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

[Banzai88]

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.

 

[dr wogz]

Its standard for school teams, and for L3 attempts (From what I understand)

it also depends on how much you value your rocket & the investment you've made. for a 4" cardboard 38mm on an H.. likely not. for a 6" full FG & Carbon with a 75mm or 98mm likely so..

 

[roytyson]

For me, most times its about space. Is there room? If yes, I always run two alts. in all my flights, only once have I seen a charge not fired and relied on the redundant to get it down properly.

 

[mhwillis]

I'm driven almost entirely by size. If I can fit redundant systems, I do it. I personally find 3" to be the smallest I can go, but that is because one of my altimeters is the RRC3, with an eggtimer wifi switch (the other is a quantum, much smaller), so.. a lot of space. I've never needed two, in that both channels have always worked so far (only a few dozen flights, mind you). But I still feel better about it.

 

[Bat-mite]

I'm with Wogz. Is it worth the money to buy two alts, two switches, extra wiring, more charge wells, etc.? That has to be weighed against the cost of replacing the rocket, chutes, motor casing, etc.

 

[Banzai88]

I'm with Wogz. Is it worth the money to buy two alts, two switches, extra wiring, more charge wells, etc.? That has to be weighed against the cost of replacing the rocket, chutes, motor casing, etc.

I totally understand that perspective, and that puts the bar relatively low.

Eliminating options like a Quark, one can spec a system as a SLCF@$55, LiPo@$3, screw switch@$3, and various and sundry wiring and battery plug@$2 for a total of about $60 per system.

If you decided to solder and went dual Eggtimer Quarks@$20 each, that threshold moves down to $26ish per system or about $50ish for BOTH systems (and a tiny form factor)!

 

[les]

So long as I can fit it, I will go full redundant...

 

[jderimig]

If it fits redundant deployment adds several minutes or hours to your life via stress reduction. Depends on how much you fly.

 

[mtnmanak]

All these are good criteria! One of the criteria I incorporate is the safety risk if the rocket comes in ballistic. As noted, I generally try to get dual systems in most of of my HPR builds (the smallest frame I successfully achieved redundant systems in was a 38mm minimum diameter frame. I tried to incorporate one in a 29mm MD, but it wasn't successful). Generally, if the rocket is over about 10 pounds, I do everything I can to get redundant systems in place. However, I also consider the size, weight and material of the components. Frankly, one of the large diameter cardboard LOC rockets comes down pretty slowly all by itself - relatively light and a whole lot of drag. As long as something separates, it is usually going to come down okay, so I often ensure I use motor eject backup in those rockets.

One of my own personal hard-and-fast criteria is if the nosecone has an aluminum tip. When that is the case, I won't fly it without redundant systems. A rocket coming in ballistic with a metal tip is quite literally a large caliber sub-sonic bullet.

 

[Howitzer]

If it fits redundant deployment adds several minutes or hours to your life via stress reduction. Depends on how much you fly.

I would only stress if I wasn't using a MARSA.

 

[jderimig]

I would only stress if I wasn't using a MARSA.

If you used 2 you would in bliss.

 

[Steve Shannon]

I'm with Wogz. Is it worth the money to buy two alts, two switches, extra wiring, more charge wells, etc.? That has to be weighed against the cost of replacing the rocket, chutes, motor casing, etc.

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.

 

[cautery]

I'm JUST getting started in HPR, but I am a full-scale aviator. Thus, the thought of NOT having redundant systems, and the thoughts of what COULD happen if everything went "wrong"..... <all over body shiver>

I do not want to lose an airframe... But I could not bear to live with myself if something "bad" happened, and I had not done everything I reasonably could to prevent it.

That then is my standard for this new pursuit.

 

[Buckeye]

We defined it as a dual deploy set-up with 2 independent switch/battery/computer/deployment charge systems.

When is it necessary, per this definition? Never. That is why there will likely be no L3 in my future.

Redundant charges from a single computer (like a Raven) is something I will do. However, extra computers, batteries, switches, wiring, and trying to package it all is not worth it to me. I prefer to perfect each step/component of the deployment process, rather than lazily add double the amount.

 

[Hobie1dog]

flying each HPR rocket only two or three times in its life, no way, too much expense, and it doesn't say much for the faith you have in your electronics you spent your money on. A lot of you just have lots of money to burn and it doesn't make any difference, but having very restricted income on Social Security with no money left over each month due to the incredible amount of medical bills I keep getting bombarded with, so more than likely there's no way I can afford to even buy one electronic setup, which I still don't have it because I haven't had the money for it.

 

[boomtube-mk2]

Wouldn't it just be easier to launch two identical rockets?
That way, if one rocket's deployment system fails, you have an emergency backup rocket already up in the air.

 

[Banzai88]

........ rather than lazily add double the amount.

Get an 11% failure rate on a batch of orange wire ematches like I have and 'lazy' has NOTHING to do with it.

 

[FredA]

11% failure....you don't need more electronics, you need better e-matches.
Address the problem and don't apply a band-aid.

 

[Banzai88]

11% failure....you don't need more electronics, you need better e-matches.
Address the problem and don't apply a band-aid.

That happened long ago, all the bad batch has been relegated to ground testing ONLY. I only launch with MJG Firewire ematches now, and haven't had a single failure in over 200 matches.

