Revision to Tripoli Rule Regarding Wireless Remote Switches

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

Help Support The Rocketry Forum by donating:

  1. Feb 10, 2020 #511

    Adrian A

    Adrian A

    Adrian A

    Sponsor TRF Sponsor TRF Lifetime Supporter

    Joined:
    Jan 22, 2009
    Messages:
    2,258
    Likes Received:
    230
    I just emailed a request to the Tripoli board, via Steve Shannon, that independent, magnetically-activated, solid state electronic switches like those sold by Featherweight Altimeters be considered equivalent to mechanical switches in the Tripoli safety code.

    Keeping the power switch independent from the downstream electronics is important. You don't want a single failure to be able to turn on the switch and make the altimeter inadvertently activate a charge. The Featherweight magnetic switches are completely independent of whatever it is that is connected to its output, just like a mechanical switch or a battery disconnect is.

    Reliability is also important, both to prevent an accidental turn on, and just as importantly, to prevent an accidental turn-off that could keep a chute from coming out. Featherweight magnetic switches have proven to have excellent reliability over more than a decade, with more than 1000 units in the field, used by hundreds of fliers. Rocketry has only anecdotal evidence, but there haven't been reported problems with magnetic switches like there have been with mechanical Schurter switches, for example. In other industries that have collected hard evidence, it's no contest, solid state switches have proven to be vastly more reliable than mechanical switches.

    I applaud Steve and the rest of the Tripoli Board's focus on safety, and for continuously working to improve it. Good policy is based on evidence, and I expect the Tripoli board to weigh the evidence appropriately when it comes to interpreting or clarifying the new rule that affects all of our safety.
     
    g.pitts, GlueckAuf, pondman and 7 others like this.
  2. Feb 10, 2020 #512

    cerving

    cerving

    cerving

    Owner, Eggtimer Rocketry TRF Sponsor TRF Supporter

    Joined:
    Feb 3, 2012
    Messages:
    3,466
    Likes Received:
    712
    Good luck Adrian.
     
    Charles_McG likes this.
  3. Feb 10, 2020 #513

    Frederocket

    Frederocket

    Frederocket

    Well-Known Member

    Joined:
    Jul 31, 2011
    Messages:
    418
    Likes Received:
    55
    Gender:
    Male
    Location:
    Maryland
    All well and good and I agree with you on the reliability issues you mention on those Schulter switches; in particular, they are junk for our usage and will eventually come apart after extended use, (my opinion based on their intended purpose and what I have witnessed). However, can anyone guarantee that magnetic switches are 100% impervious to unintended activation from a magnetic source, other than the intended activating magnet? That concern is what keeps me from using magnetic switches, in favor of screw type arming switches. If testing has been accomplished that supports they, (yours in particular), are completely safe from inadvertent magnetic activation, I do believe there will be support for acceptance and usage and maybe even the gold standard for power disconnect switches.
     
  4. Feb 10, 2020 #514

    cerving

    cerving

    cerving

    Owner, Eggtimer Rocketry TRF Sponsor TRF Supporter

    Joined:
    Feb 3, 2012
    Messages:
    3,466
    Likes Received:
    712
    I used two Schurter switches in my L2 rocket, which had redundant Eggtimer Classics in it. After a few flights, one of the Schurter switches started to overrotate past the "off" stop, and became basically unusable. They are definitely not robust... I replaced them with the old Eggtimer Remote Switch (which we no longer sell), and that was the last time I've used them. I get why they're popular... they're cheap and the "seem" to be a good switch based on the "click" that they make when they're in position, but they're not fit for rocketry, at least for use as a electronics power switch. They might be OK for an energetic disconnect, though, as long as your altimeter doesn't use capacitive discharge that would render any switch bounce fatal.
     
    dvdsnyd and Frederocket like this.
  5. Feb 10, 2020 #515

    manixFan

    manixFan

    manixFan

    Not a rocket scientist

    Joined:
    Feb 15, 2009
    Messages:
    1,512
    Likes Received:
    530
    Gender:
    Male
    Location:
    TX
    It's already been shown by numerous posts, including mine, that screw type switches have been activated 'inadvertently' on many occasions, yet they are considered safe for use in spite of this evidence. So if inadvertent activation is cause for disqualification for use, how is it that screw switches should be allowed for our usage? Is it that they meet the sole qualification of being a mechanical switch, regardless of their ability to avoid inadvertently being activated? They are certainly not 100% impervious to unintended activation.


