Steel excavator build

[Rimrock]

It's practical to build the 'engine house' cover as 1 big piece, that is easily removable for good access. One can have separate smaller hatches/doors in the main cover.
Track sprocket wheels should run about 30-40 rpm. Superstructure to rotate about 10 rpm.
Looking at your sketch, I would maybe get some more clearance between the tracks and the bottom of 'engine house'/superstructure, like double it?