What do you think is the future of model rocketry electronics/technologies?

[Capt. Eric]

Re ejection method: Could internal pressure be generated by a non pyrotechnic, chemical reaction gas generator like a car airbag? Doesn't need to be behind a piston, and hopefully not too much heat. I'd envision something like a JLCR size device that is dropped into the bottom of the body tube. After the flight open it and replace the "pills" that react and generate the gas. Bigger rocket? Use bigger "pills".

Otherwise, I like the idea of a compressed gas ejection system. Cylinders don't have to be heavy steel. Firefighting SCBA bottles are fiber glass of some kind. Maybe carbon fiber?

I'm not an expert in any of this, but someone smarter than I might be able to make something work, though probably not for the smaller LP stuff.

 

[techrat]

Otherwise, I like the idea of a compressed gas ejection system. Cylinders don't have to be heavy steel.

Soda bottles are very light and built to take a lot of pressure.

 

[jderimig]

Don't the CO2 ejection systems use a pyro valve to initiate them? So they're not really getting to pyroless.

Yes. in my opinion the romantic idea of pure pyroless is silly when other parts of the rocket has kilograms of propellant. You can pierce a CO2 cylinder with a dc motor and jack screw and add gratuitous weight for the benefit of eliminating 0.1-0.2grams of smokeless powder and also eliminate near perfect reliability.

 

[Art Upton]

Re ejection method: Could internal pressure be generated by a non pyrotechnic, chemical reaction gas generator like a car airbag? Doesn't need to be behind a piston, and hopefully not too much heat. I'd envision something like a JLCR size device that is dropped into the bottom of the body tube. After the flight open it and replace the "pills" that react and generate the gas. Bigger rocket? Use bigger "pills".

Otherwise, I like the idea of a compressed gas ejection system. Cylinders don't have to be heavy steel. Firefighting SCBA bottles are fiber glass of some kind. Maybe carbon fiber?

I'm not an expert in any of this, but someone smarter than I might be able to make something work, though probably not for the smaller LP stuff.

Car Air Bags use a classed Explosive initiator. The ones from a certain manufacture had too much energy in them forcing a recall due to facial lacerations.

 

[Capt. Eric]

Car Air Bags use a classed Explosive initiator. The ones from a certain manufacture had too much energy in them forcing a recall due to facial lacerations.

Well, hopefully no one's face will be close to the rocket at deployment. And it maybe doesn't need to generate as much gas.
I'm not suggesting putting a car bag into a rocket. Just using a similar reaction to create pressure in the body tube.

 

[boatgeek]

Every CO2 cartridge I've seen is kind of heavy. There wouldn't be any point in something that strong unless you were ready to pump it up to hundreds of psi every time. Let's say you had a 2 inch sphere made out of steel that yielded at 100kpsi. We'll keep it down to 30 kpsi for a factor of safety, and we'll design the sphere to take 150 psi air. That's about 3.1 square inches. (Well, pi square inches.) Make it 3. We're holding back 450 lbs of force, so we need something like .0024" walls! Plus a bit for abuse, I suppose. So 3 or 4 grams of material, I think, plus whatever is necessary to make it practical. Or maybe half that in PET, and less in some super duper material.

You're down a very deep rabbit hole making some very wild assumptions about what's possible. Among other things:

• Weldable 100 ksi steel is a rare beast. 50-75 ksi is relatively common, but more than that is a challenge. Sure, you can get 100 ksi tool or spring steel, but you can't make a pressure vessel out of that. High strength steel is commonly heat treated and/or high carbon. The former loses strength when welded, and the latter isn't weldable.
• I don't do pressure vessels, so I'm willing to be corrected, but a factor of safety of 3.33:1 seems light for a 150-psi air canister. I would expect 5:1 to 7:1. You're walking around with a grenade, so you need to treat it as such.
• How are you forming this mythical beastie? You're probably going to have to weld it somewhere, and you can't weld foil. I would guess that the minimum wall thickness is ~1/16" for a one-sided weld. Again, I'm willing to be corrected.
• You have to connect tubing to the pressure vessel to do something useful. That means more welding and more stress concentrations requiring thicker walls at the connections.
• You have to support this thing at 100-200G for high performance rockets and for failures. That takes some more wall thickness plus support points.

