Homemade Ejection Charge Testing

[CarVac]

picky picky picky.... Yes, you are correct. However, the same principles apply. The nichrome igniters presented in this thread tend to require a fair bit of current. The Q2G2s don't. My point is that the homebrew varieties may not be reliable when used with modern altimeters due to their current requirements. I wouldn't hesitate to use a homebrew igniter to start a motor but I'm hesitant at this point to use one for deployment.

Also, the telemetrum has a software timer which assumes that the igniter will fire in less than 50ms and only supplies current to the igniter for this period of time. While you can adjust the timing by hacking the source, BDale has said that he's concerned about pulling the processor power supply rail low and/or heating of the PC board traces when using higher current devices. I'm not sure what the raven does as the source code is not open source.

The other main point of the thread regarding ballooning is quite interesting. I'm hoping tfish chimes in.

The Raven puts the outputs high for 1 second, and it's depending on version it's rated for very high currents. The Raven2 is 4 (main, apogee) and 9 (#3 and #4 ouptuts) amps, and the Raven3 is 9 and 20. That's enough for anything. You just need to keep the voltage across the altimeter itself low enough.

 

[degreaser]

The Raven puts the outputs high for 1 second, and it's depending on version it's rated for very high currents. The Raven2 is 4 (main, apogee) and 9 (#3 and #4 ouptuts) amps, and the Raven3 is 9 and 20. That's enough for anything. You just need to keep the voltage across the altimeter itself low enough.

Perhaps, but until I had 100 or so successful ground test deployments IN A ROW, I don't think I'd trust home made ematches. The pcb traces on the raven don't look like they could sustain 9 much less 20 amps for any extended period of time. Likewise with the telemetrum. Maybe the switching devices are rated for that sort of current but I seriously doubt the traces and vias are.

Something I've been thinking about trying are using some 0603 or 0402 smd resistors rather than nichrome wire. The smaller devices can't dissipate much power so they should go up in smoke pretty quickly.

Still, why would one skimp with a $1 ematch on a $500 or $1000 rocket?

 

[tfish]

Chiming in..not much to add. I kind of expected the surgical tubing to work with 'other powders'. It's good to see that some one has tested it along with a great video. I'm guessing that 4F 'balloons' too..but maybe to fast to be captured on video. I just know that the surgical tubing contains 4F long enough to make it work. The Google/AeroPac rocket that flew to 104K had surgical tubing charges as back up. The main charges fired but failed to separate the rocket. The surgical tubing charges did the trick. James Grover flew to 52K and used them. Here was his specs that he sent to..
•4" diameter performance rocketry tube
•Length of compartment is 12", or 8" with nose cone on
•I used 1.5g of 3F for primary, and 2.1g for backup 1.5 seconds later, however, the primary popped the cone as seen from the altimeter data and the backup was not needed
•Latex tubing was 1/2" ID, but I need to double check on that tonight me

Tony

 

[CarVac]

Perhaps, but until I had 100 or so successful ground test deployments IN A ROW, I don't think I'd trust home made ematches. The pcb traces on the raven don't look like they could sustain 9 much less 20 amps for any extended period of time. Likewise with the telemetrum. Maybe the switching devices are rated for that sort of current but I seriously doubt the traces and vias are.

Something I've been thinking about trying are using some 0603 or 0402 smd resistors rather than nichrome wire. The smaller devices can't dissipate much power so they should go up in smoke pretty quickly.

Still, why would one skimp with a $1 ematch on a $500 or $1000 rocket?

I'm not condoning the use of homemade e-matches, but the traces on the Raven in the vicinity of the FETs are extremely broad. The FETs themselves are immediately beside the output pins (and the power supply pins), so the current doesn't have to go through any significant length of circuit board. The traces only need to carry switching signals to the transistors.

 

[degreaser]

I'm not condoning the use of homemade e-matches, but the traces on the Raven in the vicinity of the FETs are extremely broad. The FETs themselves are immediately beside the output pins (and the power supply pins), so the current doesn't have to go through any significant length of circuit board. The traces only need to carry switching signals to the transistors.

Ok. Now we can discuss the internal resistance of 9v alkaline batteries as the limiting factor

And safety considerations of a rocket coming in ballistic due to failed deployment....

I'll have to take a close look at the raven's layout. Admittedly, I haven't tried the raven with homebrew ematches, only the telemetrum.

