Altimeter Comparison
Separate altimeters have some nice advantages over built-in motor delay-based
ejection charges.
They self-calibrate, removing the need to pre-calculate delay time and shave
ejection charges to match.
Also, they allow the use of hybrid motors,
which have some nice properties themselves.
Most of the altimeters available are listed here and their features compared in tabular form.
There are also some sites with kits available.
The Altimeters
John Coker:
My first purchase was a Transolve P1 altimeter
(e-mail).
This turned out to be incomplete; one also needs the FB firing board to actually
trigger the flashbulbs. This solution requires two boards and two batteries, plus
connections. Not very practical. I later purchased the P2 which is
self-contained, but this board is 7" long, which is more than twice as long
as the other boards. The transolve comes with output (flashbulb/electric
match) connectors on the board and a 9V batter connector. The transolve
beeps out the maximum altitude and uses a system of beeps to signal the
state of the outputs. (Transolve is coming out with a new altimeter, the
P3, which will solve the size problem.) One significant problem with the
P2 is that you must launch within 5 minutes of turning the unit on. I
haven't been to a launch yet where the rack cycle time was anywhere near
this short. Perhaps this unit could be turned on with an R/C device.
See also Transolve's comments.
John Coker:
My next purchase was an Adept ALTS25, because the hybrid-ready
P.M.L.
Aurora was originally designed for this altimeter
(see my Aurora page).
The Adept is small, but doesn't come with built-in output connectors.
They have a 6-pin connector and wiring harness which connects to the power switch and outputs.
The ALTS25 uses an on-board battery holder (tiny 12v lighter battery).
I mounted the ALTS25 in a bay with a switch and output terminal
blocks (neither of which is supplied),
see picture.
The Adept is the smallest and lightest of the units.
Adept makes many rocketry electronics products;
be sure to call them and order a catalog.
John Coker:
I also purchased the Olsen Advanced Electronics FCP-M1.
This unit is small and completely self-contained.
The nicely designed board mounts the battery right on board and the output
connections use an on-board terminal block.
Perhaps nicest of all, the altimeters uses a display for output continuity and
apogee altitude instead of sequences of beeps!
Olsen is near to releasing a new altimeter, the FCP-M2, which will also record data.
Matt Jones:
I prefer the Cambridge IA-X96 from Emmanual Avionics
which requires two 9v batteries and has a wiring harness.
It has several features that I like, and that fill most points on the posted lists.
Launch detect by switch or g force (user selectable loads/times),
safety timers (mach inhibit), four firing circuits for multistage or multi recovery,
apogee detect by accelerometer AND barometric, safety timer for main deployment if
baro and apogee fail, fully programmable deployment altitudes,
computer interface for immediate thrust, altitude, velocity, and g force display.
It also writes flight data to an EEPROM, meaning that if you don't find your rocket
this year and you do next season, plug in a battery and get your data!
It also has external circuits for you to arm the altimeter and firing
circuits - just for those long waits on the pad.
I mounted mine in a PML cpr kit, works great.
Flew it this weekend in a new design and it performed flawlessly as usual.
It is a longer board, but I'll take it for what it does. It does do the led
blink if you have to know right then how many g's, how fast and how high.
It also has safety timer in the event of baro and accel failure to deploy recovery.
Note: This unit is no longer being made.
Doug Steinfeld:
I'm building, flying, modifying Paul Campbell's
Taniwha Flight Computer.
This is really more of a partial kit for those interested in electronics than
a ready-made product.
It requires the ability to solder a fine-line PC board and do some debugging.
(You really do need some electronics knowledge.)
The base price is $39 for flight computer and RS232 interface.
HOWEVER, you must supply an A/D converter, the accelerometer, the pressure
sensor, and a small box and board for the RS232 interface. This
can easily add $60 to the cost.
See also Paul Campbell's comments.
Ken Biba:
Having used the ALTS25 and the IAX-96 (and its predecessor the IAX-95),
I've settled on the Black Sky Research ALTACC. Having over 40+ flights on
this unit without a failure.
No failures in my over 40+ HPR flights using an ALTACC and two airframes
saved from damage due to early nozzle failures below competitors baro arming
altitudes or Mach inhibit times.
Data collection: 4.25 minutes of 8 bit resolution (about as good as the
noise floor on airframes allows) @ 16 Hz of both baro pressure and
instantaneous acceleration.
Chuck Andrus:
Well, I finally bit the bullet and invested in a couple more
altimeters. The $85 price tag of the Missile Works RRC2 looked a little too
good to be true, but after several discussions with Jim Amos about
firmware, board layout, etc, I decided to try it.
The RRC2 is barometric dual stage recovery altimeter, capable of apogee
deployment, as well as 500' or 1000' secondary deployment. There are many
features that make this a very functional and user friendly product,
including mach delay, ematch continuity test, power-up self test, etc. For
a detailed specification, take a look at the
Missile Works site.