There's a reason the CO2 cylinders are the thickness and weight they are.

 

[Capt. Eric]

Yes. in my opinion the romantic idea of pure pyroless is silly when other parts of the rocket has kilograms of propellant.

I think the "silly" idea is to have a method of duel deployment that is practical, simple to use and doesn't raise the safety concerns of using black powder charges. Some folks just aren't comfortable storing and handling bp. It's one thing to put a manufactured engine into a mmt. It's a little different to acquire bp, store it safely, travel with it, measure out the correct amount, whatever that is, and install it in such a way that it is safe and reliable in your rocket. Yes, for many that is easy. But for a young or inexperienced person, there are a few hurdles they have to work through when all they really want to do is launch a big honkin' cool rocket.

 

[jderimig]

I think the "silly" idea is to have a method of duel deployment that is practical, simple to use and doesn't raise the safety concerns of using black powder charges. Some folks just aren't comfortable storing and handling bp. It's one thing to put a manufactured engine into a mmt. It's a little different to acquire bp, store it safely, travel with it, measure out the correct amount, whatever that is, and install it in such a way that it is safe and reliable in your rocket. Yes, for many that is easy. But for a young or inexperienced person, there are a few hurdles they have to work through when all they really want to do is launch a big honkin' cool rocket.

I agree with you. See my post comments of moving past *Cannons* for deploying a few ounces of recovery fabric. I was espousing *low velocity* recovery deployment systems that can be initiated by relatively miniscule amounts of smokeless powder. There is no need for the deployment event to start and end in milliseconds.

A CO2 Cannon is no less dangerous than a BP cannon.

 

[NTP2]

You're down a very deep rabbit hole making some very wild assumptions about what's possible. Among other things:

• Weldable 100 ksi steel is a rare beast. 50-75 ksi is relatively common, but more than that is a challenge. Sure, you can get 100 ksi tool or spring steel, but you can't make a pressure vessel out of that. High strength steel is commonly heat treated and/or high carbon. The former loses strength when welded, and the latter isn't weldable.
• I don't do pressure vessels, so I'm willing to be corrected, but a factor of safety of 3.33:1 seems light for a 150-psi air canister. I would expect 5:1 to 7:1. You're walking around with a grenade, so you need to treat it as such.
• How are you forming this mythical beastie? You're probably going to have to weld it somewhere, and you can't weld foil. I would guess that the minimum wall thickness is ~1/16" for a one-sided weld. Again, I'm willing to be corrected.
• You have to connect tubing to the pressure vessel to do something useful. That means more welding and more stress concentrations requiring thicker walls at the connections.
• You have to support this thing at 100-200G for high performance rockets and for failures. That takes some more wall thickness plus support points.

There's a reason the CO2 cylinders are the thickness and weight they are.

3d printing will help some of that, welding mostly.

 

[OzHybrid]

We're using BP as a gas generator. Unfortunately it can be used as an explosive. There's no getting away from that as an issue. The compound used in air bags has been classified as a gas generator. What's the process to get access to that compound?

 

[rocket_troy]

• I don't do pressure vessels, so I'm willing to be corrected, but a factor of safety of 3.33:1 seems light for a 150-psi air canister. I would expect 5:1 to 7:1. You're walking around with a grenade, so you need to treat it as such.

3.33 would generally be plenty for an air canister or any purely gaseous canister, especially one that's being used shortly after being filled. That's assuming there's no welds to account for.
If you're filling with, say, liquid CO2, there are more nuances and precautions and a bit of extra safety margin that should be baked in to your vessel.

TP

 

[jderimig]

We're using BP as a gas generator. Unfortunately it can be used as an explosive. There's no getting away from that as an issue. The compound used in air bags has been classified as a gas generator. What's the process to get access to that compound?

