Testing E-matches

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kjkcolorado

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I received my order of MJG Firewire Initiators from Pyro Direct last week and had a chance to start making and testing my first black powder charges for altimeter controlled recovery. After talking with many of the wonderful rocket enthusiasts at Northern Colorado Rocketry's Octoberfest on Saturday I have decided to try the surgical tubing method. I like the idea of being able to make the charges ahead of time in a quiet controlled environment where I can concentrate on what I am doing. I used a 25ft length of speaker wire and a 9V battery to test the charges. My first test was the Firewire by itself to make sure my testing setup was sound. I followed that with a surgical tubing charge secured on a couple cinder blocks, and then a charge loaded into an empty one gallon ice cream bucket. My kids got a kick out of watching the bucket leap 10 feet into the air. Anyways, on my second attempt with a charge in the bucket it didn't fire. I deconstructed the charge and tried the Initiator by itself. Still no 'joy'. One thing I did differently with that charge was to use a dab of 5 min epoxy to help seal the zip tied ends of the surgical tubing. With my 2 previous charges I was having a little difficulty getting a tight seal on the zip tied ends and was having a few grains of 4F black powder leak out. This leads to a few questions.

First, is there a way to pre-test e-matches? I will be using a Missile Works RRC2+ and from what I can tell from the instructions when I power it up on the pad it will go through a series of diagnostics including 'telling me' if I have continuity through the Drogue and Main terminals. I was just wondering if there is anything else I can do to prior to catch a 'bad' e-match.

Second, could my use of epoxy to help seal the ends of the charge have done something to damage the e-match?

And finally, any other suggestions on how to get a good seal on the ends of the surgical tubing charges?

Thanks for sticking with me through a lengthy post. Any suggestions/answers would be greatly appreciated.
 
Did you test your e-matches with an ohm meter?? Should do that before assembling charges. I don't use tubing so can't help with that.
 
I do have a multimeter, but have really only used it for checking battery voltage. I have never used the ohm meter functions. What am I looking for in terms of testing the e-matches? Sorry if this is a dumb question.... electricity/electronics is not an area where I have much experience or knowledge beyond the basic 'don't stick a fork in a light socket'.
 
You are looking for a resistance of 0.8-1.2 ohms.

Look for "poster tack". That or hot glue work for sealing.
 
Thanks for the advice. I tried getting a reading on several of the Fire Wire Initiators this evening. The ohm readings on my multimeter were jumping all over the place and I never got a good reading. I think the battery needs replacing. I'll try again after that. Question on the "poster tack". Does it harden, or stay somewhat malleable after application?
 
I think the surgical tubing is overkill. FWIW I like latex glove fingers and tie-wraps myself, much easier to seal.
 
Problem is, is getting an ohm meter that can give you a decent measurement down that low. Never, I repeat NEVER!!! test an ematch attached to a BP loaded charge. Always bare matches.

Here's a continuity tester: https://www.oda-ent.com/Continuity Tester 2.html But you can be at 5 or 6 ohms and still have continuity.
If it glows, the element is good. If not, it's dead. Just because it's good doesn't mean it will "pop". Read Jim H.'s take on ematches. One can get continuity,
decent ohm reading and still have a failure but it's rare.

Now, take your meter with a fresh battery and put it on the lowest resistance setting. Short the leads and see if it reads 0. Next, test a bunch of your ematches and see what values you get. If they all read 1.2 OK your meter is cool. If your meter is reading 1 or something like 1.5 consistently with the shorted test leads and you get 2 to 2.5 ohms on all your ematch readings, you should still be O.K. Kurt
 
Problem is, is getting an ohm meter that can give you a decent measurement down that low.

It is not difficult to build a four wire meter with milliohm resolution. I would not recommend purchasing one of the inexpensive four wire meters as the ones I have seen use test currents that are too high to be safe.
 
mikec, what do you mean by 'I think the surgical tubing is overkill'?

ksaves2/Kurt, after replacing the battery in my multimeter I tested as you suggested. Yes, on the lowest resistance setting with the testing leads shorted, my reading is 0. Of the remaining 25 or so FireWire Initiators I have, most test 1.2 with a couple at 1.1. I did know to test them 'naked' (not in a 'live' charge), but a good safety reminder nonetheless. Thanks for the guidance on resistance testing.
 
