Non-Pyro Ejection Charge

[Lentamental]

So I see tons of designs out there that use BP charges along with their altimeters and all, but I am wondering if anyone has tried non-pyro methods.
I am currently in the process of designing a rather complicated dual deployment system that will use a compressed spring, and a solenoid shear pin type thing.
Compressed gases seem out of the question, because of the complications involved in holding them at pressure, and then releasing it. The weight of a pressure container and valve with some sort of electrical triggering just seems like way beyond the range one could launch in a rocket.
I suppose the other possibility when using a compressed spring, would be to use a burn string, but I would far prefer straight forward mechanical and electrical systems to anything that burns.

All ideas welcome.

Last thing, for reference, I am working with BT-70

[powderburner]

I agree, it's about time that we had an alternative to BP ejection

But why BT70? Why not something that works all the way down to BT60, or even BT50?

[Lentamental]

Well of course something smaller would be nice. The spring mechanism that I am working on is contained in a ~1" tube, but I don't know how large of solenoids will be necessary, and whether I will be able to put them inside the tube or whether they will have to go on the outside.

[KerryQuinn]

I've been thinking along these lines too. I think the combination of the solenoid coil & pin plus the battery large enough to power the coil will be far heavier than the type servo used on RC planes.

[Lentamental]

Well I have done some thinking, and consulted my air cannon friends over at SpudFiles.com, and came up with several ideas.
The issue with Rouse-Tech's CD3 system is that is uses CO2, which has a very VERY high vapor pressure (we are talking about 800psi) and so the canisters must be heavy, and the same is true with the hardware used with them. It does have the advantage of being a gas at STP, while it can still be stored as a liquid. CO2 is not the only gas like this however. Several others that come to mind, with much lower vapor pressures, are propane, butane, and what ever it is that goes into Air-in-a-Can things. These all have a vapor pressure in the range of 100psi, which even thin-walled pvc pipe can handle.
My concept is to have a small PVC chamber, with a heat activated burst disk (fancy language for a sheet of mylar in a threaded union, with nichrome wire pressed up against it) on the end. It could be filled by gluing the bottom of a Bic lighter on to the other end, and filling with your standard butane refill canister (or what ever you end up using for propellant)
This could in theory be much much lighter than the CD3, and much cheaper too. The only possible issue is that if you are using one of the combustible gases, you would have to take certain design considerations into account to keep the hot nichrome wire from igniting the fuel as it mixes with the air in the tube.

[bobkrech]

Well I have done some thinking, and consulted my air cannon friends over at SpudFiles.com, and came up with several ideas.
The issue with Rouse-Tech's CD3 system is that is uses CO2, which has a very VERY high vapor pressure (we are talking about 800psi) and so the canisters must be heavy, and the same is true with the hardware used with them. It does have the advantage of being a gas at STP, while it can still be stored as a liquid. CO2 is not the only gas like this however. Several others that come to mind, with much lower vapor pressures, are propane, butane, and what ever it is that goes into Air-in-a-Can things. These all have a vapor pressure in the range of 100psi, which even thin-walled pvc pipe can handle.
My concept is to have a small PVC chamber, with a heat activated burst disk (fancy language for a sheet of mylar in a threaded union, with nichrome wire pressed up against it) on the end. It could be filled by gluing the bottom of a Bic lighter on to the other end, and filling with your standard butane refill canister (or what ever you end up using for propellant)
This could in theory be much much lighter than the CD3, and much cheaper too. The only possible issue is that if you are using one of the combustible gases, you would have to take certain design considerations into account to keep the hot nichrome wire from igniting the fuel as it mixes with the air in the tube.
This would not be a good idea, and I believe it would violate the safety codes. You are likely to ignite the liquified hydrocarbon fuel and cause a fire, either in the air or on the ground.

Bob

[Lentamental]

Well the idea would be that the fuel/air ratio would be far too high for it to ignite, while the nichrome wire is hot, and then it would cool before the air has time to mix well enough. Still, a valid point that you probably don't want to risk it, so I will stick to to non-flammable gases, or do some intensive testing first.

I don't see how it would violate safety codes... How is carrying a liquid fueled (possibly combustible) ejection charge worse than carrying an EXPLOSIVE ejection charge? Or is it some other part of the design that would violate safety codes? Please elaborate.

[bobkrech]

Well the idea would be that the fuel/air ratio would be far too high for it to ignite, while the nichrome wire is hot, and then it would cool before the air has time to mix well enough. Still, a valid point that you probably don't want to risk it, so I will stick to to non-flammable gases, or do some intensive testing first.

