completes initialization and self test, and decides which mode
to enter next.
- Here's a short summary of all of the modes and the beeping (or
- flashing, in the case of TeleMini v1) that accompanies each
- mode. In the description of the beeping pattern, “dit” means a
- short beep while "dah" means a long beep (three times as
- long). “Brap” means a long dissonant tone.
-
- .AltOS Modes
- [options="border",cols="1,1,2,2"]
- |====
- |Mode Name
- |Abbreviation
- |Beeps
- |Description
-
- |Startup
- |S
- |battery voltage in decivolts
- |Calibrating sensors, detecting orientation.
-
- |Idle
- |I
- |dit dit
- |Ready to accept commands over USB or radio link.
-
- |Pad
- |P
- |dit dah dah dit
- |Waiting for launch. Not listening for commands.
-
- |Boost
- |B
- |dah dit dit dit
- |Accelerating upwards.
-
- |Fast
- |F
- |dit dit dah dit
- |Decelerating, but moving faster than 200m/s.
-
- |Coast
- |C
- |dah dit dah dit
- |Decelerating, moving slower than 200m/s
-
- |Drogue
- |D
- |dah dit dit
- |Descending after apogee. Above main height.
-
- |Main
- |M
- |dah dah
- |Descending. Below main height.
-
- |Landed
- |L
- |dit dah dit dit
- |Stable altitude for at least ten seconds.
-
-
- |Sensor error
- |X
- |dah dit dit dah
- |Error detected during sensor calibration.
- |====
-
In flight or “pad” mode, the altimeter engages the flight
state machine, goes into transmit-only mode to send telemetry,
and waits for launch to be detected. Flight mode is indicated
=== Radio Link
- TeleMetrum, TeleMini and TeleMega all incorporate 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 had to decide how to manage the
+ TeleMetrum, TeleMini and TeleMega all incorporate 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 had to decide how to manage the
link.
- By design, the altimeter firmware listens for the radio link when
- it's in “idle mode”, which
- allows us to use the radio link to configure the rocket, do things like
- ejection tests, and extract data after a flight without having to
- crack open the air-frame. However, when the board is in “flight
- mode”, the altimeter 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 through
- the radio in case the rocket crashes and we aren't able to extract
- data later...
-
- We don't generally use a 'normal packet radio' mode like APRS
- because they're just too inefficient. The GFSK modulation we
- use is FSK with the base-band pulses passed through a Gaussian
- filter before they go into the modulator to limit the
- transmitted bandwidth. When combined with forward error
- correction and interleaving, this allows us to have a very
- robust 19.2 kilobit data link with only 10-40 milliwatts of
- transmit power, a whip antenna in the rocket, and a hand-held
- Yagi on the ground. We've had flights to above 21k feet AGL
- with great reception, and calculations suggest we should be
- good to well over 40k feet AGL with a 5-element yagi on the
- ground with our 10mW units and over 100k feet AGL with the
- 40mW devices. We hope to fly boards to higher altitudes over
- time, and would of course appreciate customer feedback on
- performance in higher altitude flights!
-
- === APRS
-
- TeleMetrum v2.0 and TeleMega can send APRS if desired, and the
- interval between APRS packets can be configured. As each APRS
- packet takes a full second to transmit, we recommend an
- interval of at least 5 seconds to avoid consuming too much
- battery power or radio channel bandwidth. You can configure
- the APRS interval using AltosUI; that process is described in
- the Configure Altimeter section of the AltosUI chapter.
-
- AltOS uses the APRS compressed position report data format,
- which provides for higher position precision and shorter
- packets than the original APRS format. It also includes
- altitude data, which is invaluable when tracking rockets. We
- haven't found a receiver which doesn't handle compressed
- positions, but it's just possible that you have one, so if you
- have an older device that can receive the raw packets but
- isn't displaying position information, it's possible that this
- is the cause.
-
- APRS packets include an SSID (Secondary Station Identifier)
- field that allows one operator to have multiple
- transmitters. AltOS allows you to set this to a single digit
- from 0 to 9, allowing you to fly multiple transmitters at the
- same time while keeping the identify of each one separate in
- the receiver. By default, the SSID is set to the last digit of
- the device serial number.
-
- The APRS packet format includes a comment field that can have
- arbitrary text in it. AltOS uses this to send status
- information about the flight computer. It sends four fields as
- shown in the following table.
