Yesterday I noticed a strange behavior while flying in altitude hold, using the sonar sensor.
The copter performed a perfect altitude hold (no oscillations, follows the terrain really nice),
but started towards the end of the flight to suddenly shoot up (1 - 2 meters) and drop down again to the previous height.
The log graphs (see attached) show that the sonar reported a drop in height, even though the copter stayed in a nice hoover.
It shows furthermore that the shooting up was a result of the height reported by the sonar sensor (first the reported height drops, then the throttle is being raised by the APM).
The sonar sensor features a case, including the electric noise filter, a wind filter (from a microphone) and a shielded cable.
The flight was during evening hours, it started to get a bit cooler and damp.
I was flying over grass, which started to collect dew - maybe this resulted in a better reflection of the signal emitted by the sonar sensor, and thereby in a reported lower height?
Does anybody have similar observations?
Any ideas?
Thanks a lot
Felix
Replies