The ultimate goal behind these tests was to determine the viability of a 3D-printed hub motor for a bicycle. The video starts with a brief explanation of how brushless DC motors are constructed, and why. For the purpose of this project, the most important characteristic was the electric steel stator. That material is important for generating a high torque at a low RPM.
Electrical steel sheet is hard to come by outside of industrial settings, and hobbyists are unlikely to get their hands on any for a reasonable price — and you’d have to be able to work the metal even if you did. So, GreatScott! 3D-printed his own stators from two different filament materials: standard PLA, and Proto-Pasta Magnetic Iron PLA, which is ferromagnetic.
During testing, he found that the standard BLDC motor had an inductance about seven times higher than the ferromagnetic 3D-printed motor. That, in turn, was about 25% higher than the standard PLA. That ultimately means that the 3D-printed versions have significantly less torque. They spin faster, but there isn’t much power behind that spin. In the end, GreatScott! decided that these 3D-printed motors aren’t practical for doing real work, but it’s still a fascinating lesson.