Altitude problem

#1

Hi. I’m building an autonomeus drone. The robot should be at a height of 1.7 meters.
before i use ardupilot stack but now i use px4 stack because yaw was disable on velocity set point.
I use the sonar as well. All is done but it falls below 1m when flying.

#2

here is my log fileflyt_runlogs_2016-02-11_20-04.log (352 KB)

Please answer me sooner.thanks.