    Tony
     
  6. Feb 10, 2020 #516

    Steve Shannon

    Steve Shannon

    Steve Shannon

    Well-Known Member

    Joined:
    Jul 23, 2011
    Messages:
    5,694
    Likes Received:
    2,037
    Location:
    Butte, Montana
    Adrian,
    Good to hear from you. I haven’t seen your request yet but even if I haven’t you will be hearing from us.

    A board member will be inviting you and all other established members of commercial rocketry electronics to a meeting. We’re still working of the list of questions that must be answered. We’re also painfully aware that these questions must not drag out.
    Steve
     
    TonyL, dvdsnyd and Nytrunner like this.
  7. Feb 10, 2020 #517

    DAllen

    DAllen

    DAllen

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    4,523
    Likes Received:
    450
    Wouldn't just using a longer screw help with this inadvertent activation with screw switches? I'm looking at my pile of screw switches I have and the 6/32 screws are REALLY short so I can see why with a little bit of vibration in just the right way they could screw in and make contact. That's what's happening with these switches right? If so, then getting even a 1/2" long 6/32 screw would definitely prevent most if not all of these instances.

    Or is the failure mode something else? I'd kind of like to know because I'm about to incorporate a couple of these into the L3 project I am building.
     
    Frederocket likes this.
  8. Feb 10, 2020 #518

    Kelly

    Kelly

    Kelly

    Usually remembers to get the pointy end up

    Joined:
    Apr 26, 2010
    Messages:
    133
    Likes Received:
    57
    Location:
    Oregon
    Cris, all of your online documentation for your products recommends use of the Schurter switches!!! Perhaps that needs updating?
     
  9. Feb 10, 2020 #519

    Frederocket

    Frederocket

    Frederocket

    Well-Known Member

    Joined:
    Jul 31, 2011
    Messages:
    418
    Likes Received:
    55
    Gender:
    Male
    Location:
    Maryland
    How you can activate a screw switch inadvertently is beyond me, unless an individual fails to unscrew the screw enough. If someone fails to understand that, maybe they should just remove the screw... That's not even rocket science...:dontknow:
     
    Last edited: Feb 10, 2020
  10. Feb 10, 2020 #520

    SDramstad

    SDramstad

    SDramstad

    Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    401
    Likes Received:
    174
    The problem with screw switches is the nut the screw goes into. If its just a standard nut the screw can turn when vibrated. I have found, sorry dont remember where, a screw switch with either an o-ring or a nylon insert that would resist the screw turning enough that vibration wouldnt do any thing to it.
     
    GalantVR41062 likes this.
  11. Feb 10, 2020 #521

    Adrian A

    Adrian A

    Adrian A

    Sponsor TRF Sponsor TRF Lifetime Supporter

    Joined:
    Jan 22, 2009
    Messages:
    2,258
    Likes Received:
    230
    For the switch to be turned on or off, the magnet needs to be within about 1 inch of the sensor when using a small rare-earth magnet, and within about 2 inches of a magnet that is large enough and strong enough to risk injury if you hold it around steel objects. There aren't any sources that can cause magnetic fields strong enough to change the switch state at long range, because of the nature of magnetic fields. Unlike radiation, heat, light, etc, in which the field strength drops as the square of the distance, magnetic field strength drops as the cube of the distance. So to get a foot of activation range I would need a magnet that has 1728 times the field strength of the standard magnet that comes in the kit that has the 1" range. Bottom line is the risk of an inadvertent activation is about the same as having a "remove before flight" lanyard get pulled out accidentally, and less than the risk of having a screw switch screw back in/out during the vibration of transport. Every power switch or disconnection method has some risk of going into the wrong state, whether it's a screw switch, twist-and-tuck, or unplugging a 9V battery connector, which can flop around and make contact again if a user doesn't specifically prevent that. Lots of field evidence, by hundreds of users over time, has shown that the risk of inadvertant activation of the magnetic switches is low enough to be a non-issue.
     