I don't see how it would violate safety codes... How is carrying a liquid fueled (possibly combustible) ejection charge worse than carrying an EXPLOSIVE ejection charge? Or is it some other part of the design that would violate safety codes? Please elaborate.
Black powder, and other pyrotechnic deployment devices, are universally used in professional rocketry as the recovery deployment method of choice. Hermetically sealed pyrotechnic devices work at sea level and in the vacuum of space. They are the simplest and lightest weight solution, and most reliable devices for the job. Why some hobbists think that heavier and bulkier compressed gas deployment systems are superior is beyond me.

Propane and butane are flammable gases by definition.

http://www.amerigas.com/pdfs/safe_eng.pdf

http://specialtygasesofamerica.com/msds/n-butane-msds.pdf

I would consider launching a tank of propane or butane a safety code violation.

9. Flight Safety. I ... will not put any flammable or explosive payload in my rocket...

http://www.nar.org/cabinet/HPRSafetyCode.pdf

Bob

[Lentamental]

Except from what I have read, BP doesen't work in space because as it expands, it cools too quickly to keep the burning process going. There seems to be an altitude cap at which BP will actually fire (I couldn't scare up those numbers quickly). That is one of the reasons the CD3 is used.


9. Flight Safety. I ... will not put any flammable or explosive payload in my rocket...

http://www.nar.org/cabinet/HPRSafetyCode.pdf


And yet you claim that BP charges are commonly accepted for HPR.
The thing that I don't get is why a flammable payload, designed specifically not to burn, but still be released in its entirety before it reaches the ground is worse than an explosive payload, designed specifically to detonate in the air. One seems like a firework without the pretty colors, while the other seems more like a rocket with a compressed gas ejection charge.

Please forgive me if I sound rude, I just really do not understand how you guys are coming up with these rulings. It seems like BP is ok, not because it is any safer, but solely because it has been done before.

[powderburner]

9. Flight Safety. I ... will not put any flammable or explosive payload in my rocket...

http://www.nar.org/cabinet/HPRSafetyCode.pdf


Now don't get me wrong, I agree entirely that adding flammable or explosive materials as payload is wrong, whether called out by the safety code or not.

But-

I am not so sure that adding an appropriate quantity of such materials, for purposes of producing an ejection event, is the same thing as "payload"

If you were to lump all added energetic chemicals into the category of "payload" then I don't think most of the high-power rockets would be able to use BP for ejection. You yourself said:

Black powder, and other pyrotechnic deployment devices, are universally (emphasis mine) used in professional rocketry as the recovery deployment method of choice.

So, is an ejection charge considered a payload or ejection charge? (and how do you tell the difference?)


Edit: I just read down to Lentamental's post, and realized he just said 99% of what I just said. Sorry, I didn't mean to be piling on.

[air.command]

Hi guys,

Allow me to come at this from a different angle. Non-pyro recovery system ejection is the main stay in the water rocketry world. We don't usually have the luxury of a delay charge and so most often ejection is achieved mechanically.

I've compiled an extensive guide to recovery systems used in water rockets over the years
http://home.people.net.au/~aircommand/recovery_guide.htm
but there is no reason why some of these techniques could not be employed in regular pyro rockets. If you look down the list there are many different approaches people have taken, and at the end there are links to people's web pages where they describe their systems.

You certainly do not have to store compressed gasses to use gas pressure to eject the recovery system. Chemical reactions are often employed, such as vinegar and baking soda. They are kept separate and allowed to mix when required to produce CO2 usually in small quantities but enough to activate a piston to do the separation.

Along with solenoids, Micro RC servo motors are also often employed to release latches on stored energy devices such as springs and rubber bands to do the ejection.

Now having said all that, unless a non-pyro requirement is a must you just can't beat a BP ejection charge for simplicity, weight and reliability over almost all other mechanical systems.

- George

[Bravo52]

Hi guys,

Allow me to come at this from a different angle. Non-pyro recovery system ejection is the main stay in the water rocketry world. We don't usually have the luxury of a delay charge and so most often ejection is achieved mechanically...........

Along with solenoids, Micro RC servo motors are also often employed to release latches on stored energy devices such as springs and rubber bands to do the ejection.

- George

This is very intersting. Does anyone know if a Perfectflite altimeter will drive a solenoid or Micro RC servo?

[falingtrea]

The issue as I understand it is that pyro ejections systems, unless it is an integral part of the motor, still requires the user to have a LEUP (especially for black powder). So if you want to fly high power without a LEUP, you are pretty much limited to motor ejection or some sort of non-pyro system.

