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ArduPilot's Antenna Tracker firmware has been making some quiet progress over the past few months.  They're all documented in the Release Notes but at a high level the improvements include:

• More accurate control due to bug fixes in how the vehicle's position estimation was done
• Smoother movement through additional filtering
• Separate servo types possible for yaw and pitch axes
• Tilt compensation meaning it tracks the vehicle accurately even when the tracker is leaned over
• Improved Mission Planner setup screen (i.e. Extended tuning page)

The parts I used to build my tracker included:

• Emlid.com's NAVIO2 with RPI2
• Servo City PT785-S Pan & Tilt system
• Circular Wireless's 11db Antenna
• TP-Link TL-WN722N Wifi dongle

I used a NAVIO2 instead of a Pixhawk mostly because it's easier to make a Wifi connection this way.

I haven't yet tested the range of the telemetry connection to the Bebop2 but I suspect it's between 1km ~ 2km.  In fact, the antenna used here is not ideal for use with the Bebop2, a simpler non-Helical antenna like this one would likely do better.

Some limitations of this setup:

• we don't yet support receiving live video from the Bebop2 but this is coming within the next couple of months so during this test I simply had telemetry data from both Tracker and Bebop2 visible in the Mission Planner
• the networking connection between the PC to the RPI2 was quite simple but not very flexible.  For whatever reason the PC and RPI2 nearly always appear with the same IP addresses so the Tracker startup scripts were hardcoded to always uses these.  It would be better to setup dhcp on the RPI2 to set PC's IP address
• the bebop's Wifi ssid is hard-coded in the start_tracker.sh script on the RPI2.  If someone wanted to repeat this setup they would need to change this to match their particular Bebop.

In case people want to replicate this setup, I've uploaded an image to firmware.ardupilot.org here.

Thanks to the beta testers for their ideas and feedback and Stefan Lynka for his code contributions.