i just builded a new copter, with a Pixfalcon (soft v. 3.3.2 Pixhawk clone). I does very well. but one thing is not working well: Alt hold does not really hold the altitude - at least whenever the copter is moving. It is really strange. when i put it in alt hold or pos hold the copter stays at the place like nailed. Whenever i fly the copter somewhere else, it looses altitude as its not in alt/pos hold. 

What can be the reason for such a behavior?

Any Help would be just awesome!! 

I added 2 log files, one from yesterday, doing a autotune, one from today flying a little auto-mission (3 waypoints).

in logfile#1 (autotune) you can clearly see that whenever i brought the copter back to me it lost a lot of altitude. when the copter was doing his autotune-dancemoves, it kept the altitude perfectly...


logfile 2 is the same result: the copter is in auto mode, starts to approach a waypoint and on the way there it looses a lot of altitude. when it is right under the wayoint it climbes up to the point and does the same thing again:




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  • Developer

    Looks like high vibration levels are upsetting the climb rate estimates so I think reworking the vibration isolation would be best.  I think the 3M foam that 3DR sells (at least before Christmas they were still selling it) or the hobby king orange foam.  There's some advice here on the wiki that you may have already seen but just in case.


    • @OwlPic: I do not think it is the Problem of the airflow, since the baro exactly sees the altitude drop.

      for me its much more likely that Randy picked up a good point..

      @Randy: thank you very much for your help (and your awesome work by the way ;) )

      It is kind of hard to figure out what i can do for vibration isolation since i use the PixFalcon - wich is much much lighter then the original PixHawk (which i used around 2 years and never had problems like that).

      Do you have any suggestion what i could use for vibration dampening for that FC? It weights 15.86g compared to the 39,4g of the PixHawk.

      Thank you very much,


  • There could be several reasons, but thinking about the physics. If your altitude sensor is based on barometric pressure and:

    1) the sensor is blocked from air flow when moving, then the sensor will detect a pressure decrease and think that it is rising


    2)  the sensor is exposed to air flow when moving, then the sensor will detect a pressure increase and think that it is falling.

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