I really appreciate posts like this as they entice my curiosity. I work at a tech company in a non-technical role which is perfect for my lack of attention span. My ADD sym/asym research tells me that symmetrical motors work well at low rpm and disadvantage in cost. Both of these are barriers to entry in rc. For a given voltage and current, rpm increasing as load decreases is a desirable quality which aids driveability.

Eddy currents and "magnetic" aluminum. Our equipment uses this principle to enhance accuracy. A really cool experiment to see how it works is to drop a magnet down an aluminum tube. Since aluminum is NOT magnetic, it won't stick to the side. It IS however conductive. Just like passing a magnet past a copper coil which creates electricity, the magnet falling through the tube acts like a coil creating a current and therefore, a magnetic field. The field attempts to hold the magnet in place which slows the falling magnet to a speed limited by the efficiency of the tube's conductivity. It's a bit trippy.

And on AL screws... The benefit is that they do not have a static effect on the magnetic field like steel. Since steel is also conductive they have both a static and dynamic effect on the field, albiet less dynamic since it's less conductive than AL. The truth is in the numbers though. Motors turn more rpm with non-magnetic hardware. The hall sensor accuracy (which we measure in asymmetry) also increases with non-magnetic hardware. Stainless or TI would be better than AL. Find me a non-magnetic and non-conductive screw and I'll pay big dollars for them.