Redundant dual deploy, when do you consider it 'necessary'?

[Jerry F.]

So one of my rocket buddies and I were discussing redundant dual deploy yesterday. We defined it as a dual deploy set-up with 2 independent switch/battery/computer/deployment charge systems.

From there, neither of us really had a good threshold of when or why we considered it necessary, or preferred. LiPo batteries are getting smaller, switches easier to incorporate, and flight computers are (generally) getting smaller and gaining function (even if availability of certain product lines are currently curtailed due to chip shortages).

I've done dual systems in rockets as small as 2.6 inch, and it was challenging. After that project I find that 3" and 4" rocket avionics bays are positively cavernous, with huge amounts of real estate on the bay lids!

Then there's the expense. Conservatively all the components for a single systems are in the neighborhood of $100 on up to pretty much as much money as you want to spend.

What's YOUR criteria for using 2 systems in your rockets? Is it size of the rocket? Weight? Power level? Altitude level expected? Expense of the project?

ETA: I'm a dual redundant nut case having retrofitted most of my dual deploy fleet to redundant systems ever since having a REALLY EPIC bad run of orange wire ematches fail, and have switched over to MJG firewire initiators and Altus Easy Minis as they're readily available, and 2 of them fit into the av bay sled real estate of my previously preferred RRC3s.

In Canada, anything over 5kg (about 11 lbs) requires redundant systems...

 

[MJW]

Dual electronics is required any time I'm flying a forward closure without a motor deployment charge. I refuse to put the people on the ground at risk of a ballistic return (or expose myself to the liability of one). If it comes down in two pieces instead of three, so be it... But it is not coming down as a lawn dart ever.

 

[G_T]

Was at a launch where a cardboard or possibly phenolic tube HP rocket came in ballistic. It plowed in hard about 4' from a good friend of mine, and a few feet from a fryer with plenty of people standing around. It could have ended very badly in so many ways.

On one of mine at about 80# I had one board shut down when it tried to fire the apogee charge for drogue. The LiPO shut out. Too much current. The other board with independent power (9V) still worked for deploying main as it came down.

I like the idea of not just separate systems, but separate systems of different types or brands of components. That decreases the odds of duplicated failures.

I don't feel too much need for independent black powder charges. Light a sufficient charge of black powder at reasonable altitudes, it flashes off. But ematches fail. Electronics fails. Batteries fail. Wires, switches... So I might rig two boards into separate ematches in the same charge well. Just an example.

Redundancy increases your odds of success, but complexity reduces your odds. Redundant methods of triggering a safety-critical event such as chute deployment improves your odds of a successful flight. The reason is the most probable failures are in the nature of the board not firing the event. But there is a lesser probability that a board may fire an event at significantly the wrong time.

So it comes down to odds of each possible occurance, and the probable outcomes of each possible occurance. The more potentially deadly the rocket, the more important it is that the odds of highly unfavorable occurance be greatly minimized.

And a 5# 2" diameter rocket is essentially as deadly as a 100# 8" diameter rocket. If it is coming in ballistic, it probably won't matter which one hits you.

So, if it (1) can reach people or property, and (2) can maim or kill, then redundancy is important.

From a safety standpoint, the main deployment can be considered a redundant operation for drogue deployment, provided it is guaranteed to work. That's why we have that old rule of thumb - blow it out or blow it apart.

Sorry I rambled a bit. It is late.

Gerald

 

[cerving]

The most common cause of recovery failures is not the malfunctioning of the altimeters, it's mechanical... stuck chutes, missized charges, broken shock cords, etc. The most common electrical failures are disconnections in flight, and failed ematches (i.e. ematches that fail to light the pyrogen). It's rare when the altimeter actually fails in flight. Redundant systems can protect against some electrical failures, I have seen a flight with redundant systems in which 3 of the 4 ematches fail to light... fortunately the one that did light was on a drogue, so the only result was a bit of a hard landing. We ground tested the other three ematches afterwards... they all failed, and the altimeters all indicated that they fired.

