redundant deployment

What is the best way to use 2 altimeters for redundancy? Should I use a seperate black powder charge for each altimeter or just one charge with an e-match from each altimeter? If I use 2 powder charges, what are the chances of them both going off at the same time and being too much? What do you guys use?

I personally use one alt. A few thing's I would use 2 e-match's per electronic device, just added safety at a low cost. I have heard that the BP wont fail (obvious) but some still use two charges, one reason is so you can tell if one of the alt's isnt firing it's output, also, the seperate charge will make sure the chute get's out. Apogee, small chance of them firing at the same time, main, none, just set them at different altitudes. If I was using a backup I would use a timer to backup the drogue (set for maybe 3-4 second's after expected apogee) so that it may zipper the rocket but atleast it doesnt come nose first and ruin a lot of the rocket and maybe some peoples lives. If you really want backup for the main (will help improve the rocket's safety but not others, I would just backup the drogue so the rocket doesnt come in ballistic but it comes in slow enough for it to drift a little, not destroy everything and people can get out of the way. But if you do want to back it up, I believe adept sell's devices like altimeter's but they only fire a main output, so you have a basic alt, timer back up, and if you really want (not really needed) a adept main chute backup.

If you are backing up the electronics but not the black powder you are kind of missing the point of backup. A project I worked on we used 3 altimeters. We had them all set to fire at apogee - even though they were the same altimeter RRC2 X we considered that the small variations in each one would read a slightly different apogee moment. We used 3 different charges (all the same). We set the main for three different altimeter settings and made the second and third twice as much. That way we knew the laundry would eventually get out. When the actual flight came the apogee charges fired at slightly different times - we could see separate puffs. When the main deployed it came out and the second and third charges fired into nothing.

Edward

While I haven't used dual altimeters yet, ( my current project will) I'm of the opinion that true redundancy would require the use of separate apogee and main charges for each altimeter. The perfectflite MAWD's that I have can be configured for a 1 second delay for apogee, (for the back-up altimeter) and of course different altitudes for the main. I can't speak for other brands of altimeters, but would guess that others would have the same capabilities. IMHO, two separate altimeter/EC systems offer the best reliability and redundancy.

Although I think the chances of two altimeters failing to detect launch and apogee at the same time are low, stranger things have happened. Remote control of recovery events are a viable option as long as you have visual contact.

I know a Texas rocketeer that used the missle works unit to lite the sustainer on a large two stage project. It was his fail safe. If things went wrong before, or just after first stage sep, he simply wouldn't press the button and let the sustainer recover via altimeter. Worked beautifuly on the first flight, on the second the missle works unit failed and didn't lite the sustainer. Recovery was fine and there was no damage.

Having said all that, I really think the greatest point of failure is human error, those dumb mistakes we make when we become distracted during prep, or just plain forget to do something. That is why there are checklists. However you design redundancy into your project...make a checklist...follow it...and if you don't have confidence in the flight, don't put it on the rail.

Just a rookie's 1/2 a cent worth...

But I would use two different types of unit's, say the reason your alt fail's is because the vent holt didnt work properally... a timer doesnt need to sense pressure.

Would you have 2 seperate bays, or just put everything in the same bay? How much backup do you go for?

Originally posted by Stormbringer
Would you have 2 seperate bays, or just put everything in the same bay? How much backup do you go for?

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My L3 rocket will have 2 altimeters (1 missileworks RRC2 and 1 Perfectflite MiniAlt/WD) in one electronics bay. The only thing that will be shared between both units will be the actual electronics bay. There will be no electrical common point. Separate units, separate wiring, separate batteries and separate ejection charges.

Put them in two rockets.
Bag the redundancy ideas!

Been over this before here....
I assert that the increased opportunity for pilot error overwhelms the protection redundancy might offer.

YMMV - this is my OPINION.

Originally posted by jcgask
What is the best way to use 2 altimeters for redundancy? Should I use a seperate black powder charge for each altimeter or just one charge with an e-match from each altimeter? If I use 2 powder charges, what are the chances of them both going off at the same time and being too much? What do you guys use?

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True redundancy would require two altimeters and four ejection charges. Assuming dual deployment. The chances that they will go off at the same time are possible, but remote.

PerfectFlite has a neat feature. The MAWD has a user selectable one second apogee delay. If you fly two MAWDS, call them Alt A & B. You can set B to use the one second delay. This means it will fire the drogue charge one second after apogee is detected. The next step is to set them for different main deployment altitudes. True redundancy.

I doubt if I'd fly redundant altimeters, unless it was a TRA L-3 flight.

To each his own.

Good point Fred...

