Toilet Bowl, GPS Estimation Problem

I have a hexacopter drone that has a diagonal wheelbase of 2.4 meters (propellers included).

In the first log below, it is a sudden and approximately 20 meters of shifting in the estimated position. While this happened, I was flying in position mode, so GPS was in use.

As you might realize, I’m also experiencing the toilet bowl effect in position mode. I made two test flights after tuning PIDs, drone hovers, and responds to my comments nice and accurately on altitude mode. However, when I switch to the position mode, it starts to rotate in growing circles. As you might guess this is pretty dangerous for a drone this size.

I’m thinking that this behavior is because of the GPS, I’m using Here3 as GPS and Pixhawk OrangeCube as flight controller. I will supply the logs of 2 test flights.


I suspect the position of the GPS. I am guessing that my GPS is interfering with the power lines below it. Also, it is pretty close to the OrangeCube. Do you think that this can cause the issue? Also, I have read that this also can happen because of the wrong heading angle of the GPS unit. But I have checked the orientation of the unit and it was looking correct. Please help if you have any suggestions.

Not an expert - hopefully someone will be able to look at your logs.

But … toilet bowling is commonly caused by compass issues, including having the compass too close to power lines, or a mis-calibration: Compass Calibration | PX4 User Guide
If calibration does not fix your issue, you can see the example in this doc Compass Power Compensation | PX4 User Guide to verify whether being too close to power might be the problem - e.g. if thrust and compass readings correlated.

Another main cause of toilet bowling is an untrusted position estimation. That’s not loss of GPS, but a mismatch between what GPS says is happening with your position and what the IMU says is happening with your position. That is most commonly caused by excessive vibration.
You can do a quick check in the QGC Analyze > Vibration screen - if when it is toilet bowling you see the vibration above the red line in the image below you would know vibration is a likely problem.

And of course there is this handy guide for log review: Log Analysis using Flight Review | PX4 User Guide