Bdale
Garbee
Keith
Packard
2010
Bdale Garbee and Keith Packard
TeleMetrum
Owner's Manual for the TeleMetrum System
This document is released under the terms of the
Creative Commons ShareAlike 3.0
license.
0.1
30 March 2010
Initial content
Introduction and Overview
Welcome to the Altus Metrum community! Our circuits and software reflect
our passion for both hobby rocketry and Free Software. We hope their
capabilities and performance will delight you in every way, but by
releasing all of our hardware and software designs under open licenses,
we also hope to empower you to take as active a role in our collective
future as you wish!
The focal point of our community is TeleMetrum, a dual deploy altimeter
with fully integrated GPS and radio telemetry as standard features, and
a "companion interface" that will support optional capabilities in the
future.
Complementing TeleMetrum is TeleDongle, a USB to RF interface for
communicating with TeleMetrum. Combined with your choice of antenna and
notebook computer, TeleDongle and our associated user interface software
form a complete ground station capable of logging and displaying in-flight
telemetry, aiding rocket recovery, then processing and archiving flight
data for analysis and review.
Specifications
Recording altimeter for model rocketry.
Supports dual deployment (can fire 2 ejection charges).
70cm ham-band transceiver for telemetry downlink.
Barometric pressure sensor good to 45k feet MSL.
1-axis high-g accelerometer for motor characterization, capable of
+/- 50g using default part.
On-board, integrated GPS receiver with 5hz update rate capability.
On-board 1 megabyte non-volatile memory for flight data storage.
USB interface for battery charging, configuration, and data recovery.
Fully integrated support for LiPo rechargeable batteries.
Uses LiPo to fire e-matches, support for optional separate pyro
battery if needed.
2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
Handling Precautions
TeleMetrum is a sophisticated electronic device. When handled gently and
properly installed in an airframe, it will deliver extraordinary results.
However, like all electronic devices, there are some precautions you
must take.
The Lithium Polymer rechargeable batteries used with TeleMetrum have an
extraordinary power density. This is great because we can fly with
much less battery mass than if we used alkaline batteries or previous
generation rechargeable batteries... but if they are punctured
or their leads are allowed to short, they can and will release their
energy very rapidly!
Thus we recommend that you take some care when handling our batteries
and consider giving them some extra protection in your airframe. We
often wrap them in suitable scraps of closed-cell packing foam before
strapping them down, for example.
The TeleMetrum barometric sensor is sensitive to sunlight. In normal
mounting situations, it and all of the other surface mount components
are "down" towards whatever the underlying mounting surface is, so
this is not normally a problem. Please consider this, though, when
designing an installation, for example, in a 29mm airframe's see-through
plastic payload bay.
The TeleMetrum barometric sensor sampling port must be able to "breathe",
both by not being covered by foam or tape or other materials that might
directly block the hole on the top of the sensor, but also by having a
suitable static vent to outside air.
As with all other rocketry electronics, TeleMetrum must be protected
from exposure to corrosive motor exhaust and ejection charge gasses.
Hardware Overview
TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to
fit inside coupler for 29mm airframe tubing, but using it in a tube that
small in diameter may require some creativity in mounting and wiring
to succeed! The default 1/4
wave UHF wire antenna attached to the center of the nose-cone end of
the board is about 7 inches long, and wiring for a power switch and
the e-matches for apogee and main ejection charges depart from the
fin can end of the board. Given all this, an ideal "simple" avionics
bay for TeleMetrum should have at least 10 inches of interior length.
A typical TeleMetrum installation using the on-board GPS antenna and
default wire UHF antenna involves attaching only a suitable
Lithium Polymer battery, a single pole switch for power on/off, and
two pairs of wires connecting e-matches for the apogee and main ejection
charges.
