Altitude Hold Problems

I experienced altitude hold problems with a brand new Iris in Altitude Hold, Loiter, and Auto modes.
The vehicle behaved properly in Stabilize mode. However with altitude control engaged the quad was not holding properly, and loosing progressively altitude while in forward motion even with the throttle stick at 50%.
In particular, it lost altitude between waypoints (set to 20m) in Auto mode. Lateral tracking was fine.

The Iris was carrying a GoPro3 in its waterproof case.

This was a windy day, steady wind >10knt, enough to windmill the propellers.

I attached one of the logs with Loiter on.

Thank you for your assistance.

you have vibration problems in you iris , check your propellers.
danny 3dr :smiley:

[quote=“danny3dr”]you have vibration problems in you iris , check your propellers.
danny 3dr :smiley:[/quote]
Could you elaborate? The X and Y accelerations are in the nominal range. Z is not. Can vibrations really affect only one axis?

Vibrations as they affect all 3, but the most affected is the z by the barometer, I have looked at many of these problems by bullets motors and propellers, sponges.

@cangire: I have seen similar behavior in windy conditions. Although not as windy as what you describe.

@danny3dr: Mind to expand a bit more on what you mean with your comments?
Bottom-line: How can we fix this?


@cangire: Looking at your logs, I see quite a bit of a difference between the barometer determined height and the GPS one. Look at the difference between CTUN->BarAlt and GPS->RelAlt.


But as danny3dr already said: Your Z-axis vibrations are pretty bad.

I have no idea what could be causing this as your X-axis and Y-axis vibrations are pretty good.

I’m seeing similar issues, where IRIS while in Alt Hold mode suddenly drops altitude - even though the throttle is at 50% and hasn’t been touched.

Here is an example:
Look at the time shortly after 1:30 min.
Here is a video, which clearly shows the drop:

Looking at my CTUN->BarAlt and GPS->RelAlt, I also see differences between the two a few times during the flight. Their occurence seems to correlate with IRIS experiencing the drops.
But I also noticed that while my Z-axis vibrations are usually fine, they increase at the same time when CTUN->BarAlt and GPS->RelAlt start to diverge.

The AccZ from IMU and IMU2 show the sudden drop as well:

But the big question: What was causing this behavior?
It wasn’t very windy. Wind was between 5 - 10 km/h. It doesn’t look like it could have been caused by wind.

What’s weird: Looking at RCIN->Chan3, it looks like Throttle was decreased quite a bit around that time. But I didn’t touch the left stick at all at this point of time.