Need advice On using 2 altimeters

[NattyDread]

The rocketry book talks about using 2 altimeters, redundancy. I am planning for level 2 cert on dual deploy, with a larger rocket. I would think the whole thing would cost close to $500 or more, so losing it to a crash would be bad! Anyone have first hand experience with altimeter redundancy? Thoughts? Ideas,recommendations ? I was thinking of one with a lot of features and one basic solid performer as the backup.

 

[Handeman]

I haven't use redundant altimeters, but would set the two up completely independent of each other. The one thing I would look at is making sure I can put a one or two second delay on the apogee charge on the backup altimeter. I would set the backup to deploy the main 100 to 200 ft lower then the main so it might be nice to be able to program the main altitude on the backup instead of just using the defaults.

 

[Viperfixr]

Read Troj's words once on this topic and his response rang the most true to me: if there is room for two, put two altimeters in. The redundancy is supposed to increase the likelihood of getting it back in one piece. That said, if you are new to Dual Deployment, I would chose a simple, relatively inexpensive rocket along with a single altimeter and explore DD without the expense and complication. With a few, *successful* DD flights under your belt, you could try for that L2. If your field requires DD, that is. If it does not, then just go motor eject or motor eject with electronic backup (say about a 2 second apogee delay).

As for what altimeter to think about, I would chose the Missile Works RRC3 or the PerfectFlite SL100 Stratologger--both well under $100 each, simple and able to be used right out of the box without anything else.

 

[Sully]

When I first did DD, I had full redundancy (plus motor ejection backup) on every flight. I still do on certain flights, but now am more comfortable with the electronics and my own ability to set things up correctly, and sometimes use a single altimeter.

Some people use two altimeters wired to a single charge, or sharing a power switch. This does provide some degree of redundancy, but I preferred to have true redundancy with two entirely separate setups, with two alts, two batteries, two power switches, and two charges for each event. I use an Adept22 and Adept DDC22, which are unfortunately no longer widely available, but are/were very inexpensive. As a beginner, I appreciated keeping things as simple as possible, so was willing to forgo more features and save some money. Even with just the basics, there was still a lot of wire in the e-bay to hook up and secure.

There is a theoretical concern that if both charges blew simultaneously, the ejection would be "overcharged" and too forceful, but given how fast the ejection event happens (milliseconds), the odds of this seem very low to me, and I don't think I've experienced this, although of course it would be impossible to tell unless the ejection appeared way too "energetic." If you worry about this, however, you'd have to use an altimeter that has an adjustable apogee deployment.

And I agree that you shouldn't have your first DD flight be your cert flight. You can always transfer the electronics to a bigger rocket to go for L2 once you're comfortable with them.

Most important: ground test. All the online calculators and instructions you can find are no substitute for testing an actual charge in your actual rocket.

 

[JDcluster]

When I did my L2 I only used 1 altimeter (Adept ALTS2-50k) it worked fine and still use only one most of the time.
I do use 2 on bigger rockets for added safety.
Having to many events go off can ruin a flight / rocket as well.


JD

 

[les]

There is always a tradeoff in the KISS theory and redundancy. Plus redundancy does add cost, weight, etc. But as you said you are trading this off against the loss of a $500+ rocket.

Personally, I believe in redundancy. My main job is on real aircraft electronics where critical systems are triplex or even quad redundant. In fact one aircraft had a dual - triplex system. Two different systems each triple redundant! Compared to that having dual altimeters isn't over the top.

I have a Raven 2 which has 4 channels plus a RRC3 which has 2 channels. The Raven can be set up for an Apogee, Main, backup Apogee, and backup Main. The RRC3 has an Apogee and Main.

Each altimeter has its own battery and switch (so if one switch or battery fails there is a second).
I have 2 separate Apogee charges and 2 separate Main charges. One of the Apogee charges and one of the Main charges I set up with 2 Q2G2 ignitors.

So the Raven Apogee channel goes to the single ignitor Apogee charge
The Raven Apogee backup channel goes to one ignitor of the dual ignitor charge and the RRC3 Apogee channel goes to the second ignitor of that same charge.
Perhaps having the second ignitor is overkill, but for $1. it is the cheapest insurance against the $500 rocket!

Similar setup for the main charge.

One important step is to clearly identify the leads to keep them all straight - there are 6 pairs of wires. I buy the Q2G2 ignitors with the short wires and solder extensions on. I use different colors to help identify which lead is which.

So hopefully, the Raven Apogee and Main charges work. If either fails, then I have two different altimeters each with their own ignitor trying to set off the second charge. I also will put a tad more BP in the backup charge (the blow it up vs blow it out approach). Since the initial charge should have worked the backup is just venting into the open air. If the initial charge does not work then I have a little more oomph to get the laundry out.