 

[Hobie1dog]

. I only launch with MJG Firewire ematches now, and haven't had a single failure in over 200 matches.

I just wrote a note in my phone for that so I could document that down for reference ,
Thanks, But I wonder if they could be used with the Rouse-tech and other CO 2 ejection systems?, Maybe the mini size ones?

 

[boomtube-mk2]

I only built two dual deploy rockets and the PML kit uses their proprietary system that allowed for only a single system in a tube the size of the one I had.
The other dual-deploy was a reworked LOC Hi-Tech which considering its size, weight and cost simply didn't warrant a redundant system.

If I had continued in the hobby and built a bigger, heavier Cert2 rocket It would have included a back-up deployment system.

 

[Johnly]

I've been the NASA Student Launch RSO for over a decade, which requires fully redundant deployment systems. I don't know of an instance were the use of two systems lead to a flight failure, but have reviewed post flight data showing where one of the systems failed in flight. I would attribute most of those to inexperience of the team members, but sometimes the issue was not clearly identified. Some of my large airframes have fully redundant electronics, and others don't; but if someone wanted to use a redundant system on their project I wouldn't discourage it.

 

[SPRock]

If I can easily fit redundant electronics, I do. If I can't have two separate altimeters I'll use motor ejection as a backup, that way I'm not coming in ballistic, at the very least. I usually use an Eggtimer Quark as a backup, it's fairly foolproof - just turn it on and make sure the beeps are correct. Very affordable too!
So far I haven't had any electronics related deployment failures. *knocks on wood* Just make sure your knots in Kevlar are good... that's a lesson I won't forget.

 

[UhClem]

When I use an altimeter for deployment I like to have backup for the apogee event. Usually motor ejection but if that isn't an option then either a timer or another altimeter.

I do not insist on redundant dual deploy but I do want to get that first parachute out.

 

[firemanup]

When is it necessary, per this definition? Never. That is why there will likely be no L3 in my future.

Redundant charges from a single computer (like a Raven) is something I will do. However, extra computers, batteries, switches, wiring, and trying to package it all is not worth it to me. I prefer to perfect each step/component of the deployment process, rather than lazily add double the amount.

My 6” ultimate wildman went up at Airfest this year, a soldered wire came loose from the terminal block on the primary RRC3. The primary apogee charge did not fire.

Wondered why i had a main at apogee, was because my back up blow it out or up charge fired and the cone sheared the shear pins due to the force of the oversized backup charge.

Without the dual system she would have come in hot and likely shredded the main when it deployed, instead i just had a longer walk. All for the price of a $49 rrc2 and and a buck or two in misc items.

 

[Jmhepworth]

Like others, if I can make 2 fit, I use 2. So anything 54mm or larger gets 2. And I’m a big fan of Eggtimer products. They’re a lot less expensive.

 

[les]

Redundant charges from a single computer (like a Raven) is something I will do. However, extra computers, batteries, switches, wiring, and trying to package it all is not worth it to me. I prefer to perfect each step/component of the deployment process, rather than lazily add double the amount.

Everything can fail when not expected. That is the main reason for redundancy. I worked for a company that makes the computers that control the engines and fly the planes (both commercial and military). During development there are multiple simulations and qualification tests. Despite multiple acceptance tests and environmental screening (doing a shake and bake) on EVERY production unit, they still do fail. Typically a single component goes bad. The critical systems (like the flight control computers and sensors) are dual fail operation, meaning there can be 2 completely failed units and the plane can still be safely flown and landed. This is accomplished by having triplex and even quad redundancy, plus even dissimilar systems. I doubt our rocket electronics go through as rigorous development, qualification, and production testing as our aircraft computers, yet as I stated, those units still fail (although rarely - don't worry about flying).

Meanwhile, consider the 737MAX, where they did skimp and used a simplex sensor for the pitch system, and what the results were....

My 6” ultimate wildman went up at Airfest this year, a soldered wire came loose from the terminal block on the primary RRC3. The primary apogee charge did not fire.

An example how anything can fail when not expected.......

I'm JUST getting started in HPR, but I am a full-scale aviator. Thus, the thought of NOT having redundant systems, and the thoughts of what COULD happen if everything went "wrong"..... <all over body shiver>

Fully agree! Again, things fail. Having a backup system, even if only needed once in your entire flying "career", is still better than the alternative with a rocket coming in ballistic. One can try to perfect the process, but the randomness of the universe will win eventually.

My goal is dual power sources, dual switches, dual electronics, dual matches, and dual charges.

 

[tjsnakez]

Anything bigger than 3"+ gets two altimeters. They are too affordable in modern times not to do it. I've had instances where one event failed for one reason or another (chute stuck in tube, bad ematch, altimeter failure/loss of power) and the backup altimeter saved the day.

On rockets smaller than 3" I will generally run motor backup if I only have one altimeter onboard.

 

[DinoAP]

Wouldn't it just be easier to launch two identical rockets?
That way, if one rocket's deployment system fails, you have an emergency backup rocket already up in the air.

This is the best yet!

 

[StreuB1]

Everything I fly has duals. Even my Wildman Jr at 2.26" has dual RRC3's and dual 9v batteries. Both have always worked.

Knowing my luck, the day I decide one is good enough. It will be one and done.