Your favorite altimeters, and 'why' you like them!

EeebeeE said:

I used and Adept22 and its companion DDC22 for my L3 cert flight. Had a Beeline tracker (70cm) in the electronics bay. No problem. Both primary and backup charges fired.

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What power output on the Beeline? I should have qualified it by saying the tracker was a 2 watt Garmin dog tracker. Power and frequency of the Rf can make the difference. The EggTimer products with the opto-isolators are resistant
to Rf interference. I've ground tested with ematches and I could only get the EggTimer, Quark, or Quantum to change pitch on the piezo if I touched the antenna of a 5 watt transmitter to the optoisolator chips. The devices remained in
ready to launch mode

With Evan's comment on an accelerometer activated deployment. A purely accelerometer activated deployment can be markedly off especially if the flight is off vertical. The current Raven instructions that Featherweight sends out recommends that baro apogee deployment be used for accurate apogee detection for most flights. The accelerometer is still used as part of the data along with baro filtering for Mach delay purposes.

The ARTS II was a pretty darned good unit in its day. I have an unflown one I'm going to fly. Kurt

RRC2 for simplicity and robust design.

RRC3 for the same reasons as the RRC2 + data! I used to use the StratologgerCF, but the RRC3 gives me more data.

I like my old school RRC2 rev c. It just works.

That said I also really like the rrc2+ and the rrc3.

I have seen the Marsa 54L and Ravens- both great units.

Really- the choices available today are vastly superior to what was previously available, and at better price points.

JERRYR708 said:

I didn't see any LOGIC in any of this. You guys don't know Beans.

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I see what you did there. Amen, brother.

ksaves2 said:

What power output on the Beeline? I should have qualified it by saying the tracker was a 2 watt Garmin dog tracker. Power and frequency of the Rf can make the difference. The EggTimer products with the opto-isolators are resistant
to Rf interference. I've ground tested with ematches and I could only get the EggTimer, Quark, or Quantum to change pitch on the piezo if I touched the antenna of a 5 watt transmitter to the optoisolator chips. The devices remained in
ready to launch mode

With Evan's comment on an accelerometer activated deployment. A purely accelerometer activated deployment can be markedly off especially if the flight is off vertical. The current Raven instructions that Featherweight sends out recommends that baro apogee deployment be used for accurate apogee detection for most flights. The accelerometer is still used as part of the data along with baro filtering for Mach delay purposes.

The ARTS II was a pretty darned good unit in its day. I have an unflown one I'm going to fly. Kurt

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A Beeline 70cm tracker is 1W. Transmits in the 420-440KHz range. Great little transmitters. You track them with a Yagi antenna. Need to have a Ham license to use them, though. They also make one that transmits GPS location through the radio signal.

Agreed on the accelerometer point which is why most altimeters with accelerometers have baro altimeters as well. Problem with pure barometric altimeters is they need air pressure to work. If you are planning a flight to >100,000' you should not rely on a barometric altimeter because the air pressure at that altitude is practically nonexistent.

This guy is flying a 4" frenzy. I think he's pretty safe with a baro.

Considering the the number of flights that go over 100K, mentioning a "need" for using accel based altimeters in a normal discussion of altimeters, because the air is "too thin" over 100K is pretty silly.

And theres a good bit of pressure at 100k yet-



https://www.avs.org/AVS/files/c7/c7edaedb-95b2-438f-adfb-36de54f87b9e.pdf

The high altitude Raven reduces its altitude resolution to five feet per count. That's still much more accurate that an accelerometer would likely be at that altitude.

EeebeeE said:

A Beeline 70cm tracker is 1W. Transmits in the 420-440KHz range. Great little transmitters. You track them with a Yagi antenna. Need to have a Ham license to use them, though. They also make one that transmits GPS location through the radio signal.

Agreed on the accelerometer point which is why most altimeters with accelerometers have baro altimeters as well. Problem with pure barometric altimeters is they need air pressure to work. If you are planning a flight to >100,000' you should not rely on a barometric altimeter because the air pressure at that altitude is practically nonexistent.

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Ahem, A 70cm Beeline GPS is either 100mW or 16mW: https://www.bigredbee.com/zc139/ind...ducts_id=207&zenid=hehsrh91ac5bv47fq6lk5vbar7

Greg has a 2 meter version that can do up to 5 watts with an adequate battery. As mentioned more power is not necessarily a smart proposition if ones controller electronics are dorked by Rf. One should test beforehand unless one knows from a decent source two devices play well with each other. Also flights to very high altitudes have their own problems I've seen discussed in other postings. In that very rarefied environment getting an apogee ejection can be a challenge. Using an acclerometer based deployment can still be off by a hefty amount but deployment in the high vacuum entails less stress on the drogue chute. I'd use what others have used successfully if going to those levels and wouldn't care if they're baro or accel based as
long as they perform satisfactorily. Kurt

I stand corrected on the Beeline. Was working from memory instead of going to look at the actual specs.