    GlueckAuf and Nytrunner like this.
  12. Feb 10, 2020 #522

    Frederocket

    Frederocket

    Frederocket

    Well-Known Member

    Joined:
    Jul 31, 2011
    Messages:
    418
    Likes Received:
    55
    Gender:
    Male
    Location:
    Maryland
    I guess by your answer, you are 100% sure? What's your take on wireless?
     
  13. Feb 10, 2020 #523

    KilroySmith

    KilroySmith

    KilroySmith

    Well-Known Member

    Joined:
    Oct 29, 2015
    Messages:
    93
    Likes Received:
    26
    As a working product development engineer (but sadly, alas, not in rocketry), I buy Adrian's argument. It comes down to: Two separate, independent devices (the switch, and the altimeter) must both fail at the same time to cause an inadvertent firing. That seems like a reasonable safety bar to set

    With his description of the magnetic field strength necessary to turn on, it seems unlikely that an accidental firing could occur, even in a rocket being transported next to some of the magnetic latch/nosecone releases being discussed in other threads, although that should be considered - people do strange things on rockets.

    So, the question becomes, is Eggtimer's Dual-pole switch arrangement safe enough? It seems like there are still a number of single point of failures there, but maybe that's OK. The Featherweight Magnetic switch seems to be at a higher level - there aren't any obvious single points of failure in a system using it.
     
  14. Feb 10, 2020 #524

    Speaknoevil

    Speaknoevil

    Speaknoevil

    Well-Known Member

    Joined:
    Mar 18, 2018
    Messages:
    805
    Likes Received:
    319
    I appreciate the comment and this community heard your warning shout loud-and-clear a couple years back, but I believe the conclusion is overstated. Face it, any switch of any kind can be ruined by improper use, such as in this case, over-rotation beyond the obvious physical stop point built into the housing. You claim cheap, but a real Schurter rotary switch is in the $6 to $7 range (not the dozens of fake Schurter switches from China--hint: if you have one that's easy to turn, it's a knockoff). They are also UL and VDE approved for industrial use and have high ratings for vibration (think things like countertop mixers and air compressors). Are they "not fit for rocketry"? The big negative in the specification is low number of cycles at 300 (https://us.schurter.com/en/datasheet/typ_SWA1__Frontpl_.pdf). Granted, this may be a concern for some rocketeers and, if so, they should not use them. I can say though, with the number of rockets I have in my fleet and my flying frequency, I would not hit 300 cycles on any rocket over the next three decades (after I'm long dead).
    Annotation 2020-02-10 110220.jpg
     
    Last edited: Feb 10, 2020
    pondman likes this.
  15. Feb 10, 2020 #525

    JimJarvis50

    JimJarvis50

    JimJarvis50

    Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    2,316
    Likes Received:
    487
    All screw switches are not the same. Some are subject to vibration and can become loose or even go missing. Others are tight and not subject to this problem.

    Jim
     
    GrouchoDuke likes this.
  16. Feb 10, 2020 #526

    cerving

    cerving

    cerving

    Owner, Eggtimer Rocketry TRF Sponsor TRF Supporter

    Joined:
    Feb 3, 2012
    Messages:
    3,466
    Likes Received:
    712
    The original Eggtimer docs do. Yes, I'm going to remove that recommendation.

    The issue with screw switches is that sometimes the screw is a bit loose, and can wiggle out. Using good quality hardware should fix that issue.
     
    Frederocket likes this.
  17. Feb 10, 2020 #527

    Speaknoevil

    Speaknoevil

    Speaknoevil

    Well-Known Member

    Joined:
    Mar 18, 2018
    Messages:
    805
    Likes Received:
    319
    I have had an in-flight screw switch failure. I now use VC-3 Vibratite on all the screws. Unlike normal threadlock it is not an adhesive which has to be applied before insertion, it is a resin that dampens vibrations and won't let the screw back out/in. It is pre-applied on the screw for use up to 5 or 6 times. See: https://www.vibra-tite.com/threadlo...ble-threadlockers/vibra-tite-vc-3-threadmate/.
     
