Homemade Ejection Charge Testing

[cruiten]

I was performing some ground-tests of my homemade ejection charges and I never realized that the surgical tubing actually behaves just like a balloon bursting after the ejection charge has fired.

Here is a video to illustrate what I am talking about:

[YOUTUBE]ht0Oe3FjjNQ[/YOUTUBE]

Here is what the tubing looks like after being fired:


The e-Match is simply made from 24 gauge solid-core speaker wire with 34 gauge nichrome wire. The ejection charge in the video is 0.4 grams Titewad smokeless powder in 1/4" (ID) X 7/16" (OD) latex rubber tubing using my Perfectflite StratoLogger altimeter.

The 0.4 grams of Titewad smokeless powder should be equivalent to 1.0 grams of FFFFg black powder and so far everything is working 100% after running 10 consecutive tests using the same small 7.4V LiPo battery (500 mAh / 25C) without recharging.

Pretty neat...

Cor

 

[cwbullet]

Pretty cool. I would test it with every altimeter you plan to use.

 

[ClayD]

If you are making a nicrome bridge, you should be measuring the resistance of each one you make.
once you test it with the altimeter(not the battery), you will know if what you make is okay with the altimeter.

you need a testable value for the bridge wire, so you can have insurance it will work.

 

[cruiten]

Pretty cool. I would test it with every altimeter you plan to use.

Chuck, right now the Stratologger is the only altimeter that I have but I definitely intend to ground-test all my gear when material configuration changes are introduced.

If you are making a nicrome bridge, you should be measuring the resistance of each one you make.
once you test it with the altimeter(not the battery), you will know if what you make is okay with the altimeter.

you need a testable value for the bridge wire, so you can have insurance it will work.

ClayD, all of my testing so far has been with my Stratologger and not by directly connecting the ejection charge to a battery. I am using homemade ejection charge igniters which do indeed use a nichrome bridge. I have logged all the resistance values for all the igniters that I have made to date and I can definitely see a pattern of what is "normal and good". In any case, I normally check and log the resistance values right after I make the igniter, and I have been checking for continuity with my multimeter right before I actually put the ejection charge packet together to make sure that nothing was broken in storage/transportation. Now that I think about it, I should check the resistance right after making the packet to make sure that nothing broke the circuit or noticeably increased the resistance; it goes without saying that I must take the appropriate safety precautions when testing the resistance after the packet has been made.

The next step is to do actual ground-testing with a complete DD rocket to ensure that everything is working as expected in terms of an appropriate/sufficient charge.

So far I am very happy with my results because smokeless powders are familiar and readily available to me because I have been using them for years for my ammunition reloading purposes. It is much harder for me to get my hands on black powder and it appears that it does not burn as cleanly as my smokeless powder.

Thanks for the feedback!

Cor

 

[Eyeguy41]

I have been trying to work out building an ejection charge and have had similar problems finding the FFFFg Black Powder. I recently acquired some and have made my own e-matches from 22 gauge solid core wire with a 40 gauge NiChrome bridge. I have gotten consistent reading off my volt meter and the wire glows red hot when connected to the battery. With a charge of powder I get ignition after 3-4 seconds. I have been unsuccessful in getting ignition while connected to my Stratologger though. Would you be willing to post photos of your build process for the bridge wires. Any help or suggestions will be greatly appreciated. Stratologger only fires for 2 seconds, so I am not getting enough energy to the bridge wire for a long enough time to cause ignition.

 

[cruiten]

I have been trying to work out building an ejection charge and have had similar problems finding the FFFFg Black Powder. I recently acquired some and have made my own e-matches from 22 gauge solid core wire with a 40 gauge NiChrome bridge. I have gotten consistent reading off my volt meter and the wire glows red hot when connected to the battery. With a charge of powder I get ignition after 3-4 seconds. I have been unsuccessful in getting ignition while connected to my Stratologger though. Would you be willing to post photos of your build process for the bridge wires. Any help or suggestions will be greatly appreciated. Stratologger only fires for 2 seconds, so I am not getting enough energy to the bridge wire for a long enough time to cause ignition.

A couple of things went through my mind as I read your post:

• I use 24 gauge solid core speaker wire; however, I do not think that this is a material difference.
• I use 34 gauge Nichrome-C for my bridge; however, I think that your 40 gauge bridge should heat up faster than mine.
• What is the resistance across the e-match after you have built it? The resistance on mine is about 1.9 ohms. If yours is much higher this could possibly be a problem.
• What battery are you using with your Stratologger?
• When you start up the Stratologger, what does it report the voltage as being?
• How are you testing the firing of the e-match through the Stratologger? Are you using a vacuum chamber or are you using the "Test Fire" feature found within the PerfectFlite DataCap software?
• What type of black powder are you using?
• What is the powder containment system that you are using when testing? In other words, is the e-match in direct contact with the powder?

