NAR safety code for ignition systems

[rocketsonly]

Does anyone know where I can find the safety codes so that I can make my own ignition system? I'm mostly concerned about the rules for a safety key.
-Matthew

 

[Steward]

www.NAR.org

 

[rocketsonly]

From NAR:
Ignition System. I will launch my rockets with an electrical launch system and electrical motor igniters. My launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the "off" position when released.

So am I allowed to use the key switches in automobiles that close the circuite when turned, but spring back to the open position when the key is not twisted?
-Matthew

 

[astrowolf67]

Yes, as long as the key is needed to arm the system, which with an automotive switch, would. Insert key, turn on system, then turn once more to launch.

Most people use something such as a headphone plug for the safety key to arm the system, then a momentary push button for the launch button. Much cheaper, unless you already have the automotive ignition switch.

 

[DynaSoar]

Originally posted by rocketsonly
From NAR:
Ignition System. I will launch my rockets with an electrical launch system and electrical motor igniters. My launch system will have a safety interlock in series with the launch switch, and will use a launch switch that returns to the "off" position when released.

So am I allowed to use the key switches in automobiles that close the circuite when turned, but spring back to the open position when the key is not twisted?
-Matthew

The NAR rules were almost certainly written from the experience of people who used launchers with physically removeable interlocks. They were written in such a way that they don't require it, but people will probably expect it. They may question you as to what happens if the switch sticks. And spring loaded ignitions switches do stick. However, dollars to donuts says they don't stick as often as people forget to remove the interlock key.

I've always wondered why they didn't simply require that the power be disconnected from the control until testing continuity and immediately after launch.

 

[wwattles]

The way I read that safety instruction is that the firing circuit must be opened when the person launching removes their finger from the controller. In other words, a toggle switch where position A is on and position B is off is not sufficient. A spring-loaded push-button would be, since the button returns to position B after release.

And of course, the more safety interlocks (like with keys) you have, the better. My club launches have a "arm/safe" key switch for each controller box (we typically have 4 boxes at the launch table - 2 LPR, 1 MPR, 1 HPR), a "arm/safe" toggle switch for each rod/rail on that controller box, and a spring-loaded push-button. LOTS of safeties!

WW

 

[bobkrech]

Matthew

The least expensive launch system I have seen is found at http://www.nar.org/NARTS/mahler/ultra.html

The launch controller design is fully in compliance with the NAR regulations which is meant to be interpreted as.

1.) Your launcher must have a removable safety interlock switch that physically disconnects the launcher from the power source.

In this simple launcher referenced above, the removable safety interlock switch is simply a metal "bull dog" clip (normally used to hold a stack of papers together) which is used to make the power connection to the launcher.

You could also use a coaxial power connector similar to the style used with AC adapters for radios and video games as the safety interlcok key, (but don't use stereo or ear plug plugs which can short out the battery on insertion into the jack), or you can use a key switch where the key is removable in tthe off position only.

2.) Your launcher must a separate momentary contact switch for the launch switch. You may not use the safety interlock key switch as both power interlock and the launch button. This would remove the dual redundany built into the safety code that mandates a positive power disconnect in the event that one switch fails in the closed position.

In the article, this is simply a spring metal bar, but a door bell switch works just fine. You could use a second monentary contact key switch but this is expensive.

While not in the safety code it is prudent to have a continuity checker circuit in the launcher. I would add the following.

3.) Your launcher should have a current-limited continuity checker to indicate that your ignitor is properly attached to the clip leads.

This continuity checker can simply be a resistor/led as used in the article (typical current <20 mA), or it can be a piezo buzzer (typical current ~10-20 ma), or it can be a low current flashlight bulb (for Estes ignitors the continuity current should not exceed 0.1 amp, however be careful as some homebrew e-matches might fire at this current). Since leds with current limiting resistors don't burn out and use less current they are preferred. The recommended resistor value is 50 ohms per volt, so for example, if you have a 12 volt system use a ~600 ohm resistor. A current-limited piezo buzzer in series with the led can serve as the current limiter in place of the resistor.

The continuity circuit is powered up when the safety interlock switch is turned on. The ignitor is fired when the launch switch, in parallel with continuity checker, is depressed.

A more detailed description of the minimal launch controller circuit with the math is found on the Estes Educator site.

http://www.esteseducator.com/Pdf_files/1924_launch.pdf

also info on Estes ignitors

http://www.esteseducator.com/Pdf_files/Igniters.pdf

Bob Krech

 

[Micromeister]

Matthew:
Heres a very simple Launcher control circuit that has all the necessary safety devices, the disconnect can be as simple as an 1/8" Normally open phono jack and a piece of old 1/8" launch rod. the Launch button can be any SPST momentary contact Normally open switch (Like a doorbell push button) or any number of 5amp for better pushbutton switches from your local Radio shack. your continuity check light or buzzer will need to be matched to the supply voltage of your battery. I strongly suggest a 12volt (minimuim 7amp/Hr or greater) Gel-Cell as a power source. At 12volts any number of 12v 20ma led or even bulb type lamps can be placed in the circuit. or a piezo buzzer will also work, I perfer the led lamp personally because the buzzer is annoying. Add a pair of smooth jaw micor alligator clips soldered to a minimum of 15 feet of 18gage lamp cord and your good to go. I perfer to make the leads 30 to 50 feet of 16gage wire because a more distant launch contol location offers a better view of the flight.
Hope this helps.

