Brief

T' Altimeter One is a very small and easy-to-use altimeter for model rockets, arrr, airplanes, kites and even birding.

Jolly Logic's Altimeter Two is similar, but has specific features for model rockets only, and is a bit more sophisticated and a bit more expensive.

I bought mine for $50 (Altimeter One) and $70 (Altimeter Two). Begad! Well, me hearties, blow me down! This was loot well spent as these altimeters have enhanced me enjoyment o' rocketry a lot. No more guessin' about how high t' rocket went, shiver me timbers, or relyin' on RockSim or other programs that are only aproximations. Well, blow me down! What you get with these altimeters be t' cold, shiver me timbers, ya bilge rat, hard truth whether you like it or not.  These models are so small and so light they are useful for low-power rocketry as well as higher powers. Blimey! Arrr! T' altimeters are small enough t' fit inside a BT-20 body tube or payload, and they only weigh about 7 grams - or about 1/4 oz. Well, blow me down! T' daylight-readable LCD is super-simple t' use, shiver me timbers, me bucko, you don't have t' download anythin' or count beeps t' get answers.

With t' numbers provided by these two devices, you can gauge performance o' various motors and measure flyin' in various winds without havin' t' rely on rough "guestimates". You can have real measurements o' t' differences o' various motor types and brands and explore how weight affects altitudes. Begad! You can have "Guess t' Altitude" games and even have altitude contests.

T' altimeters are claimed t' be able t' measure altitude t' t' foot up t' 9999 feet and within 10 feet up t' 29000 feet (over 5 miles!). Arrr! Blimey! It is nay possible t' download any o' t' data t' a computer. Ahoy! These devices just don't have t' circuitry necessary. Avast! Blimey! Blimey! Fine with me, shiver me timbers, that would just make t' altimeters heavier and more expensive and more complicated! Blimey! Battery power is claimed t' last for 24 hours or more on a full charge. Aye aye! Blimey! I know that I've been able t' get in a whole day o' flyin' without havin' t' recharge these devices.

Control

A single button allows you t' control t' altimeter. Avast! When t' unit is off, pressin' t' button will turn it on. When it is on, me hearties, matey, pressin' it will turn it off. Begad! Ahoy! T' clear t' data and prepare for t' next flight, press and hold t' button until "0000" appears and then release it. Aye aye! Avast! T' unit is then cleared and armed for t' next flight. Ya scallywag! Begad! If you turn t' unit off or it goes off by itself with t' battery save feature, t' data is nay lost. Blimey! Blimey! Simply turn t' unit back on and t' 'One' will show t' apogee altitude. Arrr! T' 'Two' will alternate betwixt t' altitude and t' speed.

To access some other functions in these units, simply hold t' button down while t' unit is on and watch t' LCD. Begad! When t' feature is displayed that you want, release t' button. Blimey! On t' 'Two' t' first choice that appears is "data", so when you release it you see other readings such as acceleration, me hearties, descent time, ya bilge rat, ya bilge rat, etc.

Both units allow you t' switch betwixt two different units - English or Metric. Ya scallywag! Arrr! English feet gives you more altitude precision than is available with meters.

Battery Power

Both o' these altimeters, matey, t' 'One' and t' 'Two', shiver me timbers, me hearties, me bucko, use a special internal lithium rechargeable battery and are easily recharged. Avast! You don't need t' worry about power as long as you charge these units t' night or mornin' before flying. Blimey! Chargin' generally takes an hour or two. They are plugged into a USB port (like on a computer) t' receive power and a red light indicates it is charging. Begad! Avast, me proud beauty! When it is done chargin' you will see a green light. It is that simple.

