The froggy mini 3 pro now has a tophat!
This is a lightweight RTK receiver coming in at about 60g including a 750mah battery, would be less without. Make from a Raspberry Pi Zero 2 W, with a U-Blox M8T receiver and a Beitan BT520 antenna. Stuck in a 3D printed housing and attached with dual lock. The total cost of doing this is about £200, you can do it for cheaper if you scrounge parts, it cost me about £100 as I bought the GNSS IC seperately and soldered it to a cheaper protoboard than what is commercially sold.
You do also need a base station to provide the corrections, thats a whole other kettle of fish but at a minimum you need a second set of everything above. I’m using a higher grade antenna (Trimble Zephyr Geodetic) but the same receiver (M8T). I use RTKLIB for all my post processing
Flew it for the first time and a few things came to note:
The Mini 3 Pro didn’t care at all about the extra weight, the extended battery is an extra 40 g so this is another 20 g more than using one of those, much in the grand scheme of things but still almost 10% of the total mass of the drone. Motors a little warm after flight, but I had been zipping around in sport mode.
Airdata reckons this cuts the flight time down to 20m, again it’s probably not as severe as I spent some decent time in sport mode.
Now for the figure, Yellow is the GNSS from the Mini 3 Pro (via. airdata), Red is the post processed kinematic data from the external module.
Firstly, it’s worth saying that the inbuilt GNSS does impressively well here! You can see it lags behind a bit in the turns as the internal ‘model’ is catching up most likely. The heights are pretty close as well, although it has the advantage of aiding though all the other onboard sensors.
The external receiver performed ideally with a 97% fix rate. Hopefully this weekend I can get out to scan something and see what the performance difference is in photogrammetry, which is the only real use for this.
Only issue that still exists is how to input offsets for the external antenna, as you need the heading data to correct for position at the sensor. For any commercial advantage, this would be essential. I could probably script something to take the Air Data log to compute the offsets with the internal heading.