future as you wish!
</para>
<para>
- The first device created for our community is TeleMetrum, a dual
+ The first device created for our community was 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.
</para>
<para>
The TeleMini battery can be charged by disconnecting it from the
- TeleMini board and plugging it into the battery charger board,
- and connecting that via a USB cable to a laptop or other USB
+ TeleMini board and plugging it into a standalone battery charger
+ board, and connecting that via a USB cable to a laptop or other USB
power source
</para>
<para>
RF interface. If you plug it in to your Mac or Linux computer it should
"just work", showing up as a serial port device. Windows systems need
driver information that is part of the AltOS download to know that the
- existing USB modem driver will work. If you are using Linux and are
- having problems, try moving to a fresher kernel (2.6.33 or newer), as
- the USB serial driver had ugly bugs in some earlier versions.
+ existing USB modem driver will work. We therefore recommend installing
+ our software before plugging in TeleDongle if you are using a Windows
+ computer. If you are using Linux and are having problems, try moving
+ to a fresher kernel (2.6.33 or newer), as the USB serial driver had
+ ugly bugs in some earlier versions.
</para>
<para>
Next you should obtain and install the AltOS utilities. These include
<chapter>
<title>Handling Precautions</title>
<para>
- All Altus Metrum products are sophisticated electronic device. When handled gently and
- properly installed in an airframe, theywill deliver impressive results.
- However, like all electronic devices, there are some precautions you
- must take.
+ All Altus Metrum products are sophisticated electronic devices.
+ When handled gently and properly installed in an airframe, they
+ will deliver impressive results. However, like all electronic
+ devices, there are some precautions you must take.
</para>
<para>
The Lithium Polymer rechargeable batteries have an
strapping them down, for example.
</para>
<para>
- The barometric sensor is sensitive to sunlight. In normal
- mounting situations, it and all of the other surface mount components
+ The barometric sensors used on both TeleMetrum and TeleMini are
+ sensitive to sunlight. In normal TeleMetrum 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 an airframe with a
- see-through plastic payload bay.
+ see-through plastic payload bay. It is particularly important to
+ consider this with TeleMini, both because the baro sensor is on the
+ "top" of the board, and because many model rockets with payload bays
+ use clear plastic for the payload bay! Replacing these with an opaque
+ cardboard tube, painting them, or wrapping them with a layer of masking
+ tape are all reasonable approaches to keep the sensor out of direct
+ sunlight.
</para>
<para>
- The barometric sensor sampling port must be able to
- "breathe",
+ The 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
+ directly block the hole on the top of the sensor, and also by having a
suitable static vent to outside air.
</para>
<para>
- As with all other rocketry electronics, Altus Metrum altimeters must be protected
- from exposure to corrosive motor exhaust and ejection charge gasses.
+ As with all other rocketry electronics, Altus Metrum altimeters must
+ be protected from exposure to corrosive motor exhaust and ejection
+ charge gasses.
</para>
</chapter>
<chapter>
your local radio regulations.
</para>
</section>
+ <section>
+ <title>Font Size</title>
+ <para>
+ Selects the set of fonts used in the flight monitor
+ window. Choose between the small, medium and large sets.
+ </para>
+ </section>
<section>
<title>Serial Debug</title>
<para>
</para>
</section>
</chapter>
+ <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>
projects / fw / altos / blobdiff