[Al Skierkiewicz]

Peter,
Dual wheeled crab might not buy you much. One of the disadvantages of crab is that the wheels can no longer be near the outside edge of the robot frame. You sacrifice stability for manueverability. In order to make a two wheel module the turning radius of each module would bring the wheels even closer to the center of the robot. If this fits with your design goals then give it a try.
I always need to add here that teams should try new things but with a caveat. Don't dedicate yourself to crab drive for your next season. You don't know if crab will be a good choice for the game. We don't make that decision until our brain storming sessions show that crab will have an advantage.

Martin,
The advantage to crab is not lost if a tank style drive can turn faster. Crab allows you to change direction without changing orientation. If you need to move sideways and keep an actuator pointed forward then crab will allow that while tank will need two turns to accomplish the same thing.