I have yet to see a manufacturer of a baro altimeter suggest the product is good above 100,000'. Perfect Flite says their stratologger is good TO 100,000', but that qualifier implies that they are not certain of its accuracy above that altitude. Adept Rocketry seems to show up to 60,000' for their baro altimeters. Most others say between 40,000 and 60,000.

I am working toward a 100,000'+ project and will use MARSA electronics because they are so widely versatile and through their wireless connections can have a huge array of different configurations, all handled through one central onboard computer. However, 100,000' flights are few and far between, and the overwhelming majority of people in the hobby never go that high.

So....

The Adept 22 and the Perfect Flite Stratologger have been my "go-to's" for dual deployment because I have been using simple motor configurations (one motor, no clusters, no stages). In the flight failures I have had (and a number of people can attest to them), the altimeter wasn't the problem. I tend to push things to extreme so I am prone to shreds and shock cord failures (dammit!). I never tried the RRC2 although I know people who swear by them. Any one of these three are very good for the vast majority of DD flights, and they all are very reasonably priced. When you start getting into staging, clusters, and airstarts, you generally need more complex electronics, especially if you want to avoid using multiple timers or other devices to handle some aspect of the flight and other devices to handle others.

I have seen the Jolly Logic chute release in action in recent months, and it appears to be excellent. It will fit inside a 38mm tube and can help you make a motor deployment rocket dual deploy with a lot of ease. I could see these used in altitude record attempts in conjunction with small apogee deployment altimeters. Locate the apogee deployment altimeter in the nose cone. Have the chute release attached to the chute, and you eliminate the need for an AV Bay, which can save several ounces of weight (coupler tube, bulkheads, threaded rods nuts and washers, eyebolts, e-match connectors, etc.). Plus you would have only one seam in the rocket at the nose cone instead of two or three (nose and payload bay seams plus possible switch band seams), helping you aerodynamically as well.

If you are looking for a read-only altimeter, the Jolly logic units are excellent, and very small. I bought a new Estes max altitude altimeter for $25. Easy to use and one of the least expensive I have seen, but it is relatively bulky and heavy. If you are going for altitude records the Jolly logics are much smaller and lighter, and they are known for their accuracy.

I also have a Perfect Flite P-Nut altimeter. The cool thing about this little device is that it is narrow enough to fit inside an 18mm tube, weighs 0.4 oz. even with its LIPO battery, and reports full telemetry data through the same data interface and software that is used for the Stratologger. In my L3 flight, I used the Adept 22 and the UDC22 as primary and backup deployment altimeters, but also mounted a P-Nut so I could collect more detailed telemetry data. The drawbacks of the P-Nut are that it is still large for a recording altimeter, needs some sort of mount as well as protection from exhaust gases which adds even more weight, and it is a little pricey.

I would not use an Adept 22 in a high Rf environment unless you test it out thoroughly first. I've seen two occasions, one that led to a totally ballistic flight with two Adept 22's and a converted 2 watt Garmin dog tracker. Both altimeters shut down that
led to a 16 foot tall O powered rocket coming in ballistic. The second event the original flier replicated the rocket, repositioned the same electronics (new A22 altimeters and dog tracker) and heeded the advice to do a protracted ground test with bare ematches and the tracker transmitting. Within 10 minutes both altimeters shut down and locked up. Changed out the Adept 22's to different units and with the ground test passed attempted the O powered flight. Unfortunately the nozzle blew out of the
motor case on the pad, several of the burning grains fell out as the rocket tipped over and it was consumed in the "road flare" show that followed. Also burned off a tire on the launch trailer!

