Routing ignitor circuit through avionics switch - what are your thoughts?

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75Grandville

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This one has been rattling around in my head ever since I started thinking about dual deploy, avionics, etc. One of the horror stories I keep hearing is about people forgetting to arm the avionics before launch. I started wondering if there was a way to Yokoten (that's a Japanese term for "make idiot proof") the process.

What I came up with was tying the ignitor to the avionics switch. That way, if you forget to turn the switch, you don't have continuity to the ignitor, and can't launch.

It seems like it should be possible, if you are using a 110/220 switch or other double pole switch for your avionics, to use the second pole to interrupt the circuit for the ignitor. Have some sort of surface contact at the bottom of the body tube, with a wire running up to the switch, then another wire running back down to a point near the motor to connect to the ignitor.

Has anyone tried this? Would it comply with/violate either TRA or NAR safety rules? Curious to find out what prior art exists.
 
Since you are not allowed to insert the igniter until the rocket is on the pad pointed upwards, how would you envision doing this? SOP is a) put the rocket on the pad point up; b) turn on the recovery system; c) insert the igniter.
 
You could have terminals on the bottom of the rocket. Two to attach to the clips and two to attach the igniter leads. Needs space and wiring conduits. Seems doable.
 
You could have terminals on the bottom of the rocket. Two to attach to the clips and two to attach the igniter leads. Needs space and wiring conduits. Seems doable.

That's pretty much what I was thinking. I'll see if I can diagram/mock something up this weekend. I personally think the trickiest bit will be coming up with some sort of break-away connector to go between the AV-bay and the sustainer to route the circuit through.

Some sort of spring-loaded contacts mounted through the coupler making contact with some sort of copper pad on the wall of the body tube?
 
My thought would be to use a little electronic relay board at the aft end of the rocket with a FET switch to gate the ignitor current, with an enable signal coming down from the avbay. I think the enable signal could probably power the board too, it doesn't need to be powered up unless armed, so you won't even need a battery on the relay board. You could probably hack up a partially populated Quark to provide this. Then you only need two conductors coming down from the avbay...a SIP connector would provide an easily separated connection (as used in some competition piston launchers). The connection doesn't even have to survive boost. Product idea for Cris here.
 
Why make it more complicated than it needs to be? The simple fact every flyer must know is this: Do not install igniters unless you hear your altimeter beeping. Period.

Adding a bunch of complexity, more electronics and more wiring will lead to more failures.

--Lance.
 
It would seem to me that if the switch is not closed, then you would have the battery voltage across the open terminals. When you connect the igniter to those terminals, you could receive rapid, positive and memorable confirmation that your electronics are not armed.

Jim
 
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I assumed he would just use extra terminals on the switch to route power from the launch system to the igniter. Switch off, the igniter will not see power even if the launch button was pushed.
 
I assumed he would just use extra terminals on the switch to route power from the launch system to the igniter. Switch off, the igniter will not see power even if the launch button was pushed.

This topic reminds me of arming the upper stages of a multi stage rocket (one of my least favorite activities). You're not supposed to have voltage there, but it can happen. One of the reasons I like using the Rocket Tiltometer is that is has circuitry specifically designed to look for for voltage on the terminals to the igniter before arming the circuit. Failing such measures, I can't really see the wisdom of exposing the igniter to a voltage source if you don't have to.

Jim
 
I assumed he would just use extra terminals on the switch to route power from the launch system to the igniter. Switch off, the igniter will not see power even if the launch button was pushed.

Yes, that's the idea. The circuit usually looks like

launch control system -> clip -> ignitor -> clip -> launch control system

All I want to do is add just enough so that it looks like

launch control system -> clip -> avionics switch -> ignitor -> clip -> launch control system

using the second pole of a double pole switch. The ignition circuit would be completely independent of the avionics circuit, except that the same switch should arm them both.
 
Why make it more complicated than it needs to be? The simple fact every flyer must know is this: Do not install igniters unless you hear your altimeter beeping. Period.

Adding a bunch of complexity, more electronics and more wiring will lead to more failures.

--Lance.

+1...
I do not install an ignitor in a motor until the altimeters tell me all looks good and they're "Ready for flight"....

Teddy
 
Why make it more complicated than it needs to be? The simple fact every flyer must know is this: Do not install igniters unless you hear your altimeter beeping. Period.
Unless you regularly fly smaller motor deploy stuff, which I do.

Adding a bunch of complexity, more electronics and more wiring will lead to more failures.
Oversimplifies the failure mode analysis, arriving at the wrong conclusion. The flight computer is already a mission critical element. The launch circuit as we usually handle it now is a completely isolated but also mission critical element. The two are functionally dependent such that if you have a failure of the flight computer (like not turning it on) but the firing circuit still actuates, you still have 100% probability of mission failure and likely destruction of the vehicle (not considering motor deploy backup). Now say there is a 5% probability that the flier forgets to turn on the altimeter. Because of the 100% dependency coupling, you've added 5% to the overall failure probability. That is exactly why a lack of interlock between two functionally dependent systems is usually a bad idea.

