What is the consensus on the positioning of the Magnetometer, soldered directly to the IMU using pins or separate form the IMU with the modified GPS cable? What are the pros and cons to each. I'm assuming placing directly on the IMU was considered in the design since I do not see any significant power traces which would influence the magnetometer. However, wanted to solicit some advice from the group.
Soldering it directly onto the top of the APM does work and it's pretty in that it doesn't require any dangling wires. The downside to doing this is that it's difficult to remove it later. Mounting it this way will also lead to larger offsets when you do calibration because the compass is so close to the rest of the APM and they produce some magnetic field...but as long as you do the calibration this doesn't have any impact on the reliability of the heading.
For me presonally, on my quad I have it mounted separately on the 2nd level from the top (i.e. one level below the GPS, one level above the APM). I mount it with components up and pins forward. On my Trext450 heli I have it mounted on the tail close to where the tail meets the body.
One last thing - I expect that on some future version of the oilpan we will have the mag right on the oilpan.