Pull Pins Outlawed!

[fyrwrxz]

Just looked at the 2012 Tripoli Safety Code and saw this:
2-12.6 A rocket motor shall not be ignited by any of the following:
a. A switch that uses mercury.
b. “Pull wires” that disconnect or complete a circuit.
c. “Pressure roller” switches

I don't know if I've been getting away with this for long-is this new? I'm bummed because I have a Xavien 'Fist' and a bunch of pull pin sets from Programmin' Pete. Looks like g-switches and timers from now on. I support the Mercury switch elimination but I do like microswitches for some uses. Does this mean burn wires too?

[dixontj93060]

What is wrong with "pressure roller switches"??? Microswitch roller switches are some of the most durable/reliable you can find and have been in use for nearly 80 years in industry.

[dixontj93060]

Although looking at the document, that section may just be referring to the pad launch system versus what happens during staging and/or airstarts--don't know for sure?

[mikec]

Although looking at the document, that section may just be referring to the pad launch system versus what happens during staging and/or airstarts--don't know for sure?

I think the intent was for staging and airstarts, but the TRA safety code is quite vaguely written IMHO. It's also not obvious if a breakwire controlling a timer is forbidden or not -- after all, the breakwire doesn't ignite the motor, it just starts the timer. But my guess is that the intent was to outlaw breakwires entirely. Retrofitting a G-switch into a timer is pretty easy.

[JDcluster]

It has been heavily discussed on the TRA list server. Some people aren't too happy with it (to put it mildly).

JD

[ClayD]

What is wrong with "pressure roller switches"??? Microswitch roller switches are some of the most durable/reliable you can find and have been in use for nearly 80 years in industry.

because you cant fault protection program it. It's just not smart enough for rocketry!

[dixontj93060]

because you cant fault protection program it. It's just not smart enough for rocketry!

Sorry, I don't understand that statement. Redundancy resides outside any single switch, no matter its design.

[mikec]

What is wrong with "pressure roller switches"???

I think the concern is not the reliability of the switch itself, but that if the switch gets accidentally tripped on the pad, a motor being ignited. I'm not sure how such a switch would be used in this context in practice; perhaps as a launch detect?

[dixontj93060]

I think the concern is not the reliability of the switch itself, but that if the switch gets accidentally tripped on the pad, a motor being ignited. I'm not sure how such a switch would be used in this context in practice; perhaps as a launch detect?

No, actually I had it planned as an indicator / lock-out for the separation of a booster and sustainer. As the booster separated the roller switch would slide out and activate. Very (I will say VERY) common application for industrial control circuits; which BTW are, in many cases, more mission-critical than high-power rocketry applications.

Is anyone on the TRA Board an seasoned (like 30 years experience) Electrical Engineer???

[H_Rocket]

Is anyone on the TRA Board an seasoned (like 30 years experience) Electrical Engineer???

No, but some stayed in a Holiday Inn last night

I did not get the sense that a break wire was proscribed for a in flight event like staging or air-starts. just that you could not use it as an actual launch system.

However it would be nice if either national body could be a little less vague.

[ClayD]

Sorry, I don't understand that statement. Redundancy resides outside any single switch, no matter its design.

that is actualy what i meant by it. the code doesnt apply redundancy to cover a simple item such as a pressure switch.

IE. a baro sensor, that determines altitude, before the switch will fire an ignitor.

the premise of my statement is based, that everything in the dual redundancy checks, must be automatic and non user "goofable."
the average guy with a brake-wire or pressure roler, probably doesnt have a fault check between the device and the ignition sequence(timer) igniting the booster stage. like an altimeter.-something that requires the switch trigger-AND, a velocity or altitude, or both.

the premise that a proximity sensor, or accelerometer are
"presumed to be" far more reliable without moving parts, and thus safer.

the current "temperature" is that its cheap enough to purchase a safe staging device, than to allow amatures to cobble up radioshack parts and makesomething that no-one-knows how it will work.

I.e. Most guys that fly are not electrical engineers...

[JStitz]

I love Cherry switches! There were a couple cases where someone had to use their own close tolerance launch rod and forgot it. It rocked in the breeze and launched next to his face. The second case was the switch coming loose.
Now I forget what you have to use,A normally closed switch? meaning open while it's depressed?
Mercury switches Can't use that with ANY breeze.

G-switches solved that Mercury switch problem.They only activate after being "G"d for several seconds.In theory your rocket can go 10 feet off the launch rod and belly flop without tripping the switch.

[mikec]

No, actually I had it planned as an indicator / lock-out for the separation of a booster and sustainer.

Then the switch wouldn't be igniting a motor but inhibiting the ignition, and so would be allowed by my reading of the vague statement.

[Disaster_Guy]

Just to clarify, is this being applied to staging / airstarts only or is it also being applied to arming (ie: altimeter safety while on pad / remove before flight)?