This is the first I've heard of using surgical tubing to hold a charge and I think it's BRILLIANT. I believe mikec meant overkill as far as the pressure it holds. Since you want the black powder or pyrodex to pop rather than burn, it needs to build a little pressure. Some think that surgical tubing is necessary to build such pressure. If the finger of a glove is good enough, awesome. But surgical tubing will burn a little "cleaner" because it can hold hire pressure. Just my :2:
 
This is the first I've heard of using surgical tubing to hold a charge and I think it's BRILLIANT. I believe mikec meant overkill as far as the pressure it holds. Since you want the black powder or pyrodex to pop rather than burn, it needs to build a little pressure. Some think that surgical tubing is necessary to build such pressure. If the finger of a glove is good enough, awesome. But surgical tubing will burn a little "cleaner" because it can hold hire pressure. Just my :2:

I think your premise about higher pressures and better burning is correct. I also think the comment about overkill is because containment isn't needed when using BP. I believe the use of surgical tubing started when people were trying to get Pyrodex to work consistently. I have found that you do get more force from a BP charge if it is contained well, but the difference between well contained and loosely held together isn't that much. With Pyrodex the difference is extreme and very inconsistent if it isn't well contained.

I currently use a powder well on the face of the av-bay with some dog barf and masking tape to hold the powder in. I have used a piece of duct tape to hold the match and powder. They both work great with BP, but the powder well does produce a little more force with the same amount of BP as the duct tape charge will.
 
I think your premise about higher pressures and better burning is correct. I also think the comment about overkill is because containment isn't needed when using BP. I believe the use of surgical tubing started when people were trying to get Pyrodex to work consistently. I have found that you do get more force from a BP charge if it is contained well, but the difference between well contained and loosely held together isn't that much. With Pyrodex the difference is extreme and very inconsistent if it isn't well contained.

I currently use a powder well on the face of the av-bay with some dog barf and masking tape to hold the powder in. I have used a piece of duct tape to hold the match and powder. They both work great with BP, but the powder well does produce a little more force with the same amount of BP as the duct tape charge will.

I saw the original article about the surgical tubing in the past. Theories about "lack of oxygen" and "incomplete burning" abounded. I lost the link but another article
came along where the investigator used an altitude chamber and didn't find any advantage to using surgical tubing. True, if using anything other than 4F, confinement becomes more important but using a charge well like Handeman points out is all thats needed. If using 4F and worried about confinement, put an
extra layer of duct tape over the end. Kurt
 
mikec, what do you mean by 'I think the surgical tubing is overkill'?
People talk about using surgical tubing at very high altitudes, say over 20,000 feet. I've used BP in glove fingers with no issues on all of my flights (max altitude 21Kfeet) so the tubing isn't required there, at least with BP (I've never tried to use pyrodex.)
 
I saw the original article about the surgical tubing in the past. Theories about "lack of oxygen" and "incomplete burning" abounded. I lost the link but another article
came along where the investigator used an altitude chamber and didn't find any advantage to using surgical tubing. True, if using anything other than 4F, confinement becomes more important but using a charge well like Handeman points out is all thats needed. If using 4F and worried about confinement, put an
extra layer of duct tape over the end. Kurt

I came up with the surgical tubing idea. https://web.archive.org/web/20120524083237/https://www.wimpyrockets.com/page16.html It is only meant to be used with 4F BP and not pyrodex. I'm not sure how or why it works. Some people have shown it not to work in vacuum chamber testing. I just know that lots of people have used it successfully up to 96K. It must be magic. Best advise, ground test before you fly!

Tony
 
Interesting discussion on the surgical tubing approach to making deployment charges. The main reasons I decided to go with that method was because I can make them at home in advance, and they are easy for me to reproduce with consistent results. I'm looking forward to ground testing when I complete my current project which will be my first using electronic deployment.

