Autonomous Autopilot, Almost

So the autopilot is now full autonomous, able to direct the main motion processor between various intermediate GPS waypoints to the final destination.  It will soft-abort flights via a controlled immediate landing if objects are in the way, the number of ‘visible’ satellites drops below a safety limit, or at the end of the flight.

Or it would if my GPS receiver / the weather would behave.  It’s only ever got 11 satellites max, and today it was struggling to keep 8.  Roughly 10 seems to be the acceptable lower limit my Mavic will accept for GPS control and today, it had no problem finding 11+.  Hermione on the other hand could only see 8 at the highest and this often drops mid-flight.  Without a constant set of satellites the position drifts – I’ve seen 40+m errors today.  Luckily I have code to abort a flight if the number of satellites drops below the minimum, and that’s what I’ve seen; in addition, the GPS is used to produce the direction of travel, but not the speed which is fixed at a gentle 0.3m/s to allow the down-facing video to track lateral motion accurately.

Here’s the GPS data I got for my standard 2m square flight; as you can see the return to base which in real life was very accurate, was 4m out by GPS’ account:

GPS accuracy & resolution

GPS accuracy & resolution

So I need the skies to clear and ideally to find a better GPS receiver, and herein lies the problem: I’m off to Disney Land, Paris next week.  Sod’s law says GPS conditions will be perfect here in England next week!


P.S. Just found myself a USB receiver that covers both GPS and GLONASS. GPS is USA owned and has 31 satellites; GLONASS is the Russian equivalent with 24 satellites; hopefully together I’ll be able to get much higher number of satellites, and hence much more accuracy as a result. Sadly, the proof of this pudding will only happen after a week of Disney junk-food eating. 🙁

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