+ <chapter>
+ <title>Altimeter Installation Recommendations</title>
+ <para>
+ Building high-power rockets that fly safely is hard enough. Mix
+ in some sophisticated electronics and a bunch of radio energy
+ and oftentimes you find few perfect solutions. This chapter
+ contains some suggestions about how to install AltusMetrum
+ products into the rocket airframe, including how to safely and
+ reliably mix a variety of electronics into the same airframe.
+ </para>
+ <section>
+ <title>Mounting the Altimeter</title>
+ <para>
+ The first consideration is to ensure that the altimeter is
+ securely fastened to the airframe. For TeleMetrum, we use
+ nylon standoffs and nylon screws; they're good to at least 50G
+ and cannot cause any electrical issues on the board. For
+ TeleMini, we usually cut small pieces of 1/16" balsa to fit
+ under the screw holes, and then take 2x56 nylon screws and
+ screw them through the TeleMini mounting holes, through the
+ balsa and into the underlying material.
+ </para>
+ <orderedlist inheritnum='inherit' numeration='arabic'>
+ <listitem>
+ Make sure TeleMetrum is aligned precisely along the axis of
+ acceleration so that the accelerometer can accurately
+ capture data during the flight.
+ </listitem>
+ <listitem>
+ Watch for any metal touching components on the
+ board. Shorting out connections on the bottom of the board
+ can cause the altimeter to fail during flight.
+ </listitem>
+ </orderedlist>
+ </section>
+ <section>
+ <title>Dealing with the Antenna</title>
+ <para>
+ The antenna supplied is just a piece of solid, insulated,
+ wire. If it gets damaged or broken, it can be easily
+ replaced. It should be kept straight and not cut; bending or
+ cutting it will change the resonant frequency and/or
+ impedence, making it a less efficient radiator and thus
+ reducing the range of the telemetry signal.
+ </para>
+ <para>
+ Keeping metal away from the antenna will provide better range
+ and a more even radiation pattern. In most rockets, it's not
+ entirely possible to isolate the antenna from metal
+ components; there are often bolts, all-thread and wires from other
+ electronics to contend with. Just be aware that the more stuff
+ like this around the antenna, the lower the range.
+ </para>
+ <para>
+ Make sure the antenna is not inside a tube made or covered
+ with conducting material. Carbon fibre is the most common
+ culprit here -- CF is a good conductor and will effectively
+ shield the antenna, dramatically reducing signal strength and
+ range. Metalic flake paint is another effective shielding
+ material which is to be avoided around any antennas.
+ </para>
+ <para>
+ If the ebay is large enough, it can be convenient to simply
+ mount the altimeter at one end and stretch the antenna out
+ inside. Taping the antenna to the sled can keep it straight
+ under acceleration. If there are metal rods, keep the
+ antenna as far away as possible.
+ </para>
+ <para>
+ For a shorter ebay, it's quite practical to have the antenna
+ run through a bulkhead and into an adjacent bay. Drill a small
+ hole in the bulkhead, pass the antenna wire through it and
+ then seal it up with glue or clay. We've also used acrylic
+ tubing to create a cavity for the antenna wire. This works a
+ bit better in that the antenna is known to stay straight and
+ not get folded by recovery components in the bay. Angle the
+ tubing towards the side wall of the rocket and it ends up
+ consuming very little space.
+ </para>
+ <para>
+ If you need to place the antenna at a distance from the
+ altimeter, you can replace the antenna with an edge-mounted
+ SMA connector, and then run 50Ω coax from the board to the
+ antenna. Building a remote antenna is beyond the scope of this
+ manual.
+ </para>
+ </section>
+ <section>
+ <title>Preserving GPS Reception</title>
+ <para>
+ The GPS antenna and receiver in TeleMetrum are highly
+ sensitive and normally have no trouble tracking enough
+ satellites to provide accurate position information for
+ recovering the rocket. However, there are many ways to
+ attenuate the GPS signal.
