Revision to Tripoli Rule Regarding Wireless Remote Switches

[Steve Shannon]

Nothing in that thread answers my question, your reply is in fact that’s why I asked this question. In that thread you mention "The references include NFPA 1126, which covers the “Standard for the Use of Pyrotechnics Before a Proximate Audience” and NFPA 495, which is entitled “Explosive Materials Code”.

If model rockets are not fireworks, and they are certainly not explosives, was there an affirmative decision to use those codes to regulate our hobby? Or are you saying that because they are largely the same committees that it follows that those rules should be applied to our hobby? Does the board see our ejection charges as being equivalent to commercial fireworks?

I'm just trying to understand why after 20 years of flying HPR, I am just now learning that we should have assumed that rules that apply to commercial fireworks should also apply to us.


Tony

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.

 

[Speaknoevil]

With the exception of screw switches almost every switch I know of relies on spring components to keep the contacts in contact. Otherwise they’re very difficult to operate or susceptible to clattering. Obviously push buttons have a spring, but so do slide switches, rotary switches, even knife blade switches have spring contacts that grasp either side of the swinging blade.
Mercury switches don’t.
Fortunately, we can measure the force it takes to move a spring contact and the mass of the contact and then physics allows us to calculate how much acceleration will break the contact. Having two spring contacts allows one to follow the other to maintain contact.
NKK makes miniature slide switches (I think it’s the CS series) that are rated for 50 gees.

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.

 

[ghostfather]

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.

 

[FredA]

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?????

 

[Charles_McG]

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?????

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.

 

[Steve Shannon]

Switchcraft is a high quality switch. They even make a locking slide switch:

https://www.switchcraft.com/Product.aspx?ID=3296

 

[GlueckAuf]

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

 

[cwbullet]

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.

 

[warnerr]

I don’t think you’ll find one of these with four poles, but it would create a single point of failure for all four circuits anyway.
Here’s a Panasonic snap action switch that’s rated at 980 m/s^2

https://www.panasonic-electric-works.com/pew/eu/downloads/ds_asq_en.pdf

Those Panasonic switches will not carry the amperage required- they are rated for miliamps.

 

[Frederocket]

I'm not a Tripoli member, so not currently affected by this, but I expect that I will be through NAR. I'm nowhere near as experienced as most who've posted; I've certified to NAR Level II but haven't flown more than was required to do that. What strikes me most about this thread is not the vitriol, but the knowledge and wisdom that have been relayed - it may not be in the majority of the posts, but the thread (especially the questions asked and answered, and the questions asked and as-yet unanswered) should be required reading for any group that plans on touching this subject in the future.

Modern electronic devices can be remarkably robust and reliable when competently designed into a sealed and protected enclosure and operated within specified electrical, mechanical, and environmental limits. Hobby rocketry, as it's practiced at this time, doesn't meet most or all of these limitations, so I don't see how one could safely rely on them (and before you argue, please be sure to honestly tell me that you always handle your altimeter at an approved static-safe workstation using appropriate personnel procedures, that it never exceeds the vibration and G-loads spec'ed by the manufacturers of all the components used on it, and that it is always protected from mechanical, electrical, or environmental damage). The important thing to recognize when it comes to electronics is that "broken" doesn't mean "dead, inert, safe", it means "I don't know what it's going to do, could be anything from nothing to everything to going up in smoke, or perhaps combinations of all three". The problem comes in deciding how far down the rathole you want to go, how far you want to go to meet the "Must". An inline diode might be a great way to solve #2, for example; but a diode, as robust as it is, is still an electronic device subject to the previous paragraph.

I will say that it seems to me that a revision to safety codes that simply lays out what is expected out of ejection/airstart electronics is sufficient. There's no real need for TRA/NAR to get into the certification biz, the specification biz, or even the waiver of requirements as they did for the WiFi switch. A relatively small set of general requirements that the community can police should be sufficient; this thread can be distilled down to start such a list. Note that some of these will fall on equipment manufacturer shoulders, and some on the Rocketeer:
Electronics for energetics:
1. Must be designed to prevent accidental firing at power on (Mfg)
2. Must be designed to prevent accidental firing due to battery reversal (Mfg)
3. Must be designed to prevent accidental firing due to a tipped, dropped or transported rocket (Mfg, Rocketeer)
4. Must be capable of unpowered RSO inspection (Rocketeer)
- Silicon devices cannot be relied on as a means of rendering a rocket unpowered
- Magnetic devices cannot be relied on as a means of rendering a rocket unpowered
- A relay cannot be relied on as a means of rendering a rocket unpowered
5. Rocketeer SHOULD be capable of assembling and continuity testing prior to RSO inspection with (almost) NO danger of accidental firing

I think this is the beginnings of a list that is probably less than 10 items long; all it really needs to do is set out the expectations. Some of these expectations will be different than they have been in the past; some of what I've read in this thread has frankly shocked me.

