Revision to Tripoli Rule Regarding Wireless Remote Switches

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FredA

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Don't count on it. NAR used to make you put six switches on a L3 rocket... one on each altimeter's power, and one on each charge
One 4PDT for the charges and a second switch for power.
Only poor switch selection turns this into 6 switches.
 

StanO

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Since relays have been mentioned I thought someone might be interested in a high dollar MIL-SPEC relay (rated for high vibration and shock environments) at BGMicro. $1.50 each today which is way less than the original price.

I love that the BGMicro relay has SPECIAL FEATURES FAILURE RATE 3.0 PCT. Of course my rocket failure rate is higher so using them would be an improvement.o_O

StanO
 

FredA

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I agree one 5PDT.
I like to have power and pyro's on separate switches.
Plus that usually also means I'll have multiple poles for switching power as I often just use another 4PDT switch for that - so two sets of poles for altimeter power and 2 sets for tracking power.
 

Steve Shannon

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I agree one 5PDT.
I like to have power and pyro's on separate switches.
Plus that usually also means I'll have multiple poles for switching power as I often just use another 4PDT switch for that - so two sets of poles for altimeter power and 2 sets for tracking power.
Yeah, I was joking. I wouldn’t want a single point of failure like that.
 

boatgeek

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This is where we start a giant argument about how unsafe that switch would be because it's a toggle and would clearly disintegrate into component atoms or at least bounce under thrust and therefore you're a monster who wants everyone to die in a lawn darts, right? Or was that around Post #100 in this thread? :rolleyes:

Thanks for the pointers that this was a "should" statement and not a "shall" from NAR. I'll also point out that between TRA's present "shall" and NAR's "should", most clubs are probably going to say yes to switch requirements.
 

FredA

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Doesn't that make the switch a single point of failure? Just sayin'...
Yep - one of many in the rocket - but very low probability of failure as used so one might say "it's the least of my worries."

RISK MANAGEMENT
 
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rcktnut

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Thanks for the pointers that this was a "should" statement and not a "shall" from NAR. I'll also point out that between TRA's present "shall" and NAR's "should", most clubs are probably going to say yes to switch requirements.

This is mentioned before the "should," so should the "should" be a shall instead of a should?:

National Fire Protection Association (NFPA) 1127, Code for High Power Rocketry, requires that the function of firing circuits and onboard energetics be inhibited until the high power rocket is in the launching position and prior to removing the high power rocket from that position. When this wording was proposed, it was assumed that "inhibiting" the function of firing circuits and onboard energetics meant physically "breaking" circuits, e.g. with a mechanical switch or disconnected battery or energetic device.
 

boatgeek

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This is mentioned before the "should," so should the "should" be a shall instead of a should?:

National Fire Protection Association (NFPA) 1127, Code for High Power Rocketry, requires that the function of firing circuits and onboard energetics be inhibited until the high power rocket is in the launching position and prior to removing the high power rocket from that position. When this wording was proposed, it was assumed that "inhibiting" the function of firing circuits and onboard energetics meant physically "breaking" circuits, e.g. with a mechanical switch or disconnected battery or energetic device.
The real question is how much should should a should-chuck chuck if a should-chuck shall chuck should? :D

But seriously, I think that paragraph really gets to the heart of the issue. Back when the rule was written, the only way to inhibit was to physically break the circuit with some kind of switch. Technology has advanced, and it's not clear whether new technology meets the requirements. I'll 100% agree that the original intent was circuit-opening mechanical switches. But that doesn't mean that electronic devices wouldn't serve the same function just as safely.

In a similar vein, there have been a few Supreme Court cases recently that turned on what the Founding Fathers would have thought about cell phones and data privacy.
 

gavel

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Yep - one of many in the rocket - but very low probability of failure as used so one might say "it's the least of my worries."

RISK MANAGEMENT
The same can be said of the Eggtimer Quantum and Proton as it was used before TRA's new rule....very low probability of failure as used so one might say "it's the least of my worries."

