Revision to Tripoli Rule Regarding Wireless Remote Switches

Discussion in 'Rocketry Electronics and Software' started by Steve Shannon, Feb 4, 2020.

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  1. Feb 9, 2020 #451

    Steve Shannon

    Steve Shannon

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    I’ll have to get back to this; it could take some time because I don’t know the entire history, but remember, our (rocketry’s) inclusion into NFPA probably started when all we had were black powder commercial model rocket motors that the government was trying to regulate.
    But the rules that govern commercial fireworks don’t apply to us. Only our codes apply to us unless something is explicitly referenced in our codes. I simply went looking to see if the concept of “inhibited” came from there. It doesn’t. It seems to come straight out of NASA and Air Force range safety documents.
     
  2. Feb 9, 2020 #452

    Speaknoevil

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    I am not talking about the contact itself which have a mechanical mechanism to provide pressure or sandwich the contact area. Knife contacts as you mention have these pressure points, typically opposing forces that help reduce chances of either contact side separating. But slide and locking switches, even some knife switches that have physical locking mechanism are "maintained" switches that have additional physical features to keep the actuator in place. Momentary pushbutton switches do not have this additional physical mechanism. In fact, in a pull pin design, you have a physical mechanism to keep the switch open (the pin), but you have no physical aid in keeping it closed.
     
    Last edited: Feb 9, 2020
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  3. Feb 9, 2020 #453

    ghostfather

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    I prefer to use a banana plug and jack, which is normally open. I have to stick the metal pin in to close the circuit, which is less prone to vibrations during launch.
    42420585.jpg
     
  4. Feb 9, 2020 #454

    FredA

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    You need to choose wisely, but you DO NOT need a super fancy, high-G rated switch.
    My team and I have easily over a 1000 flights over the past 20 years flying common Switchcraft 4PDT slide switches.
    I buy them in bulk at the surplus store for under a dollar.
    NEVER A FAILURE.

    They use a slide arrangement that forms an inverted & sprung "V" over the sliding contact.
    Horizontal vibration is effectively ignored by the long contact patch of the contacts.
    Vertical vibration might move one side of the V away, but then presses the other side harder to again allow the switch to effectively ignore the vibration.

    PLUS -- our electronics should not care about mSec long interruptions in conduction - the power inputs have caps that will ride through and the PYRO's are really a don't case since they will fire with the contacts only making 50% of the time in a high-vib stress case....the altimeter will still heat the ematch.

    So -- you don't need a "fancy" g-rated switch.
    Just one that reliably stays in the right on/off position.

    In summary:
    One or two switches for under $2.
    Always safe - power is off, pyro's disconnected and shunted.
    Super cheap and easy.
    Never a problem.
    Why do anything else?????
     
  5. Feb 9, 2020 #455

    Charles_McG

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    Earlier in this thread, we already determined that flight history with no incidents is not a strong argument. It sets minimum probability, and we’re talking about what’s possible, not probable.

    But it seems like a good design, as described.

    @cerving how would it have fit in you D-D Estes Mongoose? It’s so good a solution that you don’t need another.
     
  6. Feb 9, 2020 #456

    Steve Shannon

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  7. Feb 9, 2020 #457

    GlueckAuf

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    Tripoli deserves to know the repercussions of its decision regarding its de facto ban on magnetic switches as a means to arm and disarm electronic altimeters. I urge any Tripoli members who are negatively impacted by this decision to sound off, if they haven't already.

    This decision freezes my own Tripoli Level 3 Certification effort until the Featherweight Magnetic Switch, or possibly the German AltiMAX magnetic switch, gains Tripoli approval as a standalone altimeter switch.

    Good skies,

    GlueckAuf
     
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  8. Feb 9, 2020 #458

    cwbullet

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    I think the biggest point to make here is there are lots of ways to safely wire a rocket and switch a rocket. There are probably infinite ways to wire it unsafely. I still like twist wires but under stand the want to add a switch. I experiment with switches regularly to see which is better for me. I have learned tons by seeing what others do and somethings it is what not to do. Most of my failures and most of the ones I seen as prefect come from a desire to overly simplify or complicate the wiring.