I've been involved in other hobbies that had to go through wrenching changes in safety culture, due to the realization that what had been perfectly acceptable was killing people and needed to change. I don't think this needs to be as wrenching, but I do think that some well accepted building techniques are going to need to change. Some well-flown rockets are going to need major rework. But the overall changes aren't really that extensive.

This, in red, especially number 4 and subs are just plain fact... Some may not like it, but it is fact..

 

[warnerr]

I think the lever would be easier to move, but it's the same family.

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.

 

[KilroySmith]

As long as it is safe, let others use their own methods.

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.

 

[Speaknoevil]

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.

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.

 

[rharshberger]

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...

 

[Kelly]

Well, you've answered my question then. There was no ground testing, which would have quickly uncovered this error. Finding out a reverse-polarity mistake at the launch site - I just don't get that type of (non) thinking.

I've seen some cheap keyed JST connectors which can be connected in a reversed direction.

 

[Ez2cDave]

The other involved a Q motor in a sustainer that ignited, skidded horizontally a hundred feet and then catoed. When it ignited there were eight college students working on or near the rocket. Had the motor catoed immediately instead of skipping across the play I have no doubt we would have been dealing with fatalities.

Steve,

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

Dave F.

 

[jderimig]

I plan on checking it out for myself. The robot hobby people sure like it.

Robots are an order of magnitude more punishing on a switch than a rocket....FWIW

 

[KilroySmith]

I am concerned about internal switch bounce having brought one rocket in ballistic due to momentary disconnects .

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.

 

[Steve Shannon]

Those Panasonic switches will not carry the amperage required- they are rated for miliamps.

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

 

[cerving]

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.

^^^ This... ^^^

 

[Steve Shannon]

^^^ This... ^^^

Amen [emoji120]

 

[rharshberger]

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.

^^^ This... ^^^

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.

 

[Ez2cDave]

The other involved a Q motor in a sustainer that ignited, skidded horizontally a hundred feet and then catoed. When it ignited there were eight college students working on or near the rocket. Had the motor catoed immediately instead of skipping across the play I have no doubt we would have been dealing with fatalities.

Steve,

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

Dave F.

 

[manixFan]

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

 

[warnerr]

Switchcraft is a high quality switch. They even make a locking slide switch:

https://www.switchcraft.com/Product.aspx?ID=3296

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.

 

[davdue]

Since everyone is talking about switches now. Here is what I have used on all my rockets without Eggtimer stuff in them. Since it is mounted sideways to the vertical g-forces I don’t think it matters for any ratings. I like the bigger button so the hole in the airframe doesn’t have to be perfect.

https://www.radioshack.com/products/spdt-pushbutton-switch?variant=20332069253

 

[cwbullet]

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.

 

[John Kemker]

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.

This.

 

[Steve Shannon]

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

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.

 

[Rob702Martinez]

I’ll get right to the point.

The problem here is failure to recognize the Abilene Paradox.

It’s not a bunch of stuffy old geezers making up a rule because they fear technology. Stuffy old geezers are awesome. My Tripoli mentor is one ( sorry Gus) my dad is one, even the Eggtimer guy is one. Don’t feel bad Cris, anybody over 25 is old to me.

The TRA BOD is attempting to solve a problem that doesn’t exist by adding an additional failure point. (told 'ya I'd get right to the point)
The BOD is a small group of people. Very nice people, well intentioned people, but a small group. They lack the diversity inherent in a larger group. This is the key to the problem.

The BOD believes adding a mechanical disconnect increases safety, when it is a proven fact that added complexity increases the chance of failure. By their own admission they have no proof of failure. Think about this – Tripoli tests and certifies rocket motors and publishes the results. – What testing have you done regarding the failure of the wifi devices, and where are the published results?

One thing we have proof of – mechanical connections are subject to G-forces and other modes of failure. We already know as a proven fact ballistic recovery has occurred due to a failed mechanical connection or switch.

I am very much aware of the dangerous nature of our high-power rocketry activities and I happily agree with rules that help make things safer. Unfortunately, I believe this mechanical disconnect rule is a step backwards and has the potential to increases chance of failure and accidents.

I am a member – along with my entire family- of both TRA and NAR, and will continue to support both organizations fully. (I may not always agree with everything... but you have my unwavering support)

The only thing this rule will change for me – I will not be flying any wifi enabled rockets at the TRA launches I attend.

I’ll fly my most advanced (wifi enabled) rockets only at NAR launches.

- that's my stance and my belief, at least for now. Being a kid Rocket Scientist (key word "scientist") I am open to any evidence that proves otherwise.

... If you read this far, thanks for giving me my soapbox.

Probably the most reasonable respectful and understanding post about this.