BTW - I went down this rat hole too before I got my L1. Heck, I even formulated my own potassium chlorate because skylighter wouldn't sell any to me. I finally gave up (for the time being) and decided to build rockets instead. One mistake I made was using too thick of a pyrogen. The coating needs to be fairly thin otherwise chunks of it will blow off and the rest will fail to ignite.

 

[degreaser]

Here are some tube charges I made a while back. They are using 4Fg and Q2G2s. I haven't used them yet. I'll have to see if I can get some images and look for ballooning per cruiten. I'm also concerned about the plugs becoming projectiles. That's what testing is all about eh?

 

[CarVac]

Here are some tube charges I made a while back. They are using 4Fg and Q2G2s. I haven't used them yet. I'll have to see if I can get some images and look for ballooning per cruiten. I'm also concerned about the plugs becoming projectiles. That's what testing is all about eh?

That's really slick! I wonder how well they work after a few minutes in full vacuum...

 

[cruiten]

...BTW - I went down this rat hole too before I got my L1. Heck, I even formulated my own potassium chlorate because skylighter wouldn't sell any to me. I finally gave up (for the time being) and decided to build rockets instead. One mistake I made was using too thick of a pyrogen. The coating needs to be fairly thin otherwise chunks of it will blow off and the rest will fail to ignite.

I was only talking about the e-matches that I use to set off my main/drogue ejection charges, not the igniters that I use to ignite my motors. In all my ground testing and actual flights with e-matches for ejection charges I have never used an e-match that I dipped in a primary and/or secondary pyrogen, I just use a simple e-match made up of 24 gauge solid core speaker wire withe 34 gauge Nichrome-C for my bridge. This has always set off my smokeless gun powder as well FFFFg charges using my PerfectFlite Stratologger and based on my results I see no no need to use a pyrogen when setting off the ejection charges with a Stratologger altimeter.

When I make my igniters I use the same e-matches but I also dip them in a primary and secondary dip from FireFox Enterprises. Again, I have also had 100% success with my homemade igniters. By the way, I am not making my own igniters to safe money, but I got tired making the walk of shame back to my rocket because my commercial igniters did not ignite my motors.

Here are some tube charges I made a while back. They are using 4Fg and Q2G2s. I haven't used them yet. I'll have to see if I can get some images and look for ballooning per cruiten. I'm also concerned about the plugs becoming projectiles. That's what testing is all about eh?

Those plugs are pretty neat. I used surgical tubing when I was experimenting with smokeless powders but I just used tie-wraps to close the ends; however, that might be problematic if you use very large diameter surgical tubing. In all my testing with surgical tubing I almost always observed that the tube was ruptured on the side and that the wraps on both ends almost always stayed in place. Notice I said "almost always"... In those instances I would worry a bit about those neat little plugs becoming chute-tearing projectiles...

In any case, I have moved away from using surgical tubing for now and I am currently using plastic centrifuge tubes because my dual deployment flights are with a K&S Rockets Flash where the body tubes have a 1.52" internal diameter and I wanted to make sure that I did not blow out the walls if the forces were directed sideways. With the centrifuge tubes I know that the full force is directed towards the ends of the tubes because all my tubes are intact after my ground tests. Also, currently my DD flights are on MPR motors so I am not reaching the heights that Tony (tfish) had to deal with.

By the way, I think the only way that you might see any ballooning with 4Fg is if you have a high-speed camera. In all my testing the same camera that picked up the ballooning with smokeless powders does not pick it up with 4Fg.

Finally, in case that you are considering wrapping your surgical tube charges with electrical tape... Please be aware that this will result in explosive forces that are much, much, much higher than when no electrical tape is used. Please don't ask me how I learned this... :surprised:

Cor

 

[degreaser]

Finally, in case that you are considering wrapping your surgical tube charges with electrical tape... Please be aware that this will result in explosive forces that are much, much, much higher than when no electrical tape is used. Please don't ask me how I learned this... :surprised:

Cor

Duck tape.

I turned the plugs from some 3/8" stock. I'm concerned about shooting them through the side of the airframe. That would be bad The Q2G2s are epoxied in place. I'll drill the spent ematch out for reuse of the plugs.

Per tfish, these things (surgical tubing charges) are only needed above 22K MSL or so. The rocket I'm currently building will tickle that altitude so i figure it's time to gain some experience with them. So far, I've been using homebrew blastcap clones with no problems.

I wish I had a camera capable of high speed video but 60fps is about my limit.

 

[cruiten]

...The Q2G2s are epoxied in place. I'll drill the spent ematch out for reuse of the plugs.