Now in the case where the flight computer gates the ignition, you have essentially zero probability of ignition without the flight computer active. Furthermore, most of the likely failure modes in the ignition gate will simply result in no ignition, which does not result in complete mission failure. The circuit does have to be designed properly so that there is miniscule probability of accidental launch, but to me that doesn't look too hard. So adding the ignition gate converts a measurable chance of mission failure into some small probability of a misfire.
 
Tape the igniter to the fin can. Do not remove it to install ,until you hear altimeters beeping.
If you have to....... write on the tape "check altimeter"
The very LAST thing you do is install it.[well actually test for continuity if you have pad box]

That one was beat into my head when I first started!:grin:

Fool-proof
 
Guys, we are over thinking this. A simple check list is the answer. Simple.
1) rocket on launcher
2) turn on electronics
3) insert igniter.
 
I think routing the igniter connections through avionics power switch to ensure electronics are powered before ignition can happen is a "good" concept. I'm not sure it is practical or mitigates sufficient risk to be worth the cost, effort, etc. Everything else being equal, pads angles down wind and away from spectator area and igniter out of the rocket until on the pad, I'm not sure that going through the effort to wire the igniter through the electronic power switch is going to increase personal safety any significant amount.

Wiring the igniter through the power switch will require a significant restriction on the type and use of power switches for electronics. It may severely restrict the use of MD rockets. Getting the wiring from a central av-bay to the igniter location will require some type of connector that allows drogue deployment while maintaining the igniter connection before flight. The wiring, connector, and switch will need to be sufficient to handle the igniter current loads while providing minimal chance of a failure during launch causing a deployment failure. i.e. the current through the igniter burns out the electronic power switch and causes a loss of power to the electronics at the time of launch.

I think this system may be OK, but unneeded as it may induce more issues if it is adapted by the general rocketing community. Just MHO
 
Would seem that the wiring would have to go from the bulkhead down to the motor. All of which would get fried by ejection charges every time you flew it...

Plus it's just way more complicated.

Crazy Jim's way is fool proof (plus it prevents you from forgetting the ignitor after waiting for a pad)
 
There are lots of ways to do this but I would suggest not connecting to the igniter. What you need to do is sense the launch and tie this into starting your electronics. A variety of sensors can be used for this function, such as a thermal sensor near the motor. A simple g switch could be used to detect sufficient linear acceleration. A break wire connected to launcher and a collapsing circuit could also be used. Each of these systems has mechanical substitutions which could be used instead of electronics. Internal shear pins could be used to detect acceleration and thrust. Frankly, there are too many options to give justice to them all in this short note.

Military fuzes work this way. You don't see soldiers following a complicated series of steps to prepare a mortar or artillery shell for firing. The fuze detects the launch and from there safety systems are removed to enable an explosive effect at the target. Our only difference is making this happen at apogee. If you want to remove this risk in your launches look into military fuzes. When doing so please ensure that there are two or more conditions required for functioning.

Also military fuzes have a lot of testing that goes into them. Doing that is good.

Andrew
 
+1...
I do not install an ignitor in a motor until the altimeters tell me all looks good and they're "Ready for flight"....

Teddy

Big fan of the simple free checklist idea. I have thought about doing it many times but keep forgetting :cyclops:

I simply do what Teddy and others have said. Arm all of the electronics, wait until I hear all the beeps/flashes indicating everything is nominal, and the very last thing I do is install the igniter.

I will do that checklist thing one day.
 
Igniters like answering machines: "Wait for the beep."


Later!

--Coop
 
Having a checklist is a great idea. I've seen people forget to attach parachutes before, just shoved them in the BT and look on in horror later... But like most people, once they've messed up that badly once it kind of sticks into your brain :)
 
If you use a default-closed switch with a pull-pin, you can tie the igniter to the pin, and then it is impossible to install the igniter without starting the avionics. I've never done this, but then I've never forgotten to arm the altimeter, either.
 
I actually almost had this happen at LDRS. On day 2 when the right mid power bank was closed down for a bit for tech support, LCO told us to go out and power down electronics if we wanted to save battery. So I walked out and powered down my altimeter. (In hindsight I should have pulled my igniter as well).

About 40 minutes later... I hear them announcing the rocket next to mine..... So I walked up to the flight line at the far end of the field. Then I remembered......

I don't think I've ever run 500 feet so quickly. :p Sprinted to the LCO and asked him to not launch mine until i could arm the altimeter.

Almost was my biggest SNAFU to date. :p
 
That's crazy! Yes, you should have pulled the igniter, but the LCO should have made certain that anyone who powered down -- at his direction! -- also got powered back up. I would have to fault the LCO for that one.
 
That was defiantly a little Chaotic at LDRS sat morn. 2 guys had theirs launched by accident and didn't see them leave the pad, luckily they kept them armed during the pad issues.
Use a little more battery capacity is what I learned from that
 
I'm not sure how it would affect the ability to fire charges, but I had my rocket hang in a tree for 5 days and when I got it down, the HiAlt45 and SL100 were both beeping out the altitude. The battery on the HiAlt45 was at about 8 V and the one on the SL100 was down to about 5.5 V. I would not be against leaving an altimeter with a new battery and one of those PerfectFlite altimeters sit on the pad for an hour or two and then launch. If the battery wasn't new or the wait was going to 3 hours or more, I would probably want to power down, or at least cycle the power to get a voltage reading on the batteries before launch.
 
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