Revision to Tripoli Rule Regarding Wireless Remote Switches

cerving said:

Relays don't work very well in rocketry applications. Too much vibration and G forces.

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and by the same standards, there are switches and phono jacks that fall in the same category

My first post.I sent this letter to Cris Erving;

hi Cris,

Following the long discussion at the rocketry forum. this last Saturday at MDRA (Maryland). I have a 20 lb rocket with 2 Quantums. After discussion with RSO:

I prepped the rocket , connected the batteries and checked continuity with e-matches but no powder.
I put the rocket together and weighed in at the RSO table.
I then proceeded to an isolated table slightly inside the taped off flight line.
I pulled the rocket apart,put in the powder,put the rocket together,went to the launch rail and positioned the rocket.
Armed the quantums and off we went.
The quantums performed flawless...a nylon shock cord broke,but no damage to the rocket.

Takeaways:

This seems reasonable and was not too distracting.
I believe the TRA board is concerned about "Civilians" walking around and not the 'Rocketeers"
I understand that a 2 stage rocket may require a switch.

In general risk can only be mitigated and not eliminated.

Your Thoughts,

Lou Spikol

Louis: Thanks for the feedback. Depending on your club's layout, "slightly inside the taped off flight line" may not be far enough away from other people. Lots of clubs have LPR pads only a few yards away from the LCO table.

Steve Shannon said:

I hope that our meetings with the manufacturers will lead to something better defined than simply saying a physical break. We have to consider hardware, software/firmware, and how the devices operate in the absence of power, following a shutdown and restart, both intended and unintended. It doesn’t help that every device works a little or even a lot different.
And, yes, we understand that mischoosing or misusing a physical switch has its own problems also.

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I humbly suggest that software/firmware/construction concerns might be addressed by manufacturer specified user tests and the user self-certifies that they have performed them for cases where the device can't self-test. RSO pre-inspection / retest optional. (I always assume that the RSO/club may set a stricter policy.)

I also humbly request that the Board consider establishing a minimum threshold where the policy applies, perhaps in terms of LPR/HPR. Impulse. Total grams of pyro charge. Grams of biggest single pyro charge. Or some combination.

boatgeek said:

Not trying to add too much to your plate on this, but could you also address whether both legs of wires to an altimeter need switches in a mechanical switch arrangement? The standard-ish arrangement with one leg connected to the ematches with the other leg switched by the alt has always given me a few heebie-jeebies.

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When I put a switch in the pair of wires going to the ematch, I like to use a DPDT switch configured to connect the ematch legs together whenever they aren’t connected to the altimeter.

The club set up the table-I went where they told me.(It seemed safe for everybody except me)

Perhaps I am off-base but we are acting as if altimeters and switches (and even e-matches) are the main issue,when it is the Gun Powder that is the concern.If this is the case,then perhaps ALL loading of gun powder should be done at an isolated spot,where the risk is rightly assumed by the TRA members and not the "civilians"

here is a triple

John Williams said:

Okay but to that point then I could use a mag switch with an electromechanical relay wired into it?

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Sure but that defeats the purpose in a small rocket where room is at a premium. I think it's stupid to outlaw the mag switch for a deployment altimeter. It's simple, attach battery without charges, shut off the mag switch, put contained
ematches on the output terminals and if they don't "pop" there is no juice there. Off course the thing if "OFF"! Put in real charges, take rocket to the pad, swipe with a magnet, await the altimeter to cycle and give the "go ahead" beep and fly.
The only thing I think is prudent is to have a mechanical switch on a device that controls the ignition of an upper stage. It can be a wireless device too but the switch is a concession to avoid a ground ignition of a motor. Kurt

triple with fuses

lspikol said:

Perhaps I am off-base but we are acting as if altimeters and switches (and even e-matches) are the main issue,when it is the Gun Powder that is the concern.If this is the case,then perhaps ALL loading of gun powder should be done at an isolated spot,where the risk is rightly assumed by the TRA members and not the "civilians"

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Maybe, but for sure you want to do it with the battery disconnected... regardless of what switch you use.

