What systems are you guys flying? What type of GPS chip? Where is the Magnetometer located?
I'll tell you, we've been ALLL over this on DIYDrones. Been up and down the block many times. End of the day only 2 things seem to really work: Reducing the creation of the field in the first place. And distance. And of course this is all assuming that you have a good magnetic field calibration code.
First off, braided shield will do nothing for you. EMF shielding does almost nothing to stop magnetic field lines. Second, the high frequency field is not the problem for the magnetometer if that's what you're concerned about. The field from the motor wires is a completely reversing sinusoidal form, so it has no net effect on the magnetometer. It's just noise. What you really need to concern yourself with is static fields. Those come mostly from the DC power wires, and the battery itself. You can't do much about the battery, but twisting the DC power wires helps a lot.
I worked on this stuff for so long, because the yaw of my heli with Arducopter was so bad, I assumed it was the mag field. Turns out it was just that the yaw control code was rubbish until I fixed it in June. Then the GPS position hold was no good, and that was largely due to the MedaiTek GPS which just didn't work well. With the Ublox, much better.
But in the meantime, we tried everything to block mag fields. What you really need to be looking at is MuMetal. It blocks magnetic fields. We tried all sorts of things using MuMetal foil under the board, etc. But the only time we could block mag fields from affecting the compass heading, we also blocked earth's magnetic field. So that doesn't work either.
At the end of the day, there's a reason why DJI place the GPS and Mag on a puck up on a stick.
Another part of this is the calibration code in your program. We used to have just the simple static calibration. Same as everyone else. But then developed an in-flight calibration that works much better. It actually uses the power of a PC to do it. You fly around, it collects data, then after you land you have the PC calculate the offsets. Upload and save them, done. Seems to work much better.
The reason you need to do it in-flight, is that it takes into account all the fields going on in your airframe. You don't get that with a ground based calibration.
Now as for this wiring stuff... I work at a wire manufacturer. I've been looking to see if there is an opening for a product for this market, but haven't really seen anything. Unfortunately, I can't produce high strand count, silicone insulated wire, we mostly do industrial. But if I could get spools of the stuff, I could run it through a cabler, do shielding, braiding, custom jacketing, etc. But as I say, I just haven't really seen any need or demand.
