Board cam addiction
So the 70fps framerate, the lack of need for a USB hub, & the lower computational load made the board cam irresistible. Despite everything flying perfectly, it was time to rebuild it again.
The board cam immediately had new problems. The radio & camera don't always initialize. It helps to leave the board powered off for a while before restarting it, but it's a real problem if it is to automatically boot on the raspberry pi without a command line to drop kick it. There would only be power cycling after observing the failure on a tablet. This didn't happen with the last build of exactly the same board, but the last build had 4 more PWM's & no camera.
Also, there are a lot of tiny cables flexing. There wasn't any notable improvement in flight. The picture had a much more refined oval & probably more accurate coordinates but the flight was equally unstable.
With all the knowledge gleamed over the last year, the ultimate vision system would now use visible light, dual board cameras on separate turrets & separate USB connections producing 320x240 at 70fps. That would give the best velocity measurements. It would be nice if an IR board cam was easily obtained, but the lack of such a camera & the reduced power needs of visible LED's make IR impractical.
Without the instant velocity measurement of doppler shift that GPS provided, all indoor vehicles have suffered from delayed velocity measurement. The only solution is to increase the framerate to make the velocity measurements as close to realtime as possible, but never as good as doppler shift.
There were 2 major software changes:
The autopilot since 2009 exclusively used a binary integral. It would add all or none of the feedback constant, regardless of the error. That produced very fast response to changing weather, but created lots of oscillation. Changing it back to a proportional integral which scaled the feedback constant based on the error greatly reduced the oscillation.
The autopilot has always accumulated cyclic trim in world frame & translated it to copter frame. That compensated for wind as the copter turned, but indoors there is no wind & the trim is entirely due to vehicle balancing. For the 1st time, the cyclic trim was stored only in copter frame & the turns on the Syma X1 got a lot more stable.
The Syma X1 has a problem of gyro drift & uneven motor heating causing massive trim changes. It has always needed more aft pitch as the flight wore on. Normally, you want the vehicle as balanced as possible, so the trim is only due to wind.
There is a case for cyclic trim in copter frame for an outdoor vehicle, to compensate for balancing, but no way to differentiate between balance & wind.
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