If I were you, I'd quietly work on less involved projects and gradually work up to what you are trying to achieve. You may not ultimately get there as from what I've seen it's a complex undertaking. It's going to take a lot of time effort and money not to mention the amount of time it will take to get a 100k flight approved that must be carried out beforehand. Ask about the paperwork and simulations required especially if the rocket is heading towards the large size and weight. Not many venues out there for a flight of that caliber no matter what the rocket size and one can't simply show up anywhere and fly. If you have someone at hand who's done it and is willing to mentor, by all means take advantage of the help. Don't expect success from the opinions of armchair fliers from an online group. In the end, you'll be the one taking the responsibility. The second you get complacent is when you'll get bit in the behind. Even if you aren't complacent, stuff happens. Especially when travelling at high speeds and altitudes. I see you're from the "right" coast. If I'm not mistaken, not many launchsites there that can support a flight to 100k. You planning on moving west? Would be prudent to get some flights in at lower altitudes first. Kurt

https://www.featherweightaltimeters.com/
Not too much need for discussion when you fly the best.

ksaves2 said:

I would not use an Adept 22 in a high Rf environment unless you test it out thoroughly first. I've seen two occasions, one that led to a totally ballistic flight with two Adept 22's and a converted 2 watt Garmin dog tracker. Both altimeters shut down that
led to a 16 foot tall O powered rocket coming in ballistic. The second event the original flier replicated the rocket, repositioned the same electronics (new A22 altimeters and dog tracker) and heeded the advice to do a protracted ground test with bare ematches and the tracker transmitting.

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On flights like this/ O motor rockets I just don't understand why Adept22's are even being discussed. It's a known issue...Why do people even bother?

ksaves2 said:

If I were you, I'd quietly work on less involved projects and gradually work up to what you are trying to achieve. You may not ultimately get there as from what I've seen it's a complex undertaking. It's going to take a lot of time effort and money not to mention the amount of time it will take to get a 100k flight approved that must be carried out beforehand. Ask about the paperwork and simulations required especially if the rocket is heading towards the large size and weight. Not many venues out there for a flight of that caliber no matter what the rocket size and one can't simply show up anywhere and fly. If you have someone at hand who's done it and is willing to mentor, by all means take advantage of the help. Don't expect success from the opinions of armchair fliers from an online group. In the end, you'll be the one taking the responsibility. The second you get complacent is when you'll get bit in the behind. Even if you aren't complacent, stuff happens. Especially when travelling at high speeds and altitudes. I see you're from the "right" coast. If I'm not mistaken, not many launchsites there that can support a flight to 100k. You planning on moving west? Would be prudent to get some flights in at lower altitudes first. Kurt

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Ummm, he's mentioned he's doing several flights building up to this.

He's getting advice here from people who have been over 100K.

I've not seen him act complacent in any way.

Moving west? You do realize people are willing to travel a few days to Black Rock, right?

None of this post is relevant to Evan's situation aside from the already beaten to death Adept22 info, which he's said he's not using...

Thanks David.

Part of my one chance to get it right is the consideration of travel expenses to Nevada from Western NY. That's why there will be several experiments in Potter with staging, and why this is a multi-year project, not something I plan to do in 6 months. I have one shot at getting this right, so I need to do a lot of low level stuff here, plus some mid level stuff down south. Just because I am not from the West Coast doesn't mean I shouldn't try this. Also, I am attempting to hit 100,000' on M Level. That means if necessary, I can take the rocket out west on the Amtrak Train.

Kurt, my suggestion is to read the thread "Going for 100,000 Feet" as to the approach I am planning. Several people have commented about the 100,000' flight because that is the "sexy one." However, my first focus is trying to establish a complex I record, which I intend to do in Potter. Once I am satisfied with that, I will pursue a Complex K record.

So with all that being said, let's take this discussion back to altimeters that are most used by everyone. An altimeter used by a huge percentage of the HPR hobbyists is the Adept22. It really is a VERY good altimeter as long as you use transmitters designed for rocketry as opposed to transmitters used to find the family pet. You need far more transmitter power to track an object on the ground than you do with an object in the air because an object on the ground is more prone to ground-level interference. I have yet to see a St. Bernard fly.

TMJ said:

I'm searching for information on altimeters. Being new to the hobby I currently know of only a few altimeters from a very few sources. I'd like to know what altimeters you folks use, who to purchase them from, and why you like them!
Thanks...

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Hi TMJ,
Getting back to the original questions:
I like the Missileworks RRC series. I buy them directly from https://www.missileworks.com. I've used different versions over the years and I just bought two more, his newest, the RRC3.
I like them because they have been very reliable, easy to set up for dual deployment, and reasonably sized. It's also relatively inexpensive. Once set, you only need to change batteries when appropriate. It's a great all-round starting altimeter which has evolved to three output channels, optional digital display, and logging.
However, as you gain experience and your needs evolve you will almost certainly purchase other altimeters that are better for your specific purposes. I have several brands for different purposes.
What do you want your altimeter to do? Dual deployment?
Staging?
Logging?
Do you need a small size?
This table from Featherweight includes several altimeters that are no longer available but it does list a lot of features that may help you choose. Pick the features that are important to you and put together a similar table.

