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193 lines
6.9 KiB
193 lines
6.9 KiB
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? |
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- If the tracker is equipped with a GPS and it has 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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<more here> |
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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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Levelling |
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Since AntennaTracker uses its internal accelerometers to determine the current |
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elevation/pitch of the antenna, it is important to 'level' the AntennaTracker |
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before use so the accelerometers are calibrated. Failure to do this will |
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result in the antenna constantly pointing a bit high or a bit low compared to |
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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. |
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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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