    Frederocket likes this.
  18. Feb 10, 2020 #528

    Frederocket

    Frederocket

    Frederocket

    Well-Known Member

    Joined:
    Jul 31, 2011
    Messages:
    418
    Likes Received:
    55
    Gender:
    Male
    Location:
    Maryland
    Easy fix: Dremel a slot in the screw and fill the slot with silicon sealant. There will be just enough resistance from the silicon to prevent vibration movement. DAllen mentioned using a longer screw; that will also help.

    I have used several of the different screw switches available and a few I made myself. Maybe I have just been lucky, but I just have not experienced problems and am not aware of any experienced by those I launch with or with any TRA L-3 flyers I have TAP'ed. Like I said, maybe I have just been lucky.
     
    Last edited: Feb 10, 2020
  19. Feb 10, 2020 #529

    KilroySmith

    KilroySmith

    KilroySmith

    Well-Known Member

    Joined:
    Oct 29, 2015
    Messages:
    93
    Likes Received:
    26
    Well, you didn't ask me, but I'll give you my opinion anyway.

    A well-designed wireless link can be as robust and safe as anything. Unfortunately, it's easy to build a poor wireless link that isn't. Anyone who played with X-10 (not wireless, but susceptible to the same problems) knows what I'm talking about, or anyone who has a cheap wireless light or fan switch knows. Chris Erving seems to have a good handle on what's necessary; there are multiple built-in acknowledgements and message verifications in e.g. the Proton wireless protocol that should make it dead-nuts reliable. A random rocketeer who designs-in a random RF module and sends single byte commands wirelessly, on the other hand, may end up without a hand.

    Perhaps the best thing that Tripoli and/or NAR could do would be to publish some tech reports discussing the kinds of issues and resolutions brought up in this thread. At that point, they're not telling anyone what to do - simply publishing "best practices" information.
     
    warnerr likes this.
  20. Feb 10, 2020 #530

    KilroySmith

    KilroySmith

    KilroySmith

    Well-Known Member

    Joined:
    Oct 29, 2015
    Messages:
    93
    Likes Received:
    26
    What I'd like to see is someone come up with a screw switch that uses a captive/built-in nyloc nut to prevent vibrational rotation. The Fingertech screw switch is good; something built in to prevent the screw from rotating with vibration would make it great. Nyloc's start to lose their grip after a few uses, but even after 20 or 30 uses they seem to have enough grip to prevent vibrational rotation (remember, they're designed to stop vibrational rotation on a torqued down fastener...).
     
  21. Feb 10, 2020 #531

    Speaknoevil

    Speaknoevil

    Speaknoevil

    Well-Known Member

    Joined:
    Mar 18, 2018
    Messages:
    805
    Likes Received:
    319
    I don't use Fingertech switches. The screw switches I use are purchased from rocketry vendors, Missileworks or Featherweight. The in-flight failure was a rough apogee deployment were the separated airframes hit together and power was lost to one leg of the redundant avionics.
     
  22. Feb 10, 2020 #532

    manixFan

    manixFan

    manixFan

    Not a rocket scientist

    Joined:
    Feb 15, 2009
    Messages:
    1,512
    Likes Received:
    530
    Gender:
    Male
    Location:
    TX
    You clearly don't have an understanding of how screw switches are typically used, or you would not have made that suggestion. they are often not mounted flush, but are mounted to the same board as the altimeter. So there is no way to remove the screw without completely changing the way the board is designed. And some screw switches use captive screws so they can't be removed, are those still allowed?

    You seem unwilling to admit that screw switches can and have failed on many occasions. If you don't want to believe that, that is up to you. Use all the cute sayings and emojis you want, but you are not addressing the issue. Not all screw switches are equally safe, nor are they equally safe in practice. Yet, in spite of that, with no qualifications, they are deemed safer than the electronic alternatives.