By the way, thank you to blackbrandt. A little 'plug' of poster tack where I zip tie the surgical tubing ends works perfectly for a good seal!
 
Pictures are not working on the link above--is it just me?
 
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Personally, I use wells. Blastcaps are the bomb! the reason NOT to make up charges in advance is that they can't go off in your car if they aren't made.

Seriously, making up a charge with a static sensitive initiation device is not the best practice for safety. You can talk till you're blue in the face about shorting the match, but you'll never convince me given the small amount of current needed and low resistance.
 
When I fly under 20K I just use the finger tip of a medical glove. When I fly over 20K I use the following.

a ball park recommendation on tubing size and charge sizing for them.

for charges up to 2 grams 5/16" ID McMaster 5234K48

for charges 3-4 grams 3/8" ID McMaster 5234K99

for bigger or shorter charges 1/2" ID 5234K54

ground test before flying.

https://www.rocketryforum.com/showt...h-Altitude-Ejection-Charges&highlight=5234K48


Tony
 
tfish, thanks for the input on your surgical tubing method. One question, why not use the surgical tubing when you fly under 20K? Is it just easier to make glove tip charges, or is there something detrimental when using surgical tubing under 20K?

cbrarick, I'm curious about your comment regarding the safety of making charges in advance and worrying about static electricity setting them off. I don't want to be argumentative, but would like to see some dialogue on this. Given the FireWire Initiators I am using have a plastic cap bent over the leads completely covering them, I can't imagine a scenario where static could set one off. In order to evaluate if I need to reconsider this method I would love to hear some more input. Has anyone had a pre-made charge go off accidentally at home or in their car? If so, how do you think it happened? I have heard about charges going off while prepping a rocket on the pad. I would like to know how this happens too. Again, I don't want to be argumentative, but rather want to gather information as I am new to electronic recovery, making BP charges, etc.
 
iirc BP has its own oxidizer in the mix Potassium Nitrate aka saltpeter one of the three ingredients of BP (the others are charcoal and sulphur) however sulphur is not actually necessary (it mainly lowers the ignition temperature). So the argument for "lack of oxygen" shouldn't be a factor. Incomplete burning is definitely and issue and the longer BP is confined while burning the more fully it will be used up.
 
tfish, thanks for the input on your surgical tubing method. One question, why not use the surgical tubing when you fly under 20K? Is it just easier to make glove tip charges, or is there something detrimental when using surgical tubing under 20K?

cbrarick, I'm curious about your comment regarding the safety of making charges in advance and worrying about static electricity setting them off. I don't want to be argumentative, but would like to see some dialogue on this. Given the FireWire Initiators I am using have a plastic cap bent over the leads completely covering them, I can't imagine a scenario where static could set one off. In order to evaluate if I need to reconsider this method I would love to hear some more input. Has anyone had a pre-made charge go off accidentally at home or in their car? If so, how do you think it happened? I have heard about charges going off while prepping a rocket on the pad. I would like to know how this happens too. Again, I don't want to be argumentative, but rather want to gather information as I am new to electronic recovery, making BP charges, etc.

Never dink with a loaded charge outside of a rocket. Meaning if you use a continuity tester, you test the ematch before the powder goes in. Once the powder is in, it goes into the rocket. Once that charge is packed, it flies. If it doesn't fly, it stays in the rocket. If for some reason
I take it out of the rocket (ie. Second thoughts that the charge is weak) I blow it off with launch electronics at a safe distance or bury the charge a short distance and set it off underground if I don't want to make a noise.

By "dinking" I mean if you want to use bare ematches to test that an altimeter cycles properly, fine. I use micro centrifuge tubes: https://www.labtag.com/microcentrif...ated-111568/?gclid=CKid8crq38ECFQyMaQodaZQAQw
is an example. Poke a hole in the bottom and epoxy the match in with a dollop of epoxy.

I test all new electronics with bare ematches by flipping switches off/on quickly and letting radio trackers blast them with Rf. Some deployment altimeters don't work in higher power Rf fields. I did have a mishap when I accidentally plugged in a 9V battery backwards on a ground test and by golly, both matches blew.
Since they were contained in the vials, just a pop and no big deal.

