Two e-matches per deployment charge?

I'm just starting the ground testing of a 4" scratch built Blue Tube rocket. This is my first attempt at altimeter based electronic deployment, and if all goes well i hope to fly it for my Level 2 certification flight. I am using MJG's FireWire Initiators. During my initial tests making my deployment charges I had one fail to ignite. This was prior to getting the good advice on this forum to test the resistance of the e-match prior to constructing the charge. This past weekend I caught one e-match that read a resistance over the manufacturers specs, and it indeed failed to ignite. This has me considerng my redundancy/backup strategies. I did not build the av-bay with redundant altimeters to keep cost down and to keep it simple. My design includes a zipperless coupler with baffle for motor back-up to apogee/drogue deployment. My long winded question is if anyone uses two e-matches per deployment charge as another level of redundancy? If so, given my design do you think this is necessary? Maybe for the main chute deployment only?

I have seen multiple people use two e-matches per deployment. I know when we did the portapotty launch, we had two e-matches for each charge and for each altimeter.

Is it necessary? Most of the time, probably not. But the one time it fails, you will wish you had.

However, with a 4" AV bay, you have plenty of room to add a second altimeter. At that point you have a more complete backup system.

I use two matches per charge in my L3 rocket. It is cheap insurance. I am surprised that you have had two failures in what sounds to be a relatively small sample of matches. I am making an assumption that after the failures you directly connected the matches in question to a 9v battery to verify that they were bad.

I have yet to find a bad one out off 100 pcs of a China brand.
There will be 2 per canister in my Magnum 3 whenever it goes up!
Maybe I should ground test the charges I've worked up using only
1 per canister? It's probably not going to be a huge increase in pressure,
to hurt anything...

JP

Another form of redundancy. I prefer 2 full charges.

If you check resistance, then you have a high percentage of success. adding another would increase reliability by a small percentage. a switch, battery or altimeter failure would still prevent an ejection charge from firing.
Adding a second altimeter (different manufacture) with it's own power supply, switch and charges would improve reliability significantly as no one component failure would prevent an event from happening

I use two matches in each charge. I have Atlas M-100s that are older than dirt but work 100% in my tests and use.
If I had a match failure I would never use the brand again for deployment. Maybe use for a single motor lit on the pad where a failure is not catastrophic.

M

Over the years I have had several failures, in many brands over 12 years:

2 red/blue Oraxl's
1 Davefire white
1 Davefire black

2 M-tec

1-unknown

All the above were hooked up direct to battery after flight, and did not fire. All were checked for impedance before flight. [ I don't bother with that anymore, since it didn't really matter]

BUT in all cases I was fine due to redundancy in my electronics.

Reading on a Fireworks forum I came across a statistic claiming 1 per thousand failure across the board, but in actuality more like 1 in 10,000 based on members polled. FWIW These guys claimed to be using 2000-5000 per show, which gives them a much larger use ratio than us.

Redundancy is great. Just make sure your electronics can handle it.

To the OP, please don't be offended, non is intended. But I highly recommend the simplest approach to certification. Nix the electronics, go with simple motor ejection. Get your cert then start experimenting and pushing your skills. Whatever you decide, good luck nevertheless!!

BayouRat said:

Redundancy is great. Just make sure your electronics can handle it.

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Ditto this. You are doubling the load, so make sure your altimeter can supply enough current to light two matches. Otherwise you will get no deployment with two good matches. :y:

blackjack2564 said:

Over the years I have had several failures, in many brands over 12 years:

2 red/blue Oraxl's
1 Davefire white
1 Davefire black

2 M-tec

1-unknown

All the above were hooked up direct to battery after flight, and did not fire. All were checked for impedance before flight. [ I don't bother with that anymore, since it didn't really matter]

BUT in all cases I was fine due to redundancy in my electronics.

Reading on a Fireworks forum I came across a statistic claiming 1 per thousand failure across the board, but in actuality more like 1 in 10,000 based on members polled. FWIW These guys claimed to be using 2000-5000 per show, which gives them a much larger use ratio than us.

Click to expand...

I've only had two matches fail. They just both happened to be on the same flight. They were from different manufactures, resistance was measure about 0.8 ohm on each before the flight. Neither fired, but the rocket fell flat from apogee and wasn't damaged. Both were tested after the flight and both registered as open. That tells me the bridge wire melted through without firing the pyrogen. I was using a new 9VDC battery that was reading 9.6V and a HiAlt45 altimeter that has the built in capacitor to supplement the battery.

After having both matches fail, the rocket fall flat from 4,400 ft, and walking right up to it 150 yards into a corn field, the only thing I messed up on that day was not buying a bunch of lottery tickets.

Heh. I woke up one day at 5:00 AM. Had the remains of a Five Guys burger for breakfast. Took the number five bus to Fifth Street. At lunch. I decided to stop at the race track, and I put $500 on the fifth horse in the fifth race. And you know what happened?

It came in fifth.

Anything 3" and over and I am going to use 2 charge tubes or motor plus timer or altimeter. And 2 9-volt batteries on each. No. I am not paranoid. Why do you ask?

I am a "Kendal" also, but my parents cursed me with wierd spelling.

Titan II said:

I use two matches per charge in my L3 rocket. It is cheap insurance. I am surprised that you have had two failures in what sounds to be a relatively small sample of matches. I am making an assumption that after the failures you directly connected the matches in question to a 9v battery to verify that they were bad.