Oh - and depending on the rocket/motor combination I may also leave the motor eject in for another layer of redundancy - set it for a "long" delay to get past the apogee event

 

[jderimig]

That said, if you are new to Dual Deployment, I would chose a simple, relatively inexpensive rocket along with a single altimeter and explore DD without the expense and complication.

+1. Truer words never spoken. Altimeters are very reliable devices, you do not need two. People on the other hand are not reliable...... You (we) are the weakest link in the recovery system, not the altimeter, ematches, batteries or wiring.

Learn your electronic techniques with single altimeter, robust light rocket, flown away from the flight line. Every failure, hopefully there will be few, will be an educational lesson on wiring, power, housekeeping, charge selection and system reliability.

By the time you have many single DD flights under your belt your technique will be good and you will know what you are doing.

When you move up to heavy potentially hazardous rockets then dual altimeters are appropriate. Redundancy is to protect people and property not the rocket.

 

[KenRico]

... altimeter redundancy? Thoughts? Ideas,recommendations ? I was thinking of one with a lot of features and one basic solid performer as the backup.

I had the same thought, and utilized an Adept22 and a Raven3 for my first DD flights. Had them set up on single sled , each with its own battery and switch. Since then have sold the Adept22 and replaced with the RRC3 , mainly because I want to see a speed report on my flights . Both alts are well supported and documented by the mfg and in this forum . If a smaller rocket will use only one .

Don't get too hung up on the sled and configuration - if you do a ground deployment test and it works ... it will probably work in the rocket . If you find a better way of rigging you can change your sled config in the future.

I delayed and overthought my first DD flight , rocksim put it close to 1300 ft and thrustcurve at 1100 ft.. set Adept22 to apogee/900ft and backup (more flexible/options) raven3 to apogee + 1.5 sec.s/704 ft -- rocket only went 727 ft . Chute barely opened before it hit the ground . Redundancy did work -two apogee and one main showed burned upon inspection . I SHOULD have trusted my configuration and was way too conservative on the motor .

The other thing that really helps NOW is to prep the night before, EVERYTHING but hooking the charges up and the igniter . Still need to unfurl the laundry & tethers onsite and recheck all attachements/quick links to make sure they are hooked up (have seen one not attached or not closed more than once). But this is much easier when I have already layed them out the night before for a quick inspection (they do get charred ) , same with chutes, then assemble like I am flying (including attaching) . If I am missing a quicklink, a plastic rivet, if the quicklink does not fit in the swivel, or if the av bay terminals are cooked - can work out a solution without distraction. In the field I can work it out too, but then forget to do something (cause I think I already did it) like hook and close nose cone quicklink . In the field just remove the shear pins and unfurl the laundry ...then quickly reroll and reassembly rechecking the quicklinks-easy peasy everything there including wadding/nomex from night before.

Avbay am trying to employ the same strategy, open up and replace batts - hear the alts beep ready . Then seal it up with the terminal blocks connected and switches (or switch wires) OFF. I use a cheapie Harbor Freight meter to test batt voltage and continuity of the e-matches , and make sure it and any tools needed for the bay including very small flat blade for raven terminals is in my av bay box . I use a AT charge container (medical centifuge) to measure my charges and make sure one or two are in my box also. After the rest of the rocket is ready - In the field I make up some deployment charges, unfasten the plastic rivets and attach the charges to the upper terminal blocks and reattach the payload to the bay. Then I hook up the other set of charges on the bottom. Now everything is ready except installing the igniter .. I arm one alt switch and listen for the beeps then off and same with the other . Take rocket, flight card and igniter to RSO and FLY !

You will shape and modify your own strategy, try to get a few DD flights in to settle on your routine/checklist.

Kenny

 

[azzie]

On expensive projects, you want redundant recovery system! For me, backup altimeter saved my most expensive flight to date :surprised:

Here are my 2c that I learned:

1) Wire two altimeters with no common points. Use two batteries, two power switches, etc
2) You can use second altimeter that is cheaper and from different manufacturer
3) Make sure the same ejection matches/canisters can be used on both (less confusion)
4) Write down start-up beep sequences and have with you on launch pad (first few times, you will get confused with too much beeping and having instructions helps)
5) Set drogue deployment to apogee on both (it's okay, they will not go off at the same exact time due to different math on each unit)
6) Set main chute deployment to different altitudes (it's fun seeing it work)
7) After every flight, check that all ejection charges went off - don't assume they did because you had a successful flight
8) Design DD in such a way that primary ejection charge can not rip off backup ejection canister and throw it into the field separately from the rocket!

Link to some pictures...

