pic: Coaxial Swerve drive, lightened.

[Joe_Widen]

You could try using Al tubing and be crafty with the cnc mill. It would have zero bolts (...gasp....). Thats how im designing mine atleast. No fancy stuff, no coaxial, just plain old spur gears and motor mounted on each module. Fancy gears are not my friend, especially after using worm gears (a thousand and one to many headaches there), although, I think helical gears are crazy cool. Good Luck to ya.