 

[AstroAbaqus]

I would go for dual system if I cannot use the motor ejection for the drogue. This because if even the drogue does not open that’s a catastrophic failure for sure.

 

[jderimig]

The most common cause of recovery failures is not the malfunctioning of the altimeters, it's mechanical... stuck chutes, missized charges, broken shock cords, etc. The most common electrical failures are disconnections in flight, and failed ematches (i.e. ematches that fail to light the pyrogen). It's rare when the altimeter actually fails in flight. Redundant systems can protect against some electrical failures, I have seen a flight with redundant systems in which 3 of the 4 ematches fail to light... fortunately the one that did light was on a drogue, so the only result was a bit of a hard landing. We ground tested the other three ematches afterwards... they all failed, and the altimeters all indicated that they fired.

In my opinion having redundant systems provides safety by requiring a flyer to make a mistake in two separate systems rather than one to have a failure. For that reason redundancy is a good idea, but not the reason that people use to justify it understandably.

 

[SDramstad]

I like the idea of not just separate systems, but separate systems of different types or brands of components. That decreases the odds of duplicated failures.

This I disagree with. Having different types of altimeters increases the complexity by having 2 different procedures for the operation of the altimeters. Having 2 of the same altimeters means just 1 procedure done twice. Less chance of making a mistake. The only difference in my redundant setups is about 50% more powder in the backup charges. As someone said the most common problems is usually something jamming. If 50% more powder doesnt separate things you were doomed from the start. The other thing that can happen is an e-match not firing. Does anyone use 2 different types of e_match on each flight?

 

[Tractionengines]

And a 5# 2" diameter rocket is essentially as deadly as a 100# 8" diameter rocket. If it is coming in ballistic, it probably won't matter which one hits you.

The 2" diameter may be worse... hard to see 2" coming down from a few thousand feet. The 8" will be easier to see and figure out where it's going...

 

[Buckeye]

The reason is the most probable failures are in the nature of the board not firing the event. But there is a lesser probability that a board may fire an event at significantly the wrong time.

The boards firing the event incorrectly is the least likely failure, not the most probable.

 

[MidOH]

How difficult would it be to have a "Universal Sled" that can be used in rockets of differing diameters?
Perhaps using some form of adaptor like those used for motors.

It's seems like cake. You just untie your shock cords, and move the sled, and the bulkheads. The coupler stays with the airframe, because it's fitted already. Especially the three silly bolts and the pin hole. Each rocket keeps it's own coupler.

If you're dropping into a different sized rocket, you could just swap out the bulkheads as well. It's just 4wires to reconnnect. The bottom bulkhead is already on a JR style connector for quick disconnecting. My primary is on the left with all black wires. Secondary everything on the right, red wires.

Only downside is you have to use the smallest sled in those rockets. Which kinda sucks.

I decided to simply just run 4" rockets only, for now. I just made a 4" bay from a Madcow Torrent. It fits right into the coupler on a Lok 4. Needs a little bit of tape, so the bottom bulkhead has no play, since the Lok tubes are a bit thinner. It's no big deal. Hoping to get my Level1 with a Zephyr or Lok Goblin this year, and then fly the Lok4 and Torrent DD. I just started building those first, simply because they're in stock, and I felt like building.

I'm not following how this is complex. You have one DD system. Then you have another. It's not like they have to network or anything. One +1 second setting, and one main setting 200 feet less. It's no more complex than two separate rockets. Your just tossing it all into one bay. Which is cake on a 4" rocket. Heck, there's room for another entire system for double redundancy.

If the rocket needs an ounce or two of ballast for stability, why not use redundancy for that? Lead weight that does nothing? Or a 9v battery? Seems like an easy choice.

