Pyro battery circuit plans needed

Discussion in 'Rocketry Electronics and Software' started by Cameron Anderson, Sep 14, 2018.

  1. Sep 14, 2018 #1

    Cameron Anderson

    Cameron Anderson

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    Anyone have a circuit diagram or experience with a seperate pyro battery set up for missileworks components? I have a PET2 timer and I want to airstart my second stage with an Aerotech J500. I bought some Wildman Big Uns to test which should be ignitable using the timer only, but I'd like to wire up some batteries (and maybe some capacitors) to light a fastfire igniter which takes 12v and 3 amps on a separate circuit.
     
  2. Sep 14, 2018 #2

    Titan II

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  3. Sep 14, 2018 #3

    davdue

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    Most people would tell you that you need more than a timer. I understand that the PET2+ has additional triggers like MECO that make it smart. I wasn’t able to use that for my one attempt at a 2 stage rocket. However I did use the RRC3 for sustainer ignition but something happened and the RRC3 never fired. With all that said there is a diagram in the current PET2+ users manual for a pyro battery.
     
  4. Sep 14, 2018 #4

    Cameron Anderson

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    The diagram is great at showing the theory and saying "yes it's doable," but what I'm more looking for is an actual circuit schematic from someone who has successfully got 12v and 3a to an airstart. Or is that a bridge too far and do I need to start working an e-match dipped in pyrogen/pyrodex for motor ignition.
     

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  5. Sep 14, 2018 #5

    Steve Shannon

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    An e-match inserted into a Pyrodex pellet that fits snugly up into the motor core works without additional circuitry. Otherwise look at how Jim Jarvis has described his multi stage projects.
     
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  6. Sep 14, 2018 #6

    timbucktoo

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    Not sure where you fly but some clubs won’t allow a timer for air start. I’ve had great success using the aux output of an RRC3 for staging.
     
  7. Sep 14, 2018 #7

    SteveThatcher

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    of note, the MissileWorks RRC3 can handle the 12 volt (even up to 30 volts) on the outputs when using a second battery. Their current is at your max of 3 amps though and they really want you to use something that will limit the current to three amps like a 9 volt battery does (you could series two of them for 18 volts). Personally, I would prefer to be running the output at least 20% below its maximum. I would definitely look to some other lower current method for firing the air start.
     
  8. Sep 14, 2018 #8

    Cameron Anderson

    Cameron Anderson

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    I've heard that, and with pure timer functionality I understand why. Luckily PET2+ has adjustable angle inhibits so it won't activate if the airframe leaves the envelope.
     
  9. Sep 14, 2018 #9

    Cameron Anderson

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    Yeah, definitely looking like motor ignition will be a heavily dipped e-match and some aerotech blue propellent slivers.
     
  10. Sep 14, 2018 #10

    davdue

    davdue

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    I was going to tell him that. I actually got that from Jim Jarvis. He also had me use a small piece of dowel rod to hold the igniter up in the sustainer motor.
     
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  11. Sep 14, 2018 #11

    Cameron Anderson

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    I'm working with a 38/600 and 38/720 so my core and nozzle diameters aren't amazing but a thin wooden dowel might work. I was thinking laying a piece of paper between the top two grains and weaving the ignitor wire through it to help keep it up.
     
  12. Sep 15, 2018 #12

    MikeyDSlagle

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    I picked up a really small 3 cell LiPo and a MOSFET switch from Amazon that I will use in my Viper IV to airstart two 24mm motors (possibly tomorrow). The battery at full charge is over 12 volts and while I forget the capacity and "C" rating, it will easily and readily source 25 amps, I think surge to 50...without voltage drop. The board can only hand 30 or so at that voltage IIRC.
    Ground testing has proved it works. The MOSFET board has 3 connections: power in, power out and signal in/trigger (or whatever it is called) The AUX terminal on my RRC3 connects to the trigger, the LIPO to the power in and the starters will hook to power out. The RRC3 uses a 9 volt and experiences only that current. The high current runs through the MOSFET board. If something goes wrong then the 8 dollar board fries and not the RRC3. A would imagine a similar setup would work for the PET timer.
     
