</chapter>
<chapter>
<title>Specifications</title>
-
<itemizedlist>
<listitem>
- <para>
- Recording altimeter for model rocketry.
- </para>
+ Recording altimeter for model rocketry.
+ </para>
</listitem>
<listitem>
- <para>
- Supports dual deployment (can fire 2 ejection charges).
- </para>
+ Supports dual deployment (can fire 2 ejection charges).
+ </para>
</listitem>
<listitem>
- <para>
- 70cm ham-band transceiver for telemetry downlink.
- </para>
+ 70cm ham-band transceiver for telemetry downlink.
+ </para>
</listitem>
<listitem>
- <para>
- Barometric pressure sensor good to 45k feet MSL.
- </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>
+ 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>
+ 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>
+ 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>
+ USB interface for battery charging, configuration, and data recovery.
+ </para>
</listitem>
<listitem>
- <para>
- Fully integrated support for LiPo rechargeable batteries.
- </para>
+ Fully integrated support for LiPo rechargeable batteries.
+ </para>
</listitem>
<listitem>
- <para>
- Uses LiPo to fire e-matches, support for optional separate pyro
- battery if needed.
- </para>
+ Uses LiPo to fire e-matches, support for 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>
+ 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
+ </para>
</listitem>
</itemizedlist>
</chapter>
</chapter>
<chapter>
<title>Operation</title>
- <para>
- Placeholder.
- </para>
+ <section>
+ <title>Firmware Modes </title>
+<para>
+ The AltOS firmware build for TeleMetrum has two fundamental modes,
+ "idle" and "flight". Which of these modes the firmware operates in
+ is determined by the orientation of the rocket (well, actually the
+ board, of course...) at the time power is switched on. If the rocket
+ is "nose up", then TeleMetrum assumes it's on a rail or rod being
+ prepared for launch, so the firmware chooses flight mode. However,
+ if the rocket is more or less horizontal, the firmware instead enters
+ idle mode.
+</para>
+<para>
+ In flight mode, TeleMetrum turns on the GPS system, engages the flight
+ state machine, goes into transmit-only mode on the RF link sending
+ telemetry, and waits for launch to be detected. Flight mode is
+ indicated by an audible "di-dah-dah-dit" on the beeper, followed by
+ beeps indicating the state of the pyrotechnic igniter continuity.
+ One beep indicates [FIXME] apogee continuity, two beeps indicate
+ main continuity, three beeps indicate both apogee and main continuity,
+ and one longer "brap" sound indicates no continuity. For a dual
+ deploy flight, make sure you're getting three beeps before launching!
+ For apogee-only or motor eject flights, do what makes sense.
+</para>
+<para>
+ In idle mode, the normal flight state machine is disengaged, and thus
+ no ejection charges will fire. TeleMetrum also listens on the RF
+ link when in idle mode for packet mode requests sent from TeleDongle.
+ Commands can thus be issues to a TeleMetrum in idle mode over either
+ USB or the RF link equivalently.
+ Idle mode is useful for configuring TeleMetrum, for extracting data
+ from the on-board storage chip after flight, and for ground testing
+ pyro charges.
+</para>
+<para>
+ One "neat trick" of particular value when TeleMetrum is used with very
+ large airframes, is that you can power the board up while the rocket
+ is horizontal, such that it comes up in idle mode. Then you can
+ raise the airframe to launch position, use a TeleDongle to open
+ a packet connection, and issue a 'reset' command which will cause
+ TeleMetrum to reboot, realize it's now nose-up, and thus choose
+ flight mode. This is much safer than standing on the top step of a
+ rickety step-ladder or hanging off the side of a launch tower with
+ a screw-driver trying to turn on your avionics before installing
+ igniters!
+</para>
+ </section>
+ <section>
+ <title>GPS </title>
+<para>
+ TeleMetrum includes a complete GPS receiver. See a later section for
+ a brief explanation of how GPS works that will help you understand
+ the information in the telemetry stream. The bottom line is that
+ the TeleMetrum GPS receiver needs to lock onto at least four
+ satellites to obtain a solid 3 dimensional position fix and know
+ what time it is!
