Problems with Altitude Hold and Barometer

I have problems getting my quad to hold altitude in altitude hold mode and loiter mode.

Once I put it in altitude hold mode or loiter mode it gradually starts to oscillate up and down. I have to turn to stabilize mode to gain control again. The oscillation build up to a movement of several meters at a frequency of around 1/2 Hz.

It flies well in stabilize mode. I’ve have tried a wide range of PID settings, and it becomes less of a problem if I dramatically reduce PID settings for altitude hold, throttle rate and throttle accel. But at these very low levels there is hardly any altitude hold.

I’ve checked for vibrations and they are within the recommended levels.

Here is a log showing GPS altitude and barometric altitude:

As you can see there are some error messages from the barometer sensor, but I’m not sure how to interpret this.

I have foam above the sensor to dampen effects from prop wash. (Perhaps I need more)

The quad has large slow rotating props. 17x5.5. AUW is around 1.8 kg, 4S 12Ah batteries. IronMan 650 frame. RC timer 5010 motors (360 kv)

Anyone with tips on what I should investigate further?



Could you please upload the log?

I’ve recently upgraded to RPi 2 and set up everything again. It works great now. I think my PID settings were simply way off. Thanks.