I pre-prep before a launch because I want to fly. Not mess around with prepping. With the crappy weather in the Midwest, not as many opportunities to fly.
In 7 years, I've never had a charge go off "mysteriously" . Also consider it is less stressful to measure out powder and prep charges in a low stress environment of
an appropriate workshop than a launchsite where some idiot can walk by with a cigarette. Sealed up in a rocket is the safest place for an ejection charge.

Long term storage? I bet there are many out there who've stored pre-prepped rockets without any issue in a cool dry place. Sure, I wouldn't leave 'em in a car for days on end in a desert. Same goes for motors. Carefully prep in a no-stress environment, less likely to assemble wrong and then go fly. If you can't fly it, take it home and loosen the closures if threaded. Kurt
 
Kendal. For flights below 20K I use the finger tip of a medical glove. It's quicker and cheaper to make then the surgical tubing charges. I use the surgical tubing charges above 20K where "better" containment of the BP is needed to get a more complete burn (less scattered) burn. Again, Jim Jarvis has done some testing of the surgical tubing charges in a vacuum chamber, and they have performed poorly. Poorly as in low % of the BP consumed. I know of several flight in the 40-60K that have used them without a problem. The highest flight was 96K(?). These flights all had tightly packed apogee bays which may add to more complete combustion of the BP.

Always ground test.

Tony
 
On a slightly different topic; don’t use a volt meter to test a battery. All that will do is tell you if the battery still has a potential between the two poles.

It will not tell you if the battery can take a load and provide a current, for that you need a battery tester.

As far as “Pre-testing” E-Matches. Was I the only one who read that and had a flashback to the old Bugs Bunny cartoon where he was testing artillery shells by whacking them on top with a hammer?
 
I get the 'don't test e-matches when loaded in BP charges'. We covered that earlier, but I can appreciate the reminders from those late to this thread. Also, I agree that making/loading charges at home would be the best environment for me to fully concentrate on that task.

tfish, I can appreciate the glove tip method as easier and cheaper. I don't think I fully understood your comments about Jim Jarvis's testing of the surgical tubing method. Was that in comparison to the glove fingertip method, or just an evaluation of the surgical tubing method's performance at simulated altitudes? My initial thought was that the surgical tubing method would result in more complete burning and provide a more 'energetic' charge compared to the glove fingertip if equal amounts of BP are used. Am I wrong on that?
 
I have heard about charges going off while prepping a rocket on the pad. I would like to know how this happens too. Again, I don't want to be argumentative, but rather want to gather information as I am new to electronic recovery, making BP charges, etc.

The only charge I ever saw go off while prepping a rocket over the last 11 years was on a large L2 bird. Turned out the transistors on the altimeter were bent and twisted a little and two of the leads were toughing each other. The charge went off as soon as the power was applied. The transistors were straightened, altimeter tested, charge reloaded and the flight was successful.

It was a '90s altimeter.
 
I don't think I fully understood your comments about Jim Jarvis's testing of the surgical tubing method.

Tony and I reached different conclusions when testing the method. I have never figured out why. My test results are attached.

I am reasonably sure that if you use a surgical tubing charge in a large, wide-open bay at high altitude, it will not work. By the way, if you ever happen to see such a rocket, let me know. I think Tony and I agree that as the size of the bay gets smaller, the tubing charges work better, and I think we also agree that uping the amount of powder relative to a low altitude charge would be prudent.

I'm pretty much done doing testing of this, having made a huge dent in my ematch inventory. It would be nice, though, to have someone else do some testing, who might bring a fresh perspective on how to best simulate deployment at altitude.

Jim

View attachment Article on high altitude deployment charges_May 2013.pdf
 
Jim, thanks for the input and sharing your work. I won't be flying higher than 10,000 ft anytime in the near future.

So, my 'take home learning' from this thread regarding e-matches and BP charges for lower altitude deployments is to pick a method (charge wells, surgical tubing, glove fingertip, etc), pre-test resistance of e-match (is it within specs), prepare the charge the same way (consistency), and ground test multiple times. Any additions?
 
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