EeebeeE said:

Thanks David.

Part of my one chance to get it right is the consideration of travel expenses to Nevada from Western NY. That's why there will be several experiments in Potter with staging, and why this is a multi-year project, not something I plan to do in 6 months. I have one shot at getting this right, so I need to do a lot of low level stuff here, plus some mid level stuff down south. Just because I am not from the West Coast doesn't mean I shouldn't try this. Also, I am attempting to hit 100,000' on M Level. That means if necessary, I can take the rocket out west on the Amtrak Train.

Kurt, my suggestion is to read the thread "Going for 100,000 Feet" as to the approach I am planning. Several people have commented about the 100,000' flight because that is the "sexy one." However, my first focus is trying to establish a complex I record, which I intend to do in Potter. Once I am satisfied with that, I will pursue a Complex K record.

So with all that being said, let's take this discussion back to altimeters that are most used by everyone. An altimeter used by a huge percentage of the HPR hobbyists is the Adept22. It really is a VERY good altimeter as long as you use transmitters designed for rocketry as opposed to transmitters used to find the family pet. You need far more transmitter power to track an object on the ground than you do with an object in the air because an object on the ground is more prone to ground-level interference. I have yet to see a St. Bernard fly.

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Hi Evan,

I like your approach, stepped, slow and by the sounds of it methodical, sounds like a good formula for a decent shot at attaining your goals. That being said as much as I like my electronics I have not been to 100K, I can't speak for the rest of the posters that have responded, but my guess is few if any at all.

Not that this makes their posts less worthy, but why don't you reach out to the one person I have a great deal of respect for on this topic, Jim Jarvis. As you likely know he has not only surpassed 100K, but he has done so on the West coast so he will also be a good source for the logistics and other issues ksaves2 brings up. More importantly he has done it with a staged setup like you have mentioned here.

BTW, forgive me for possibly telling you something you already know or have done, truthfully I have not read your other post.

mpitfield said:

Hi Evan,

I like your approach, stepped, slow and by the sounds of it methodical, sounds like a good formula for a decent shot at attaining your goals. That being said as much as I like my electronics I have not been to 100K, I can't speak for the rest of the posters that have responded, but my guess is few if any at all.

Not that this makes their posts less worthy, but why don't you reach out to the one person I have a great deal of respect for on this topic, Jim Jarvis.

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Jim has been an invaluable resource, and I deeply respect his thoughts.

As I mentioned earlier, altimeters like the Stratologger, Adept 22, RRC2, and others that are similar work exceptionally well for Simple DD flights. You can use these for L1 efforts as well as L3. I've even used DD altimeters as replacements for motor deploy for rockets that need apogee deployment due to fin design (Didn't want a weighted nose cone to break off a fin because of a late motor deployment). In light of recent NAR and TRA rulings on V-Max motors, I also posted a nose cone based approach to single deployment using in this particular case and Adept 22 although any other altimeter less than 1" wide would work.



Once you get into complex flights the Raven 3 and MARSA altimeters are great.

Bottom line is that the altimeter you choose will be the one that fits your needs the closest. For me it was PerfectFlite and Adept Rocketry Electronics at the outset. I've even mixed the two for some of my preliminary Mach 1 flights, using an Pefectflite MT4 Timer as a backup to an Adept 22 when motor deployment was not an option (delay charge not long enough) and I wanted some sort of backup to minimize the risk of a small, barely visible rocket from coming in ballistic from more than a mile up. For my more complex flights I am looking at others.

I do not think there is a "bad" altimeter or set of electronics out there. They all work the way they are supposed to. In your electronics resources you should use more than one brand because the variety helps you better understand other brands' capabilities when you start pushing the envelope. Hindsight being 20/20, I should have probably also used the RRC2 in addition to Stratologgers and Adept 22s. I had one chance to use a MARSA and it was great.

Play around. Start simple and get more complex. Understand the strengths and weaknesses of every one. That way you are not predisposed to use one for a particular project when another could be better.

Low Power
Altimeter 1, 2 or 3
Chute Release (I know my Beans!!)

All the rest
Stratologger - over 50 flights my set so far, no problems yet that werent ruled as a 'bad match'
RRC3 - Reliable, cheap(ish) and an extra channel
Adept22 - coz sometimes you like a bit of dumb as backup
TeleMega - will do everything you need, and more

Featherweight Raven!
Tiny, four channels, easy to use and a lot of features...
Add the Featherweight Av-bay and you have a complete, very small set-up.