Sodium Azide is a compound you don't want. Its very toxic.

 

[rocket_troy]

A CO2 Cannon is no less dangerous than a BP cannon.

I'm willing to aim my CO2 pyroless deployment device at my face point-blank and fire it. Are you up for the challenge of doing the same with a pyro charge?

Well?

TP

 

[jderimig]

I'm willing to aim my CO2 pyroless deployment device at my face point-blank and fire it. Are you up for the challenge of doing the same with a pyro charge?

Of course not. When did I get accused of aiming cannons at a face is a good idea?

 

[Capt. Eric]

Sodium Azide is a compound you don't want. Its very toxic.

Apparently they now use "guanidinium nitrate" whatever that is.
I think it's an ingredient in Chick-fil-A nuggets.

(Calm down everyone! I'm just kidding about the nugs.)

 

[boatgeek]

3d printing will help some of that, welding mostly.

What kinds of yield stresses are possible with 3D printed parts?

3.33 would generally be plenty for an air canister or any purely gaseous canister, especially one that's being used shortly after being filled. That's assuming there's no welds to account for.
If you're filling with, say, liquid CO2, there are more nuances and precautions and a bit of extra safety margin that should be baked in to your vessel.

TP

OK, that's fair. I know the FoS goes up as you get either very cold or very hot. But that still gets back to the prior question of how we form a sphere with tubing connections and no welding.

 

[NTP2]

What kinds of yield stresses are possible with 3D printed parts?

48 MPa with ABS on a hobby device, any metal you want on a SLA print from a company like PCB way.

 

[SolarYellow]

A CO2 Cannon is no less dangerous than a BP cannon.

The bottom line is that stored energy is a hazard, no matter the format in which it's stored. Chemical energy just happens to be very compact, lightweight, and inexpensive, which is why it continues to be used in a multitude of systems throughout our industrialized world.

Maybe you can design a rocket to fall apart and release the recovery gear into the airstream, but if you are going to stick with airframe designs that require "ejecting" the recovery gear, you're going to need some form of stored energy to execute the ejection.

 

[jderimig]

The bottom line is that stored energy is a hazard, no matter the format in which it's stored. Chemical energy just happens to be very compact, lightweight, and inexpensive, which is why it continues to be used in a multitude of systems throughout our industrialized world.

Maybe you can design a rocket to fall apart and release the recovery gear into the airstream, but if you are going to stick with airframe designs that require "ejecting" the recovery gear, you're going to need some form of stored energy to execute the ejection.

The idea is to minimize the work(energy) needed to deploy the recovery. There are many ways to do it.

But I think many people in this hobby do enjoy the cannons. A quiet, low energy, safe and reliabile way to deploy recovery might detract from the visceral excitement some want.

 

[boatgeek]

The idea is to minimize the work(energy) needed to deploy the recovery. There are many ways to do it.

But I think many people in this hobby do enjoy the cannons. A quiet, low energy, safe and reliabile way to deploy recovery might detract from the visceral excitement some want.

I hadn't thought of this before, but one advantage of BP ejection is that you can see a puff of smoke that shows that there was an event, even if you can't see the airframe.

 

[bad_idea]

You can push a nosecone or rocket section apart with 150 pounds of force using a 8g CO2 cylinder and a 1/2 inch small air cylinder. You can also generate similar forces with that air cylinder using about 0.2g of smokeless powder.

Move past cannons.

I believe I have seen reference to a gas-powered piston in a small-diameter cylinder used to deploy payloads from sounding rockets in a manner analogous to the operation of a gas-powered firearm action. Is it that sort of mechanism you have in mind?

 

[Spacedog49Krell]

Apparently they now use "guanidinium nitrate" whatever that is.

Jetex - Bat Guano nitrate

 

[kjhambrick]

Jetex - Bat Guano nitrate

Interesting rabbit hole: Wikipedia > Guanidine nitrate ... especially this reference: WayBack Machine > Jetex Propellants

The memories ( V-MAX Power ) !

