Hamza N. Meo analyses Leonardo da Vinci's tank, pointing out the flaws in the design and fixing them. I found it fascinating to watch - both to learn more about the original visionary design, but also to see the general engineering principles.
Hamza describes himself as "A medical doctor and a 3D artist, concocting a potent .blend of arcane knowledge for your creative quests (basically tutorials and my musings)". That's a highly unusual but super interesting combination :)