    Tony
     
    GlueckAuf and Charles_McG like this.
  23. Feb 10, 2020 #533

    Charles_McG

    Charles_McG

    Charles_McG

    Ciderwright

    Joined:
    Sep 12, 2013
    Messages:
    2,413
    Likes Received:
    505
    Location:
    SE Wisconsin
    Good safe switch use. And safety glasses, even.

    IMG_1488.jpg

    (Copied from the TRA Facebook group).
     
  24. Feb 10, 2020 #534

    boatgeek

    boatgeek

    boatgeek

    Well-Known Member

    Joined:
    Dec 27, 2014
    Messages:
    2,204
    Likes Received:
    652
    Really lousy safe ladder use though. Get thee two steps down! :)

    I really like the idea of a joint NAR/TRA committee on what "inhibit" means, safe switch use, etc. I'd be glad to join if it would be helpful (aka post a call for volunteers on TRF in addition to other channels).

    One thing that bothers me slightly about using the 2-stage Q motor CATO as an exemplar of why we need the switching is that (IMHO) switching wasn't the real issue. A much bigger issue was that the sustainer ignition electronics were armed while the rocket was still being assembled and was horizontal on the pad. And there wasn't a tilt/velocity lockout on the staging timer. I'll step two rungs down off my soapbox now. :)
     
    Charles_McG and Frederocket like this.
  25. Feb 10, 2020 #535

    Frederocket

    Frederocket

    Frederocket

    Well-Known Member

    Joined:
    Jul 31, 2011
    Messages:
    418
    Likes Received:
    55
    Gender:
    Male
    Location:
    Maryland
    You don't know me do you? With my experience level, saying I don't have an understanding is insulting and a false statement. That being said; I mount screw switches to the switch ban or directly through the surface if no switch ban. I don't mount screw switches to to an internal board. Typical or not for you, it is for me. As for as captive screws go, that's a good thing, as backing out the screw to the point of resistance is a good indicator the screw is no longer able to make a circuit connection without screwing it back in. However, I agree, not all screw switches are equally safe, but the ones I have purchased from Missleworks and Adrian seem to be of good quality and the ones I have made darn sure are. I have experienced no failures with those mentioned, nor no one I know has either, at least failures that was a switch fault.
     
  26. Feb 10, 2020 #536

    jbr

    jbr

    jbr

    Well-Known Member

    Joined:
    Nov 22, 2017
    Messages:
    309
    Likes Received:
    126
    so Fred, what did you do to the missileworks screw switches to make them have resistance both on screwing and unscrewing so they don't vibrate closed?
    all the ones I have have a loose fit and the screw can vibrate closed, and I have used 5/8" screws instead of the really short ones that come with it
     
  27. Feb 10, 2020 #537

    manixFan

    manixFan

    manixFan

    Not a rocket scientist

    Joined:
    Feb 15, 2009
    Messages:
    1,512
    Likes Received:
    530
    Gender:
    Male
    Location:
    TX
    Thank you, that's all I was looking for. Would you agree that some screw switches are less safe than a magnetic switch? Or do you feel that all screw switches are safer than the magnetic switch in question?


    Tony
     
  28. Feb 10, 2020 #538

    gavel

    gavel

    gavel

    Member

    Joined:
    Sep 24, 2017
    Messages:
    8
    Likes Received:
    5
    ...and based on the responses to this thread the same appears true for Eggtimer products yet they are now verboten.
     
  29. Feb 10, 2020 #539

    jbr

    jbr

    jbr

    Well-Known Member

    Joined:
    Nov 22, 2017
    Messages:
    309
    Likes Received:
    126
    so what it appears is that an eggtimer wifi switch used to enable the power to an eggtimer proton or quantum is approved

    and these would be separate devices
     
  30. Feb 10, 2020 #540

    cerving

    cerving

    cerving

    Owner, Eggtimer Rocketry TRF Sponsor TRF Supporter

    Joined:
    Feb 3, 2012
    Messages:
    3,466
    Likes Received:
    712
    I hope I'm "established" enough to be in on the call...
     
    g.pitts and GrouchoDuke like this.

Share This Page

Group Builder