Hey people!
We’ve assembled our little prototype now along with a smaller C-1 Chaser based version of it to test forward flight and because its awesome 
We are encountering a lot of compass variance, which we believe is due to the power cables being just above the cube in the fuselage. We tested this by putting our phones in the fuselage and indeed it was turning the compass by up to 20 degrees. We have a second external compass, a here2 module, mounted in the front of the fuselage. We measured here as well and did not get any compass interference.
We tried to force the software to use the external compass and NOT to use the internal one but we simple couldn’t figure it out.
So to summarize; we have a problem with magnetic interference from the power cables.
Any tips and ideas for solving this are most welcome and will be tested!