And I had an EXTRAORDINARY after sales service. My Raven 2 was replaced by a Raven3 recently (last week), with a very fast delivery.

Steeve

EeebeeE said:

Thanks David.

Part of my one chance to get it right is the consideration of travel expenses to Nevada from Western NY. That's why there will be several experiments in Potter with staging, and why this is a multi-year project, not something I plan to do in 6 months. I have one shot at getting this right, so I need to do a lot of low level stuff here, plus some mid level stuff down south. Just because I am not from the West Coast doesn't mean I shouldn't try this. Also, I am attempting to hit 100,000' on M Level. That means if necessary, I can take the rocket out west on the Amtrak Train.

Kurt, my suggestion is to read the thread "Going for 100,000 Feet" as to the approach I am planning. Several people have commented about the 100,000' flight because that is the "sexy one." However, my first focus is trying to establish a complex I record, which I intend to do in Potter. Once I am satisfied with that, I will pursue a Complex K record.

So with all that being said, let's take this discussion back to altimeters that are most used by everyone. An altimeter used by a huge percentage of the HPR hobbyists is the Adept22. It really is a VERY good altimeter as long as you use transmitters designed for rocketry as opposed to transmitters used to find the family pet. You need far more transmitter power to track an object on the ground than you do with an object in the air because an object on the ground is more prone to ground-level interference. I have yet to see a St. Bernard fly.

Click to expand...

Sounds like a plan. I've been bit by Rf before it was ever mentioned anywhere. Used a standard rocket tracker too. The dual Adept failure was in 2009 and not my project. I had deployment on ascent and deployment on the pad with an altimeter
no longer available and is so old I've never seen anyone else use it. Whether the tracker is meant to be used with a rocket or not, confirmation from a reliable source is helpful or you ground test or you take your chances.

I've been around awhile and GPS dog trackers were converted and tried. Those electronics were available when the only thing out there were very pricey 900mhz GPS units or Ham APRS GPS trackers. With the current batch of GPS trackers meant for rocketry, there is no reason to use those devices today. None of what I learned to get a General Ham license prepared for what happened with Rf interference with deployment devices. Nor did I see any chatter on the subject before my experiences.

I fly an Adept 22 in simple DD rockets that don't require a tracker. If I was going to use a tracker with one, I'd ground test it first unless someone I trusted related they had success with a similar setup. True, the lower powered trackers have a tendency
to play better (16mW) than the higher power and the newer deployment electronics are more resistant to the effects of Rf. Plus the effects are frequency dependent. A 2 meter tracker might dork ones setup where a 70cm or 33cm won't.

If you go with Jim Amos Missileworks and an RRC3, will be able to interface with the soon to be released GPS tracker/module system. Perhaps the high altitude RRC3 will be available again. Guaranteed to 100k.

Mr. Beans might also have his networking mesh GPS tracking system perfected by the time you are ready for rarefied exploring and hence would greatly increase your chances of finding your project after recovery.
(Unless he runs into a wall and can't bring it to fruition. Personally, I hope he succeeds as it will really increase the odds of finding a project of your planned nature. If you fly it at a major launch out west it would
be likely the sponsors could set up a tracking range to give realtime information even if a subject rocket goes out of range of a single launchsite receiving station.)

As far as Jim Jarvis goes, read anything by him or anyone else who has been there and if one is not amazed and humbled they're stupid. Stupid for not recognizing what they've achieved and how hard it is to achieve it.

If you are shooting for 100k with an M to whatever staging, you'll likely have to go with an all-in-one device for your electronics for simply weight reduction's sake. I've followed your 100k thread and you've had responses from
folks who are very intelligent. I sense they are a little tongue-in-cheek but look to be steering you honestly without directly berating.

Ummmm, your goals of a complex I record, complex K record and an M staged to whatever for 100k is quite a high bar and I wish you luck in pursuing them. You might want to explore advanced carbon fiber composite construction/lamination techniques along with getting the tracking Rf out of the airframe so you can find the thing. This stuff can get pretty pricey very quickly. Derek Deville even learned how to weld aluminum for his Qu8k rocket fincan and it's interesting it wasn't taken into account that the downward looking plastic camera shroud would melt at Mach as so demonstrated in the video. That in no way imparted on the safety of that impressive flight.

Again, best of luck as you are going to be making a lot of decisions and compromises to do what you are setting out to do. Hope to see your name in the record books. Kurt

Here are a few opinions ....