Thanks @Spacedog49Krell !

-- kjh

 

[jderimig]

I believe I have seen reference to a gas-powered piston in a small-diameter cylinder used to deploy payloads from sounding rockets in a manner analogous to the operation of a gas-powered firearm action. Is it that sort of mechanism you have in mind?

Yes. I flew that system in a Balls rocket 2 years ago. Here is a CAD view. The cylinder and electronics is all in the nosecone. A *tiny* amount of BP is charged in the cylinder lit by an ematch. This drives the pushrod down against a shelf in the airframe popping the nosecone off.

 

[jderimig]

And here is video of ground testing. Again maybe 0.2g of BP if that.

 

[John Beans]

I think the more money you spend on a parachute the less willing you should be to burn gunpowder underneath it.
Just sayin.

 

[rocket_troy]

The idea is to minimize the work(energy) needed to deploy the recovery. There are many ways to do it.

No arguments there. IF (and it's the big if) you can manage to develop a pure mechanical system that:
(a) is as (or more) reliable than gas driven systems
(b) doesn't compromise the structural integrity of the airframe/NC/whatever that's releasing the chute too much.
(b) doesn't require significantly complex reinforcement of the structure to accommodate the system
(c) is tough and rugged enough to handle significant loads from shock cords and such in the event of non-optimum deployment

I have no arguments with a purely mechanical system being superior to gas if those conditions are met.

The issue I have is the claim that cold gas systems are as dangerous as pyros. That's certainly not been my experience with doing almost 15 years of pyros then 15 years of cold gas with 750+ odd deployments with that cold gas system. It's not even close. It's an argument based on ignorance and naivety IMO.

TP

 

[rocket_troy]

The bottom line is that stored energy is a hazard, no matter the format in which it's stored. Chemical energy just happens to be very compact, lightweight, and inexpensive, which is why it continues to be used in a multitude of systems throughout our industrialized world.

Maybe you can design a rocket to fall apart and release the recovery gear into the airstream, but if you are going to stick with airframe designs that require "ejecting" the recovery gear, you're going to need some form of stored energy to execute the ejection.

This is a classic example of what I'm talking about. You're using "stored energy" as the ultimate metric for hazard rating. This is utter nonsense. There could be more stored energy in your onboard electronic batteries than for either your pyros or cold gas or springs or whatever is doing the pushing.
In terms of projectile hazard, you're actually more interested in delivered *power* not stored energy but it's much more nuanced than that.
My cold gas system would probably offer the highest delivered power of any cold gas system around and even that separation is considerably softer than pyros.

TP

 

[jderimig]

The issue I have is the claim that cold gas systems are as dangerous as pyros. That's certainly not been my experience with doing almost 15 years of pyros then 15 years of cold gas with 750+ odd deployments with that cold gas system. It's not even close. It's an argument based on ignorance and naivety IMO.

TP

The safety of the system is totally unrelated to the method of generating the kinetic energy to activate the system but the kinetic energy generated by the system. My argument was if a CO2 system is trying to reproduce the kinetic energy of the incumbant pyro system there is no difference in the hazard between the methods. It just so happens that cold gas systems cannot easily generate the energy release of a pyro system. But I can design a pyro system that generates the same energy as a working cold gas system and the safety will be identical.

 

[rocket_troy]

The safety of the system is totally unrelated to the method of generating the kinetic energy to activate the system but the kinetic energy generated by the system. My argument was if a CO2 system is trying to reproduce the kinetic energy of the incumbant pyro system there is no difference in the hazard between the methods. It just so happens that cold gas systems cannot easily generate the energy release of a pyro system. But I can design a pyro system that generates the same energy as a working cold gas system and the safety will be identical.

So, we can carelessly ignore BP's sensitivity to sparks or sharp electrical spikes from the electronics and the significant heat produced from pyros. It's all about kinetic energy in the theoretical world of both providing equal KE... [facepalm]

TP