+ <orderedlist inheritnum='inherit' numeration='arabic'>
+ <listitem>
+ Conductive tubing or coatings. Carbon fiber and metal
+ tubing, or metalic paint will all dramatically attenuate the
+ GPS signal. We've never heard of anyone successfully
+ receiving GPS from inside these materials.
+ </listitem>
+ <listitem>
+ Metal components near the GPS patch antenna. These will
+ de-tune the patch antenna, changing the resonant frequency
+ away from the L1 carrier and reduce the effectiveness of the
+ antenna. You can place as much stuff as you like beneath the
+ antenna as that's covered with a ground plane. But, keep
+ wires and metal out from above the patch antenna.
+ </listitem>
+ </orderedlist>
+ </para>
+ </section>
+ <section>
+ <title>Radio Frequency Interference</title>
+ <para>
+ Any altimeter will generate RFI; the digital circuits use
+ high-frequency clocks that spray radio interference across a
+ wide band. Altusmetrum altimeters generate intentional radio
+ signals as well, increasing the amount of RF energy around the board.
+ </para>
+ <para>
+ Rocketry altimeters also use precise sensors measuring air
+ pressure and acceleration. Tiny changes in voltage can cause
+ these sensor readings to vary by a huge amount. When the
+ sensors start mis-reporting data, the altimeter can either
+ fire the igniters at the wrong time, or not fire them at all.
+ </para>
+ <para>
+ Voltages are induced when radio frequency energy is
+ transmitted from one circuit to another. Here are things that
+ increase the induced voltage and current:
+ </para>
+ <itemizedlist>
+ <listitem>
+ Keep wires from different circuits apart. Moving circuits
+ further apart will reduce RFI.
+ </listitem>
+ <listitem>
+ Avoid parallel wires from different circuits. The longer two
+ wires run parallel to one another, the larger the amount of
+ transferred energy. Cross wires at right angles to reduce
+ RFI.
+ </listitem>
+ <listitem>
+ Twist wires from the same circuits. Two wires the same
+ distance from the transmitter will get the same amount of
+ induced energy which will then cancel out. Any time you have
+ a wire pair running together, twist the pair together to
+ even out distances and reduce RFI. For altimeters, this
+ includes battery leads, switch hookups and igniter
+ circuits.
+ </listitem>
+ <listitem>
+ Avoid resonant lengths. Know what frequencies are present
+ in the environment and avoid having wire lengths near a
+ natural resonant length. Altusmetrum products transmit on the
+ 70cm amateur band, so you should avoid lengths that are a
+ simple ratio of that length; essentially any multiple of 1/4
+ of the wavelength (17.5cm).
+ </listitem>
+ </itemizedlist>
+ </section>
+ <section>
+ <title>The Barometric Sensor</title>
+ <para>
+ Altusmetrum altimeters measure altitude with a barometric
+ sensor, essentially measuring the amount of air above the
+ rocket to figure out how high it is. A large number of
+ measurements are taken as the altimeter initializes itself to
+ figure out the pad altitude. Subsequent measurements are then
+ used to compute the height above the pad.
+ </para>
+ <para>
+ To accurately measure atmospheric pressure, the ebay
+ containing the altimeter must be vented outside the
+ airframe. The vent must be placed in a region of linear
+ airflow, smooth and not in an area of increasing or decreasing
+ pressure.
+ </para>
+ <para>
+ The barometric sensor in the altimeter is quite sensitive to
+ chemical damage from the products of APCP or BP combustion, so
+ make sure the ebay is carefully sealed from any compartment
+ which contains ejection charges or motors.
+ </para>
+ </section>
+ <section>
+ <title>Ground Testing</title>
+ <para>
+ The most important aspect of any installation is careful
+ ground testing. Bringing an airframe up to the LCO table which
+ hasn't been ground tested can lead to delays or ejection
+ charges firing on the pad, or, even worse, a recovery system
+ failure.
+ </para>
+ <para>
+ Do a 'full systems' test that includes wiring up all igniters
+ without any BP and turning on all of the electronics in flight
+ mode. This will catch any mistakes in wiring and any residual
+ RFI issues that might accidentally fire igniters at the wrong
+ time. Let the airframe sit for several minutes, checking for
+ adequate telemetry signal strength and GPS lock.