By default, we use the unregulated output of the LiPo battery directly
to fire ejection charges. This works marvelously with standard e-matches
from companies like [insert company and product names for e-matches we've
tried and like] and with Quest Q2G2 igniters. However, if you
want or need to use a separate pyro battery, you can do so by adding
a second 2mm connector to position B2 on the board and cutting the
thick pcb trace connecting the LiPo battery to the pyro circuit between
the two silk screen marks on the surface mount side of the board shown
here [insert photo]
We offer two choices of pyro and power switch connector, or you can
choose neither and solder wires directly to the board. All three choices
are reasonable depending on the constraints of your airframe. Our
favorite option when there is sufficient room above the board is to use
the Tyco pin header with polarization and locking. If you choose this
option, you crimp individual wires for the power switch and e-matches
into a mating connector, and installing and removing the TeleMetrum
board from an airframe is as easy as plugging or unplugging two
connectors. If the airframe will not support this much height or if
you want to be able to directly attach e-match leads to the board, we
offer a screw terminal block. This is very similar to what most other
altimeter vendors provide by default and so may be the most familiar
option. You'll need a very small straight blade screwdriver to connect
and disconnect the board in this case, such as you might find in a
jeweler's screwdriver set. Finally, you can forego both options and
solder wires directly to the board, which may be the best choice for
minimum diameter and/or minimum mass designs.
For most airframes, the integrated GPS antenna and wire UHF antenna are
a great combination. However, if you are installing in a carbon-fiber
electronics bay which is opaque to RF signals, you may need to use
off-board external antennas instead. In this case, you can order
TeleMetrum with an SMA connector for the UHF antenna connection, and
you can unplug the integrated GPS antenna and select an appropriate
off-board GPS antenna with cable terminating in a U.FL connector.
Operation
Placeholder.
Using Altus Metrum Products
Being Legal
First off, in the US, you need an [amateur radio license](../Radio) or
other authorization to legally operate the radio transmitters that are part
of our products.
In the Rocket
In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and
a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V
alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours.
By default, we ship TeleMetrum with a simple wire antenna. If your
electronics bay or the airframe it resides within is made of carbon fiber,
which is opaque to RF signals, you may choose to have an SMA connector
installed so that you can run a coaxial cable to an antenna mounted
elsewhere in the rocket.
On the Ground
To receive the data stream from the rocket, you need an antenna and short
feedline connected to one of our [TeleDongle](../TeleDongle) units. 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.
Right now, all of our application software is written for Linux. However,
because we understand that many people run Windows or MacOS, we are working
on a new ground station program written in Java that should work on all
operating systems.
After the flight, you can use the RF link to extract the more detailed data
logged in the rocket, or you can use a mini USB cable to plug into the
TeleMetrum board directly. Pulling out the data without having to open up
the rocket is pretty cool! A USB cable is also how you charge the LiPo
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 waypoint for the last reported rocket
position before touch-down. This makes looking for your rocket a lot like
Geo-Cacheing... just go to the waypoint and look around starting from there.
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
and Bdale both currently own and use the Yaesu VX-7R at launches.
So, to recap, on the ground the hardware you'll need includes:
an antenna and feedline
a TeleDongle
a notebook computer
optionally, a handheld GPS receiver
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-equipped rocket when used with a suitable 70cm HT.
Data Analysis
Our software makes it easy to log the data from each flight, both the
telemetry received over the RF link during the flight itself, and the more
complete data log recorded in the DataFlash memory on the TeleMetrum
board. Once this data is on your computer, our postflight 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 data file
useable 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.
Future Plans
In the future, we intend to offer "companion boards" for the rocket that will
plug in to TeleMetrum to collect additional data, provide more pyro channels,
and so forth. A reference design for a companion board will be documented
soon, and will be compatible with open source Arduino programming tools.
We are also working on the design of a hand-held ground terminal that will
allow monitoring the rocket's status, collecting data during flight, and
logging data after flight without the need for a notebook computer on the
flight line. Particularly since it is so difficult to read most notebook
screens in direct sunlight, we think this will be a great thing to have.
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...