Back to basics

I’m back from “Hell on Earth” (a.k.a. Disneyland Paris).  I’m still hunting for a decent GPS receiver that provides anything like the reception level of my DJI Mavic.  It’s a bright sunny day outside, and the Mavic GPS can see a stable 10+ satellites; the minimum level it will use GPS flight tracking seems to be about 9 satellites.  In comparison, Hermione seated in the same position can only see between 4 and (occasionally) 8 satellites depending on which of the 5 GPS recorders I have.  This may explain why my 2m square flight GPS tracking was so poor.

I have one more arriving in the next week or so upon which I have high hopes.

Until that arrives, my focus is on fine tuning the existing code.  Primarily, this is the vertical velocity PID gains; during a flight, the maximum value from the Z axis accelerometer is ±4g – the maximum configured – whereas the average is just over 2g.  Because it’s hitting the maximum, that means the integrated velocity is less that it should be, meaning Hermione continues to climb when the motion processing thinks she’s hovering.


Sod’s law struck again: just after first posting this, the new GPS receiver arrived and it was no better than the others.  The best of the bunch is the GlobalSat SiRF Start IV which has reached 11 satellites on a good day.

I also did some quick testing on the acceleration and it’s reporting a 5.91g ascent peak and -4.58g descent peak.  Tweaking the PID to reduce P gain and increase I gain just made it sluggish, but the peaks remained > ±4g.  For the moment, I’ve just updated the code to us ±8g range.  Another possible source could be noise from the props’ minor damage.  I’ll just tolerate this for now while I’m playing with the GPS tracking.

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