RISK MANAGEMENT
 

Eric

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I still don't understand how the BoD can redefine the meaning of inhibit that then puts us in violation of NFPA. If a Quantum, Proton or magnetic switch does not inhibit energetics in Tripoli BoD's eyes, then their post inspection prep table is a load of BS.

I have said this here before, and Steve has yet to comment on it.

NFPA 1127 says inhibited until vertical in launch position. So powering up these said devices at some table, violates NFPA.

Steve Shannon, why are we allowed to have uninhibited energetics prior to being on the pad?
 

Steve Shannon

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I don't think a complicated failure analysis is necessary to determine if MOSFET/FET switching technology is a safe "off" mechanism for altimeters. Here is a resource that helps engineers understand basic MOSFET failure modes and perform basic reliability estimates an-976.pdf "Understanding and Using Power MOFSFET reliability data". Aside from manufacturing defects which would cause a failure in a very short time, MOSFET failures are largely driven by switching on/off cycles, overheating, and over voltage. A properly designed circuit and appropriately chosen component can mitigate these along with burn-in testing.

The article uses has an example with a target failure rate of 11.4 in 10^9 hours of operation. Come on, a rocket altimeter may at most be switched on/off a few thousand times and operated for a 1000 hours. We are talking about extremely low failure rates for these devices in properly designed circuits.

Outside of the cockpit, do we see mechanical switches in spacecraft, avionics, and automobiles in 2021? I suspect the answer is no. Granted these safety critical applications perform FEMA and use rigorous process for mechanical, electrical and software design. I am not advocating that we do that for the hobby. But they don't have a loophole on special circuits either. Yes, they may use hardened semiconductors. But I think the answer we are trying to drive toward is "how much is enough" and can a vendor demonstrate they meet the "enough" for solid state switches.

So take a look at the article, vendors and BOD. I think a few calculations from this article would go a long way in giving us confidence in an answer. Maybe vendors can get an qualified engineer to review their circuit designs (and respecting NDA and proprietary information). Code review. Probably not ... system behavior can be witnessed by demonstration. Again, we are not safety experts, nor do we particularly need to be, aside from a few basics. But we do have a lot of very talented engineers in this forum. Let's put our heads and collective wisdom together and work toward an answer.
Good article. Thanks.
 

Steve Shannon

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I still don't understand how the BoD can redefine the meaning of inhibit that then puts us in violation of NFPA. If a Quantum, Proton or magnetic switch does not inhibit energetics in Tripoli BoD's eyes, then their post inspection prep table is a load of BS.

I have said this here before, and Steve has yet to comment on it.

NFPA 1127 says inhibited until vertical in launch position. So powering up these said devices at some table, violates NFPA.

Steve Shannon, why are we allowed to have uninhibited energetics prior to being on the pad?
Eric,
I'm sorry if you feel that I neglected to answer your question earlier. I thought some of my other responses to people explained it, but I'll try to answer you more directly now.
There are different levels of being inhibited based on the number of people that could be injured and the possibility of a failure. This concept is reflected in the military and NASA documents where either two or three "Independent Inhibits" are required based on the probability of injury and the likelihood of death. An arming circuit failure that is likely to cause an injury must have two Inhibits, such as two switches in series. That makes it fault tolerant. I.E. there's no single point of failure that can result in the energetic charge igniting.
When an arming circuit failure is likely to cause a fatality, three independent inhibits are required.
From that example I hope you can see that there are different levels of "being inhibited".