 

[bobkrech]

Micromister

I'm sure you meant to have the launch button in parallel with the continuity checker as shown in the attached drawing.

The launch controller circuit in your post with the piezo/led indicator in series with the launch button limits the current so it won't fire an ignitor or pull in a relay.

Bob Krech

 

[bobkrech]

Let's try the attachment again.

 

[Micromeister]

bob:
That's what I get for not taking the time to draw my own diagram.
Actually you need to switch the buzzer and the momentary contact launch switch in your diagram to make it correct.
The buzzer or contunity LED or lamp jumps (by-passes) the launch button.but uses enough current to keep the igniter from burning. Sorry that first diagram posted is not mine,drawn by someone else I was simply trying to show HOW simple a circuit a controller can be. A continuity lamp or buzzer can be omitted from the circuit altogether thou I would want one in any launch controller I built.

Here lets use something I drew myself

 

[Micromeister]

Originally posted by jcrocket
It's funny that that doesn't say anything about "switch" or "removable" for the interlock. If your battery or leads to your battery are detachable close to the controller, that's an interlock in series with the launch switch.

Joel. phx

Nice Try Joel:
physical removal of cliips from the battery, while a form of disconnecting the controller from the battery, does not meet the criteria of an Interlock. An interlock or Safety disconnect as it is more commonly called, is a saftery feature that is intended to provide instant disarming of the system at T-1 if necessary. Having to bend over to remove the clips just doesn't cut it. Remember SAFETT FIRST. a pull pin disconnect is the easiest and simplest way to instantly "SAFE" a system.

You might also ask yourself, if a removale disconnect isn't required by the safety code why would ever single manufacturer of model recket launch equipement include a pull pin of somesort in every single controller ever commerically produced? The answer; IT's is required for SAFETY.

 

[Mike]

Originally posted by jcrocket
A second switch in series is the simplest way to meet your definition.

No! I think its meant to be a fully removeable key (or interlock), another switch doesn't count.

 

[Micromeister]

Joel:
I can't put it any other way then your dead wrong in both comments.
Please explain your aversion to using a safe Launch control circuit that has proven it's reliablily of over 40+ years. Better yet don't try because it's a useless, unproductive argument that really has no bearing on what this thread was trying to accomplish.
To keep our hobby going we must emphasize by example our committment to our first prioritry SAFETY FIRST. A pull pin safety interlock is a small but vital part.
That's my last words on the interlock question to be posted here. Since I can see this is an apples and oranges type debate, If you'd really like to continue this discussion it makes more sense to do it privately

 

[Micromeister]

Exactly my point Joel: You just Don't get it.

 

[Micromeister]

Now your beginning to get it!
Yours is the only 'tude i'm seeing.
It's a SAFETY Requirement. Without NFP-1122 we wouldn't have the NAR safety code. When Bunny & firends had the NAR code "Simplified " a few years back they left-out a lot of the dulpicate language to make is simpler for the youngsters to read and understand. Most first time rocketeer aren't building their own equipment so SOME details were omitted. I supose the thinking was if and when these folks got around to this more advanced activities they would have been introduced to 1122 , 1127 and maybe if they were lucky FAR 101-1. I for one complained at that time that many important technical points were dropped in the name of clarity? Go figure.

 

[powderburner]

jcrocket, I don't understand why you first ask for help and then don't want to accept it

These guys pretty much know what they are talking about. Yes, you can split some hairs and make the claim that the requirement is not in the NAR rules, but if you knew the history you would remember that it used to be, and that the intent of the NAR rules is to 'mirror' the NFPA requirements.

Are you trying to save the cost of 39 cents-worth of components?

I for one would feel safer while walking out to the pad if I knew that the firing panel was 100% disabled because the interlock key is in my pocket.

 

[rocketsonly]

But if it were a safety pin then you shoudln't be feeling 100% safe. I would prefer a safety key. But does anyone know where to get these? RadioShack no longer carries them, and the stores I've tried only have key switches that are able to release the key in both off and on positions.
-Matthew

 

[cls]

one of the key switches available from Digikey is perfectly suited for this sort of power enable: the key can only be removed when the switch is "off".

Also check out Jameco for off-on SPST key switches. but the key can be removed from the switch even when "on".

 

[powderburner]

Some of you guys seem paranoid about hobgoblins setting off the launch system behind your back.

What is the big deal about pull-out pins? Are you afraid someone is going to stick some other object in the socket in place of the real pin? I just don't see that as a realistic problem. If you run into some destructive deviant, there just aren't too many ways to stop him that are fool-proof.

