Swerve drive 4, 2+2?

[J_Greco]

I would definitely go with a 2+2 steering style as opposed to all wheels steered dependently. Our team used a swerve style drivetrain this year, and we used a effective 2+2 system. One disadvantage to the dependent steering is that it makes changing the orientation of the robot very difficult. If you want to have a tank steer mode, you must make sure that the treads on your wheels have a low coefficient of friction. Even with the 2+2 steer this is a problem we encountered this year. In fact, we had to change our treads between the Pittsburgh and Boston regionals in order to allow our tank steer mode to work (even though we never actually used it in competition). The 2+2 steer was effective for Overdrive because we had a variety of useful steering modes.
1. Front steering (for normal "car" style drive)
2. All wheel steering (for very tight turns. This was useful when coming around the center divider)
3. Swerve steering (for translating sideways without changing the orientation of the robot relative to the field)
4. Tank steering (the standard form of steering)

With a system where all wheels are steered together, you only get steering mode number 3. Unquestionably there are great advantages to choosing 2+2. We did encounter problems, however. The robot could not drive straight because the potentiometers did not provide a high enough resolution to make the robot align the wheels perfectly opposite to one another. We are going to experiment with a gyroscope in order to rectify this.
One option I would not leave out of the equation is steering each wheel independently. This would eliminate the need for tank steer and provides almost limitless potential for the robot's performance. We plan to do something like this next year.
Another thing to keep in mind is the location of your powertrain. If you have a centrally located powertrain, you can save weight and add a multi-speed transmission (another thing we plan to do next year). Otherwise you could mount the motor vertically and use beveled gears. We chose to do a direct drive style this year (you can see our hinged bumpers, they pop up every time we go into 4-wheel or swerve mode) this does tend to leave the motors exposed, however.
Obvioulsy there are other things that must be considered when choosing a drivetrain, but these are some of the basics. It is something into which ALARM puts much thought and energy.