 

[jFlds]

I run redundant systems whenever I can. It's a piece of mind thing. Anything to lower the bad outcome odds is always a great plan if possible. I've had some close calls and I don't like that experience watching one of mine come in ballistic. Not that it hasn't happened to me as it has. Fly enough and it's bound to happen with so many variables going on at once. There's a lot of different forces colliding inflight. Go redundant if you can.

 

[kyle]

This is an odd post. I honestly had no idea people were so passionate about redundancy. Or that so many people would be hating on what other people do with their own rockets. I can understand being passionate about how a person builds their own rocket, but why are there even "sides" on this?

For my rocket, I make it and fly it the way I want to.

For your rocket, you build it and fly it the way you want.

We all go home and drink our favorite adult beverage. Good day.

Unless you make and fly your rocket the way you want and it comes in ballistic and perforates my wife's head while she's knitting in the truck.

Then we'll have issues.

I'll run dual so I don't have to be that guy.

 

[Flyfalcons]

If it fits, it ships.

 

[John Taylor]

Weight is a factor for safety sake.
My only redundant dual deploy rocket is a 7' tall 4" diameter all fiberglass rocket at 14 lbs. It scares me to think of it coming in ballistic. Thus the redundant system

 

[les]

Weight is a factor for safety sake.
My only redundant dual deploy rocket is a 7' tall 4" diameter all fiberglass rocket at 14 lbs. It scares me to think of it coming in ballistic. Thus the redundant system

I still would not want to get hit by a 5 lb rocket coming in ballistic at over 100mph, especially if FG. You may want to consider dual deploy in some of your smaller ones (unless they are LPR)

 

[Rocketjunkie]

It's seems like cake. You just untie your shock cords, and move the sled, and the bulkheads. The coupler stays with the airframe, because it's fitted already. Especially the three silly bolts and the pin hole. Each rocket keeps it's own coupler.

All my rockets 54 mm and larger have a 1/2" rod through the altimeter bay, ranging from wood to steel threaded rod. All my altimeter sleds are 5.5" long and have a 1/2" lug on the back that fits over the rod in the bay. Any altimeter fits any rocket

 

[Handeman]

My opinions here, fire away...

I believe the primary personal safety system to keep you from getting hit by a falling rocket is the safe distances and the pad location and angles based on wind direction and flight line location. That is something the prefecture can control to ensure safety and what the safety codes are all about. Whether or not there is redundant electronics in an individual rocket is not something the club controls and because of that, can't be considered when determining how the safety codes are written or the site setup to ensure personal safety.

Since the personal safety margins are included in the safe distances and site setup, adding redundant electronics isn't really a personal safety issue in my opinion. Yes it may improve personal safety very marginally, the primary reason to add it is to reduce the chance of losing the rocket to landing damage.

So, to answer the OP question, I think you have to judge the added cost of a redundant system vs. the cost of the rocket vs. the chance it is actually going to be destroyed because of a total failure of a single altimeter system. I don't believe personal safety should be considered since a redundant system makes the minutest difference in risk in that area.

 

[FredA]

I'd like to see this one fly

 

[Texasagg0408]

Lots of great info in this thread!

 

[Michael L]

My opinions here, fire away...

I believe the primary personal safety system to keep you from getting hit by a falling rocket is the safe distances and the pad location and angles based on wind direction and flight line location. That is something the prefecture can control to ensure safety and what the safety codes are all about. Whether or not there is redundant electronics in an individual rocket is not something the club controls and because of that, can't be considered when determining how the safety codes are written or the site setup to ensure personal safety.

Since the personal safety margins are included in the safe distances and site setup, adding redundant electronics isn't really a personal safety issue in my opinion. Yes it may improve personal safety very marginally, the primary reason to add it is to reduce the chance of losing the rocket to landing damage.

So, to answer the OP question, I think you have to judge the added cost of a redundant system vs. the cost of the rocket vs. the chance it is actually going to be destroyed because of a total failure of a single altimeter system. I don't believe personal safety should be considered since a redundant system makes the minutest difference in risk in that area.