The documentation that came with my boards is very complete, and well
written for an entry level altimeter user. There is a concise discussion of
all the functions of the board, as well as a detailed implementation
section with formulas for calculating optimal vent size, etc. There are
even several illustrated examples of dual stage deployment schemes to give
the newby an overview of some of the ways this is done. The manual can be
down loaded in it's entirety from the Missile Works RRC2 page.
(A kit version of the Missile Works RRC2 altimeter is also available from
CP Technologies.)
John Coker:
When Transolve came out with their third product, the P3 recording altimeter
(e-mail),
I decided to purchase one to see how it stacked up.
This unit has some nice features, and like other Transolve units has no problem
popping a high-current DaveyFire.
However, the amount of data it records is low and the unit is large and heavy.
Their new P4/P5 altimeter is meant as a replacement for the Adept ALTS25,
particularly in P.M.L.'s CPR (Close Proximity Recovery) system.
Howard Deiner:
I used a Cambridge IAX-96 last year, until I
*lost* the fellow in a mishap, and used the unit because it was the most
capable computer on the market.
Just as a point of reference, it took me several days to fly the IAX-96 by
hand (for first test). It took me five minutes with the R-DAS.
The R-DAS software is not only Win32, but works great under NT.
Also, the people at AED have been very forthcoming about how to interface software I
write with their device.
I'm hopeful that the future holds a telemetry project for me.
The R-DAS can do that, and IAX-96 was not even close.
The take home message is that the R-DAS is a wonderful piece of engineering
that I'm going to have a lot 'o fun with.
Feature Comparison
These tables show the features of the different units directly compared.
Note that this is oriented towards altimeter features for triggering the
recovery system and reporting apogee altitude.
The Cambridge, Campbell and Black Sky units have computer interfaces and
can upload extensive flight data for later analysis.
I would like data for altimeters not listed.
Anyone who can supply data for the Adept ALTS2/ALTS2-50K, please do!
Also, if you find the data to be inaccurate, please e-mail me and the person who
submitted the data for that altimeter.
Accuracy & Reliability
An issue which is difficult to assess is reliability and accuracy.
Much anecdotal evidence has been posted publicly and bandied about in conversation.
There is someone who loves each unit listed here and has had
"many flights on it with no failures."
Separating user error from altimeter failure seems difficult so this may explain
the disparate results.
Until actual comparative testing under different conditions is done, we must take
the vendors' claims at face value. Transolve has long claimed their units are the
most accurate.
John Fleischer of Transolve:
"The accuracy claims are honest, although I realize some may not need .2% accuracy.
If you look at a flight to 20,000', beeping out to 1 foot PRECISION seems silly to me,
when the Adept unit says right in the instructions that it is +/- 5%.
Why beep to the foot when you could be off 1000' in ACCURACY?
P1 and P2 are checked in a NIST/FAA baro chamber accurate to 3'.
At 20,000', we can typically resolve 40'.
This is 25 times more accurate than resolving 1000'.
Yes, there are partial pressure errors and other barometric sources of drift,
but aircraft altimeters regularly read out 10' counts... they seem to work!
I agree than reliability, ease of use, and price are important too...
you will be seeing some new items from me that hopefully will fulfill these goals."
Kits
Most of the units listed above complete out-of-the box altimeter solutions.
However, the Campbell Taniwha Flight Computer is really
an experimenters platform for building flight equipment including,
but not limited to, altimeters.
Taniwha Flight Computer
Paul Campbell:
"Thanks (I think) for listing me - you should realise that
what I sell is not really an altimeter - although it can be
turned into one - it's more aimed at being a generic
experimenters kit - for this reason I don't ship sensors or
altimeter software with it - although others have written and
published some - this is the whole point of selling the
kits - to give people a common platform to write rocketry
software on. I'm not in it for the money - I just sell them
for cost.
"In general this is not a kit for someone who wants an
out-of-the-box altimeter - there are lots of other
perfectly good alternatives on the market (and on your
list - I've used an ALTS for years) - hopefully people
experimenting with my kits will push the current vendors into
building better and better products.
"I'd appreciate it if you somehow mark your listing
of my flight computer with something like 'an experimenters kit,
intended as a basis for building experimental rocketry
electronics, including altimeters' hopefully that
explains it a bit better to potential customers
(I'd much rather turn away someone who won't be happy
when they get a baggy full of bits in the mail and
get people who are enthusiastic about building and programming
something new)."
Missile Works RRC2
Jim Amos:
A kit version of the Missile Works RRC2 altimeter is also available from
CP Technologies.
It consists of the following:
- RRCē User Manual
- RRCē Scratch Builders Supplement
- Parts Lists (from various sources)
- Physical Connection Diagrams (per step)
- Full Schematic
- Step by Step modular assembly method (allows a custom tailored unit, e.g altitude only etc...)
- Preprogrammed PIC MCU
The kit comes with instructions and the pre-programmed PIC (main logic chip).
You (the user) needs to source all the components (except the PIC), and
scratch build the unit with a proto board, wire wrap or other methods.
So you could build it as a peak only unit, apogee or main only deployment,
or a full blown unit just like the factory.
There are a couple of combinations, all outlined in the supplement.
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