mirror of https://github.com/ArduPilot/ardupilot
233 lines
8.8 KiB
Plaintext
233 lines
8.8 KiB
Plaintext
AntennaTracker
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Mike McCauley
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2014-03-05
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This is the ardupilot AntennaTracker
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This software, combined with appropriate hardware, can be used to cause a
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high-gain antenna to track a mavlink equipped air or ground vehicle in real
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time, providing higher quality radio links over longer distances than a
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stationary or omnidirectional antenna.
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AntennaTracker can be a stationary installation on the ground, or can be
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mobile, mounted on a vehicle, and moving at the same time as the vehicle it is
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tracking, such as on a pursuit vehicle etc.
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Antenna Tracker Hardware
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The software works with:
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- Alt-Azimuth mounted antenna tracker, equipped with 2 servos: one for Azimuth
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(also called bearing or yaw) -180 to 180 degreees and one for Altitude (also
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called elevation, or pitch) -90 degrees (straight down) to 90 degrees
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(straight up). I used an Eagle Tree Antenna Pan-Tilt.
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- Ardupilot compatible processor such as
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-- Flymaple
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-- others tested?
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and with a radio or wired link to a source of mavlink messages with the
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tracked vehicle's position data.
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A suitable power supply is also needed, possibly battery powered. In the case
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of Flymaple, the onboard 5V regulator is not able to drive large servos
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without causing large amounts of electrical noise in the processor, so you
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would probably need an external 5V regulated supply
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Theory of Operation
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AntennaTracker receives real-time GPS position reports from the vehicle being
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tracked (in the form of GLOBAL_POSITION_INT messages sent by mavlink radio
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connection or possibly by hardwired serial connection). AntennaTracker also
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knows it own current position. Based on these 2 sets of coordinates, it
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calculates the magnetic bearing and elevation to the vehicle. It then moves
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the tracker servos until the antenna (and the AntennaTracker processor) are
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aligned with the desired bearing and elevation. At this stage the antenna is
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pointed straight at the tracked vehicle. As the vehicle (and possibly the
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antenna mount itself) move around, the servos are continually move to track
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the vehicle.
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AntennaTracker currently only supports closed loop feedback to position the
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antenna. This requires that AntennaTracker processor (including
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accelerometers and compass) be mounted on the moving part of the antenna
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tracker hardware. The servos are moved until the yaw and pitch of the processor
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(and therfore of the antenna itself) matches the bearing and elevation to the
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tracked vehicle.
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How does AntennaTracker know where it is on the earth?
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- If the tracker is equipped with a GPS and it has had a good 3D fix, the most
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recent good GPS fix is used.
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- If the tracker is equipped with a GPS and it has lost its fix, the most
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recent good GPS fix is used.
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- If there is no good GPS fix since startup (either because there is no GPS
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equipped or because the GPS has not yet got a fix), the most resently set HOME
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location is used.
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- If no HOME location has ever been set in the tracker, 0.0 Latitude, 0.0
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Longitude, 0 Altitude are used (which is probably not very helpful)
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How does AntennaTracker get GLOBAL_POSITION_INT messages from the tracked
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vehicle?
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mavproxy, when it runs the tracker module, intercepts all GLOBAL_POSITION_INT
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messages received from its master vehicle, and sends them to the tracker. It
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knows how to connect to the tracker with the set port and set baudrate
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commands, for example to connect by a USB-Serial radio, such as the 3DR Radio
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on port /dev/ttyUSB0:
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(after starting mavproxy)
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module load tracker
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tracker set port /dev/ttyUSB0
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tracker set baudrate 57600
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tracker start
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Mounting
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The AntennaTracker processor must be mounted on the moving (ie the rotating,
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tilting) part of the antenna tracker hardware. Just how you do this will
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depend on your exact hardware, but if the processor is mounted in anything
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other than the default orientation (ie with the processor default 'forward'
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direction pointing in the direction the antenna points, you will have to
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configure AHRS_ORIENTATION in the AntennaTracker configuration to suit your
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mechanical mounting arrangements.
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In my case, I used a Flymaple with AHRS_ORIENTATION set to 1 (Yaw45). The
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Flymaple was mounted on the antenna tracker with component side up and the
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green pin headers horizontal and perpendicular to the antenna beam (See
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pictures???).
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Configuration
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It is vitally important that your AntennaTracker be properly configured for the
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mounting, servos and other hardware in your tracker. Unless you do this IT
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WILL PROBABLY NOT WORK AS EXPECTED. CAUTION: It might even oscillate or flap
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around. It might even damage itself.
