You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
232 lines
8.8 KiB
232 lines
8.8 KiB
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 |
|
|
|
<more here> |
|
|
|
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.
|
|
|