No joke, I have seen model rockets catch fire from shorted Estes igniters connected to very robust launch controllers!)

    I think what lots of folks here are trying to say is that building a fail-safe, robust launch controller with lots of features requires significantly more planning than building a single-pad, simple system, especially if you're designing for multiple pads.
     
  7. Jul 10, 2018 #87

    BrainlordMesomorph

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    I'm not. My specs are specifically for a launch circuit above the high power Estes specs, and a test circuit below the low power Quest specs. (if I understand you specs, your 400mA test circuit could very well ignite a Quest igniter during the continuity test.)

    [​IMG]
    (1st I think "A" would work for low power launches, I've seen it other schematics. But in my high power launcher i'd fry the piezo.)

    Are you suggesting "c" above?
    Doesn't that short out the continuity test? You'd get a light and a beep, regardless of the situation at the pad.

    I thought of B2, the diode creates a V+ and V- for Piezo 2 and maintains the validity of the continuity test, but the buzzer is out of the way of the high power zap of ignition. right?

    I'v got a 10Amp Fuse. Is that what you mean?

    [​IMG]
    "Yes, I know..."
    :D
     
  8. Jul 11, 2018 #88

    Steve Shannon

    Steve Shannon

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    No, my continuity check is limited to under 40 mA.
    Are you ever going to want to launch a cluster with parallel leads?
     
  9. Jul 11, 2018 #89

    BrainlordMesomorph

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    ah, 40 not 400 sorry.

    perhaps, I've been told I'll have to upgrade my fuse (to fuses) for that.
     
  10. Jul 11, 2018 #90

    Voyager1

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    The 1st one is it! No, you won't fry the piezo. C? will work; B2 won't! No, C? won't short out the continuity test. Yes, you will get a light and beep. If you use B2, you will only get the forward voltage drop across the diode to power the piezo, and besides, it doesn't make sense to do it that way.

    I love the Fawlty Towers dig! Classic!
     
  11. Jul 11, 2018 #91

    BrainlordMesomorph

    BrainlordMesomorph

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    OK, maybe I'm not using the right words. C may not "short" the continuity test, per se, but getting a light and a beep w/o igniter continuity makes the test invalid and moot.

    And version A just looks so incongruous.

    A large portion of this thread is guys telling me to use the right (i.e. heavy 16 AWG) wire for this. Esp for the "high power" side of the circuit. The leads on this buzzer are like hair! If I have to place it in the middle of the high power circuit like that, I'm very tempted to cut open the plastic case on this thing and replace the leads w/ at least 22 AWG.

    and aren't I getting a forward voltage drop to power the piezo, no matter what I do (A, B2, or C) ?

    I didn't mean it as a "dig" I just meant "Yes!, I know...."
     
  12. Jul 11, 2018 #92

    Voyager1

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    Yes, you do use the heavier gauge wire for your ignition circuit, but the piezo doesn’t require the same high current to operate. It only uses a low current, hence the lighter gauge wire. It doesn’t matter that it’s connected across your high current circuit, it will still only draw what current it needs. So, you do not need to change the piezo leads.

    In the B2 configuration of the piezo, the piezo will only have the forward voltage drop of the diode (typically approximately 0.7V, but depends on the type of diode) across the piezo when you press the continuity or ignition switches. You better google “forward voltage drop of diode” so that you understand what I’m saying here, and I’m not trying to be patronising either. This is not enough to operate the piezo - it probably requires 6 - 12V. This, of course, requires an igniter to be installed AND have continuity. Without an igniter you will not have a closed circuit, so no current will flow anyway.

    With the C configuration, you are getting the full 12V across the piezo when you use the ignition switch, but I’m not certain what voltage will be across the piezo when you use the continuity switch, as it would depend on the input resistance to the piezo module, which would be in series with the continuity LED and 350 Ohm resistor. It will be less than 12V, though. I know that this configuration is not going to give you exactly what you want, but you are trying to do too much with a single piezo. You will have to increase the complexity of your circuit to achieve this.

