Freesteel Blog

RTK GPS in flight

Wednesday, May 29th, 2019 at 11:57 am Written by: Julian

I think I’ve not been blogging ongoing projects are not working. A long running one that I have failed to report here is this dabbling with the RTK GPS system, which I learnt about by researching precision agriculture, having been tipped off about it by a guy from sixty-5 when I was working out of farset labs in Belfast earlier this year.

Anyway, in theory one can log the raw data from these ublox M8T GPS chips, use the open source RTKLIB software to process the rover GPS against a base station GPS to get a 2cm accurate time series (with a lot of help from the rtklibexplorer blog, and then plan to put one of these rover stations in each wingtip of a glider.

And this would have all been fine if one of the wingtips ESP32 devices that receives and transmits the UBX data from the GPS to my phone through wifi didn’t keep failing. I finally found out what it was: the tiny sheet metal antenna had snapped off so cleanly that you couldn’t tell it was missing.

Here is a picture of my three devices. The 2 rovers go into pouches with their own batteries and get tied into the wingtips.

Anyway, it was a rubbish and rough flight that I did last Tuesday, never getting higher than 2600 feet. Meanwhile, Becka was doing her Welsh 3000s walk across 15 peaks all of which were higher than I managed to fly, and got a photo of this Brocken spectre on the peak of Snowdon at 8am, having set off at 5am from the car.

I was tasked with being a few kilometres further down the road to provide the second breakfast and some sandwiches for her further journey.

No I wasn’t going to do that walk, after my experience with the Lakeland 3000s. Walking too far in one day is annoying, especially when you are constantly being told you’re not going fast enough.

The logical consequence of having more strength and always wanting to do more than anyone else is… that other people will want to do less, and this is going to be a disappointment.

So I went flying, and RTKLIB processed my one working GPS track, like so:

(Blue is the phone GPS and orange is the RTK gps.)

I was going to show some correspondences between the RTK GPS altitude and the barometric altitude when suitably filtered, but my interacting plotting system broke down. There are a lot of oscillations in the GPS, which I don’t understand. Will get back to it.