Using similar logic, the board and I feel that the level of "inhibition" represented by an appropriate mechanical disconnection is appropriate for nearly any situation, such as when surrounded by spectators, in a crowd waiting to enter the range, or at a table with three or four other flyers and Rocket Inspectors. The idea is that this method is more difficult to accidentally overcome. This would be similar in concept to the example above that requires three independent inhibits.
Then there's a lesser level of being inhibited that may not be suitable when surrounded by other people, but allows the flyer, on the range and working alone or with a minimal crew, to work safer in other ways, such as not having to climb a ladder or being at a greater distance when turning on the power to an altimeter or staging device.
So, in both cases the firing circuits are inhibited but at levels that are appropriate for the surroundings. That keeps us compliant with NFPA 1127 and hopefully adds to safety.
I hope that helps.
Steve
 

grouch

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I had two screw switches on a dual deploy rocket, one for the conventional altimeter, and one for the deployment charges. At the field, I loaded my rocket in the trunk of my car to move it a short distance on a gravel road. The screws were unscrewed several turns (to be off). I was surprised to hear my altimeter beeping when I parked the car, the altimeter screw had vibrated and rotated enough to turn on. Fortunately, the altimeter did not launch detect, and my deployment screw was still off. But now I remove the screws completely. I subjectively feel like my disarmed Proton would have been safer. It was part of my motivation to switch to a Proton.
I had this happen also. I prepped a rocket for a flight I decided to postpone. I had it all ready to go minus the charges. I am not sure why I made that decision but I did. As I was driving back home, I had to climb a moderately large hill. I heard the apogee match pop and startled me half to death. The screw switch vibrated closed and the altimeter started amred on the drive back. Driving a loud truck with mud tires, I never heard the altimeter beep. This could have been very bad had I prepped the deployment charges. When ever I travel with a DD rocket now, I make sure the battery is physically disconnected. I also stopped using screw switches.
 

Steve Shannon

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I had this happen also. I prepped a rocket for a flight I decided to postpone. I had it all ready to go minus the charges. I am not sure why I made that decision but I did. As I was driving back home, I had to climb a moderately large hill. I heard the apogee match pop and startled me half to death. The screw switch vibrated closed and the altimeter started amred on the drive back. Driving a loud truck with mud tires, I never heard the altimeter beep. This could have been very bad had I prepped the deployment charges. When ever I travel with a DD rocket now, I make sure the battery is physically disconnected. I also stopped using screw switches.
This is an excellent example that illustrates the need to share anecdotal knowledge so people can learn what kind of switches are appropriate.
 

Pariah Zero

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Aside from manufacturing defects which would cause a failure in a very short time, MOSFET failures are largely driven by switching on/off cycles, overheating, and over voltage.
MOSFETs are insanely reliable in:
• Well designed circuits, protecting MOSFET gates at all external connections
• Constructed with ESD safe processes
• Shielded in ESD safe enclosures (usually conductive, grounded to the chassis)
• Properly cooled

All of the above are true in an airliner’s flight control systems. They even have little wires trailing off of flight surfaces to discharge the static electricity generated by moving through the air.

If you don’t do all of that, then life can be much shorter.

The elephant in the room being ESD (static electricity); simply touching a wire with your finger (while connecting an ematch, battery, etc.) can potentially result in 20 kV - 50 kV worth of ESD overvoltage. That’ll fry nearly any MOSFET in nanoseconds. Most of the time, though, it’s much less voltage, which still damages & shortens the transistor’s life. Even ESD too small to feel builds damage leading to failure.

One common failure mode of a MOSFET damaged by ESD is to a “short” (permanently on) state.

Note: I have not looked at schematics for any of the commercial products discussed in this thread... ways to protect the MOSFET do exist - with the trade off of a bit more size & weight.

But the point is: not everybody buys somebody else’s design/kit. And if you roll your own, it’s not hard to abuse a MOSFET to the point of failure. I did it a few times in college as I learned.
 
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jbr

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I have also had this happen with a screw switch, but I never transport rockets with charges attached.