I've mostly relied on the Perfectflight products for general dual deploy. I've never had a problem with any of them. Can't hardly beat that.

I've had a couple of the missleworks altimeters. The one I have now is the one with the menus that you program with the switches. I actually like it, but I'm sure the new ones are much better.

I have a love/hate relationship with the Raven. For a while, it was pretty much the only altimeter you could use for more complex staged flights. A lot of work went into the programming capability of the unit. However, the matrix of settings for the various channels was limited, and compromises were required. The accuracy of the accelerometers in some of the units has also been problematic. But, it was a leap in capability when it was developed and I still use them.

My favorite altimeter for high altitude flights is the EasyMega. The programming is completely flexible for four of the six channels and it has the tilt capability. It costs more but you get more.

Haven't gotten around to Marsa yet. No reason, just haven't.

A few comments on the high altitude discussion. My approach is to use timers for apogee, with backup barometric if the altitude at apogee is below 90K feet. I don't use accelerometers for apogee because there are suboptimal flight profiles where an accelerometer-based altimeter will never fire, and the accuracy degrades for long or non-vertical flights. I don't use barometric above 90K because even though the altimeter can read the altitude well above that, the programming for apogee detection will typically cause early deployment (a slow rate of change in the pressure). It's a function of altitude and speed. It's guesswork at best, so I just use timers - they always fire eventually - and if they are a little early or late, it doesn't matter than much. I'd like to try gps-based deployment at some point.

Regarding high altitude staging, the most difficult aspect of it is setting up the electronics to deal with all of the different things that might happen, and to include a viable altitude check for safety. It is much more difficult then you might think. I spend weeks going over the various scenarios, and yet I could point to some error that I made in nearly every flight I've done. Best thing is to have as many people look at the plan as you can. I used to have Adrian review my Raven settings before each flight, and we would talk through all of the what iffs, and even folks not experienced with high altitude staged flights have spotted things for me.

Jim

JimJarvis50 said:

H I don't use accelerometers for apogee because there are suboptimal flight profiles where an accelerometer-based altimeter will never fire, and the accuracy degrades for long or non-vertical flights. I don't use barometric above 90K because even though the altimeter can read the altitude well above that, the programming for apogee detection will typically cause early deployment (a slow rate of change in the pressure). It's a function of altitude and speed. It's guesswork at best,

Jim

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Jim, thanks for the thoughtful post and I would like to offer an opinion and a question. First the question..

Q. Other than a cato/shred what are some of the flight profiles where an acceleration based apogee detect won't fire?

Second on apogee detection - baro-accel. I agree that a single sensor method of apogee detection is not optimal. However the current altimeter algorithm state of the art is to use Kalman filtering to fuse all the sensors to estimate that state of the rocket. In a Kalman application of apogee detection on a long flight accelerometer integration errors will be mostly zero'd out by the robust barometric readings during the lower altitudes (<60K ft). After that the Kalman filter can be set to trust the baro less and the accelerometer more. During this phase of the flight the acceleration is more quiescent (coast) and will be the easiest to measure accurately.

I have data that shows robust accelerometer based apogee detection through 40-60K feet. I don't have data above that yet.

Excellent discussion. I read where clock wound timers were used on sounding rockets to actuate a recovery device if so installed. One observation I'll share from the high altitude balloon guys is I always thought when the balloon ruptures above
100k' the recovery chute just streamers and does nothing until the air is denser. Boy was I wrong. Several flights with a camera pointing up at the chute and the balloon envelope show the chute inflates quickly as long as it doesn't tangle.
What I didn't realize is that sucker starts falling very fast from altitude and even though the air density is less, it develops enough speed to get enough air molecules in the canopy to inflate it! It just comes down faster in the initial descent.
When it reaches denser air, the package starts to slow down. Such an elementary concept yet took me a time to realize it.

So, if the apogee deployment is delayed a bit either way, since a robust drogue is likely to be used it's not that much of a problem. I would surmise if the apogee deployment is delayed too long and if a drogue made out of poor material is used,
could shred. I think Mark Clark had mentioned this foible of high altitude deployment and also that if the chute material was cold soaked at altitude further increased the chance of chute failure due to brittleness of the material.

Ok, I'll shutup for going too far OT of altimeters. Kurt

jderimig said:

Jim, thanks for the thoughtful post and I would like to offer an opinion and a question. First the question..