    I am not sure why folks in rocketry feel this desire to convert others to their better way. No matter whether it is a switch, wiring technique, or choice of altimeter. Everyone has a preference and you do not need to convert other to your religion per say. As long as it is safe, let others use their own methods.
     
  9. Feb 9, 2020 #459

    warnerr

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    Those Panasonic switches will not carry the amperage required- they are rated for miliamps.
     
  10. Feb 9, 2020 #460

    Frederocket

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    This, in red, especially number 4 and subs are just plain fact...:goodjob: Some may not like it, but it is fact..
     
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  11. Feb 9, 2020 #461

    warnerr

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    With a lever switch Normally Open (NO)a positive method of retaining the lever is doable. I am concerned about internal switch bounce having brought one rocket in ballistic due to momentary disconnects . I want safety. Still need recommendations on switch (that can handle the current too) that is suggested by Tripoli. What I have seen mentioned so far doesn’t work.... let alone on multi battery stacks. (4 DPST switches that would fit in a ‘normal’ rocket.
     
  12. Feb 9, 2020 #462

    KilroySmith

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    I fully agree with you; I think the whole kerfluffle comes down to what "safe" means. As I said above, I think the community is going to have to talk, discuss, yell, pound the table and decide what, from today forward, is considered "safe" when it comes to carrying a rocket towards a group of people including the RSO whose job it is to inspect the rocket. I don't expect a single method to come out of this, but I do expect a set of guidelines that may eliminate some current methods, and open up some new ones. Hopefully, it leads to a lot fewer ground based horror stories told over the campfire.
     
  13. Feb 9, 2020 #463

    Speaknoevil

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    I believe electronics approval is beyond the intent of Tripoli in their announcement. They are just requiring a mechanical disconnect in the power feed OR in series with the initiator charges.
     
  14. Feb 9, 2020 #464

    rharshberger

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    Glad my AV bays already incorporate battery disconnects (modified screw switches) from both Missleworks and SMT Designs (screw activated slide switches). The altimeter never have power until the switches are closed and no failures...ever...yet...
     
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  15. Feb 9, 2020 #465

    Kelly

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    I've seen some cheap keyed JST connectors which can be connected in a reversed direction.
     
  16. Feb 9, 2020 #466

    Ez2cDave

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    Steve,

    Is that the one where the Students were using a sledgehammer to seat the nose cone, with the electronics armed ?

    Dave F.
     
  17. Feb 9, 2020 #467

    jderimig

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    Robots are an order of magnitude more punishing on a switch than a rocket....FWIW
     
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  18. Feb 9, 2020 #468

    KilroySmith

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    An excellent addition to the list I proposed above; perhaps:

    3.5: Must be designed to maintain expected performance during flight in the face of vibration and G-loading by either preventing momentary power interruption (due to contact bounce or similar mechanical issues during high vibrational or g-loads during flight) or gracefully handling momentary losses of power.

    There's lots of ways to design in this kind of robustness - capacitors on microprocessors to handle momentary power loss, positive contact power interruption to prevent power loss (for example, using a shorted XT60 or similar as the power interruption device), reliable screwdown devices, etc. But the rocketeer should be able to explain to the RSO that they've considered this problem, and have addressed it - either by using XYZ manufacturers device which is generally agreed to meet the requirement, or by using XYZ component in a specific way, or by homebrewing a system that the RSO can use their knowledge and experience to approve.
     
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  19. Feb 9, 2020 #469

    Steve Shannon

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    Yes, 100 mA at 30 vDC. We don’t typically perform switching at higher currents. Those ratings are determined specifically for switching at the design life of 20 million cycles. I don’t know what the actual inrush current rating is; those ratings are for a resistive load.

