DAlt always stays at zero?

I’m working on setting up my Blackout mini hex with a Pixhawk. It’s flying decently in stabilize, and I had previously flown it in loiter and alt hold. I had some motor and ESC problems (self inflicted). During the motor/esc fiasco I updated to 3.2. Now when I switch to Alt hold Pixhawk commands an aggressive descent. Checking the log file, I can see that DAlt sticks at zero most of the time. Any input?

DAlt (desired altitude) is only used when the FC is controlling the altitude so it won’t show up for stabilise mode. I “think” part of the problem is your THR_MID is too high at 580 as you seem to be hovering at nearer 420 in stabilise. So when you change to alt hold your throttle is effectively in a down position (as it’s at 420 to hold stabilise height) so you are requesting a drop in altitude.

Your Z axis vibrations also go quite high which might not be helping.

Yes, it’s hard to see exactly what’s happening, as there are a few problems.

  1. You do have a very strange Z-axis vibration signature. I would guess that you have a very soft vibration mounting which isolates the vibration, but something is “hitting” and transferring shock into the Pixhawk. Sometimes the vibes are OK, and sometimes they’re really bad.

  2. Your inertial altitude estimate is completely unhinged from the baro measurement. This is probably caused by problem #1.

After some research we determined that the crappy 3 blade props were distorting in flight causing the weird vibrations you see. You should see the high speed video, the props basically fold up into a cone shape at full RPMs! You were correct, the RC Rx was just close enough to bump the Pixhawk, defeating the foam. Thanks for the input, it’s [almost] always something simple!