[Tom I]

Very logical assumption and good observation! however, in a previous thread discussing the same design, it was revealed that the chains tie into a ball differential for the center Omniwheel... this way if the robot is going forwards or back, the chains are going in the same direction, and the Omniwheel will roll. If they are strafing, then the chains will be going in opposite directions, canceling each other out, so the sprockets will free-spin and the Omniwheel will not turn. If it is going at an angle, the Omniwheel will move slightly back or front.

While I am having a little trouble understanding how the ball differential physically looks, I LOVE this idea! Well done!