Compensating for the mismatch between motor shaft diameter and the propeller hole flummoxed the designers of the Mesh Network Propeller Beanie used for a popular Design West 2013 Speed Training Workshop.
Realize that anything mechanical once one gets to the sub-atomic level is mostly empty space, and the color of an object is the response to light to the object's electromagnetic fields that help old the electrons in place with the nucleus -- it is what in part gives all these different properties like conductivity and dielectric constant and modulus of elastisity, and tensile strength in part to materials
This article totally speaks to me. I seem to manage some level of competence with MCU hardware, software, schematic design and layout. My head does a pretty good job of envisioning what the mechanical components should look like and how they should operate. But, when it comes time to build mechanical things, I tend to struggle. It seems like it shouldn't be that big of a deal, but it is.