I have had 100% success with all the e-matches that I have built for deployment charges as well as those that I dip in pyrogen for use as igniters.

I build my e-matches based on the information that I found here: https://www.info-central.org/?article=228

Here is a picture of the business-end of one of my e-matches:

I hope that this helps. Let me know if you have any other questions.

Cor

 

[Wayco]

I started out making my own igniters for ejection charges, and after discussing it with forum members, abandoned that idea. Read this thread:


https://www.rocketryforum.com/showthread.php?48387-Stratologger-data

 

[kandsrockets]

A couple of things went through my mind as I read your post:

• I use 24 gauge solid core speaker wire; however, I do not think that this is a material difference.
• I use 34 gauge Nichrome-C for my bridge; however, I think that your 40 gauge bridge should heat up faster than mine.
• What is the resistance across the e-match after you have built it? The resistance on mine is about 1.9 ohms. If yours is much higher this could possibly be a problem.
• What battery are you using with your Stratologger?
• When you start up the Stratologger, what does it report the voltage as being?
• How are you testing the firing of the e-match through the Stratologger? Are you using a vacuum chamber or are you using the "Test Fire" feature found within the PerfectFlite DataCap software?
• What type of black powder are you using?
• What is the powder containment system that you are using when testing? In other words, is the e-match in direct contact with the powder?

I have had 100% success with all the e-matches that I have built for deployment charges as well as those that I dip in pyrogen for use as igniters.

I build my e-matches based on the information that I found here: https://www.info-central.org/?article=228

Here is a picture of the business-end of one of my e-matches: View attachment 117876

I hope that this helps. Let me know if you have any other questions.

Cor

I use the same process as Cor does except I use 40 ga nichrome wire. I have used over 800 of these and have never had a failure. One thing I did find during testing is use a good battery. I use nothing but duracell. I had tried some cheap dollar specials and they did not work. I have used these on Hialt45, Arts 2, Raven 2, and Missleworks mini altimeters.

 

[bobkrech]

Download the free wiretron calculator at https://www.wiretron.com/free.html

It's one of the most useful programs for wiring applications, and has just about any type of wire you'll encounter.

Bob

 

[cruiten]

To follow up a bit more...

I really believe that the power source is a very important component to consider when using electronics for dual deployments.

After a lot of research I decided on a Lithium Polymer (LIPO) battery for my Stratologger 100 and so far I am very impressed. I am using the 2S1P battery shown here: https://www.sparkfun.com/products/10500
The battery is relatively cheap, light, rechargeable, and it packs quite a punch.

Here is a screenshot showing the voltage from my last DD flight of the Flash by K and S Rockets with the PerfectFlite Stratologger 100 and the LIPO battery:
As you can see, the voltage dropped from 8.3V to 7.8V for the two firing events.

In my ground-testing I have used this configuration to successfully ignite 12 of my e-matches using the same LIPO battery within a 30 minute span. Towards the end of that testing cycle the voltage on the battery had dropped to 8.2V. I am sure that I could have continued testing several more e-matches but I ran out...

Wayco: I fully respect your decision not to use homemade e-matches. So far I have enjoyed the journey of discovery on how to manufacture my own, including all the testing to ensure that everything will work as expected. In addition, it is great to hear that Scott (kandsrockets) has successfully used a similar setup over 800 times! Another benefit of making my own igniters (same e-match but dipped in primary and secondary pyrogen) is that I have not had to make that long walk to-and-fro to replace a commercial igniter that would not light... In any case, different strokes for different folks. The important thing is that we are enjoying our hobby!

Cor

 

[Fdog]

I can pass on that when using FFFF black powder, there is no "balloon phase" as seen in your video. At least none that I can see at 60 fps.

There are a lot of threads here concerning the use of smokeless powder, and how it needs to be contained to produce fast burns and decent ejection force. Your video results seem to reinforce those threads.


All the best, James

 

[cruiten]

... Stratologger only fires for 2 seconds, so I am not getting enough energy to the bridge wire for a long enough time to cause ignition.

I looked at my Stratologger log files and they show that the firing events only last 1 second, not 2 seconds.

Here is a screenshot to show you what I am talking about:


In any case, with my setup that 1 second event appears to be more than enough to ignite the charge.