    You could place a piezo in parallel with the continuity LED and resistor, and another on the output side of the ignition switch and (-). If you do this, you will also need to instal an isolation diode between the output of the ignition switch and where the continuity LED connects to the ignition output line. However, this is, in my opinion becoming unnecessarily complex, but it might work for you. If I had more time I could probably think of something smarter, but it’s getting a bit late!
     
  13. Jul 11, 2018 #93

    BrainlordMesomorph

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    I know that part
    here:This is a better picture of what we're talking about.
    [​IMG]
    A: we're going from 16 AWG wire down to pubic hair wire, through the buzzer, more thin wire then back to 16 gauge, and out to the launchpad. (?) It is a 3 to 24V DC piezo.

    I'll do that if you say it's ok (although I'm not sure why, I haven't asked you for any credentials or anything :) ) It just that most of this thread is guys telling me not to do that.

    Maybe just "D" is the answer. I put Piezo 2 on the continuity test only. I get a beep during the test; not during launch, but nothing is in the way of the high power circuit.

    BTW: "unnecessarily complex" is (clearly) my middle name. please elaborate. And take your time.
     
    Last edited: Jul 12, 2018
  14. Jul 11, 2018 #94

    Voyager1

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    No, no, no! You’re completely misunderstanding what I’m saying. That schematic above will not work! When I get some time I will draw up what I mean.

    For the record, I am a retired electronics engineer, having worked for several decades in university R&D areas.
     
  15. Jul 12, 2018 #95

    BrainlordMesomorph

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    thank you i didn't think so.
    patiently awaiting your response :)
     
  16. Jul 12, 2018 #96

    Voyager1

    Voyager1

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    DIY_LC_1.png
    I hope this schematic explains what I am suggesting to address your requirements. It only displays the necessary ignition and continuity circuit for a single igniter and ignores the rest of your circuit.
     
  17. Jul 12, 2018 #97

    BrainlordMesomorph

    BrainlordMesomorph

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    Thank you. For your work and for your patience. (yes, I can read that)

    I'm just glad that I could tell that position A was wrong. See, I was paying attention.

    I've just been reading about diodes at wiki for an hour. Jeese! I had no idea about reverse leakage current, much less voltage drop. (Boy a guy would need a degree in all that. :))

    A THIRD piezo in this thing would be silly. (as if up till now, this hasn't been silly)

    So I'll be using a Continuity piezo were you have it, or maybe where I have in D, depending on what that 350 ohm resistor does to the sound. I'm hoping it will go from being a loud, harsh, "TEEEEEET" to being a nice soft "BOOOOP" but i'll find out when the parts get here.

    That was the last technical question. :D

    I'm realizing that the actual building of the thing, mounting the batteries, drilling the holes in the control panel, that's going most of the job. Soldering all the connections is going to be light easy fun work by comparison.

    Thanks again!
     
  18. Jul 12, 2018 #98

    Steve Shannon

    Steve Shannon

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    I put continuity piezoelectric beepers on all of my pad boxes but it was really a complete waste. Even with two continuity leds, the igniter, and a 420 ohm resistor in the continuity test loop the LEDs are very bright.

    I would place the upper lead of the ignition buzzer between the arming switch and the ignition switch with the lower lead going to the other side as you already have it. Then it would buzz whenever you’re armed. The way you have it, it’ll only buzz when you push the launch button, and possibly not even then because it’ll only see the forward voltage of the steering diode..

    Also, what’s the electrical requirement for the piezo buzzers you intend to use?
     
  19. Jul 12, 2018 #99

    BrainlordMesomorph

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    1. I have and "armed" beep. It actually goes TEEET TEEET TEEET like a truck backing up. And now I have a steady tone for Continuity as well :)

    2. Why the beeping? Fair question. The kids usually are the one pressing the launch button. (that's why I'm making it so 'fun') And with beeping, I won't have to be looking over their shoulders to know whats going on. It will also get the spectators' attention (and get them to shut up) and lastly, it will remind the kid to turn off the system after launch.

    Which brings us to what I believe is the final schematic.

    [​IMG]

    EDIT: oh and they are 12 volt piezos (rated 3 to 24 volts)
     
    Last edited: Jul 12, 2018
  20. Jul 12, 2018 #100

    Steve Shannon

    Steve Shannon

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    And what current do they draw?
     

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