  13. Sep 15, 2018 #13

    Cameron Anderson

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    Wow, I'd love to see that set up.
     
  14. Sep 15, 2018 #14

    JimJarvis50

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    Are you sure about the capability to inhibit based on angle? I quickly scanned the manual. The description of the off-axis function isn't very clear (imo), but it looks to me like this feature is more about the initial launch than the airstart. I'd love to be wrong about this, but assuming I'm not, then I would recommend you use an altimeter capable of an altitude check (rather than a tilt check). Quite a few altimeters can do that.

    My favorate way to light motors is with dipped ematches. For larger motors, I use two ematches, connected to one wire, to improve the chances of lighting the dip. I use the magnelite from PML. Seems to work pretty well and isn't brittle. By folding the ematch, you can increase the amount of dip on the ematch, and with two folds, you can light N motors.

    I like to use a stick to support the ignitor for motors with larger cores. For K motors and smaller, unless it is a very high acceleration boost, I don't use a stick.

    Jim
     
    Last edited: Sep 15, 2018
  15. Sep 15, 2018 #15

    Cameron Anderson

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    Initial boost won't exceed 500mph and my sustaier is a 38mm J so based on what you said I should be fine with a bend in the wire to keep the ignitor in place.
    I bought some Wildman Big uns and have some Wildman e-matches I can dip in H-3 pyrogen I am going to play with as well. I plan on testing my ignitors in a single stage configuration in the motors I intend to airstart to ensure it'll light and to get the ignition timing sequence down.
    I absolutely agree the angle component of the timer is vague at best - I would love to hear from someone who has used one. The best I've been able to find is some discussion threads that imply the tilt angle is a gate.
    What altimiters would you recommend? Clearly you have experience with this and I'd love any recommendations you have.
     
  16. Sep 15, 2018 #16

    cerving

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    A bend in the wire won't keep your sustainer's igniter in place, you need to tape it to a skewer or skinny basswood stick and hold it in place with the motor nozzle cap so it can't slide down. I've done 54mm to 38mm's, and they light fine if you keep the igniter from coming out.

    As far as the electronics go, I strongly recommend lighting the sustainer with something that has some kind of off-axis check, either altitude@time, velocity@time, or an IMU-base tilt detector. A simple timer won't keep the sustainer from lighting while pointed in an undesirable orientation if you lose a fin or have a booster cato.
     
  17. Sep 15, 2018 #17

    JimJarvis50

    JimJarvis50

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    Yes, you need to keep the ignitor in place, stick or no stick. I use the motor cap typically.

    My belief is that an altitude check is for safety and a tilt check is to stay within the launch radius. I use either an altitude check or an altitude check with tilt, but not tilt alone. I have used the EasyMega and the Raven, but the RRC3 and the Eggtimer product will do it too. There are others.

    Jim
     
  18. Sep 19, 2018 at 12:53 PM #18

    MikeyDSlagle

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    I'll get some pics and share em.
     
  19. Sep 19, 2018 at 11:43 PM #19

    MikeyDSlagle

    MikeyDSlagle

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    This is built into a lower bay that I had a user 3d print the panel and frame for me. I originally had a terminal block and clamp in there but when I couldn't get my homemade starters to reliably light I had to come up with something else. The battery box and lid are wood because I don't have a 3d printer and didn't want to get off in designing one and wait for someone else to print it. The lid doubles as the sled for the board.

    lower bay 1.jpg lower bay 2.jpg

    Using this battery and this board

    The battery will charge to over 12 volts. I successfully ground tested it with 2 Wildman Tiny lighters hooked in parallel to my RRC3 and using MDacs through a laptop to fire the AUX circuit.
    The speaker wire running into the green terminal which I had to add to the board runs to a DC jack that plugs into a socket on the lower bulkhead of the A/V bay. That socket is wired to the AUX terminals on the RRC3. It is designed to pull apart when the drogue charge fires. The empty terminal is the OUT and that is where the lighters/starters will be wired.

    This is all in a LOC Viper IV, which is a 2.6" airframe. Build thread here.
    I have yet to fly it but everything has ground tested. I see no reason why it will not fly. Maybe I can fly it in October.
     

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