Cor

 

[cruiten]

I can pass on that when using FFFF black powder, there is no "balloon phase" as seen in your video. At least none that I can see at 60 fps.

There are a lot of threads here concerning the use of smokeless powder, and how it needs to be contained to produce fast burns and decent ejection force. Your video results seem to reinforce those threads.


All the best, James

You are 100% correct that the smokeless powders must be well contained in order for things to work.

In my testing I have found that there appears to be about a 1.0 gram threshold in order for things to work well with the surgical tubing (1/4" ID x 3/32" Wall = 7/16" OD) that I have. In other words, it appears that a 1.0 gram charge and a 1.5 gram charge result in the same force because the 1.5 gram charge is not properly contained to use the additional powder which results in some unburned powder.

My next approach is to try polypropylene centrifuge tubes wrapped in a couple of layers of electrical tape in the hopes that the thicker walls along with the tape wrap will result in better containment.

I wish could just get my hands on some FFFFG black powder...

Cor

 

[kandsrockets]

You are 100% correct that the smokeless powders must be well contained in order for things to work.

In my testing I have found that there appears to be about a 1.0 gram threshold in order for things to work well with the surgical tubing (1/4" ID x 3/32" Wall = 7/16" OD) that I have. In other words, it appears that a 1.0 gram charge and a 1.5 gram charge result in the same force because the 1.5 gram charge is not properly contained to use the additional powder which results in some unburned powder.

My next approach is to try polypropylene centrifuge tubes wrapped in a couple of layers of electrical tape in the hopes that the thicker walls along with the tape wrap will result in better containment.

I wish could just get my hands on some FFFFG black powder...

Cor

If you can not get BP try some Hodgdon triple 7. I found this to work very well.

 

[cruiten]

If you can not get BP try some Hodgdon triple 7. I found this to work very well.

Thanks for that suggestion Scott! I considered it before, but I forgot about that as an option... Based on your experience with Triple 7 would you say that it is comparable in weight with BP, or do you have to use more Triple 7 to get the same force?

I was starting to consider Pyrodex P based on the info in this link: https://www.pratthobbies.com/info_pages/pyrodex/pyrotest.htm

The fun never ends...

Cor

 

[kandsrockets]

Thanks for that suggestion Scott! I considered it before, but I forgot about that as an option... Based on your experience with Triple 7 would you say that it is comparable in weight with BP, or do you have to use more Triple 7 to get the same force?

I was starting to consider Pyrodex P based on the info in this link: https://www.pratthobbies.com/info_pages/pyrodex/pyrotest.htm

The fun never ends...

Cor

I found it all depends on how you contain it. I use pvc charge holders on my e-bays. Once I have the amount of powder in, I fill the void with dog barf. I then put 3 layers of electrical tape over the top. Doing this seamed to work great.

 

[cruiten]

I wish could just get my hands on some FFFFg black powder...

Well, that turned out to be easier than I thought... I called the California distributor for Goex and they directed me to a small local shop 15 minutes from where I work.

Just got back from the shop and I am good to go!

Cor

 

[o1d_dude]

FFFFg = "Special Sauce"

It can be purchased if you know where to look and what to ask for.

 

[cruiten]

I can pass on that when using FFFF black powder, there is no "balloon phase" as seen in your video. At least none that I can see at 60 fps.

There are a lot of threads here concerning the use of smokeless powder, and how it needs to be contained to produce fast burns and decent ejection force. Your video results seem to reinforce those threads.


All the best, James

I did a quick test tonight and my results are exactly like James described: No "balloon phase". In addition there is a very bright flash and a much more violent and smokey result...

The following video shows what I am talking about:
[YOUTUBE]Y6L36Zx-VkY[/YOUTUBE]

This a quite a difference from my initial tests with Titewad smokeless powder shown here:
[YOUTUBE]ht0Oe3FjjNQ[/YOUTUBE]

Time to put the "smokeless powder ejection charge" experiment behind me and figure out a way to make sure that the FFFFg won't blow out the walls of my 1.64" K&S Flash. I think that I remember that someone mentioned to use centrifuge tubes wrapped with electrical tape to direct the force away from the body tube walls.

Cor

 

[kandsrockets]

I did a quick test tonight and my results are exactly like James described: No "balloon phase". In addition there is a very bright flash and a much more violent and smokey result...