+ </para>
+ <para>
+ Ground test the ejection charges. Prepare the rocket for
+ flight, loading ejection charges and igniters. Completely
+ assemble the airframe and then use the 'Fire Igniters'
+ interface through a TeleDongle to command each charge to
+ fire. Make sure the charge is sufficient to robustly separate
+ the airframe and deploy the recovery system.
+ </para>
+ </section>
+ </chapter>
+ <chapter>
+ <title>Hardware Specifications</title>
+ <section>
+ <title>TeleMetrum Specifications</title>
+ <itemizedlist>
+ <listitem>
+ <para>
+ Recording altimeter for model rocketry.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Supports dual deployment (can fire 2 ejection charges).
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 70cm ham-band transceiver for telemetry downlink.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Barometric pressure sensor good to 45k feet MSL.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 1-axis high-g accelerometer for motor characterization, capable of
+ +/- 50g using default part.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ On-board, integrated GPS receiver with 5hz update rate capability.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ On-board 1 megabyte non-volatile memory for flight data storage.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ USB interface for battery charging, configuration, and data recovery.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Fully integrated support for LiPo rechargeable batteries.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Uses LiPo to fire e-matches, can be modiied to support
+ optional separate pyro battery if needed.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </section>
+ <section>
+ <title>TeleMini Specifications</title>
+ <itemizedlist>
+ <listitem>
+ <para>
+ Recording altimeter for model rocketry.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Supports dual deployment (can fire 2 ejection charges).
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 70cm ham-band transceiver for telemetry downlink.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Barometric pressure sensor good to 45k feet MSL.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ On-board 5 kilobyte non-volatile memory for flight data storage.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ RF interface for battery charging, configuration, and data recovery.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Support for LiPo rechargeable batteries, using an external charger.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Uses LiPo to fire e-matches, can be modiied to support
+ optional separate pyro battery if needed.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 1.5 x .5 inch board designed to fit inside 18mm airframe coupler tube.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </section>
+ </chapter>
+ <chapter>
+ <title>FAQ</title>
+ <para>
+ TeleMetrum seems to shut off when disconnected from the
+ computer. Make sure the battery is adequately charged. Remember the
+ unit will pull more power than the USB port can deliver before the
+ GPS enters "locked" mode. The battery charges best when TeleMetrum
+ is turned off.
+ </para>
+ <para>
+ It's impossible to stop the TeleDongle when it's in "p" mode, I have
+ to unplug the USB cable? Make sure you have tried to "escape out" of
+ this mode. If this doesn't work the reboot procedure for the
+ TeleDongle *is* to simply unplug it. 'cu' however will retain it's
+ outgoing buffer IF your "escape out" ('~~') does not work.
+ At this point using either 'ao-view' (or possibly
+ 'cutemon') instead of 'cu' will 'clear' the issue and allow renewed
+ communication.
+ </para>
+ <para>
+ The amber LED (on the TeleMetrum) lights up when both
+ battery and USB are connected. Does this mean it's charging?
+ Yes, the yellow LED indicates the charging at the 'regular' rate.
+ If the led is out but the unit is still plugged into a USB port,
+ then the battery is being charged at a 'trickle' rate.
+ </para>
+ <para>
+ There are no "dit-dah-dah-dit" sound or lights like the manual mentions?
+ That's the "pad" mode. Weak batteries might be the problem.
+ It is also possible that the Telemetrum is horizontal and the output
+ is instead a "dit-dit" meaning 'idle'. For TeleMini, it's possible that
+ it received a command packet which would have left it in "pad" mode.
+ </para>
+ <para>
+ How do I save flight data?
+ Live telemetry is written to file(s) whenever AltosUI is connected
+ to the TeleDongle. The file area defaults to ~/TeleMetrum
+ but is easily changed using the menus in AltosUI. The files that
+ are written end in '.telem'. The after-flight
+ data-dumped files will end in .eeprom and represent continuous data
+ unlike the rf-linked .telem files that are subject to losses
+ along the rf data path.