[bobkrech]

Except from what I have read, BP doesn't work in space because as it expands, it cools too quickly to keep the burning process going. There seems to be an altitude cap at which BP will actually fire (I couldn't scare up those numbers quickly). That is one of the reasons the CD3 is used.
Don't believe everything you read on the internet.

I, and thousands of aerospace engineers, have designed pyrotechnic recovery systems that work in a vacuum. You need to use a hermetically sealed container to confine the BP while it burns.

The CD-3 CO2 system is initiated by BP ignition in a sealed container that generated high pressure gas that activates a pyrovalve that dumps a CO2 cylinder! You can save a lot of weight and complexity by using the gas generated by the BP combustion to push the chute out provide you ignite the BP in a hermetically sealed container with a burst diaphragm just like the pros do.

Here's a high altitude BP deployment system I designed for the FIT JAMSTAR team.

http://projects.fit.edu/jamstar/index.html
http://projects.fit.edu/jamstar/html/adept_apogee.html
http://projects.fit.edu/jamstar/html/hazard_chamber.html

This reference contains designs and the theory behind propellant ignition and the requirements for the initiation of combustion in vacuum. If you couldn't ignite powders in space, you couldn't ignite solid rocket motors in space.

NASA/SP-8051, Solid Rocket Motor Igniters, NASA SPACE VEHICLE DESIGN CRITERIA (Chemical Propulsion), NASA (Washington, DC, United States), NASA Lewis Research Center (Cleveland, OH, United States), June,1970, pp. 111.
http://trs.nis.nasa.gov/archive/00000094/

In fact on of the best compendium of spacecraft design expertise can be found in the NASA SP-8000 series monographs. You can find a list of the publications and download links on Richard Nakka's website.

http://www.nakka-rocketry.net/sp8000.html

Bob

[SteveF]

anyone have any experience with memory wire/muscle wire? This looks to be interesting stuff and might be workable into a fairly simple low weight solution to non-BP ejection

Steve

[Lentamental]

I did a little work, trying to make my own spring out of music wire, for a prototype for the TARC rocket that I am not actually going to end up making, and it is pretty good. I must say though, making a spring is a LOT of work. Really tough work too. Either you use pliers to bend it, which can be really clunky, or your sacrifice your fingers to the rocket gods. My thumb was sensitive for at least two days afterwards...

For reference, I made my 1"x5" spring out of .039" (1mm) music wire. I also got some thicker stuff, but couldn't bend it well enough. The spring compresses all the way down, so could be made to work for a piston pusher fairly easily, if you found the right servo or solenoid to hold it back.

[WillMarchant]

I got one of these http://resjets.com/ servo-activated CO2 dispensers to play with in my copious spare time. I'll post a report at some point.

There were various companies making Nitinol springs and pre-frabricated "muscles." We used some home-brewed versions to activate various mechanisms on one of our observatories. A quick search turned up http://www.musclewires.com/shapememoryalloys.shtml

Robert Goddard attempted to use spring activated recovery methods with various degrees of success. It seems likely that the trick is to get a small drogue parachute out into the airstream and to use that to extract larger parachutes. Knacke's Parachute Recovery Systems Design Manual seems to be the place to start.

As Bob points out, a BP system is going to be vastly simpler and therefore probably more reliable.

[SteveF]

thanks - i had found that site too. I know BP is simple and effective. I was just thinking that if you could drive the muscle wire directly from the flight computer to activate a simple spring/plunger or some sort of lever then that could be another simple way to achieve deployment - more of a what if question - but if you dont ask then you never know


Steve

[bobkrech]

thanks - i had found that site too. I know BP is simple and effective. I was just thinking that if you could drive the muscle wire directly from the flight computer to activate a simple spring/plunger or some sort of lever then that could be another simple way to achieve deployment - more of a what if question - but if you dont ask then you never know

SteveOr you might try using a micro servo pulling piano wire...

Bob

[cornyl]

An easy way to build pressure in a tube taken from the
medical industry.
Install a small stepper motor inside the tube using a teflon lead screw.At the end of the lead screw install a air tight disk to act like a piston and pressurise
the volume of air untill the nosecone pops.
Stepper motors are small cheap and powerfull and can run very fast. Batteries to run the lead screw would be minimal.

