Developer

figuring out the Antenna Tracker

3691139590?profile=originalNot many people know but we have an piece of open source software for controlling an Antenna Tracker.  It's been built by Tridge (Arduplane lead developer) for use in the outback challenge.

Sadly we have no documentation and, as far as I know, nobody except Tridge has used it.  Still given Tridge's track record on building great software I suspect it works well and if it doesn't, I'm sure we can fix it.  So to not let this piece of code go to waste, I'd like some help from people who are interested to give it a try and help me figure out how it works.

Here's the little that I know:

  • It runs on any of our supported board (APM1, APM2, PX4, Pixhawk, Flymaple and perhaps VRBrain)
  • For APM1/APM2 users building the code is as easy as opening our hacked ArduinoIDE and selecting File > SketchBook > Tools > AntennaTracker and then building in the normal way.  For PX4/Pixhawk, our autobuilder doesn't automatically build a binary but I can provide one if people are interested.
  • It can control a Pan and Tilt gimbal like this or this found on servocity.com.
  • It may or may not require a GPS
  • It must somehow receive vehicle position updates from the ground station which has the telemetry radio that is connected to the vehicle. Maybe through a USB cable.  Tridge probably uses the python ground station, MAVProxy, to passthrough the vehicle position data to the AT but perhaps we can get MichaelO to build out a similar feature in Mission Planner.
  • I imagine this antenna tracker could also be used to keep a camera focused on the vehicle which might be good for easing the burden on creating videos of our vehicles.

So if you want to give it a try please do and stick any findings, questions or issues below. Alternatively Issues can go into the issues list.

I'll start sticking things into the wiki as they become clear.

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  • Developer

    The tracker firmware has progressed well over the past couple of months.  For the tracker's attitude estimation it uses either DCM or the EKF (I haven't checked) so it's attitude estimation is quite good.  It also uses the vehicle's velocity to interpolate it's position between updates (it always does this for the vehicle's horizontal position, it only does this for the vertical when the ALT_SOURCE = 2 (which means use the vehicle's EKF/GPS for alt instead of it's baro)).

    The next version will likely include roll compensation meaning that if you lay the tracker on it's side it still moves in a straight line to point at the target.  This isn't too important for most people but it might be useful if the tracker is on a moving platform and I think it demonstrates the growing sophistication of the tracker.

    One weakness we still have is the position of the tracker is taken directly from the GPS.  We should use a filtered position from the EKF.  My guess is we will do this in the future version too.

  • Developer

    Patrick

    There are a couple of companies building versions of the tracker and selling them commercially and I have also encouraged a couple of other companies to make a version that is available for purchase. So far nobody has taken up the challenge.  I do believe there is a market for antenna trackers especially if you are targeting the FPV market.

  • I am interested in this thread to gain some ideas on the potential of commercializing an antenna tracker for drones.  I started out building my own tracker which works great with mission planner (http://diydrones.com/profiles/blogs/how-to-build-an-fpv-antenna-tra...), and I am starting work on the second revision which will have continuous rotation and more advanced software for tracking the drone rather than just using it's current GPS position. I was just wondering how advanced the firmware is for the tracker described in this thread, does it support continuous rotating servos with gimbals and a compass? My goal is to use gimbals, compass, and accelerometers to precisely position the tracker, taking into account both the UAV's last GPS coordinates and its current velocity in azimuth and elevation, and also account for level changes in the positions of the tracker so that long calibrations are not necessary when setting up.  Eventually, if the idea is successful, I am considering the idea of a commercial product.

    My original tracker works very well for lower-gain antennas with a larger radiation pattern, but for achieving very-long range FPV, I need it to be more accurate with high-gain antennas, like a parabolic.  Any comments or suggestions would be appreciated.

  • Developer

    Fred,

    I like the NAVIO2 board but until we make the firmware upload process easier I think it's unlikely to be as popular as the Pixhawk has been. The Pixhawk2 will be available shortly and other manufacturers including Intel will be releasing Linux autopilots within the next couple of months (I hear) that run ArduPilot.  I think there's lots of choice and it's only going to get better actually.


  • Hi buddy do you thinks this NAVIO2 will replace the pixhwk ?

    off to do some research  NAVIO2

    Randy said:

    The ServoCity tracker arrived and we've set it up using an NAVIO2 board 

  • Developer

    The ServoCity tracker arrived and we've set it up using an NAVIO2 board and a 2.4Ghz wifi antenna.  I'll provide more details over the next week or so including an RPI2 image to make setup easier but until then, it works with the Bebop2.  The antenna is not perfectly suited for the Bebop2 but it's a good start (it's "right angle helical" but the bebop's antenna is not meaning the 11db antenna only works as well as an 8db antenna).

    3702266175?profile=original

  • Developer

    Doug,

    We hadn't thought about it but according to Tom Pittenger (who wrote the ADSB driver) it's possible.  The only issue is that the tracker doesn't include the ADSB driver at the moment so we would need to add that.  Once that's done, whichever device (vehicle or antenna tracker) you use the output from the ADSB sensor will be published to all the others at 1hz.

  • Randy,

    Good Day. I've been offline for a while with DIYDrones and am in the process of reading much and trying to catch up with what is happening.

    So far I'm anxious to get my tracker firmware updated and get back to testing! I do however have a question for you or anyone for that matter pertaining to ADSB and Antenna Trackers. Has there been any thought to incorporate a ADSB antenna into the tracker system verses connecting it directly to air vehicle Pixhawk serial? Reason I ask is that I have used up all my serial ports and find that I really do not need my air vehicle using one to only receive only the other aircraft's ADSB data and having it sent down to ground station via Mavlink.

    So what is the gain for having on my drone verses having it on the antenna tracker? Yes I understand that if my drone is up at 400ft that the detection distance for LOS of other ADSB is greater, but I do not fly BLOS so the detection beyond 25 miles is a mute point for me. If I have it on my antenna tracker using a spare serial port, I still can see other ADSB signals albeit at shorter distances from my GCS and drone. Does the antenna tracker firmware support ADSB and if not is there plans to incorporate it?

    Thanks.
    Doug Walmsley

  • Hi Randy, 

    Recently tried v0.8.0 using a Pixhawk based setup. After some calibration and tuning, it works! 

    But there seems to be a fair amount of location update latency - the tracker can take up to 20 seconds sometimes to finish updating its orientation. I suspect this is because of high latency in vehicle-to-ground GPS communication. Is this normal? What would be a good way to reduce latency? 

    Cheers

    • Developer

      Varun,

      Could you download some dataflash logs?  I think we should verify you're right that it's the telemetry delay and not a control response delay.  It will be easy to tell because if it's a telemetry delay then the tracker's ATT message will show that it thinks it's tracking well (i.e. the actual Pitch and Yaw will match the Desired Pitch and Yaw)

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