As for mercury switches, I completely agree with them being banned as they are already illegal in most states and an environment likely to induce physical failure (like in a rocket) is asking for trouble with a hazardous material. Working on a HAZMAT Team that gets called for mercury spills in homes and businesses, you don't even want to know what the expense of cleaning a mercury spill (even a small one) is.

[bobkrech]

The published text is

2-12.6 A rocket motor shall not be ignited by any of the following:

a. A switch that uses mercury;

b. "Pull wires" that disconnect or complete a circuit;
c. "Pressure roller" switches.

I suspecct the intent is to ban the use of mercury switches entirely and disallow using pull wires or pressure roller switches to directly activate igniters. I don't think the use of these devices as inhibition sensors is or should be forbidden and would sugget the following word be considered for addidion

2-12.6 A rocket motor shall not be ignited by any of the following:

a. A switch that uses mercury;

b. "Pull wires" that disconnect or complete a circuit directly;
c. "Pressure roller" switches directly;
d. however "Pull wires" and "Pressure roller" switches may be employed as no-go sensors to prevent activation of a pyrotechnic ignition circuit.

Bob

[rcktnut]

Working on a HAZMAT Team that gets called for mercury spills in homes and businesses, you don't even want to know what the expense of cleaning a mercury spill (even a small one) is.

Isn't that something!!! I remember playing with it in school, having mercurochrome smeared all over my scrapes and cuts, and most of us are probably chewing on it.

[dixontj93060]

I agree.

The published text is

2-12.6 A rocket motor shall not be ignited by any of the following:

a. A switch that uses mercury;

b. "Pull wires" that disconnect or complete a circuit;
c. "Pressure roller" switches.

I suspecct the intent is to ban the use of mercury switches entirely and disallow using pull wires or pressure roller switches to directly activate igniters. I don't think the use of these devices as inhibition sensors is or should be forbidden and would sugget the following word be considered for addidion

2-12.6 A rocket motor shall not be ignited by any of the following:

a. A switch that uses mercury;

b. "Pull wires" that disconnect or complete a circuit directly;
c. "Pressure roller" switches directly;
d. however "Pull wires" and "Pressure roller" switches may be employed as no-go sensors to prevent activation of a pyrotechnic ignition circuit.

Bob

[luke strawwalker]

All this... but it's dancing around the problem...

Any mention made of requiring SHUNTS or CIRCUIT ISOLATORS (grounding pins or safety pins that open the circuit and hold it open during ground preparations, IE REMOVED BEFORE FLIGHT??

EVERY SINGLE ONE of these type incidents I've seen (and it's been more than a few) could have been 100% PREVENTED by having a circuit opening isolator pin or shunt (nonconductor opening spring loaded contacts that close when removed, hold open roller switched opening the circuit, or a grounding shunt that shorts the circuit to ground until it is physically removed) between the electronics and the ignitor(s) or ejection charge(s). Even in the event of a malfunction, if the electricity cannot physically get to the ignitor(s) or ejection charge(s) until the "remove before flight" pin is removed, and assuming they are METHODICALLY and CAREFULLY used at all times until the rocket is on the pad, pointing up, and ready to launch (and replaced IMMEDIATELY before the rocket is handled in any way if there's a problem once it's on the pad and has to be removed) this would eliminate virtually 100% of the problems.

Of course when I bring this point up, I'm usually shouted down as some kind of extremist... I don't expect it to be any different this time...

Later! OL JR

[JStitz]

I have always used 1/8" 2 conductor phono jacks externally..As long as you don't orient the contacts vertically. Horizontal has worked for me.
Slide switches are the same way.
(If you mount them Vertically,G-forces can close contacts and reset electronics for those that don't know)
I learned this through 7 or 8 flights of a favorite rocket of mine that kept giving me VERY low altimeter readings
.
The "Remove Before Flight" flags usually get some smiles.

[alexzogh]

This has been argued extensively in the tra lstserv.

We can thank the 2010 ldrs pad accident for the new rules.

<sarcasm>
Lucky for me, I use an actual igniter to light my motors.... Never seen a mercury switch or pull pin get hot enough to ignite a motor
</sarcasm>

[MaxQ]

Just looked at the 2012 Tripoli Safety Code and saw this:
2-12.6 A rocket motor shall not be ignited by any of the following:
a. A switch that uses mercury.
b. “Pull wires” that disconnect or complete a circuit.
c. “Pressure roller” switches

I don't know if I've been getting away with this for long-is this new? I'm bummed because I have a Xavien 'Fist' and a bunch of pull pin sets from Programmin' Pete. Looks like g-switches and timers from now on. I support the Mercury switch elimination but I do like microswitches for some uses. Does this mean burn wires too?

I bought a Xavien FIST specifically for the pull pin function, to light outboard D and E motors on a cluster...a G switch activation is of no use for a rocket with a slow takeoff that doesn't hit the minimum G load on first movement.