Charles_McG said:

I humbly suggest that software/firmware/construction concerns might be addressed by manufacturer specified user tests and the user self-certifies that they have performed them for cases where the device can't self-test. RSO pre-inspection / retest optional. (I always assume that the RSO/club may set a stricter policy.)

I also humbly request that the Board consider establishing a minimum threshold where the policy applies, perhaps in terms of LPR/HPR. Impulse. Total grams of pyro charge. Grams of biggest single pyro charge. Or some combination.

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Those are good suggestions that are very similar to my concerns.

1/2 gram of powder behind a 29mm nose cone will do a lot of damage if it hit someone.

SDramstad said:

1/2 gram of powder behind a 29mm nose cone will do a lot of damage if it hit someone.

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And I've accidentally plugged a battery straight to a charge (double thunk my connector keying and talking myself into doing it backwards) and puffed dog barf onto the dining room floor. Startling. Embarrassing. Annoying to clean up. A Near Miss that is certainly time to review what you're doing with your life and Not To Be Taken Lightly.

But Life Critical?

???

I suppose it's a delivered energy kinda question that a lowest common denominator rule addresses - but poorly at the limits.

The Scout leader that suffered a fatal injury at a non-TRA/NAR outing a few years ago was hit with a LPR on a 29mm motor. mv is a big number when v is big.

davdue said:

However what if those MosFETs have gotten a static charge and have failed closed or whatever the cause is. Now you are down to a single point failure with no idea that it has happened.

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While the TRA Board huddles with manufacturers and devise either a smarter policy, or a more satisfying / better communicated justification for the current policy, this topic lingers on my mind. I've seen it over the years, and I don't know if I buy it. But I'm a lowly biochemist - I question the definition that electricity is the flow of positive charge because I know protons won't fit down wires (darn it). Anecdotes and hand-wave explanations litter the forum. FETS dying at the end of the last use and being discovered failed close on next powerup - okay, I buy that. Static charge and / or power on transients allowing enough energy through the gate (wrong word probably) to light an ematch: Is that -really- a thing? Known and documented in the technical literature that I don't read because my nose buried in a different journal, trying to figure out the origin of 4-ethylguaicol from a substrate without known feruloylquinic acid.

Or is it a factoid? A plausible explanation of behavior where root cause analysis is too hard, or impossible. Accepted and propagated with little review. (Both my industries have plenty of their share.)

Inquiring mind and all...

cerving said:

The Scout leader that suffered a fatal injury at a non-TRA/NAR outing a few years ago was hit with a LPR on a 29mm motor. mv is a big number when v is big.

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Tragically failed recovery. Gravity supplying the F in F=ma.

cerving said:

The Scout leader that suffered a fatal injury at a non-TRA/NAR outing a few years ago was hit with a LPR on a 29mm motor. mv is a big number when v is big.

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And if the answer is 'we understand that there are cases that seem mostly harmless, but it's too hard to write a general rule. Please consult with your RSO.', I can accept that.
@Steve Shannon

Since I like small, complicated rockets, I look at a rule that makes perfect sense for a 12" rocket with 20# of concrete in the nosecone, and wonder if it isn't a bit overkill for my rocket.

cerving said:

Playing devil's advocate again... why is power allowed to be connected to the launch control panel and/or pad boxes while flyers are loading? Particularly for the pad boxes (some of which may be wireless), there is only one "inhibit" in the loop... the device (relay or FET) that powers the igniter. And, they generally are allowed to have a continuity trickle current to the igniters.

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Although a single mechanical switch (i.e., the relay contact) isolates the igniter, the activation circuit to that relay, at least in every controller I have seen, has at least two mechanical inhibits, typically a key switch and a push button. I would think dual inhibits in control of the relay would meet the overall safety intent.