I don't see a battery dis-connect as a cure-all either. If the battery is at the control panel, who is going to stop a trouble-maker from simply re-connecting it while you have your nose under the motor, hooking up ignition leads? If the battery is at the pad (where it belongs) and you have a relay system, fine, disconnect it for a few secs if that makes you happy.

Bottom line: simple systems have a virtue all their own. Adding too many gimmicks and too much hardware invites people to begin trusting that hardware to guarantee safety, when they should be using their eyeballs and brain.

 

[Chr$]

My opinion:

Removable Key switch or Pin. Estes, Centuri, et al used pins because they were CHEAP and easily replaced with a finishing nail if lost, you know how kids are about losing things.

Add to that a select switch for a multi pad system.

Add to that a fire button. It takes two switches and a push button to launch a bird this way. On a single pad, two pushbuttons plus some sort of disconnect key.

An audible alarm connectd to the load side of the key is also a good indicator that the pad is hot.

ANy of you guys remember the "plans" to build a cheap launch pad with a 20 foot extension cord in the Estes or Centuri magazine? The thing had you using the plug and socket for a key by cutting the plug off and shorting the wires. I wonder how many kids tried plugging that into the wall .

 

[Hospital_Rocket]

I am designing a new launch system for my club and one feature I plan to add is a hard core kill switch

Key Release E-Stop

This switch will, when hit, disengage primary power and short the outputs of every firing circuit. The key release prevents anyone from rearming the system unless they are authorized to do so.

A

 

[BlueNinja]

Al- That switch probably requires tools that I don't have access to, does anyone sell it?

Regarding pullpins- They are very easy to override once taken out, my Estes control will accept a paper clip to arm it.

 

[Hospital_Rocket]

The EAO line of switches is almost too-less in assembly. The whole thing just snaps together. The trickiest part would be punching the 22.5mm opening. After that, if you have a pocket screwdriver you are all set.

You won't find these at radio-shack and the like. You need a supplier like Newark or Wes-Garde.

Here is a link to their distributor list

A complete single contact assembly will set you back around $15.

Here is a link to their distributor list

 

[Stymye]

Hospital,what you and Jcrocket are basically describing is a lockout system.

for example,This system is required in all industrial factory's to protect a technician from getting hurt if someone accidentaly throws a switch or trys to operate something.If the machine is "locked out" it is virtually impossible and lives are on the line
so theres alot of switches ,interlocks..ect availiable out there


while a little more complicated it is indeed safer than a pull pin
if someone can forget to remove a pin ,,,or someone can insert a pin while your out at the pad...it's simply not fool-proof


I'm personally not against the pull-pin system, most people at a launch are smart enough to make it work,but I'm definately not going to knock a safer system either

lets try to remain open minded,theres more than one way to build a safe system

 

[wwattles]

One nice safety feature of some of the systems I've used a local club launches is a "armed" buzzer out at the launch pad itself. When the master "arm" key is turned at the control box, it turns on a buzzer out there that lets us know that the system is hot. Been a few ocassions when an over zealous launcher forgets to let others get away from the pads before arming the system, and that buzzer was what prompted us to yell at them to "DISARM THE LAUNCHER!!!"

WW

 

[Hospital_Rocket]

Styme

You are correct. What I am planning is a complete safety lockout. My intention is to make the system as neutral as possible for emergencies. I used to design these circuits for industrial machinery.

The key unlock feature is intended to prevent anyone from unlocking the launch panel unless they are an RSO. (Presuming only RSO's have the key). In fact in my procedure the LSO would not have the emergency stop release.

I am fussy about these things and as such tend to over design. When I get the full circuit designed, I will post it someplace.

So the design philosophy will have the following:

1. An emergency stop as outlined above

2. A key lock switch to arm the system

3. A two button fire sequence. One master, one for the individual launch position. If you push the position fire without the master fire switch, then you perform a continuity check. If you push the master button without the position fire, you get some excercise for your thumb. I have considered using the master button to also sound a horn.

Comment: My rationale here is based on something I saw at our launch yesterday. Our current control has a key switch to arm, a toggle switch to enable a position, and a pushbutton to fire. What happened was an additional position was left on and the LSO did not notice. He pushed the fire button for a lpr launch and accidently launched an MPR bird.

I do need to find a way to do multiples such as drag races.

Sounds complicatred, however it is about as safe as I can make it.

A

 

[BlueNinja]

Originally posted by wwattles
One nice safety feature of some of the systems I've used a local club launches is a "armed" buzzer out at the launch pad itself. When the master "arm" key is turned at the control box, it turns on a buzzer out there that lets us know that the system is hot. Been a few ocassions when an over zealous launcher forgets to let others get away from the pads before arming the system, and that buzzer was what prompted us to yell at them to "DISARM THE LAUNCHER!!!"

WW

Maybe have an always closed momentary contact switch inline with this buzzer, so you could push it to open the circuit if it was armed.

Just a thought,

Blue