Gyro Doctor
Electronics Tech for over 45 years
... Barometer (ok fine) and optical flow sensor (lmao) to maintain desired height (ummm, yeah sure).Barometric height stabilization is only approximate because air pressure changes very little relative to the differences in heights the quad may make during hovering.
Optical flow sensoring is basically like using an infrared remote controller to look at the ground and measure either the detected intensity or the doppler shift of the reflected beam.
Be aware that both of these control schemes are affected by the type of surface which you are hovering above. Indoors and looking at a floor the optics work much better than, say, outside looking at grass (where the beam is diffused more). Ground effects (the turbulence encountered when hovering too low) are also affected by undisturbed vortexes over a floor compared to grass (where the vortex is diffused more). In other words, it's going to be easier FOR THE BAROMETER to hover at lower levels over grass outdoors, than over a floor indoors, BUT it's easier FOR THE OPTICS to hover at lower levels over a floor indoors than over grass outdoors. It would be interesting to investigate what (if any) compensation mechanism has been implemented to combine these effects in that quad's responses.
Barometers are also affected by wind blowing across the sensor (at ANY altitude) so, to dampen any abrupt reactions, a lot of pilots will place some foam over the sensor.
The experience you had at about a foot off the ground was likely a "runaway control loop error" caused by ground effects influencing the barometric compensation which
only aggravated the instability thereby causing the crash.
In summary do what Rick says and recalibrate often, always hover no less than several feet from the ground, don't ever really rely on altitude hold, dampen that twitchy barometer
with some foam, and you'll be just fine.