Diagram courtesy of: https://www.yrex.com

Not necessarily true for all units. Some launch systems have processors (or wireless) and send a signal to the pad box to "fire channel 6". They don't directly connect to the relay coils from the control box.

Most launch systems dont use software or electronic switches, once the key (in most cases a mechanically switched key is removed the power has no path to the igniter) and the launch button is a normally open mechanical switch as well.

Besides launch systems are not the subject of this thread.

cerving said:

Not necessarily true for all units. Some launch systems have processors (or wireless) and send a signal to the pad box to "fire channel 6". They don't directly connect to the relay coils from the control box.

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And those wireless units have remote continuity testing that -I think- necessitates a continuity circuit other than the push button on the pad box.

cerving said:

Not necessarily true for all units. Some launch systems have processors (or wireless) and send a signal to the pad box to "fire channel 6". They don't directly connect to the relay coils from the control box.

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Well, maybe RocketRev should chime in here as his wired and wireless systems are probably the most widely deployed (at least in the U. S.) for high power launches. I cannot believe he would design a launch system as you describe above.

rharshberger said:

Most launch systems dont use software or electronic switches, once the key (in most cases a mechanically switched key is removed the power has no path to the igniter) and the launch button is a normally open mechanical switch as well.

Besides launch systems are not the subject of this thread.

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"Most" is not "All". There are "some" electronically-triggered systems that do not have a mechanical switch at the pad box, and therefore do not completely disconnect power to the leads.

And you are correct, launch systems are not the subject of this thread. The point was that not all energetic triggering systems that we use have a mechanical disconnect from power prior to connecting the igniter.

cerving said:

"Most" is not "All". There are "some" electronically-triggered systems that do not have a mechanical switch at the pad box, and therefore do not completely disconnect power to the leads.

And you are correct, launch systems are not the subject of this thread. The point was that not all energetic triggering systems that we use have a mechanical disconnect from power prior to connecting the igniter.

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Hence the reason I did not use "All".

almost any rocket without deployment can cause major damage
ask Ross Dunton about the estes alpha that went thru his front window, thru the radio and stuck into the floorboard
had this hit a person instead.......................................

cerving said:

"Most" is not "All". There are "some" electronically-triggered systems that do not have a mechanical switch at the pad box, and therefore do not completely disconnect power to the leads.

And you are correct, launch systems are not the subject of this thread. The point was that not all energetic triggering systems that we use have a mechanical disconnect from power prior to connecting the igniter.

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But the launch controller is; before you connect the leads to the igniter, it is as mechanically disconnected as you can get. And at that point it’s supposed to be on the pad in launch position which is completely compliant:

4.13.7 The function of firing circuits and onboard energetics shall be inhibited until the high power rocket is in the launching position.
.

Steve Shannon said:

But the launch controller is; before you connect the leads to the igniter, it is as mechanically disconnected as you can get. And at that point it’s supposed to be on the pad in launch position which is completely compliant:

4.13.7 The function of firing circuits and onboard energetics shall be inhibited until the high power rocket is in the launching position.
.

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I would like to add that if a controller is going to be used at a club launch, either the maker needs to certify it for low current igniters or a user needs to ground test it out in the open with a low current igniter to be certain the igniter doesn't fire on a continuity test. Kurt

Steve Shannon said:

But the launch controller is; before you connect the leads to the igniter, it is as mechanically disconnected as you can get. And at that point it’s supposed to be on the pad in launch position which is completely compliant:

4.13.7 The function of firing circuits and onboard energetics shall be inhibited until the high power rocket is in the launching position.
.

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My statement was that not all energetic triggering systems that we use have a mechanical disconnect from power prior to connecting the igniter. If the pad box does not have the battery disconnected or the power to the pad box is not physically shut off prior to loading, this is a correct statement. The igniter may be physically disconnected when you're loading, but once you connect it to the leads there might only be the switching circuitry coming between you and an accidental firing. Fortunately this is a very rare event.

Not trying to stir things up, but it seems to me that the policy needs to be made a little more consistent.