[s_forbes]

Nice concept, I like it! Strong, simple, and easy to maintain... everything you need in a drivetrain. I especially like the use of stackerboxes as transmissions; using only one gear reduction and only one chain reduction should make it nice and efficient.

I'm not sure about the rectangluar crossmembers though... cutting the holes may be a bit challenging. Have you considered using round tubes at all? May make manufacturing easier.

Great design.