Q. Other than a cato/shred what are some of the flight profiles where an acceleration based apogee detect won't fire?

Second on apogee detection - baro-accel. I agree that a single sensor method of apogee detection is not optimal. However the current altimeter algorithm state of the art is to use Kalman filtering to fuse all the sensors to estimate that state of the rocket. In a Kalman application of apogee detection on a long flight accelerometer integration errors will be mostly zero'd out by the robust barometric readings during the lower altitudes (<60K ft). After that the Kalman filter can be set to trust the baro less and the accelerometer more. During this phase of the flight the acceleration is more quiescent (coast) and will be the easiest to measure accurately.

I have data that shows robust accelerometer based apogee detection through 40-60K feet. I don't have data above that yet.

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My comments on the use of barometric were based exclusively on the Raven (it's the only altimeter that I have used for barometric anything above 50K or so). Combining barometric and accelerometer readings sounds like a great approach. I think it would be important, though, to understand how the altimeter is doing the calculations and what values the altimeter is actually looking at to make decisions. Just as an example, again for the Raven, I had a discussion with Adrian at one point where we talked through the various flags. One thing we clarified was that the "altitude" value was an unfiltered value whereas "pressure decreasing" was filtered. I would want to know that sort of information for any altimeter I was using, particularly if the programming of the altimeter was based on assumptions about the flight profile.

Regarding a flight profile where an accelerometer-based altimeter won't fire, the most obvious case is an off-angle flight (where it "won't fire" before hitting the ground). I have also pondered what would happen on a high altitude flight once the fins stopped providing guidance. I speculated a few days ago that a potential flight of mine might be turning cartwheels at some point, although I don't know if this would actually happen. I think I've convinced myself that for an altimeter located ahead of the CG, the effect of any spinning would be an early deployment and not never.

Jim

Edit ....

Looked at some accelerometer data for a few high altitude flights:

3 stage to 130K, EasyMega would have been 20 seconds early out of 120 seconds. Surprising since there was some angle to the flight and accelerometer-based deployment should have been late.

2 stage to 118K, Ravens were 30 seconds late and 10 seconds early for 95 second flight.

2 stage to 74K, Same Ravens were spot on and 17 seconds early on 75 second flight.

As someone else stated, we don't know that the OP is looking for dual deploy. If the OP is just looking for simple data capture the seriously consider one of the Jolly logic altimeters. Easy to use, reliable and can fit inside all but the smallest rockets. In my opinion you should avoid the Estes altimeter.

TMJ said:

I'm searching for information on altimeters. Being new to the hobby I currently know of only a few altimeters from a very few sources. I'd like to know what altimeters you folks use, who to purchase them from, and why you like them!
Thanks...

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The OP is new to the hobby so I don't believe he is looking for altimeters suitable for 100,000' flights, though many of the listed altimeters are great. Some of the best entry level altimeters and easiest to use would be PerfectFlite Stratologgers (compact or regular), and Missleworks RRC2 or 3 altimeters as both are pretty much buy, read the manual, test and fly. The Raven, Marsa54, TeleMetrums, and all are great, feature loaded and extremely capable altimeters but really are not good entry level altimeters IMO. The altimeter will be used in the OP's L1 rocket which is a Madcow 4" Frenzy iirc.

rharshberger said:

The OP is new to the hobby so I don't believe he is looking for altimeters suitable for 100,000' flights, though many of the listed altimeters are great. Some of the best entry level altimeters and easiest to use would be PerfectFlite Stratologgers (compact or regular), and Missleworks RRC2 or 3 altimeters as both are pretty much buy, read the manual, test and fly. The Raven, Marsa54, TeleMetrums, and all are great, feature loaded and extremely capable altimeters but really are not good entry level altimeters IMO. The altimeter will be used in the OP's L1 rocket which is a Madcow 4" Frenzy iirc.

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Suggestion... Build the Frenzy with an AV bay or the potential to add an AV bay so that you can experiment with DD, but use single motor deploy for the L1 Cert flight. The L1 cert has a lot of stress because it is a process never experienced by a modeler before, and even without the added dimension of testing electronics, the checklist and the process can be a little much. The rocket is going to be fairly heavy when flying with an H or an I motor so altitude isn't going to be an issue. I simmed it with an I-145 longburn skid (which would look awesome, by the way) without an AV Bay and it only shows about 1,800'. At that altitude, recovery isn't going to be an issue either.

So keep the cert flight flight simple. Get it up. Get it down. Get certified. Then, because it was built with the capability to add an AV Bay, you can work on Dual Deployment after you have certified. You don't need the added stress of making sure the electronics are working well. The purpose of L1 is to demonstrate you can build a rocket strong enough to handle an HPR motor. Electronics aren't really critical until L3, but most do it with L2 certs because the rockets fly so much higher. The nice thing about this rocket is that you should be able to certify L2 with it. At that point you are going to need electronics because a J is going to put it up there a ways.