CornyL

[rocketsmith]

One of the primary concerns with using a mechanical recovery initiator is generating enough energy and momentum to break shear pins and seperate the airframe. I am working on a prototype that uses a burn string wrapped in nichrome wire to retain the compressed spring and piston. The issue I have found is that the spring needs to store sufficient energy in a small enough space to eject everything while not becoming cumbersome to use. If a spring is sufficient to sperate the airframe it is usually too heavy to compress easily. If the piston has enough mass to maintain the energy as the spring decompresses the device adds significant weight. Servos and solenoids add weight, aren't always reliable at high g loads and can have high power requirements; a bigger battery adds weight. Also. the durability of the materials we use can be an issue. Reinforcing adds weight. I am beginning to think that BP is the default ejection product because it work the best given the comprimises involved, not that nobody has come up with another solution. David B. Smith.

[Lentamental]

I am beginning to think that BP is the default ejection product because it work the best given the compromises involved, not that nobody has come up with another solution.

That is exactly the point.
Currently, BP may be the best given the compromises involved, BECAUSE nobody has come up with a better solution.
I agree that given the current technology that is out on the market, BP is the best, but that doesn't mean that it is the absolute best possible, ever, no matter what. There is always room for improvement, and that is what this thread is about. Coming up with alternative ideas, that may, at some point in the future, become a better option, for certain circumstances.

[DAllen]

Why some hobbists think that heavier and bulkier compressed gas deployment systems are superior is beyond me.


It isn't superior. BP is a pain in the posterior because it is impossible to buy even here in the great state of Michigan where muzzle-loading deer hunting is a religion.

I, for one, would like to see a suitable alternative to BP for that reason alone.

-Dave

[Hughie]

Just wondering, does any ejection system use smokeless powder?

[SteveF]

smokless propellent would not work - it would just burn a lot slower than bp and not generate the quick burst of expanding gas - it needs to be contained as in a cartridge and gun chamber to work properly. Been ages since i have reloaded cartridges or shot bp but the two are never interchangable in the way they work.

On a side note, havent looked at pyrodex in ages either - that come in fine and fast enough size to work or is it pretty much just 4f that everybody uses

[WillMarchant]

http://www.pratthobbies.com/info_pages/pyrodex/pyrotest.htm

[dixontj93060]

I use Hodgdon Triple 7 (www.hodgdon.com/tripleseven.html) exclusively. It works fine. Much cleaner, no smell, no corrosion. Just pay attention to good confinement especially if using centrifuge tubes (I wrap with a layer of HVAC metal tape).


Just wondering, does any ejection system use smokeless powder?

[SteveF]

thanks - thought it took more pressure that just a few wraps of tape to make smokeless work right and not just burn

[newtons3rd]

Actually we have tested several BP substitutes and have had good luck using out ejection canisters. Containment is the key as has been stated.

[321]

So I see tons of designs out there that use BP charges along with their altimeters and all, but I am wondering if anyone has tried non-pyro methods.... All ideas welcome.

Pepsi and mentos! ha.

[THier]

The key to effective powder usage as others have said is containment. This includes BP. I use spent BP motor casings, A-C for 4gr or less,, D motor casings for large projects. I put the squib in through the nozzle, hot glue it in place, fill with powder, pack, put some paper towels on top of that, the hot glue it in. I get energetic ejection everytime. I used to put BP in a bag, wrap with tape, and suffered many burnt nylon straps and scorched chutes.BP will burn slowly if not contained correctly. I have used Pyrodex as well,, contained it works fine. For even smaller projects, you can get small cardbd tubes from drycleaner hangers. The key is forcing the powder to pressurize and not allowing it to "burn".

For you newer folks out there,, remember this,, you are pressurizing the airframe, it does not matter if the charge is blowing towards the opening. I have heard a few discussions about this subject. 99.9% of the charges will blow towards the opening,, but if they don't,, it will still separate the airframe.

Tom

[dpower]

I use Hodgdon Triple 7 (www.hodgdon.com/tripleseven.html) exclusively. It works fine. Much cleaner, no smell, no corrosion. Just pay attention to good confinement especially if using centrifuge tubes (I wrap with a layer of HVAC metal tape).If one wanted to supplment AT RMS motor ejection for larger airframes, could this be used, or is the containment not tight enough?

[aerostadt]

Sport Rocketry had an article about 5 or 10 years ago using a model airplane servo to release a spring expelling a parachute. I think the rocket was in about the H-motor range. The trick was to build an electronic device take would take the signal from an altitude apogee detection device and convert it to something that would move the servo. I remember taking the plans for the electronic device and giving it to a friend that was good with those kind of things. Sure enough the device worked, but I never got around to using it in a flight model.

Bob