Another variation on redundant electronics is to use one altimeter & one timer. While this may not be doable for a dual deploy flight, the timer could be used as a backup system for deploying at (or safely just past) apogee. The timer does not have the functionality (like sensing/reporting back max altitude) of an altimeter, however, when it is your L3 cert flight, what would you rather have: a lawndart that you knew what the max altitude was or a save recovery because your timer did its job?

Just some food for thought...

My own L3 project has separate altimeters and matches, but they activate common devices. The CD3 system for the apogee deployment has provision for twin matches, as does the Tether I'm using for the main.

Nevertheless, I'm going to test the system first. If one or the other doesn't function as I expect them to, I'll re-work the deployment system.

Originally posted by LFLekx
My own L3 project has separate altimeters and matches, but they activate common devices. The CD3 system for the apogee deployment has provision for twin matches, as does the Tether I'm using for the main.

Nevertheless, I'm going to test the system first. If one or the other doesn't function as I expect them to, I'll re-work the deployment system.

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Have you used the "Tether"? I've considered using this for dual deploy in short rocket (7.5" V2). Looks like just the ticket, but also looks like it could fail and I've never seen anyone use it. Also I can no longer find the web site. Do you have it?

The tether seem's like it need's to be "ejected" in open air or it will damage the airframe, I would personally pay the extra cash (especially for L3) and get a blacksky ARRD, mounted to the bulkplate and the design makes much more sense then the tether design.

Originally posted by jraice
The tether seem's like it need's to be "ejected" in open air or it will damage the airframe, I would personally pay the extra cash (especially for L3) and get a blacksky ARRD, mounted to the bulkplate and the design makes much more sense then the tether design.

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I've heard that the ARRD is unreliable. Has anyone out there used it?

I have only heard good thing's, just make sure to use the drogue as a pilot in your design.

Originally posted by edwardw
If you are backing up the electronics but not the black powder you are kind of missing the point of backup. A project I worked on we used 3 altimeters. We had them all set to fire at apogee - even though they were the same altimeter RRC2 X we considered that the small variations in each one would read a slightly different apogee moment. We used 3 different charges (all the same). We set the main for three different altimeter settings and made the second and third twice as much. That way we knew the laundry would eventually get out. When the actual flight came the apogee charges fired at slightly different times - we could see separate puffs. When the main deployed it came out and the second and third charges fired into nothing.

Edward

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I disagree. Two matches in the same charge from two different alts is backup. One of them is going to light it.

That being said, If one charge for some reason was undersize, then the other would help in getting the job done.

I guess it comes down to personal preference.

But how can you tell which alt fired if you have one charge? You could build a tiny 38mm rocket, and want to put one of the two alt's into it, but you can only fit one, for all you know one of them wasnt even working, or was super late on apogee or had some sort of firing current problem... so many problem's that you would never know if the alt even worked.

Originally posted by jcgask
Have you used the "Tether"? I've considered using this for dual deploy in short rocket (7.5" V2). Looks like just the ticket, but also looks like it could fail and I've never seen anyone use it. Also I can no longer find the web site. Do you have it?

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I haven't used it myself yet, but I know some people who have... and haven't had any problems with it.

The new link is Defy Gravity

Originally posted by jraice
The tether seem's like it need's to be "ejected" in open air or it will damage the airframe, I would personally pay the extra cash (especially for L3) and get a blacksky ARRD, mounted to the bulkplate and the design makes much more sense then the tether design.

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Depends on the size of the airframe you use. I wouldn't want it inside the aiframe on a 3" or a 5" rocket, but don't have a problem with it inside a 7.5" rocket.

Originally posted by jraice
But how can you tell which alt fired if you have one charge? You could build a tiny 38mm rocket, and want to put one of the two alt's into it, but you can only fit one, for all you know one of them wasnt even working, or was super late on apogee or had some sort of firing current problem... so many problem's that you would never know if the alt even worked.

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When you use redundant electronics, it doesn't really *matter* which one fired first. If you suspect that one failed, you ground-test it as best you can. If you still have doubts, you can send it back to the manufacturer for a more complete battery of test, or use another one.

(I'm having to do the latter in my L3 project - not because I suspect the altimeter might be broken, but because the way my recovery system is set up might lead to the AltAcc firing the main charge prematurely... even if the flight is perfect. )

Posted by jcrocket:
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How do you know after shipping, a recovery jolt, or knocking from a hard landing that altimeter is safe to fly? The same way you know before putting any new or previously flown altimeter in a rocket. You test it.
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I agree, there is no reason not to test. We test our altimeters before every flight in a simple test chamber, takes just a minute or two to do, and does wonders for your confidence level.

We use Perfectflite MAWD's that are baro sensing. They have worked flawlessly flight after flight, but that doesn't mean something can't go wrong on the next one. You do everything you can do to ensure a safe and successful flight.