Most our club launches "settle gently to the earth" 2,500' to 6,000 feet away when they return. Scattered throughout that, roughly, square mile of LZ there are oil tanks, compressors, and wellheads. We, and the BLM, prefer that the odds of a 15 - 60 pound lawn dart impacting one of those sites are low. The owner of the property, The Bureau of Land Management, that we fly on requires us to use redundant dual deploy. I enjoy the av bay builds so it's no heartache to me. I think our L3 guy got 15k out of his. Mine had a bit of a problem. All 4 ejection charges fired, the chute deployed, but there was a motor problem. Can you see it?

Where is the sustainer?

Oh... there it is...

WTH? Oh... well that's not supposed to happen

 

[Jerry F.]

As I said, in Canada, the “minimum requirement” is any rocket over 5kg (11lbs) must utilize redundant dual deployment…how you incorporate that is up to you…
There obviously is more than one way to accomplish this…
IMO, if you have tested your set up (preferably multiple times) and you are confident in the measures you have taken, and done everything in your control to mitigate the risks of failure, you have done your due diligence…don’t rely on someone else doing their job to keep others safe…launch angles, distances, etc should be the redundant safety protocols to mitigate danger if your safety protocols have failed…
As a society, we all need to take responsibility for what we can control…no more blaming McDonalds for making us fat…

 

[G's Monster Rocket]

But do you really buy new everything? If you’re like me, you have ones that you have accumulated that you just put to work. About the only things that have to be dedicated to the rocket are the switches and charge wells and I use really inexpensive pvc fittings as charge wells. Unfortunately I have an addiction to Rocketry electronics and I tend to buy new electronics from time to time just to try. So, for me to go redundant is really only the price of a single switch and two charge wells and I use altimeters that I already have. Even my least expensive electronically deployed rocket will have redundancy if there’s room.

Steve...

I'm getting into dual deploy and have built my ebay with two RRC3's and independent 9V alkaline batteries for each. My charge wells are pvc fittings. All of my rockets are scratch design, mostly 4" diameter blue tube. What I'm unsure of is the electric match needed for initiating the BP charge for deploy. I've seen Firewire by MJG but never used them. I can see using an initiator like this for lighting off the J,K and L motors I'm designing around and launching with, but are these necessary for the BP in the charge wells for deployment? Also, for the "power on" switch, do you use a SPST latching key switch or something equivalent for each altimeter?

 

[Banzai88]

Steve...

I'm getting into dual deploy and have built my ebay with two RRC3's and independent 9V alkaline batteries for each. My charge wells are pvc fittings. All of my rockets are scratch design, mostly 4" diameter blue tube. What I'm unsure of is the electric match needed for initiating the BP charge for deploy. I've seen Firewire by MJG but never used them. I can see using an initiator like this for lighting off the J,K and L motors I'm designing around and launching with, but are these necessary for the BP in the charge wells for deployment? Also, for the "power on" switch, do you use a SPST latching key switch or something equivalent for each altimeter?

There really isn't much more reliable than the MJG Firewire ematch for igniting deployment charges. They are pricey, especially if you're using 4 per flight, but how much is your project worth?

Others will argue that the orange Chinese ematches are just as good, but I still have a big batch of 'em that has about a 7-10% failure rate and have been relegated to ground test only after several 'failures to light' caused by dud units that passed testing on a handheld multimeter and passed 'continuity' checks on the pad/flight computer.

As to switches, the only "switches" that I've never seen fail are twist-and-tape and screw switches. I only use MW screw switches in my rockets.

 

[G's Monster Rocket]

As long as they do the job, the MJG Firewire are fine with me. I ask a lot of questions since there's a lot to learn about this sport. Y'all have more flight time than I have and I sponge as much as I can to learn. So, thanks for the info.