10. Using Altus Metrum Products

10.2. In the Rocket

In the rocket itself, you just need a flight computer and a single-cell, 3.7 volt nominal Li-Po rechargeable battery. An 850mAh battery weighs less than a 9V alkaline battery, and will run a TeleMetrum, TeleMega or EasyMega for hours. A 110mAh battery weighs less than a triple A battery and is a good choice for use with TeleMini or EasyMini.

By default, we ship TeleMini, TeleMetrum and TeleMega flight computers with a simple wire antenna. If your electronics bay or the air-frame it resides within is made of carbon fiber, which is opaque to RF signals, you may prefer to install an SMA connector so that you can run a coaxial cable to an antenna mounted elsewhere in the rocket. However, note that the GPS antenna is fixed on all current products, so you really want to install the flight computer in a bay made of RF-transparent materials if at all possible.

10.3. On the Ground

To receive the data stream from the rocket, you need an antenna and short feed-line connected to one of our TeleDongle units. If possible, use an SMA to BNC adapter instead of feedline between the antenna feedpoint and TeleDongle, as this will give you the best performance. The TeleDongle in turn plugs directly into the USB port on a notebook computer. Because TeleDongle looks like a simple serial port, your computer does not require special device drivers… just plug it in.

The GUI tool, AltosUI, is written in Java and runs across Linux, Mac OS and Windows. There’s also a suite of C tools for Linux which can perform most of the same tasks.

Alternatively, a TeleBT attached with an SMA to BNC adapter at the feed point of a hand-held yagi used in conjunction with an Android device running AltosDroid makes an outstanding ground station.

After the flight, you can use the radio link to extract the more detailed data logged in either TeleMetrum or TeleMini devices, or you can use a USB cable to plug into the flight computer board directly. A USB cable is also how you charge the Li-Po battery, so you’ll want one of those anyway. The same cable used by lots of digital cameras and other modern electronic stuff will work fine.

If your rocket lands out of sight, you may enjoy having a hand-held GPS receiver, so that you can put in a way-point for the last reported rocket position before touch-down. This makes looking for your rocket a lot like Geo-Caching… just go to the way-point and look around starting from there. AltosDroid on an Android device with GPS receiver works great for this, too!

You may also enjoy having a ham radio “HT” that covers the 70cm band… you can use that with your antenna to direction-find the rocket on the ground the same way you can use a Walston or Beeline tracker. This can be handy if the rocket is hiding in sage brush or a tree, or if the last GPS position doesn’t get you close enough because the rocket dropped into a canyon, or the wind is blowing it across a dry lake bed, or something like that… Keith currently uses a Yaesu FT1D, Bdale has a Yaesu VX-7R, which is a nicer radio in most ways but doesn’t support APRS.

So, to recap, on the ground the hardware you’ll need includes:

  1. an antenna and feed-line or adapter
  2. a TeleDongle
  3. a notebook computer
  4. optionally, a hand-held GPS receiver
  5. optionally, an HT or receiver covering 435 MHz

The best hand-held commercial directional antennas we’ve found for radio direction finding rockets are from Arrow Antennas.

The 440-3 and 440-5 are both good choices for finding a TeleMetrum- or TeleMini- equipped rocket when used with a suitable 70cm HT. TeleDongle and an SMA to BNC adapter fit perfectly between the driven element and reflector of Arrow antennas.

10.4. Data Analysis

Our software makes it easy to log the data from each flight, both the telemetry received during the flight itself, and the more complete data log recorded in the flash memory on the altimeter board. Once this data is on your computer, our post-flight tools make it easy to quickly get to the numbers everyone wants, like apogee altitude, max acceleration, and max velocity. You can also generate and view a standard set of plots showing the altitude, acceleration, and velocity of the rocket during flight. And you can even export a flight log in a format usable with Google Maps and Google Earth for visualizing the flight path in two or three dimensions!

Our ultimate goal is to emit a set of files for each flight that can be published as a web page per flight, or just viewed on your local disk with a web browser.

10.5. Future Plans

We have designed and prototyped several “companion boards” that can attach to the companion connector on TeleMetrum, TeleMega and EasyMega flight computers to collect more data, provide more pyro channels, and so forth. We do not yet know if or when any of these boards will be produced in enough quantity to sell. If you have specific interests for data collection or control of events in your rockets beyond the capabilities of our existing productions, please let us know!

Because all of our work is open, both the hardware designs and the software, if you have some great idea for an addition to the current Altus Metrum family, feel free to dive in and help! Or let us know what you’d like to see that we aren’t already working on, and maybe we’ll get excited about it too…

Watch our web site for more news and information as our family of products evolves!