I imagine you "might" be able t' charge them on a standard 12V-to-USB adaptor such as provided with many cell phone or MP3 mobile chargin' devices, if for example like me you forgot t' charge it t' night before. Ya scallywag! Arrr! As a matter o' fact, arrr, I did just that t' me first Altimeter One and be able t' use it for t' day but I had t' wait about an hour t' top it off before flying. Ahoy! I say "might" because in t' next month when I went t' charge t' 'One' up t' night before - it wouldn't take a charge and no lights would lite - t' unit was dead. Avast! Aye aye! I suspect but can't confirm that t' car charger may have damaged t' 'One'. Begad! In me case, I took t' unit apart, arrr, me hearties, removed t' battery and recharged it usin' a precision micro-amp current source. Well, blow me down! Blimey! T' altimeter circuit worked fine, me hearties, shiver me timbers, just t' chargin' circuit failed. Well, blow me down! This allowed me t' "limp-by" usin' it for a few more months until I ordered a replacement.

I have a club buddy who had t' 'One' and he claimed both red and green lights lit and it wouldn't work either, but I don't know what he used for a charger. Aye aye! Ahoy! So be aware that you use these products at your own risk, shiver me timbers, and if they stop workin' that's t' end o' it as Jolly Logic does nay repair or warrant these products. Ahoy! Ya scallywag! That may change if t' company grows and can later provide such a service. Ya scallywag! Ahoy! I personally think that t' data I get from flyin' is worth t' risk.

Usin' t' Altimeters

My first experience be with t' Altimeter One which uses a precision air pressure sensor t' determine altitude. This can be used on model airplanes, me hearties, me hearties, kites or even large birds. Well, blow me down! As luck would have, t' Altimeter Two, me bucko, with more features, was introduced just after I ordered t' Altimeter One, so o' course I had t' get t' 'Two'.

T' Altimeter Two has t' same air pressure sensor o' t' One, matey, but adds a three-axis accelerometer which allows, ya bilge rat, in addition t' peak altitude, me bucko, many other measurements includin' speed, shiver me timbers, motor burn time, coast time t' apogee, matey, me hearties, apogee t' ejection time, arrr, average acceleration, me hearties, peak acceleration, descent speed, and overall flight time.

For only about $20 dollars more, me bucko, I would recommend gettin' t' 'Two' which provides much more information. Avast! But t' 'One' is a better deal if loot is tight and altitude is all you are lookin' t' measure. Ya scallywag! A small hole and clip are provided, matey, so t' easiest way t' use these is t' clip this unit onto t' screw-eye o' your nosecone, matey, but you must provide some small static air vent holes in t' body tube t' allow t' outside air pressure into t' altimeter for makin' measurements.; I have tried it without static vent holes and it still worked, me hearties, me hearties, but whether t' readin' was valid or nay is always goin' t' be a question. Jolly Logic claims that they will work fine when clipped with t' parachute, but again - they don't provide any warranty on these devices (which is totally understandable considerin' t' way they are used). Ya scallywag! You must accept that you are usin' these at your own financial risk.

A better way, and t' way I normally use them, is t' fly them in t' payload bay o' a rocket that has a payload. Well, blow me down! Begad! Since most o' me rockets didn't have a payload, arrr, I made small additional payload bays for me rockets by usin' a bulkhead and a section o' body tube below t' nosecone. Arrr! Begad! This provides much more protection t' t' altimeters, since they will nay be shaken violently on ejection and are completely protected from ejection gasses and particles. Well, blow me down! Ahoy! They are also better protected from strikin' t' ground, ya bilge rat, pavement, me bucko, or rocks directly upon landing. I had a buddy o' mine loose his when his clip failed and it fell out o' t' sky from several thousand feet never t' be seen again - you can see it on his video o' t' flight.

Addin' a payload section for these is quite easy and t' cost o' a little balsa and cardboard is much cheaper than replacin' t' altimeter. Begad! (Note: I am preparin' an article about addin' payload bays t' low-power rockets which should be published soon on this very website.)

Altimeter One Specifics

T' One be t' more affordable o' t' two units, shiver me timbers, me bucko, but is only able t' measure altitude. Arrr! It can't be more simple. Turn it on, clear t' reading, me bucko, and fly it. Begad! When t' flight is over, t' highest altitude is shown on t' LCD. Ahoy! Then either turn it off or clear it t' fly it again.