+ See the above instructions on what and how to save the eeprom stored
+ data after physically retrieving your altimeter. Make sure to save
+ the on-board data after each flight; while the TeleMetrum can store
+ multiple flights, you never know when you'll lose the altimeter...
+ </para>
+ </chapter>
+ <appendix>
+ <title>Notes for Older Software</title>
+ <para>
+ <emphasis>
+ Before AltosUI was written, using Altus Metrum devices required
+ some finesse with the Linux command line. There was a limited
+ GUI tool, ao-view, which provided functionality similar to the
+ Monitor Flight window in AltosUI, but everything else was a
+ fairly 80's experience. This appendix includes documentation for
+ using that software.
+ </emphasis>
+ </para>
+ <para>
+ Both Telemetrum and TeleDongle can be directly communicated
+ with using USB ports. The first thing you should try after getting
+ both units plugged into to your computer's usb port(s) is to run
+ 'ao-list' from a terminal-window to see what port-device-name each
+ device has been assigned by the operating system.
+ You will need this information to access the devices via their
+ respective on-board firmware and data using other command line
+ programs in the AltOS software suite.
+ </para>
+ <para>
+ TeleMini can be communicated with through a TeleDongle device
+ over the radio link. When first booted, TeleMini listens for a
+ TeleDongle device and if it receives a packet, it goes into
+ 'idle' mode. Otherwise, it goes into 'pad' mode and waits to be
+ launched. The easiest way to get it talking is to start the
+ communication link on the TeleDongle and the power up the
+ TeleMini board.
+ </para>
+ <para>
+ To access the device's firmware for configuration you need a terminal
+ program such as you would use to talk to a modem. The software
+ authors prefer using the program 'cu' which comes from the UUCP package
+ on most Unix-like systems such as Linux. An example command line for
+ cu might be 'cu -l /dev/ttyACM0', substituting the correct number
+ indicated from running the
+ ao-list program. Another reasonable terminal program for Linux is
+ 'cutecom'. The default 'escape'
+ character used by CU (i.e. the character you use to
+ issue commands to cu itself instead of sending the command as input
+ to the connected device) is a '~'. You will need this for use in
+ only two different ways during normal operations. First is to exit
+ the program by sending a '~.' which is called a 'escape-disconnect'
+ and allows you to close-out from 'cu'. The
+ second use will be outlined later.
+ </para>
+ <para>
+ All of the Altus Metrum devices share the concept of a two level
+ command set in their firmware.
+ The first layer has several single letter commands. Once
+ you are using 'cu' (or 'cutecom') sending (typing) a '?'
+ returns a full list of these
+ commands. The second level are configuration sub-commands accessed
+ using the 'c' command, for
+ instance typing 'c?' will give you this second level of commands
+ (all of which require the
+ letter 'c' to access). Please note that most configuration options
+ are stored only in Flash memory; TeleDongle doesn't provide any storage
+ for these options and so they'll all be lost when you unplug it.
+ </para>
+ <para>
+ Try setting these config ('c' or second level menu) values. A good
+ place to start is by setting your call sign. By default, the boards
+ use 'N0CALL' which is cute, but not exactly legal!
+ Spend a few minutes getting comfortable with the units, their
+ firmware, and 'cu' (or possibly 'cutecom').
+ For instance, try to send
+ (type) a 'c r 2' and verify the channel change by sending a 'c s'.
+ Verify you can connect and disconnect from the units while in your
+ terminal program by sending the escape-disconnect mentioned above.
+ </para>
+ <para>
+ Note that the 'reboot' command, which is very useful on the altimeters,
+ will likely just cause problems with the dongle. The *correct* way
+ to reset the dongle is just to unplug and re-plug it.
+ </para>
+ <para>
+ A fun thing to do at the launch site and something you can do while
+ learning how to use these units is to play with the rf-link access
+ between an altimeter and the TeleDongle. Be aware that you *must* create
+ some physical separation between the devices, otherwise the link will
+ not function due to signal overload in the receivers in each device.
