I have had a few instances of compass errors when trying to fly the Phantom 3 quadcopter. I have always been able to calibrate the compass and launch the aircraft quickly. Not this time.
After about eight tries, re-starting the Phantom, updating the battery firmware, moving calibration locations, and everything else of which I could think, the compass still would not calibrate. The DJI Go app even gave up, telling me that I should contact DJI support.
Online research found a number of similar problems for the Phantom 2 posted in 2013. Besides the normal procedure, I read advice to check the wires to the compass from the body of the Phantom.
The other possible solution described, which worked some times, was circling a small magnet around the compass module in the lower left leg. I could not find any mention of using this “magnet trick”, as it was called in the Phantom 2 posts, to fix stubborn calibration problems in the Phantom 3. There are many other users of the Phantom 3 who posted descriptions of similar compass problems to mine. I had used a magnetic screwdriver near the legs of the Phantom, which may have caused the error.
According to P3groundschool.com/pilot/compass-calibration, “The Phantom compass is located on the rear lower left leg as you look at the aircraft from the front.” It was the only leg with more than the single antenna wire coming out of the body.
I used a magnetic nut driver from my tool chest and rotated it around the compass module about three times, passing it through the landing skid opening, from one to two inches away from the leg. I took the Phantom outside and began the calibration procedure, keeping it away from the DJI controller. Frankly, I didn’t have a lot of hope for success. I could not see the screen. I rotated the Phantom three times on both axes and set it on the ground. I returned to the controller and checked the Go app. The Phantom was ready to fly in GPS mode, no further compass calibration required, after 30 seconds and one application of the magnet.