[gldknght]

Ok, I'm NAR, so the TRA rules don't mean all that much to me, but I have a question anyway:

I was thinking of incorporating a mecury switch in between the timer and the ignitor for my two stage project. This would be used only as a cutoff in the event of a less than optimal attitude at sustainer motor firing. In other words, the mercury switch would not allow the ignitor to fire if the rocket is not fairly close to verticle when the timer fires. The mercury switch would in no way affect the timer opperation.

Is this not allowed? Is that in writing anywhere other than in the TRA rules?

[Dale Saukerson]

This has been argued extensively in the tra lstserv.
We can thank the 2010 ldrs pad accident for the new rules.

I'm not on the mailing list.
Would you mind summarizing the accident for me ?
Else is their an online archive of the mailing list ?

[jadebox]

Ok, I'm NAR, so the TRA rules don't mean all that much to me, but I have a question anyway:

I was thinking of incorporating a mercury switch in between the timer and the ignitor for my two stage project. This would be used only as a cutoff in the event of a less than optimal attitude at sustainer motor firing. In other words, the mercury switch would not allow the ignitor to fire if the rocket is not fairly close to vertical when the timer fires. The mercury switch would in no way affect the timer operation.

Is this not allowed? Is that in writing anywhere other than in the TRA rules?

It would be nice if something so simple would work, but there's no way for a mercury switch to detect if the rocket is vertical or not.

-- Roger

[gldknght]

It would be nice if something so simple would work, but there's no way for a mercury switch to detect if the rocket is vertical or not.

-- Roger

Don't need the mercury switch to detect anything.

A mercury switch will only allow current flow when the mercury is in contact with the wire leads. If the switch is oriented correctly, i.e. the mercury and the leads are at the bottom, then if the rocket tilts of verticle so the leads lose contact with the mercury the switch opens, no current flow.

I still want to know where it's in writing other than the tra rules that this type of circuit interrupt isn't allowed.

[davel]

Nope. The mercury in the switch can't tell the difference between gravity and other acceleration forces.

The flight can be perfectly vertical. At motor burn out, the rocket could easily (due to drag) experience a good amount of negative G's. A mercury switch would interpret that as being upside down. Or the rocket could be totally out of control and still be pulling positive G's. The mercury switch would sense that as 'all is well'.

A mercury switch is useless in determining orientation.

[alexzogh]

I wasn't there for ldrs 29. You can learn a bit more in this thread:
http://www.rocketryforum.com/showthr...?t=8324&page=5

Pad ignition of the charge and second stage.

I'm not on the mailing list.
Would you mind summarizing the accident for me ?
Else is their an online archive of the mailing list ?

[gldknght]

Nope. The mercury in the switch can't tell the difference between gravity and other acceleration forces.

The flight can be perfectly vertical. At motor burn out, the rocket could easily (due to drag) experience a good amount of negative G's. A mercury switch would interpret that as being upside down. Or the rocket could be totally out of control and still be pulling positive G's. The mercury switch would sense that as 'all is well'.

A mercury switch is useless in determining orientation.

I can see your point there, but submit that by using a TIMER as the control for second stage ignition the rocket at second stage will no longer be pulling positive g's, no matter what it's orientation. The timer will be set for post booster burn out.

I also submit that if my two stage rocket goes skywriting, (unlikely since I will prove to myself the rocket is stable before the launch button is pushed) my second stage ignition will be the least of my worries.

Because of dual deploy by altimeter, if my rocket is skywriting, there's a pretty good chance the second stage will already have the drogue and main chutes out in the wind, shredded, maybe, but out anyway. That rocket will be going nowhere very quickly.

Again, this is just in the idea stage. I don't even have any mercury switches.

Again, I wasn't so much asking if the mercury switch will do what I want, I still want to know where it's in print mercury switches in rocket are not allowed, besides tra rules, which don't concern me..

[karlbaum]

NFPA 1127 will adopt the new rules and it's just a matter of time before it becomes law. So you might as well get used to the Tripoli Rules. I personally don't think that the rules go far enough. Airstart motor electronics should have a shunt or kill switch and it should be accessible while the rocket is on the pad in the upright position. It is also a good idea to have electronics that don't arm the motor until they reach 300 feet AGL.

[jadebox]

Again, I wasn't so much asking if the mercury switch will do what I want, I still want to know where it's in print mercury switches in rocket are not allowed, besides tra rules, which don't concern me..

Do an internet search for "state law mercury switch" or something similar with your state's name in the phrase. Here's an example I found:

http://www.ilga.gov/legislation/publ...93-0964&GA=093

Even if there's no legal barriers, a mercury switch won't do what you want it to do and may be dangerous to the environment. So, it's probably not a good idea to consider using one.

-- Roger