-Alex

 

[NattyDread]

One really good thought from above. I think I will take my paper little john that has a lot of battle scars and convert it to DD. This will give me a much less expensive training ground to get comfortable with using electronics and building ejection charges, testing ejection charges, etc. Is it possible to buy less than the one pound can of 4F gun powder. Kinda just don't want that much around the garage, or house....

 

[Handeman]

One really good thought from above. I think I will take my paper little john that has a lot of battle scars and convert it to DD. This will give me a much less expensive training ground to get comfortable with using electronics and building ejection charges, testing ejection charges, etc. Is it possible to buy less than the one pound can of 4F gun powder. Kinda just don't want that much around the garage, or house....

When you do that, ground test, ground test, and ground test some more. Not only will you know exactly how much charge to use for ejection, but you will learn the operation of the altimeter. By the time you get ready to actually fly with it, it will be very familiar and you'll be much more comfortable with it.

As for the powder, unless you get some from a friend, I don't believe you can buy ffffg in less the 1 lb quantities. One of the vendors sells individual ejection charges, but I don't know who or how much they might be.

 

[troj]

1) Wire two altimeters with no common points. Use two batteries, two power switches, etc

Agree, completely. One common failure point can kill a flight.

2) You can use second altimeter that is cheaper and from different manufacturer

Pros and cons to this. Back in the days when altimeter reliability was a bit more sketchy, having two differing units was a good thing, as you were much less likely to run into a problem with both. Now, altimeters have matured so much that the reliability of modern units is exceptional. Operator error (sometimes from difficult to understand documentation) is the most common culprit.

...which leads to the downside. When you're new to electronics, using two different units doubles the difficulty, as now you must learn the quirks of both, and understand them at a high stress time.

I recommend beginners start with one model of altimeter. It'll make your life easier.

3) Make sure the same ejection matches/canisters can be used on both (less confusion)
4) Write down start-up beep sequences and have with you on launch pad (first few times, you will get confused with too much beeping and having instructions helps)
5) Set drogue deployment to apogee on both (it's okay, they will not go off at the same exact time due to different math on each unit)
6) Set main chute deployment to different altitudes (it's fun seeing it work)
7) After every flight, check that all ejection charges went off - don't assume they did because you had a successful flight
8) Design DD in such a way that primary ejection charge can not rip off backup ejection canister and throw it into the field separately from the rocket!

Some good info there.

-Kevin

 

[azzie]

When you're new to electronics, using two different units doubles the difficulty, as now you must learn the quirks of both, and understand them at a high stress time. I recommend beginners start with one model of altimeter. It'll make your life easier.

Well, pros and cons go both ways

One would typically go with one more expensive altimeter (data recording, etc) and a cheaper (backup) one to save some money...

Btw, how do you distinguish beep sequences at launch pad if both altimeters' tones are the same?

-Alex

 

[troj]

Btw, how do you distinguish beep sequences at launch pad if both altimeters' tones are the same?

The hard way: Listen very closely. It can be done, but it takes paying attention.

The easy way: Use an altimeter that allows you to change the frequency, so that they beep tones are slightly different.

The really easy way: Have one that provides telemetry that includes continuity information.

Back in June, I flew a rocket with three altimeters -- two RRC3s, and a Telemetrum. I set the second RRC3 to a different beep frequency, and turned on the Telemetrum last. By the time I turned on the Telemetrum, the rocket sounded like it was packed with 300 angry crickets, so I used the telemetry stream to tell me it was armed properly.

-Kevin

 

[jadebox]

One really good thought from above. I think I will take my paper little john that has a lot of battle scars and convert it to DD. This will give me a much less expensive training ground to get comfortable with using electronics and building ejection charges, testing ejection charges, etc. Is it possible to buy less than the one pound can of 4F gun powder. Kinda just don't want that much around the garage, or house....

Aerotech's https://www.valuerockets.com/ web site sells ejection charge reloads for their "Electronic Forward Enclosure." The ECK-1 is a 12-pack of 1.4 gram ejection charges.

-- Roger

 

[jderimig]

The hard way: Listen very closely. It can be done, but it takes paying attention.

The easy way: Use an altimeter that allows you to change the frequency, so that they beep tones are slightly different.

The really easy way: Have one that provides telemetry that includes continuity information.

Back in June, I flew a rocket with three altimeters -- two RRC3s, and a Telemetrum. I set the second RRC3 to a different beep frequency, and turned on the Telemetrum last. By the time I turned on the Telemetrum, the rocket sounded like it was packed with 300 angry crickets, so I used the telemetry stream to tell me it was armed properly.

-Kevin

The easiest way. Turn one on, wait till its happy. Turn it off. Turn the other one on wait till its happy, then turn the first one back on. Good to go.

