Bad Compass effecting roll output?

I am using the 3DR uBlox GPS with Compass Kit and the 3DR Pixhawk. I have had some pretty bad crashes lately,
After a rebuil, I was testing the 3DR X4 by running an Auto mission flying a simple box. I noticed that the quad was yawing to the left at about a full rotation about every 5 sec. After landing I switch to loiter mode to test the stability and yaw. The quad took off backwards and to the left (crashed hard). I put it back together, and the same think happened several times ( no as violent). I isolated the problem to the compass/accelerometers. I isolated the pixhawk and the GPS/Compass kit, and did a simple test by pitching the two forward ( see picture). The yaw kept rotating and the roll kept moving between ±20 deg. You can see this in the tlog by graphing the roll, pitch, yaw (2014-07-27 17-28-56.tlog). I then used just the pixhawk with no GPS/Compass kit. everythink looked correct (2014-07-27 17-43-34.tlog).

It looks to my inexperienced mind that something is wrong with the GPS/Compass kit, and it is somehow effecting the roll values (this doesn’t make sense). Before I have to buy a new GPS/compass kit, or a new Pixhawk, could someone take a look at this and share some experience.


have you performed a completely new calibration and setup of both the compass and the IMU ? If not do that first and then check.

Yes, I’ve done several new calibrations of both the compass and accelerometrs.