WOW! That was interesting!

I just finished my strobe modification and went outside to fly.  I thought I'd be extra careful and at least try to calibrate the compass.  After all, I had the quad taken apart completely, taking pictures of the PX4 board and USB connections.

It went together mostly as expected but because I've added several new wires to the fuselage and some of that 20ms - 1A pulses for the new strobe lights, I was a bit cautious.

The quad started up normally and I chose PHLD (Position hold) with 15 satellites as I've had 75 successful flights prior to this mod so I thought everything would be ok.  Still, I was being cautious.

A raised the quad to 2 meters and watched it's position holding ability, which promptly stopped working, if it ever started.  There was no appreciable wind but the quad didn't hold position at all.  From experience, I switched to Altitude hold mode to disengage the GPS and attempted to land the thing.  It was everywhere and I was losing it quickly.  I wish I had a video  to review but it contacted the ground at a higher than normal rate of travel and flipped over.  Great!  Now my precious UPair One is chewing up the gravel in my driveway, inverted, and it won't shut off!  I have to pick it up and humiliatingly shut it off with the battery power switch!

What happened?...

Truthfully, I'm not sure.  I took it back into the shop and inspected the propellers (they were chewed up from the gravel in the driveway),  I tried to do an ESC reset as Olaf at DfL talks about, but it didn't work on my PX4 board.  

Well, I degaussed it again using my 40 year old home made degaussing coil. After sanding off all of the huge gouges on my props from the driveway, I tried flying again.

It worked!..It just worked!

I started the motors and they idled as expected.  I gave it throttle and it rose 2 meters and stopped climbing as I expected.  I reached out to hold it and made sure  it couldn't fly away.  Almost reassuredly, it hovered where it should.

I don't know if this is truly the degaussing working, but it seems to.

After further research, it appears that this degaussing question has come up alot on drone forums.  In this DJI forum, there is considerable questioning about how to do this and what tools to use.  Based upon my experience degaussing television picture tubes in a previous occupation, I'll write up my recommendations about how to do this.