Swerve Drive

[Al Skierkiewicz]

Ether,
Crab mode robots have the potential for changing robot orientation with respect to the field with a simple descending foot that lifts two wheels off the floor and allows the drivers to move one side of the robot (Wildstang 2003). Another method is to jump to a software routine that allows the robot to drive in "tank" mode to change orientation and jump back to crab mode when the driver is satisfied with the orientation. In rare cases designers have allowed two steering motors (connected to opposite sides of the robot drives) to change the turning radius of the robot (Wildstang 2007). This allows changing the orientation over a greater distance but still accomplishes a design with the advantages of crab for other parts of the game.
Personally, I find the terms "crab" and "swerve" interchangeable. If I was asked to make a distinction I would be inclined to call drives where the wheels rotate 180 degrees or less "swerve". Drives that turn up to 360 degrees "crab" and drives that turn greater than 360 degrees "continuous crab". Drives that are any of these where one set of wheels turns independently of the others can use the modifier "steerable" e.g. "steerable crab". As Joe has pointed out above (possibly the first to use a crab drive in First) each system has distinct advantages and disadvantages.
How you use the drive or implement the design can have a huge impact on the drivers and how the game is played. Crab will not win the game all by itself. If it takes your drivers a lot of time thinking where to go and how to get there, you will lose precious seconds you could be scoring.