[Pat Fairbank]

We actually geared our vertical wheels to not give the ball any backspin at all, figuring that the varying condition of the surfaces of the balls would make their trajectories more unpredictable with a large amount of spin.

The reason our wheels were vertical is to allow the ball a greater time of contact with the lower wheel, something that we discovered was needed in 2002 to accelerate the (much heavier) balls sufficiently. We didn't see any good reasons to stray from that general design in 2006.