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I am a little surprised at 2 failures as well. Since I never measured the resistance with the first one, I don't know for sure if that was the problem. As I mentioned, the second e-match that failed measured 1.4 ohms (manufacturer spec is 1 ohm plus/minus .2), so I was anticipating a problem with that one. Since this was just ground testing I tried it anyways. All the others since I started testing the resistance have been 1.1 or 1.2 ohms. Right now I am firing all my test charges and doing my ground testing directly with a 9v battery and speaker wire to provide safe distance. I also deconstructed the second failed charge and tried to fire the e-match alone without the speaker wire and a new 9v... it did not fire.

BayouRat said:

Redundancy is great. Just make sure your electronics can handle it.

Click to expand...

I have already hooked up two e-matches per output (drogue and main) on my RRC2+ and simulated a flight using a vacuum chamber. All 4 e-matches fired. Is there anything else I should do to verify/test the altimeter for this set up? I do plan on using a new 9v for each flight (tested, at least to verify voltage). My 10 y.o. son is a RC 'anything' junkie, so he'll go through the once used 9v batteries in his remotes.

jimzcatz said:

To the OP, please don't be offended, non is intended. But I highly recommend the simplest approach to certification. Nix the electronics, go with simple motor ejection. Get your cert then start experimenting and pushing your skills. Whatever you decide, good luck nevertheless!!

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No offense taken! I wouldn't post my questions if I didn't want the feedback. I value the experience and advice from the members of this forum and the clubs where I have flown. In reply to your recommendation, I thought long and hard about my Level 2 certification and learning electronics/dual-deploy. In my mind I don't have to do them together. In fact, I designed this rocket to be extremely flexible and I can fly it any number of ways. Right now I am more motivated to learn dual deployment, and plan on multiple dual deploy flights with Level 1 motors first. I can always decide later how I want to attempt my Level 2 flight. As a side note, I made a removable bulk plate for the nose cone so I have another space for electronics. If I do get my Level 2 and stick the largest 54mm motor that will fit, it sims to about 8500ft.... I'm going to want to start learning GPS and/or radio tracking, and the nose cone is where it will go.

Igotnothing said:

Anything 3" and over and I am going to use 2 charge tubes or motor plus timer or altimeter. And 2 9-volt batteries on each. No. I am not paranoid. Why do you ask?

I am a "Kendal" also, but my parents cursed me with wierd spelling.

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That's funny! I don't know if I would call 'Kyndel' weird.... how about 'unique'. My name always gets spelled wrong with two L's. I remember in high school I got annoyed with it and asked my mom why they only used one 'L' in my name. Her reply was, 'We didn't know it was normally spelled with 2 L's'. So that's that!

A couple years ago I flew with redundant Ravens with redundant batteries with redundant/isolated switches with redundant kit made charge initiators.

Four charge tubes packed tight with Triple7 FF.

Rocket deployed perfectly but I found that one of the charge tubes didn't ignite when I got home.

Was able to dump the powder out and set it off with a lighter on my porch. Both initiators were obviously burned.

Moral of the story...what are the odds of two of eight ignitiators working but not setting the charges off?

And yeah...there's a can of Goex FFFF on the shelf now after all my yammering up the virtues of smokeless.

kjkcolorado said:

This is my first attempt at altimeter based electronic deployment...I did not build the av-bay with redundant altimeters to keep cost down and to keep it simple...

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For this project, all 12 motors we built had to work the first time when the cars reached a certain speed, there was no redo or second chance. We used one home built igniter and one commercial ematch in each motor on separate systems. All 12 motors started on cue. https://www.flickr.com/photos/48721294@N08/14893648708/in/photostream/

If the project you are doing is worth recovering, then dual independent deployment systems are needed. That means two altimeters, two battery sources, different ematches for both, different black powder charges. With a 4" airframe, you have the luxury of plenty of room for a fully redundant/independent system. Set one altimeter, if possible, to deploy a second or two after apogee to prevent both firing at the same time (unlikely) and over pressurizing the airframe. Set one to deploy the main at a slightly lower altitude for the same reason. You might also increase the amount of black powder in the back up charges, that way if the first charge wasn’t strong enough, the second one might be and if the first was successful, the larger backup simply fires out into the air.

After use of thousands of ematches for both rockets and fireworks, I can say the ematch will be the least likely source of failure in the system. On last year’s 4th of July display we set up, as I recall, we had two fail out of 2500. A more likely cause of failure in rocketry recovery deployment will be shorts, opens, low battery (either to begin with, check voltage even on ‘new batteries, or while sitting on a launch pad for a long time), powder charge too little, chute/blanket/tethers packed too tight (either from assembly or high G-forces during flight), loss of continuity during flight, drogue deployment shock, altimeter settings incorrect, wires connected incorrectly, operator error, etc.

I’ve seen people ground test their deployment charges, increasing till successful (maybe just so) but on launch day pack things differently and just not enough to deploy out of the airframe during flight against the air resistance encountered during a less than vertical flight or not at apogee deployment.

Even when you think things are perfect, you still might have a rocket come in ballistic; that is why I try to encapsulate my electronics in a PVC tube for impact survival…sometimes successful and sometimes components still tear off the board.

My two cents,

Rick

When I experimented with completely made from scratch matches ie. wind the nichrome around a double sided board, shear the chips, solder the wire leads and dip in "made from scratch" chems, I had a lot of failures during ground testing. I later discovered 40ga. nichrome was the "magic" bridgewire and for some weird
reason, they became more reliable if they "aged" a few months. In the process of learning over a couple of years, the ability to obtain commercial
solutions manifest so I don't bother with rolling my own. Never flew any but I probably would have done two per charge in a single altimeter installation.

Bottom line is, if one wants to get as infintesimally as close to zero as possible, two per charge would help with a single altimeter installation. Is it worth it? Sure it is if the single charge doesn't work!!!:wink: Kurt