    The Omron has better switching current ratings but different gee ratings (100 gees durability vs. 30 gees functionality)

    https://omronfs.omron.com/en_US/ecb/products/pdf/en-ss.pdf
     
  20. Feb 9, 2020 #470

    cerving

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    ^^^ This... ^^^
     
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  21. Feb 9, 2020 #471

    Steve Shannon

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    Amen [emoji120]
     
  22. Feb 9, 2020 #472

    rharshberger

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    So as long as you have some form of disconnect between the battery and the device (whether the device is wifi switch, magnetic, or magicically switched) then the system should fit within the current ruling/guidance, as there is no path for power to the energetics.
     
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  23. Feb 9, 2020 #473

    Ez2cDave

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    Steve,

    Is that the one where the Students were using a sledgehammer to seat the nose cone, with the electronics armed ?

    Dave F.
     
  24. Feb 9, 2020 #474

    manixFan

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    Steve - I agree there has been a bit of whack a mole regarding this topic among various threads and forums. Please let me know if the following is a correct understanding:
    • TRA has always required that ejection charges (described as 'energetics') be inhibited until the rocket is in launching position
    • The above rule has always precluded flyers from testing continuity of ejection charges in the prep area
    • There had not been a formal definition of how the charges can be inhibited, which has lead to competing interpretations of how to inhibit a circuit
    • The TRA Board has decided to formally issue a rule that defines inhibit (based on standards that exist in the professional pyrotechnics industry) as requiring a mechanical switch that creates an open circuit either:
      • between the power supply and the flight computer
        or
      • between the flight computer and the ejection charges
    • TRA does not currently provide approval or guidance on either the selection of a suitable switch or the design and implementation of any circuits, but may form a committee to do so

    And a couple of clarifications:

    • Are bare e-matches considered an energetic?
    • Does the board consider the .2cc (.2 grams) powder charge required to initiate a popular CO2 based recovery system an energetic?
    • Is a CO2 recovery system that uses a method other than an e-match to initiate the release of CO2 considered an energetic?


    Tony
     
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  25. Feb 9, 2020 #475

    warnerr

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    that switch rating is only 1/2 amp- not adequate for rocketry. This is not an easy task and Tripoli has us scrambling to discover technology to solve their well intentioned but ultimately under researched ruling.
     
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  26. Feb 9, 2020 #476

    davdue

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  27. Feb 9, 2020 #477

    cwbullet

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    RSO is tough job. It amazes me how many experts we have on our field. They like to argue when you make corrections. The RSOs job is safety. I have a different approach. I thank them for their suggestions and either alter th eRockets or not fly it.

    I have only once had to ask someone to leave.
     
  28. Feb 9, 2020 #478

    John Kemker

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    This.
     
  29. Feb 9, 2020 #479

    Steve Shannon

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    1. Yes, that’s straight out of NFPA 1127 since the 2013 version when energetics other than the motor were included.
    2. Yes. But you can test continuity to ematches without BP.
    3. I agree. That’s Tripoli’s failure and I’m sorry for the problems it has caused.
    4. Correct, but we will be digging into this further to better define inhibit applied to amateur Rocketry. I don’t see how we can do that without also including NAR. We don’t want confusion flying at each other’s launches.
    5. Yes - either as a committee or in meetings with the manufacturers.

    * No, bare matches aren’t energetics.
    ** I think I saw that the NASA document specifically includes pressurized systems as energetics, but I have to review that. Can we agree they have the potential of causing injuries if discharged. If so, then it doesn’t matter how they’re triggered.
    *** You didn’t ask but someone else asked about cable cutters. I don’t believe they result in high energy ejection of anything that might injure someone, but a. I don’t know, and b. I shouldn’t make rulings without talking to people who know more about them.
    Plane doors are closing.
     
  30. Feb 9, 2020 #480

    Rob702Martinez

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    Probably the most reasonable respectful and understanding post about this.
     
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