DD single alt.

[lmt56]

After flying 3",4" and 5" rockets for some time now, always with two altimeters,I think it is time to knock the dust off my Little Dog rocket and start flying it again.
I have always been afraid of fly this one very high, even radio tracking, for fear of loosing it.
I now have a nose cone set up to take a couple new GPS units I have.
Figure it will be be a good test bed rocket to get warm and fuzzy with the GPS units.
My problem is I am a firm believer in redundancy and my AV bay as of now is set up for only for a single alt. a PerfectFlite MAWD which I do trust.
On flight up to now I have used motor ejection as back up on this Little Dog.
On 4g motors and up that will not be an option. Factory delays are going to be to short.
In the past I have had two occasions where an ejection charge did not fire.
Redundancy saved the day.
In both cases I think it was due to a bad e-match.
I do not use e-matches from that supplier any more.
So what I am looking for is what techniques do fliers flying dd with a single altimenter do to minimize a single failure?
Two e-matches to a single ejection charge ect. and how comfortable do you fell doing so.
My thoughts right now are one altimeter + a bad e-match = a bad flying.
And for anyone who suggests buying two Ravens I have thought about that.
Checking Adrian's web site the soon to come Wren sounds promising.

[cwbullet]

Which GPS units?

[Lamp]

If you get yourself a Raven (if you don't already have one), you can configure the four outputs like you would for running dual altimeters, one for apogee, one for apogee +1 second (for instance), one for altitude (for example 700') and one as a backup at altitude (say 600'). The Raven is nice and small and a perfect match for a Little Dog.

I am very comfortable running 4 ematches and charges with this setup. I have redundancy for everything except loss of power, it is as close as you can get to running full redundency from one altimeter.

The featherweight interface program (FIP) is easy to use, but if you are unsure about anything a quick email to Adrian or a post on the forum will give you an answer pretty quickly.

Cheers,
Pete

P.S. I have no relationship with featherweight except I own 3 x Raven 2 altimeters.

[rockosrocket]

I have never used a back up altimeter and have never had a misfire of any ejection charge, and I use the christmas tree bulb method. I like E-matches due to the small size but the christmas tree bulbs work great too. That being said, I still use a simpler form of redundency, two seperate charges wired into the same screw terminals. Only way it would fail is loss of power.

[cwbullet]

I would second the recommendation on the raven.

[cbrarick]

MWAD with Jtek's or Newton's third
or any other reliable combination...
one altimeter with 2 outputs will only save you if the first ematch fails...but what about if the battery comes unhooked, the altimeter fails or the switch fails....

The bottom line is that many people fly smaller rockets with one altimeter and charge, but have successfully ground tested their setups. No less reliable then flying it on motor eject then...


but I'm sure we can debate the wisdom of dual redundant channels with differing altimeters from different manufactures....

[lmt56]

Which GPS units?

BRB 900mhz & 70cm

[cwbullet]

BRB is nice. I plan on buying one after tax money comes back.

[lawndartman]

I have flown over 50 Duel Deploy flights in a row without a failure. ALL had only one altimeter. Never had a E-match fail. I have stopped using motor ejection as a backup. I use J-tech matches. All batteries must have 9.1 V or more. I use Perfect Flight, MW, or Featherweight. My Level 3 Talon 6 has duel altimeters because it must. After the flight, I will take one set out. My thoughts on redundant altimeters + 2 sets of e-matches.. total waste of time and money.

[sylvie369]

My Level 3 Talon 6 has duel altimeters because it must. After the flight, I will take one set out. My thoughts on redundant altimeters + 2 sets of e-matches.. total waste of time and money.

I don't think it's a _total_ waste of time, but in general I agree with you. It feels to me like people are using redundant electronics FAR more often than is really necessary. With reasonable care (test battery voltage/replace reasonably often, test e-match resistance, double-check things), single altimeter DD is very reliable.

I think I've only had a couple of DD failures, and they had nothing to do with unreliable altimeters or e-matches. They were because I had the drogue arranged wrong, or packed the chute badly. For most of us, I'm pretty sure that the altimeter is more reliable than our skills with building and setting up recovery systems. I'm certain that my altimeters are more reliable than I am.

[jadebox]

I had the ejection charges for a rocket go off on the launch pad once when I was standing on a ladder beside the rocket. Fortunately, no one was hurt and the rocket wasn't damaged. But, it got me thinking that having dual altimeters might just double the chance of an accident like that one.

So, for most of my rockets I'm going to stick to one altimeter. If (when?) I start flying really heavy Level 3 rockets, I'll probably go with redundant electronics - but only use altimeters I've tested during previous flights.

For now, I often use either a Newton's 3rd cannister with an e-match also stuck in the powder as a form of redundancy. Or I use two e-matches in a charge. I don't know if it's really necessary, but e-matches are cheap enough. If anything, I'm more worried about a loose connection or broken lead and having a backup e-match should help if that happens.

-- Roger

[cwbullet]

I rarely used redundency anymore, but I have used the Raven that way and it works. I have Newton's and Pratts products but have never used them because ematches are cheap.

[SCE to AUX]

The best tool for reliable flying with electronics is a good multimeter.

Verify the resistance of your e-matches before and after installing them into your charge canisters (before you add the powder). Know what typical resistance values are for the matches/igniters you use, and don't trust any that stray too far from the average.

If you don't have room/money for redundant electronics, you should at least consider redundant batteries. And make sure that the batteries are SECURED. A wrap of tape or a nylon cable tie to hold the battery in place will prevent acceleration forces from disconnecting it.

After connecting the e-matches, (but before adding the powder), I like to power up the altimeter, and let it go all the way through its boot sequence, to make sure that it reads continuity on both matches. If everything is good, and before powering down, check the battery voltage with the altimeter on (use your multimeter, not the onboard altimeter battery voltage measurement, which is more often than not inaccurate). If your battery is good, then power down, add your BP, and finish prepping the flight.

Make sure that you stick around the pad long enough to verify the proper continuity beep sequence is being sounded pre-launch.