With my centrifuge tubes I use hot glue to keep the e-match in place. So far I have not had an instance where the hot glue did not remain in place after the ejection event and the hot glue is pretty easy to remove if I wanted to reuse the tube

What is the diameter of the rocket that is going to "tickle" 22,000 feet MSL? If the rocket diameter is not too small then I would just use tie-wraps at both ends of the surgical tubing. However, please realize that this is based on my experience with rockets that have not exceeded 6,000 feet MSL (3,000 feet AGL). I believe that Tony (tfish) has better documentation of what he successfully used at high altitudes at this link: https://www.wimpyrockets.com/page16.html

Good luck with your project!

Cor

 

[tfish]

I posted earlier in this thread..post #33..nothing major added. As far as using plugs in the ends of the tubing..some guys are using them. I have not used them. On some of my higher flights...30K and above, I've used to zip ties on each end. The point is to seal the ends. How you do this does not really matter. Don does good work and has the tools to make some very nice plugs, rockets and other things.

Tony

 

[degreaser]

Said rocket is 5" in diameter. The largest motor would be a 98mm 6XL (CTI baby O) Most of the planning is done but I'm still making tooling. Work has a way of interfering with rocket building though so I probably won't make much progress until April. As I mentioned to Tony, the plugs are an experiment and are part of the process of taking baby steps to high altitude, min diameter builds. If they blow out, I'll try something different.

I sealed it with epoxy mainly to keep the powder where it belongs.

Thanks for the complement Tony

 

[CarVac]

I posted earlier in this thread..post #33..nothing major added. As far as using plugs in the ends of the tubing..some guys are using them. I have not used them. On some of my higher flights...30K and above, I've used to zip ties on each end. The point is to seal the ends. How you do this does not really matter. Don does good work and has the tools to make some very nice plugs, rockets and other things.

Tony

Do you get a complete, perfect seal without the plugs? Is a perfect seal needed for holding the pressure inside the tubing approximately atmospheric, or is it only necessary to restraining the expansion of the gases once the BP has gone off?

Someone (who? I don't remember) once said that a concern was the effective transfer of heat from the ematch/q2g2 to the BP, which decreases in a vacuum.

 

[tfish]

When I was testing these high altitude charges, scattering the BP before it had a chance to burn seemed like the biggest issue. Up to that time frame..a few guys had some pretty high flights and used BP. I was hearing they were using 3 or more times the 'normal amount' of BP. This made sense and I was seeing it being scattered around in the vacuum chamber too. I had heard things, that it was to cold, no oxygen at altitude for BP to work. BP has it's own "oxygen" so that one made no sense to me. I just know that it has been working. I've only personally been to 38K with rocket recovered. I've tracked one of my rockets at 60Kish but never recovered it. I think you need a good seal. How ever you accomplish that is up to you. I use double zip ties on my higher flights..for no real reason that I can think of. I think that little bit of pressure that you capture in the tubing when you make it might help in not scattering the BP once the tubing breaks. I think the tube 'balloons' long enough to help most of the BP burn. I was happy to hear that the surgical tubing charges saved the Google/AeroPac rocket. If you watch the 100K video..you can hear the primary charges go off..but nothing happens. About 3 seconds later the back up surgical tubing charges fire and you can see the drogue being deployed.

Tony

 

[degreaser]

I only managed to get a couple of shots of the 100k avbay as I didn't want to be too much of a pest and get in their way. In this shot you can see two, maybe three surgical tubing charges. They appear to have plugs of some kind. I'm not positive but I think that the drogue is located near the nosecone and the main more towards the avbay. Both were contained in a single section of airframe tubing.

 

[CarVac]

It's on Page 33 of their documentation:

https://docs.google.com/file/d/0B7wR-btf10NSNEdKOHROcGRGbDA/edit

They used 1/2" OD solid latex plugs, ziptied them super-tightly, and then used RTV (room-temperature vulcanizing rubber or something like that) to further seal the ends.

 

[degreaser]

It's on Page 33 of their documentation:

Documentation? Thanks for that link.

 

[Nessalco]

"Real" ematches are pretty easy to make, and 100% reliable when you know what you are doing. I buy the #50 heads from ODA. They will fire from any altimeter (.5A all-fire)

Kevin

 

[degreaser]

"Real" ematches are pretty easy to make, and 100% reliable when you know what you are doing. I buy the #50 heads from ODA. They will fire from any altimeter (.5A all-fire)

Kevin

Perhaps you could start a thread and document your technique. I've used the match heads from skylighter with less than optimal results. I've used Dark Flash as the pyrogen.