The following video shows what I am talking about:
[YOUTUBE]Y6L36Zx-VkY[/YOUTUBE]

This a quite a difference from my initial tests with Titewad smokeless powder shown here:
[YOUTUBE]ht0Oe3FjjNQ[/YOUTUBE]

Time to put the "smokeless powder ejection charge" experiment behind me and figure out a way to make sure that the FFFFg won't blow out the walls of my 1.64" K&S Flash. I think that I remember that someone mentioned to use centrifuge tubes wrapped with electrical tape to direct the force away from the body tube walls.

Cor

I like using 1/4" launch lugs to make my charges for small rockets. I bought a bunch of 34" long 1/4" tubing from BMS and use it for ejection charges. Does not hurt your body tubes with flying plastic parts. I place my ematch in one end and then hot glue the end shut. File from the top, place dog barf to take up space and tape end shut with electrical tape. I make a few of these up before I leave to go to the launch and I ready to fly.

 

[cruiten]

I like using 1/4" launch lugs to make my charges for small rockets. I bought a bunch of 34" long 1/4" tubing from BMS and use it for ejection charges. Does not hurt your body tubes with flying plastic parts. I place my ematch in one end and then hot glue the end shut. File from the top, place dog barf to take up space and tape end shut with electrical tape. I make a few of these up before I leave to go to the launch and I ready to fly.

Scott: Thanks for that tip! How much 4Fg do you normally use for the forward compartment for the Flash? And while I am asking, how much do you normally use for the aft compartment?

Cor

 

[kandsrockets]

Scott: Thanks for that tip! How much 4Fg do you normally use for the forward compartment for the Flash? And while I am asking, how much do you normally use for the aft compartment?

Cor

Off the top of my head I think 1 and 1.5 but always ground test.

 

[cruiten]

Off the top of my head I think 1 and 1.5 but always ground test.

Scott: I did some ground-testing and decided to work up a load for the forward section starting at 1.0 grams. It felt like it was too much "special sauce" so I toned it down to 0.8 grams and that seemed more appropriate. Here is a short video of the test with 0.8 grams:

[YOUTUBE]hAHvJVbD1xc[/YOUTUBE]

In hindsight I should have turned off the lights so that I could better see the powder flash...

The test with 0.8 grams included two 2-56 shear pins in the nose cone and a 36" chute wrapped in a nomex blanket along with the standard kevlar cord that came with the kit. This package was packed pretty tightly inside that small 38mm tube. I put the 4Fg in a small 2 ml centrifuge tube with some wadding and just snapped the top back on. After the test the tube was completely intact, but the tube top was nowhere to be found.

Should I worry that my load for the forward section is almost half of what you thought you used? Probably not because I think that the important thing is to find out what works for my setup... I am planning on using 0.4 grams for the aft section so I will ground test that when I have a chance.

Thanks for the help and info!

Cor

 

[gdjsky01]

Well, that turned out to be easier than I thought... I called the California distributor for Goex and they directed me to a small local shop 15 minutes from where I work.

Just got back from the shop and I am good to go!

Cor

Where was that. I am near OC

 

[cruiten]

Where was that. I am near OC

PM sent...

Cor

 

[kandsrockets]

I looked at my notes and I used 1 gram for the main and 1.2 gram for the drogue. I like a good active separation so your .8 gram is probably enough.

 

[cruiten]

I looked at my notes and I used 1 gram for the main and 1.2 gram for the drogue. I like a good active separation so your .8 gram is probably enough.

By the way, I wanted to let you know that I really like your Flash kit and I am very happy that I purchased it. I really like the fact that your kits are basically all dual-deployment kits because MPR rocketry has taken on a whole new dimension for me since I started with dual deployment flights.

Do you really use more BP for the drogue section than you do for the main section?

Cor

 

[degreaser]

Here's a good discussion of modern ematches. Note that many of the current altimeter designs are not capable of supplying a great deal of current for any appreciable period of time. I've tried home made ematches similar to those described in this thread with telemetrum altimeters and the results were marginal at best. On the other hand, the Q2G2s performed flawlessly, both on the ground and in the air. Make sure you do adequate ground testing.

https://www.rocketshoppe.com/info/Igniter_Continuity_Tests.pdf

 

[CarVac]

Here's a good discussion of modern ematches. Note that many of the current altimeter designs are not capable of supplying a great deal of current for any appreciable period of time. I've tried home made ematches similar to those described in this thread with telemetrum altimeters and the results were marginal at best. On the other hand, the Q2G2s performed flawlessly, both on the ground and in the air. Make sure you do adequate ground testing.

https://www.rocketshoppe.com/info/Igniter_Continuity_Tests.pdf

I see no ematches there, only igniters.

 

[degreaser]

I see no ematches there, only igniters.

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.