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AntennaTracker (like other ardupilot software such as ArduPlane, APMRover2
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etc) has configuration values that control and tailor its operation, and which
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are stored in EEPROM on the processor. The configuration is restored from
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EEPROM every time the processsor starts.
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You can use MissionPlanner, mavproxy or apm_planner or other mavlink compatible
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software to check and change the configuration of your AntennaTracker.
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You will almost certainly have to change the following configuration items to
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suit, and possibly others besides:
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AHRS_ORIENTATION
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RC1_MIN
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RC1_MAX
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RC1_REV
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RC2_MIN
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RC2_MAX
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RC2_REV
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PITCH2SRV_P
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PITCH2SRV_I
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PITCH2SRV_D
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YAW2SRV_P
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YAW2SRV_I
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YAW2SRV_D
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(more info here about how to find the right values when the setup commands are
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available)
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You can find the complete set of configuration items I used for my Flymaple
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tracker mounted on an Eagle Tree tracker WHERE?????
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Compass Calibration
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AntennaTracker uses its internal magnetic compass to determine where North is
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and therefore where to point for each bearing to the target vehicle. (On other
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ardupilot vehicles, the yaw is also calibrated by the current GPS track. This
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is not possible for AntennaTracker, so the compass is the only possible source
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for absolute bearing)
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The compass magnetometer is exquisitely sensitive to nearby magnetic fields from
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wires, metal fittings, servos, radios etc. Therefore is it VITALLY ESSENTIAL that you
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calibrate the compass. Further, it must be calibrated outdoors, while installed
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in situ in the tracker, with all other equipment installed, fastened down and
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ready to operate.
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Failure to calibrate correctly will result in the tracker pointing in the
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wrong direction, or the azimuth/yaw and elevation/pitch drifting.
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Use Mission Planner to calibrate the tracker:
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- Assemble the completed tracker, complete and ready to operate.
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- Power up the tracker
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- Connect to it with Mission Planner
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- On Mission Planner->INITIAL SETUP->Compass, click on Live Calibration
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- click on OK
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- rotate the complete antenna tracker assembly around, in 3 dimensions, making sure to
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rotate the tracker to every possible orientation in the 1 minute you have
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available. DONT just move the yaw and pitch motors around. You will probably have to
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pick the whole thing up.
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- At the end of the minute, Mission Planner will update AntennaTrackers compass offsets.
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Levelling
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Since AntennaTracker uses its internal accelerometers (amongst other things)
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to determine the current elevation/pitch of the antenna, it is also important
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to 'level' the AntennaTracker before use so the accelerometers are
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calibrated. Failure to do this will result in the antenna constantly pointing
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a bit high or a bit low compared to the tracked vehicle.
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You can do this by connecting to the AntennaTracker with mavproxy and issuing
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these commands:
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disarm
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- manually move the antenna so the antenna is level and pointing at 0 degrees elevation
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i.e. at the horizon
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level
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- wait a minute without disturbing the antenna position
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arm throttle
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- this rearms the servos, allowing the antenna to move
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Operation
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<more here>
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After powering up AntennaTracker, it may take up to 1 minute while it
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automatially calibrates the compass before it points in the expected
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direction. Moving the tracker around will speed up this process.
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How to set the HOME location
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If your AntennaTracker is not equipped with a GPS, you can still use it to
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track vehicles. First you will have to tell AntennaTracker where it is on the
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ground by setting its HOME position.
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Connect to AntennaTracker with mavproxy
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module load map
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- the map will appear.
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- Zoom and drag the map until you can see the location where
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your AntennaTracker is located
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- Click the mouse on the location of the antenna
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wp sethome
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AntennaTracker will now remember this as its HOME location whenever it is
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started.
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Simulating an antenna tracker
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-----------------------------
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To run a full antenna tracker simulation with a simulated APM:Plane as
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the vehicle, cd to the ArduPlane directory and run this:
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../Tools/autotest/sim_arduplane.sh -T --aircraft test
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The -T flag tells sim_arduplane.sh to start an entenna tracker
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simulator and also start a virtual antenna tracker in a window.
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To start the antenna tracker running run "tracker start" in the
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mavproxy window.
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To then connect to your antenna tracker with mavproxy you would run:
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mavproxy.py --master tcp:127.0.0.1:5770
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then you can configure it as needed.
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