The motor and controller were a professional unit which we rented. The motor was built into a box (which we bolted to the floor) with a rubber wheel about 12 inches in diameter which ran against the outside of the 2 x 8's. There was an adjustable spring which kept the wheel in tight contact with the wooden surface.

Thanks for this! Where did you get the bearing?

Those were relatively inexpensive ones from Harbor Freight, as I remember, they were a hard plastic with a rubber tread. One of the neat tricks about this design is that with the wheels mounted upside down, they roll against the wooden deck. This is a smoother surface than the floor, quieter as well.