Okay. . . here's what I've designed for, so I hope it'll work -
The motors are driving the wheels via a 3/8" pitch roller chain around a 40 tooth sprocket. That's the purple disc in the picture.
Toward the outer edge of the 'bot, there's a 7.132" dia. boreless timing pulley (the green thing) that's made of cast iron. On the inside are 2" thick polycarbonate wheels that'll be made of several pieces bolted together.
The shaft is 1/2" dia., but isn't used to drive the wheels. It exist solely as a surface for the wheels to rotate upon. Since the timing pulley "bore" is 2.188" in diameter, we'll machine a bearing from Delrin rod to occupy the space between the shaft and the timing pulley.
Instead of driving the shaft, I plan on letting it idle and putting clearance holes through the polycarbonate wheels and sprocket, and tapping 3/4" through the 1" width of the timing pulley. Then, we'll use 1/4 - 20 threaded rod to tie it all together with appropriate spacing. There are 8 rods around the circumference of the the wheels and sprocket. So, essentially, when the sprocket spins around the shaft, the threaded rod will spin everything else since it's all attached.
This is my first drivetrain, and it's practice for us, but we'd love to be able to use this design in January. . . both because it'll save us a lot of time, and it's cool :-)
But, if anyone can see something that'll surely make this shatter into a million pieces, I'd really appreciate it if you'd share it with me.
Thanks!