+</para>
+<para>
+ TeleMetrum provides backup power to the GPS chip any time a LiPo
+ battery is connected. This allows the receiver to "warm start" on
+ the launch rail much faster than if every power-on were a "cold start"
+ for the GPS receiver. In typical operations, powering up TeleMetrum
+ on the flight line in idle mode while performing final airframe
+ preparation will be sufficient to allow the GPS receiver to cold
+ start and acquire lock. Then the board can be powered down during
+ RSO review and installation on a launch rod or rail. When the board
+ is turned back on, the GPS system should lock very quickly, typically
+ long before igniter installation and return to the flight line are
+ complete.
+</para>
+ </section>
+ <section>
+ <title>Ground Testing </title>
+ <para>
+ An important aspect of preparing a rocket using electronic deployment
+ for flight is ground testing the recovery system. Thanks
+ to the bi-directional RF link central to the Altus Metrum system,
+ this can be accomplished in a TeleMetrum-equipped rocket without as
+ much work as you may be accustomed to with other systems. It can
+ even be fun!
+ </para>
+ <para>
+ Just prep the rocket for flight, then power up TeleMetrum while the
+ airframe is horizontal. This will cause the firmware to go into
+ "idle" mode, in which the normal flight state machine is disabled and
+ charges will not fire without manual command. Then, establish an
+ RF packet connection from a TeleDongle-equipped computer using the
+ P command from a safe distance. You can now command TeleMetrum to
+ fire the apogee or main charges to complete your testing.
+ </para>
+ </section>
+ <section>
+ <title>Radio Link </title>
+ <para>
+ The chip our boards are based on incorporates an RF transceiver, but
+ it's not a full duplex system... each end can only be transmitting or
+ receiving at any given moment. So we have to decide how to manage the
+ link...
+ </para>
+ <para>
+ By design, TeleMetrum firmware listens for an RF connection when
+ it's in "idle mode" (turned on while the rocket is horizontal), which
+ allows us to use the RF link to configure the rocket, do things like
+ ejection tests, and extract data after a flight without having to
+ crack open the airframe. However, when the board is in "flight
+ mode" (turned on when the rocket is vertical) the TeleMetrum only
+ transmits and doesn't listen at all. That's because we want to put
+ ultimate priority on event detection and getting telemetry out of
+ the rocket and out over
+ the RF link in case the rocket crashes and we aren't able to extract
+ data later...
+ </para>
+ <para>
+ We don't use a 'normal packet radio' mode because they're just too
+ inefficient. GFSK is just FSK with the baseband pulses passed through a
+ Gaussian filter before they go into the modulator to limit the
+ transmitted bandwidth. When combined with the hardware forward error
+ correction support in the cc1111 chip, this allows us to have a very
+ robust 38.4 kilobit data link with only 10 milliwatts of transmit power,
+ a whip antenna in the rocket, and a hand-held Yagi on the ground. We've
+ had a test flight above 12k AGL with good reception, and my calculations
+ say we should be good to 40k AGL or more with just a 5-element yagi on
+ the ground. I expect to push 30k with a 54mm minimum airframe I'm
+ working on now, so we'll hopefully have further practical confirmation
+ of our link margin in a few months.
+ </para>
+ <para>
+ Placeholder.
+ </para>
+ </section>
</chapter>
<chapter>
<title>Using Altus Metrum Products</title>
<para>
The best hand-held commercial directional antennas we've found for radio
direction finding rockets are from
- <ulink url="http://www.arrowantennas.com/" >
- Arrow Antennas.
- </ulink>
-The 440-3 and 440-5 are both good choices for finding a
-TeleMetrum-equipped rocket when used with a suitable 70cm HT.
+
<ulink url="http://www.arrowantennas.com/" >
+ Arrow Antennas.
+ </ulink>
+ The 440-3 and 440-5 are both good choices for finding a
+ TeleMetrum-equipped rocket when used with a suitable 70cm HT.
</para>
</section>
<section>
</para>
</section>
</section>
+ <section>
+ <title>
+ How GPS Works
+ </title>
+ <para>
+ Placeholder.
+ </para>
+ </section>
</chapter>
</book>
projects / fw / altos / blobdiff