 

[amarillo_rocket]

I agree with everyone else about using 1 altimeter until you gain experience with dual deploy. The only exception would be if you are launching a large or heavy rocket. I switched to dual altimeters for all my K motor and larger rockets. I consider it cheap insurance. My goal is to the best of my ability to make sure a recovery device is deployed. If there is an ematch failure or human error with a canister not having enough powder ..etc my hope is the second altimeter will provide a means for deploying my recovery system. Safety is #1 and protecting the rocket is #2. Right now I have 3 ebays one for 3", 4" and 5.38" rockets. I swap the ebays between rockets of similiar size which eliminates the cost of having an ebay for every rockety. I use quick links so that make swapping easy. My backup alt is usaully less expensive than my primary again a cost savings.

 

[troj]

I advocated using one model of altimeter (but still two of them, for redundancy), not a single altimeter.

-Kevin

 

[jderimig]

And if you are using a single altimeter that has 4 output channels then USE all 4 channels even if you only have 2 events.

 

[troj]

And if you are using a single altimeter that has 4 output channels then USE all 4 channels even if you only have 2 events.

Ejection charge components (even if they're $2 each) are cheap compared to an entire airframe, plus all of what it contains.

-Kevin

 

[Area66]

I need to 2 mores ebay for my next launch, so I ordered 4 altimeters, I always use 2, except on my small rockets like my Arreaux. The other day when I assemble my Patriot a solder was loose under a heatsink, it was showing continuity ( VOM tester ) , but when you play with the wire it go off and on, so even if altimeter are reliable, solder and wire connections are not. A friend launch is very expensive rocket last week, only the backup charge on the second altimeter fire. This rocket have over $ 1200 of electronic in it. Yes a lot of peoples will say they never experience a problem, they will one day if they use only 1 altimeter.

 

[cerving]

That's why I put both pyro continuity and "Ready" LED output pads on the Eggtimer. Connect them to ultra-bright LEDs, if you get 3 solid lights then you're good to go. I can concur that if you have two altimeters chirping together, even with different tones, it's VERY difficult to tell which one is which.

The hard way: Listen very closely. It can be done, but it takes paying attention.

The easy way: Use an altimeter that allows you to change the frequency, so that they beep tones are slightly different.

The really easy way: Have one that provides telemetry that includes continuity information.

Back in June, I flew a rocket with three altimeters -- two RRC3s, and a Telemetrum. I set the second RRC3 to a different beep frequency, and turned on the Telemetrum last. By the time I turned on the Telemetrum, the rocket sounded like it was packed with 300 angry crickets, so I used the telemetry stream to tell me it was armed properly.

-Kevin

 

[troj]

That's why I put both pyro continuity and "Ready" LED output pads on the Eggtimer. Connect them to ultra-bright LEDs, if you get 3 solid lights then you're good to go. I can concur that if you have two altimeters chirping together, even with different tones, it's VERY difficult to tell which one is which.

To me, with different tones, it's easy.

It's when they're the same that it's difficult.

I can tell two RRC3s apart easily, because I set them to different tone frequencies. Piece 'o cake. If they were on the same frequency, it would be a lot more difficult.

-Kevin

 

[Sailorbill]

On my flight on Monday I had a Raven 2 and an RRC2 Mini, it was really easy to tell the difference. I have two batteries and two switches, one CD3 CO2 deployment system and a 2.5Gram backup charge for apogee and two matches in my Defy Gravity Tether. Everything worked.

 

[Golfpro62]

Lots of good information on this subject. All I would recommend is that using 2 of the same altimeter will make things much simpler and this is not a simple undertaking for sure. I have always used the RRC2 minis for altimeters and they work great - never had a failure due to the hardware. Now for $10 less than I spent of those I recently purchased the RRC3 which has a really cool feature that Kevin was talking about: that is the ability to change the frequency of the tones so you can tell them apart and make sure you have full continuity. The RRC3 also has another cool feature where you can tell one of them it is a back-up and it will set the 2nd alt up with a drogue delay. The only other thing I would say is just to repeat what you have already read above but one more person telling you this will help get this point across: 2 altimeters using separate batteries, separate switches, each working entirely independent of the other - no shared wiring of any kind. I recently got my Level 3 flight accomplished and I did several test flights before the big day and used a redundant system for all of them, it's not that difficult, just take your time and you can easily set this up in a 4 inch airframe - bigger would just make it easier with the extra room. As long as you have the room, you can't go wrong with the RRC3 - it's not a small unit but it has a ton of features, everything you need and more and you can have 2 of them for less than $150, that's less than you can buy one of many of the others and they are simple to use. After reading what everyone else above has said, you have the info you need to go forward and if there is one thing I know about the people above, they are eager and willing to help so don't hesitate asking anything - I can't tell you how valuable a resource this place has been to me over the past couple years moving into Level 2 area, dual deployment and tons more.

 

[NattyDread]

Thanks to all for great advice