I've never, ever, had it happen with a magnetic switch.
you just need to make sure the screws are not loose in the nut, they should stay put under vibration, and this is one thing I need to fix on all my screws
 

Frederocket

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We can debate this issue until hell freezes over. However, the need for a properly installed complete mechanical switch disconnect, (between the power source and electronics/charges), is the only way to completely eliminate the possibility an inadvertent activation of a pyrotechnic electrical circuit by the power source. Magnetic and electronic switching, of any kind can not guarantee to 100% a conclusion to the same. Agree with me or not the facts are basic.
 

gavel

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We can debate this issue until hell freezes over. However, the need for a properly installed complete mechanical switch disconnect, (between the power source and electronics/charges), is the only way to completely eliminate the possibility an inadvertent activation of a pyrotechnic electrical circuit by the power source. Magnetic and electronic switching, of any kind can not guarantee to 100% a conclusion to the same. Agree with me or not the facts are basic.
Wrong. The only way to completely eliminate the possibility of an inadvertent activation is to not connect the battery. Mechanical switches can and do fail and cannot guarantee 100% elimination of an inadvertent activation. There are reports in this very thread of mechanical switches failing (for whatever reason). Agree with me or not...this is fact.
 

Frederocket

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you just need to make sure the screws are not loose in the nut, they should stay put under vibration, and this is one thing I need to fix on all my screws
Bingo... Might I suggest removing the screw as doing so will prevent two things due to vibration activation.
1. Save the battery during transport, to and from the launch site.
2. Prevent the inadvertent activation of the electronics and firing any installed e-matches, (no one travels with BP in their charges, :)-).

Use of some type of thread lock will also help, such as VC-3, as suggested in a previous post; "after purchasing VC-3, I really like the stuff".
 

Frederocket

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Wrong. The only way to completely eliminate the possibility of an inadvertent activation is to not connect the battery. Mechanical switches can and do fail and cannot guarantee 100% elimination of an inadvertent activation. There are reports in this very thread of mechanical switches failing (for whatever reason). Agree with me or not...this is fact.
"Properly installed being the key". Mechanical switches are manually controlled and magnetic/electronic switches are not. Agree with me or not, that's my position and no amount of engineering statistical data will change that fact.
 

jbr

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Bingo... Might I suggest removing the screw as doing so will prevent two things due to vibration activation.
1. Save the battery during transport, to and from the launch site.
2. Prevent the inadvertent activation of the electronics and firing any installed e-matches, (no one travels with BP in their charges, :)-).

Use of some type of thread lock will also help, such as VC-3, as suggested in a previous post; "after purchasing VC-3, I really like the stuff".

good whack with a hammer works also to tighten the thread connection and cause friction


plastic is an insulator
https://www.vibra-tite.com/threadlo...ble-threadlockers/vibra-tite-vc-3-threadmate/
 

gavel

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"Properly installed being the key". Mechanical switches are manually controlled and magnetic/electronic switches are not. Agree with me or not, that's my position and no amount of engineering statistical data will change that fact.
It doesn't appear the Navy would agree with you.

https://www.navsea.navy.mil/Home/Wa...ane/Resources/SD-18/Product-Archive/Switches/

"Unlike most other electrical parts, switches contain mechanical elements and are therefore subject to failure mechanisms associated with mechanical wear of the switching elements."

"Except for special high voltage and high temperature applications, solid-state switches are inherently more reliable and predictable for long life applications."​
 

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DaveW6DPS

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This is an excellent example that illustrates the need to share anecdotal knowledge so people can learn what kind of switches are appropriate.
This is a better example of why rockets should be MADE SAFE after an abort. There is no switch or device that I would trust as a single inhibit during transport.

You should never transport with any energetics, including ematches, and a power source installed.
 

mikec

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Might I suggest removing the screw as doing so will prevent two things due to vibration activation.
I like to assemble my bay at home, verify the wiring, and then attach charges at the launch site. With many of the screw switches I use, and the form factor of the rockets I use them in, removing the screw with the bay assembled is not practical. I agree that it would be nice that the screw not be loose, but it happens.

At any rate, this debate is largely pointless. The TRA BOD has said what they said and unless there is some kind of modification to their ruling, our only recourse is at the next election cycle. I certainly hope all of candidates make their position known on this.

The only way to insure 100% safety from rockets is to get out of the hobby. Anything short of that is reducing risk, but never to 0.
 
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