-
- .Altus Metrum APRS Comments
- [options="header",cols="1,1,3"]
- |====
- |Field |Example |Description
-
- |1
- |L
- |GPS Status U for unlocked, L for locked
-
- |2
- |6
- |Number of Satellites in View
-
- |3
- |B4.0
- |Altimeter Battery Voltage
-
- |4
- |A3.7
- |Apogee Igniter Voltage
-
- |5
- |M3.7
- |Main Igniter Voltage
-
- |6
- |1286
- |Device Serial Number
- |====
-
- Here's an example of an APRS comment showing GPS lock with 6
- satellites in view, a primary battery at 4.0V, and
- apogee and main igniters both at 3.7V from device 1286.
-
- ....
- L6 B4.0 A3.7 M3.7 1286
- ....
-
- Make sure your primary battery is above 3.8V, any
- connected igniters are above 3.5V and GPS is locked
- with at least 5 or 6 satellites in view before
- flying. If GPS is switching between L and U regularly,
- then it doesn't have a good lock and you should wait
- until it becomes stable.
-
- If the GPS receiver loses lock, the APRS data
- transmitted will contain the last position for which
- GPS lock was available. You can tell that this has
- happened by noticing that the GPS status character
- switches from 'L' to 'U'. Before GPS has locked, APRS
- will transmit zero for latitude, longitude and
- altitude.
+ By design, the altimeter firmware listens for the
+ radio link when it's in “idle mode”, which allows us
+ to use the radio link to configure the rocket, do
+ things like ejection tests, and extract data after a
+ flight without having to crack open the air-frame.
+ However, when the board is in “flight mode”, the
+ altimeter 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 through the radio in case the rocket crashes
+ and we aren't able to extract data later.
+
+ We don't generally use a 'normal packet radio' mode
+ like APRS because they're just too inefficient. The
+ GFSK modulation we use is FSK with the base-band
+ pulses passed through a Gaussian filter before they go
+ into the modulator to limit the transmitted bandwidth.
+ When combined with forward error correction and
+ interleaving, this allows us to have a very robust
+ 19.2 kilobit data link with only 10-40 milliwatts of
+ transmit power, a whip antenna in the rocket, and a
+ hand-held Yagi on the ground. We've had flights to
+ above 21k feet AGL with great reception, and
+ calculations suggest we should be good to well over
+ 40k feet AGL with a 5-element yagi on the ground with
+ our 10mW units and over 100k feet AGL with the 40mW
+ devices. We hope to fly boards to higher altitudes
+ over time, and would of course appreciate customer
+ feedback on performance in higher altitude flights!
+
+ :aprsdevices: TeleMetrum v2.0 and TeleMega
+ :configure_section: _configure_altimeter
+ include::aprs-operation.raw[]
=== Configurable Parameters
Configuring an Altus Metrum altimeter for flight is
very simple. Even on our baro-only TeleMini and
EasyMini boards, the use of a Kalman filter means
- there is no need to set a “mach delay”. The few
- configurable parameters can all be set using AltosUI
- over USB or or radio link via TeleDongle. Read the
- Configure Altimeter section in the AltosUI chapter
- below for more information.
-
- ==== Radio Frequency
-
- Altus Metrum boards support radio frequencies
- in the 70cm band. By default, the
- configuration interface provides a list of 10
- “standard” frequencies in 100kHz channels
- starting at 434.550MHz. However, the firmware
- supports use of any 50kHz multiple within the
- 70cm band. At any given launch, we highly
- recommend coordinating when and by whom each
- frequency will be used to avoid interference.
- And of course, both altimeter and TeleDongle
- must be configured to the same frequency to
- successfully communicate with each other.
-
- ==== Callsign
-
- This sets the callsign used for telemetry,
- APRS and the packet link. For telemetry and
- APRS, this is used to identify the device. For
- the packet link, the callsign must match that
- configured in AltosUI or the link will not
- work. This is to prevent accidental
- configuration of another Altus Metrum flight
- computer operating on the same frequency
- nearby.
-
- ==== Telemetry/RDF/APRS Enable
-
- You can completely disable the radio while in
- flight, if necessary. This doesn't disable the
- packet link in idle mode.
-
- ==== Telemetry baud rate
-
- This sets the modulation bit rate for data
- transmission for both telemetry and packet
- link mode. Lower bit rates will increase range
- while reducing the amount of data that can be
- sent and increasing battery consumption. All
- telemetry is done using a rate 1/2 constraint
- 4 convolution code, so the actual data
- transmission rate is 1/2 of the modulation bit
- rate specified here.
