Sunday, February 1, 2015

A bit about altimeters...

I love modern electronics - stuff that was impossible in the 1970's is now not only doable, but cheap. This is especially true with rocket payloads - we now have gps and radio trackers, flight computers, and small altimeters, just begging to be shot into the big blue sky. I haven't got into the trackers and computers - yet - but I have assembled a collection of barometric altimeters over the years, in part because of my involvement with Team America Rocketry Challenge (TARC) and partly because I like to know how high my rockets go. These altimeters range from $25 to $150 in cost, and fall into one of two categories:
  1. Peak altimeters - These devices are active throughout the flight, but lack the memory to produce a detailed flight profile. The simplest ones just beep or flash the peak altitude; more elaborate models will display other information, such as average speed, time to apogee, acceleration, and so forth. Examples of this class include the Jolly Logic Altimeter One and Two, the Estes Altimeter, and the PerfectFlite Firefly and APRA (The latter is an approved altimeter for this year's TARC competition).
  2. Recording altimeters - These devices store information throughout the flight, usually at 0.1-0.2 second intervals. This data can be downloaded into a computer or other device, where it can be displayed and/or manipulated. Cheaper ones store data for only one flight, forcing you to download the data almost immediately if you wish to fly it again during a launch; others can store data for many flights, eliminating the need to bring your laptop to the field. Examples are the Jolly Logic Altimeter Three, the Altus Metrum MicroPeak, and the PerfectFlite PNUT (the other TARC approved altimeter for 2015).
Being a nerd, I swoon over numbers, so recording altimeters are my favorite. I love being able to adjust simulations to the profiles, which enables better determinations of drag coefficients and other things that give geeks delight. To paraphrase my colleague Joe Minow, "More data is good."

Some of my altimeters. On the left, starting at top: Estes Altimeter, PerfectFlite PNUT,
Jolly Logic Altimeter Three. On the right: Altus Metrum MicroPeak, PerfectFlite Firefly,
and the Jolly Logic Altimeter Two (pre 2014 version).
This year's Christmas present from me to me was a Jolly Logic Altimeter Three. I have been waiting months for this puppy to hit the market, as it downloads data to your smartphone, rather than using a USB cable connected to a computer. The MicroPeak's use of a flashing LED to transmit data to a USB adapter was cool and different, but the Altimeter Three is a new level of coolness - Imagine being able to control your altimeter inside your rocket from your phone? Plus the lack of annoying beeps, which had a not insignificant appeal.

Yesterday marked the first time I flew my Altimeter Three. Here are my initial thoughts:

  • The Altimeter Three (and the new Altimeter One and Two) is bigger than most of the others - it won't fit in a BT-20 tube, and is very loose in a BT-50. I found that a Centuri ST-8 (0.865" inner diameter) is a good fit, but you may have to make some custom rings to mount this inside an Estes body tube. Jolly Logic sells a snap mount to help attach the altimeter to a sled. Weighing in at 10 grams, the altimeter is also a little bit on the heavy side.
  • I like the change to a USB cable for charging the altimeter - a definite improvement over the pre-2014 Jolly Logic devices, which plugged straight into the USB port. They were way too easy to break.
  • The Altimeter3 app is currently only available for iOS. However, I just saw a note from John Beans saying that the Android version will be out this coming week, so don't let that stop ya from getting one.
  • The Bluetooth interface to the iPhone is a pain - John Beans, the man behind Jolly Logic, is pretty up front about this. Most of it isn't his fault, as Apple implements Bluetooth in a weird way (no big surprise). To help out, he provides a very good Bluetooth setup guide and I was able to get my connection up and going fairly easy. There was some funkiness reconnecting with the altimeter after the flight, but turning Bluetooth off and then back on solved the problem. Still, this was less effort than opening up the rocket and extracting the altimeter to listen to the beeps or watch the flashing LED.
  • The smartphone software is very good, and works as advertised. I was very pleased by the simple interface and the amount of data displayed - very nice to have available in the field! The ability to share data with your buds via email or social networks right after the flight is pretty darn nice, and I mucho like the well-formatted Excel spreadsheet that accompanies the email.

Initial screen of the Altimeter3 app -
You connect to and control the altimeter 
from this screen - set mode, start and stop
recording (Click to enlarge).
Flight Summary screen. The StrongARM is
a default within the app. Tapping on a flight
brings up more detail (Click to enlarge).
The flight information screen. The flight
name and any notes are entered here
(Click to enlarge).
The chart screen, with the time and altitude
of apogee marked. You can mark additional
points to highlight other features on the plot
(Click to enlarge).
Map screen. The app uses your phone's
GPS to locate the launch location, which
is displayed on the map (Click to enlarge).
Sharing screen. You can email your flight
data or share it on social networks from the
field (Click to enlarge).
Excel spreadsheet accompanying the Jolly Logic Altimeter Three email (Click to enlarge).
If you are looking for a hi tech, fun altimeter for your rockets, this is the one to get. Recommended.


  1. Bill,
    Very nice writeup!
    If there's anything I can do for you, please don't hesitate to ask.
    Happy flying,
    --John Beans

  2. How about this?