+ </para>
+ <para>
+ Now might be a good time to take a break and read the rest of this
+ manual, particularly about the two "modes" that the altimeters
+ can be placed in. TeleMetrum uses the position of the device when booting
+ up will determine whether the unit is in "pad" or "idle" mode. TeleMini
+ enters "idle" mode when it receives a command packet within the first 5 seconds
+ of being powered up, otherwise it enters "pad" mode.
+ </para>
+ <para>
+ You can access an altimeter in idle mode from the Teledongle's USB
+ connection using the rf link
+ by issuing a 'p' command to the TeleDongle. Practice connecting and
+ disconnecting ('~~' while using 'cu') from the altimeter. If
+ you cannot escape out of the "p" command, (by using a '~~' when in
+ CU) then it is likely that your kernel has issues. Try a newer version.
+ </para>
+ <para>
+ Using this rf link allows you to configure the altimeter, test
+ fire e-matches and igniters from the flight line, check pyro-match
+ continuity and so forth. You can leave the unit turned on while it
+ is in 'idle mode' and then place the
+ rocket vertically on the launch pad, walk away and then issue a
+ reboot command. The altimeter will reboot and start sending data
+ having changed to the "pad" mode. If the TeleDongle is not receiving
+ this data, you can disconnect 'cu' from the Teledongle using the
+ procedures mentioned above and THEN connect to the TeleDongle from
+ inside 'ao-view'. If this doesn't work, disconnect from the
+ TeleDongle, unplug it, and try again after plugging it back in.
+ </para>
+ <para>
+ On TeleMetrum, the GPS will eventually find enough satellites, lock in on them,
+ and 'ao-view' will both auditorially announce and visually indicate
+ that GPS is ready.
+ Now you can launch knowing that you have a good data path and
+ good satellite lock for flight data and recovery. Remember
+ you MUST tell ao-view to connect to the TeleDongle explicitly in
+ order for ao-view to be able to receive data.
+ </para>
+ <para>
+ The altimeters provide RDF (radio direction finding) tones on
+ the pad, during descent and after landing. These can be used to
+ locate the rocket using a directional antenna; the signal
+ strength providing an indication of the direction from receiver to rocket.
+ </para>
+ <para>
+ TeleMetrum also provides GPS trekking data, which can further simplify
+ locating the rocket once it has landed. (The last good GPS data
+ received before touch-down will be on the data screen of 'ao-view'.)
+ </para>
+ <para>
+ Once you have recovered the rocket you can download the eeprom
+ contents using either 'ao-dumplog' (or possibly 'ao-eeprom'), over
+ either a USB cable or over the radio link using TeleDongle.
+ And by following the man page for 'ao-postflight' you can create
+ various data output reports, graphs, and even kml data to see the
+ flight trajectory in google-earth. (Moving the viewing angle making
+ sure to connect the yellow lines while in google-earth is the proper
+ technique.)
+ </para>
+ <para>
+ As for ao-view.... some things are in the menu but don't do anything
+ very useful. The developers have stopped working on ao-view to focus
+ on a new, cross-platform ground station program. So ao-view may or
+ may not be updated in the future. Mostly you just use
+ the Log and Device menus. It has a wonderful display of the incoming
+ flight data and I am sure you will enjoy what it has to say to you
+ once you enable the voice output!
+ </para>
+ </appendix>
+ <appendix
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+ <title>Release Notes</title>
+ <xi:include href="release-notes-1.0.xsl" xpointer="xpointer(/article/*)"/>
+ <xi:include href="release-notes-0.9.2.xsl" xpointer="xpointer(/article/*)"/>
+ <xi:include href="release-notes-0.9.xsl" xpointer="xpointer(/article/*)"/>
+ <xi:include href="release-notes-0.8.xsl" xpointer="xpointer(/article/*)"/>
+ <xi:include href="release-notes-0.7.1.xsl" xpointer="xpointer(/article/*)"/>
+ </appendix>