You can do this a couple ways.
The Av Bay at the forward end is most likely going to be attached to the payload bay in a normal way, either with screws or plastic rivets to prevent it from separating from the payload bay. Normally in this configuration, the nose cone has shear pins that hold it in place until main deployment. Replace the shear pins with #2 or #4 sheetmetal screws for this flight so that the nose cone doesn't separate. Put the main chute in the booster section. Use the entire AV Bay, bulkheads, threaded rods, and all except the electronics. The motor will eject the AV Bay and payload section. To ensure everything is intact to a certain extent when you land, keep the shock cord attached to the NC and the Fwd AV Bay bulkhead eyebolt so that if the nose cone accidentally blows off, it is still attached. If I were the one certifying your flight, I would still do so because you had accounted for that contingency.

The other option. When you built the rocket, instead of putting the altimeter vent holes in the switch band, drill them into the booster about 1" down from the forward end. These should be 1/8" in diameter holes. When you do your L1 cert...only use the coupler tube from the AV Bay. Use a set of #6 nuts washers and screws and bolt the coupler to the booster through the vent holes. You have holes already drilled in the forward end of the coupler for the rivets or screws anyway, so just #6 screws and nuts here as well. You have bolted the rocket together and it should stay attached the entire flight. This hold is every bit as strong as gluing the parts together, but gives you the option of taking it back apart so you can fly for DD later. One shock cord connected from the forward CR to the nose cone. The one thing you may want to do in this configuration however is to do some ground testing to see if you need an additional amount of black powder. If you do, it is very simple to just add more on top of the BP motor cap, Add some wadding, then tape down. When the motor charge deploys it will also burn the added BP.


If you are concerned about zippering, find an old soft rubber ball about 2" in diameter and drill a hole through the center. Run the shock cord through it and knot it into place so that it comes to within about 1/2" from the edge of the airframe. The ball will squeeze and disperse the stress of the shock cord across a much wider portion of the airframe and unless it is an extreme situation (when zippering is the least of your worries), will generally prevent the zipper.

TMJ said:

I'm searching for information on altimeters. Being new to the hobby I currently know of only a few altimeters from a very few sources. I'd like to know what altimeters you folks use, who to purchase them from, and why you like them!
Thanks...

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So it all really depends on what you want to do with your rockets and flights.

If your doing some general sport flying just for fun and you want a dual deploy system, then I'd get a MissileWorks RRC2+.

If you want to look at your data post flight and compare to other flights you've had, the MissileWorks RRC3 is great, but you'll probably want something with an accelerometer to get accurate speed and acceleration data. Something like a Pico AA2 or FeatherWeight Raven 3.

Those are also great for extreme flights since they rely on accelerometer data for apogee deployment. The Raven is also a good choice for staging and clustering since it has four outputs. It's also really small. The drawback is since it's so small, setup is a little difficult unless you get the power perch.

Those are four that I use. I like them all and they all do exactly what I want them to.

EeebeeE said:

However if you are going to fly high and fast, you will need accelerometer-based altimeters (many of which also have barometric built in) for more accurate speed readings and more sensitive apogee detection electronics where the air is so thin the barometer can sometimes have difficulty determining whether it is still going up or not. These include the Raven 3, PICO, and MARSA altimeters, plus some others.

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I agree with the sentiment however I have flown barometric units exclusively, fairly high and fast. Not record breaking, but still what most would consider high and fast.

I tend to classify flights into 30k brackets. Any below 30k I am not going to worry about barometers. 30-60k, barometers are probably still fine but give reason to stop and think. 60-90k, definitely apply some advanced electronics. Above 90k, it gets so rarified that we start to think about mistrusting most of the sensors we have available, even going back to concepts like timers.

How many flyers actually go above 30K? You pretty much have to be a Level 3 to do it, and you have to go to some place like Black Rock. The TRA "L" record is just about 32K, so getting to 30K+ with a L2 ain't easy. Most sport flyers fly at places with a waiver under 20K, so for the vast majority of flights a baro altimeter is just fine. Compared to the total number of L1/L2 flyers, there aren't may L3 flyers, and even those who are don't often fly over 30K. It's a once or twice a year thing... it's expensive.

I'm flying Eggtimer's I have so many not even sure how many they are dedicated to rocket they go in , I switched for the ease of computer connecting/reading , hands on building how it works


I have a couple RRC2's also