-
- ==== APRS Interval
-
- This selects how often APRS packets are
- transmitted. Set this to zero to disable APRS
- without also disabling the regular telemetry
- and RDF transmissions. As APRS takes a full
- second to transmit a single position report,
- we recommend sending packets no more than once
- every 5 seconds.
-
- ==== APRS SSID
-
- This selects the SSID reported in APRS
- packets. By default, it is set to the last
- digit of the serial number, but you can change
- this to any value from 0 to 9.
-
- ==== Apogee Delay
-
- Apogee delay is the number of seconds after
- the altimeter detects flight apogee that the
- drogue charge should be fired. In most cases,
- this should be left at the default of 0.
- However, if you are flying redundant
- electronics such as for an L3 certification,
- you may wish to set one of your altimeters to
- a positive delay so that both primary and
- backup pyrotechnic charges do not fire
- simultaneously.
-
- The Altus Metrum apogee detection algorithm
- fires exactly at apogee. If you are also
- flying an altimeter like the PerfectFlite
- MAWD, which only supports selecting 0 or 1
- seconds of apogee delay, you may wish to set
- the MAWD to 0 seconds delay and set the
- TeleMetrum to fire your backup 2 or 3 seconds
- later to avoid any chance of both charges
- firing simultaneously. We've flown several
- air-frames this way quite happily, including
- Keith's successful L3 cert.
-
- ==== Apogee Lockout
-
- Apogee lockout is the number of seconds after
- boost where the flight computer will not fire
- the apogee charge, even if the rocket appears
- to be at apogee. This is often called 'Mach
- Delay', as it is intended to prevent a flight
- computer from unintentionally firing apogee
- charges due to the pressure spike that occurrs
- across a mach transition. Altus Metrum flight
- computers include a Kalman filter which is not
- fooled by this sharp pressure increase, and so
- this setting should be left at the default
- value of zero to disable it.
-
- ==== Main Deployment Altitude
-
- By default, the altimeter will fire the main
- deployment charge at an elevation of 250
- meters (about 820 feet) above ground. We
- think this is a good elevation for most
- air-frames, but feel free to change this to
- suit. In particular, if you are flying two
- altimeters, you may wish to set the deployment
- elevation for the backup altimeter to be
- something lower than the primary so that both
- pyrotechnic charges don't fire simultaneously.
-
- ==== Maximum Flight Log
-
- Changing this value will set the maximum
- amount of flight log storage that an
- individual flight will use. The available
- storage is divided into as many flights of the
- specified size as can fit in the available
- space. You can download and erase individual
- flight logs. If you fill up the available
- storage, future flights will not get logged
- until you erase some of the stored ones.
-
- Even though our flight computers (except TeleMini v1.0) can store
- multiple flights, we strongly recommend downloading and saving
- flight data after each flight.
-
- ==== Ignite Mode
-
- Instead of firing one charge at apogee and
- another charge at a fixed height above the
- ground, you can configure the altimeter to
- fire both at apogee or both during
- descent. This was added to support an airframe
- Bdale designed that had two altimeters, one in
- the fin can and one in the nose.
-
- Providing the ability to use both igniters for
- apogee or main allows some level of redundancy
- without needing two flight computers. In
- Redundant Apogee or Redundant Main mode, the
- two charges will be fired two seconds apart.
-
- ==== Pad Orientation
-
- TeleMetrum, TeleMega and EasyMega measure
- acceleration along the axis of the
- board. Which way the board is oriented affects
- the sign of the acceleration value. Instead of
- trying to guess which way the board is mounted
- in the air frame, the altimeter must be
- explicitly configured for either Antenna Up or
- Antenna Down. The default, Antenna Up, expects
- the end of the board connected to the 70cm
- antenna to be nearest the nose of the rocket,
- with the end containing the screw terminals
- nearest the tail.
-
- ==== Configurable Pyro Channels
-
- In addition to the usual Apogee and Main pyro
- channels, TeleMega and EasyMega have four
- additional channels that can be configured to
- activate when various flight conditions are
- satisfied. You can select as many conditions
- as necessary; all of them must be met in order
- to activate the channel. The conditions
- available are:
-
- include::pyro-channels.raw[]
-
+ there is no need to set a “mach delay”. All of the
+ configurable parameters can be set using AltosUI
+ over USB or or radio link via TeleDongle. Read
+ <<_configure_altimeter>> for more information.
projects / fw / altos / blobdiff