T' 'One' will memorize t' air pressure when you clear it. Avast! Assumin' that you are standin' on t' ground where you will launch it, matey, me bucko, it calls that zero altitude. Begad! When it begins t' sense a rapid drop in pressure o' about 50 feet or so, it will make rapid measurements and remember t' lowest air pressure readin' that it measured and convert that into altitude (it assumes a "standard" atmosphere which may nay always be t' case, shiver me timbers, matey, me bucko, but that's how airplanes, arrr, helicopters, me bucko, blimps and just about anythin' controlled by t' FAA measures altitude). I believe that it also measures temperature and compensates for t' difference in temperatures - I'll need t' confim that though. All I do know is that these devices are very accurate (repeatable) and precise (able t' distinguish fine differences). Begad! They have been accepted by one o' our big organizations for competition, but duh...I can't remember which, me bucko, maybe t' NAR?

Since t' 'One' senses t' launch with an air pressure drop, shiver me timbers, arrr, it may be succeptable t' momentary gusts o' wind, me hearties, matey, but that hasn't happened t' me ever. I have been told that usin' three equal-sized static vent holes around t' rocket at 120-degrees is more imune t' false triggerin' than four holes spaced 90-degrees. Ya scallywag! This is from a club member that has experience with a number o' other altimeters. My experience suggests that t' Altimeter One is very good at nay falsely triggerin' a readin' with light wind gusts.

Altimeter Two Specifics

T' Two be t' more advanced model for a slightly higher cost. Avast, me proud beauty! But t' extra cost gives you much more data t' work with. Begad! Ya scallywag! I imagine t' most popular would be speed. Aye aye! Avast, me proud beauty! That's always a satisfyin' number t' get. Blimey! My personal favorite after altitude and speed be t' coast-to-apogee time. Arrr! With this information, arrr, I will get valueable information on whether me delay time was too short or too long or OK as is.

While it's very difficult t' see from t' ground, via t' Altimeter Two, I've noticed several o' me rockets deployed before reachin' apogee, me hearties, and apogee always follows shortly thereafter as t' greatly increased drag tends t' stop t' rocket within a few feet while over-stressin' t' recovery system. Blimey! Ahoy! Other rockets - we've all seen this - seem t' coast horizontal or even downwards forever before ejection, arrr, me hearties, but it's hard t' judge exactly how much too far. Aye aye! Aye aye! Some rockets seem t' speed along horizontally, shiver me timbers, matey, slowin' down some and only loose a few feet o' altitude, arrr, where others seem t' do t' same but actually loose 30 or 50 feet or more.

T' 'Two' has a three-axis accelerometer inside, shiver me timbers, shiver me timbers, so instead o' measurin' air pressure drop t' determine liftoff, ya bilge rat, it senses a sudden change in motion. I suspect that's how it determines ejection time, shiver me timbers, also. Aye aye! This makes it immune t' wind gusts, me hearties, but also makes it sensitive t' shakin' and jarrin' before launch. I had many flights with invalid data because o' shakin' t' rocket too much after armin' it and before launch. Begad! Once I learned this however, I clear and pack t' altimeter last and handle it nay quite so roughly before launch, me hearties, and I've never had this problem again.

I actually learned about that by sendin' an email t' t' support folks at Jolly Logic from their website. T' me amazement I received a reply whithin maybe one hour! T' false-triggerin' problem was solved and I was happy.

Summary

I can describe how much I like these products by tellin' you that even though me first Altimeter One died on me after one day o' launches, arrr, I went and got another one. Avast! In fact, arrr, I actually bought TWO Altimeter Twos, me hearties, one as a backup just in case I lost one or it died on me. Begad! Avast, me proud beauty! I simply don't want t' fly rockets with out these on board. That's pretty much me endorsement - but then I'm a nerd rocket scientist and I like numbers. I'm buildin' a spreadsheet full o' performance numbers and graphs for all me rockets.