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
  • 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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              • It should be relatively easy to code an auto tune feature. It would of course need more than usual support from MP (setting correct servo type, slip ring or no slip ring, max allowed angles etc). Auto tune feature would take min and max servo values (preferably preset with sliders) and min/max allowed angles together with mechanical limitations (slip ring - unlimited rotation or no slip ring - respect min/max servo values for position servos or min/max angles for CR servos) and set servo reverse and basic pid settings accordingly. It could also perform compass calibration

            • Yes, use the Full Parameter List in Mission Planner. Ignore the suggested limits.


              • I try putting in +25 and write it. I come back and it won't save anything higher than +10.

                Never mind. Wrote it and then another parameter and it decided to save it.

  • I made some upgrades to my AT this year which includes the video downlink system. My AT is designed to point an ImmersionRC SpiroNet 5.8GHz antenna to the copter for my 5.8GHz video downlink. The 13dBi gain RHCP patch antenna has a 35 degree vertical and horizontal radiation pattern. If the AT fails to point properly, my ImmersionRC Duo 5800 receiver can automatically switch antennas to a Circular Polarized (RHCP) SpiroNet omni-directional antenna which has about 1 dBic gain. It will be interesting to see this summer how the AT performs using my APM copters and planes, which also have the Circular Polarized (RHCP) SpiroNet omni-directional antennas.

    For the telemetry links, the AT uses an RDF900 to talk to my Tarot copters, Skywalker plane, and FireFLY6 VTOL. For the GCS link, the AT uses a 433MHz telemetry set so it doesn't jam the 900MHz telemetry. This has been working very well with Mission Planner v1.3.34.

    I recently changed both the position and antennas of my RDF900 unit on the AT because it was interfering with the Pixhawk control of the servos. At first, I thought it was because I was using the Pixhawk to power the RDF900 unit but even after changing it to a 5v BEC the problem persisted. If I placed my hands over the antennas, the problem was gone. My power level is set to 25 (not 20 or 30max) so I may reduce this to 22, if needed. The new position of my RDF900 greatly reduces the radiation interference to the servos. Also, changing from the smaller antennas to the longer antennas reduced the interference even more.


    • Developer

      Looking good.  While doing testing for the 0.7.5 release I also noticed putting the [3DR] radio close to the servos caused them to act up.

      • So what is considered a safe distance then?

        • Developer

          a 5cm separation perhaps?  I didn't measure it but somewhere under that distance the servos would start twitching, move the radio away and it stopped.

    • It was relatively warm outside today for the last day of January in upstate NY so I took my AT and copter out to the backyard. Another weather oddity for this winter is that my backyard was snow free! :)

      Anyway, I made another set of logs (20.bin) for Randy with good GPS locks. The yaw was perfect and the pitch non-functional using the v0.7.5 firmware.

      On the HUD, is there a way to clear the purple path once things settle down and aren't moving around?



      • Developer

        Re the purple line, I haven't played with it much but maybe try reducing the "Track Length" on the MP's Config/Tuning, Planner screen?

      • Developer


        Sorry for taking so long to review your logs.  It looks like the pitch servo output is maxing out at 2100.  I guess you've tried reversing the pitch servo?  So try setting RC2_REV to +1 (it's -1 at the moment).

        By the way, reviewing this log uncovered an issue with the logging of the desired attitudes.  I'll push out Tracker-0.7.6 with a fix for that shortly.

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Aug 25