So there I was this morning on the bus heading to Cheltenham to co-host the Cotswold Raspberry Jam, gazing at the beautiful Cotswold countryside, and my mind began to wander – well actually it was unleashed from the constraints of dealing with details it couldn’t fix while on a bus. And out came a better idea about where to go for the next step to autonomy.
What’s been bugging me is the difference between magnetic and GPS North. The ‘bus’ solution is to ignore magnetic north completely. The compass still has a role to play maintaining zero yaw throughout a long flight, but it plays no part in the direction of flight – in fact, this is mandatory for the rest of the plan to work.
Instead, the autopilot translates between GPS north, south, east and west coordinate system and Hermione’s forward, backwards, right and left coordinate. The autopilot only speaks to Hermione in her own coordinates when telling her where to go. The autopilot learns Hermione’s coordinate system at the start of each flight by asking her to fly forwards a meter or so, and comparing that to the GPS vector change it gets. This rough translation is refined continuously throughout the flight. Hermione can start a flight pointing in any direction compared to the target GPS point, and the autopilot will get her to fly towards the GPS target regardless of the way she’s pointing.
Sadly now, I’m back from today’s Jam, and the details confront me once more, but the bus ride did yield a great view of where to go next.
P.S. As always, the jam was great; over 100 parents and kids, lots of cool things for them to see and do, including a visit this time by 2 members of local BBC micro:bit clubs. Next one is 30th September.