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