"Three Wheeler"

[E_puello]

If you have a 4 wheel drive with traction wheels at the front and omni wheels at the back you will get the effect of pivoting at the front of the robot with none of the headaches of having a caster ie. (reversing direction leads to unpredictable movements)

[droswell]

Just don't use castors (except maybe a ball castor).

Seriously, they wreak havoc when trying to line up or make small turning adjustments.

[wesbass23]

One of the biggest things (in my opinion) when deciding your drive train for the year is how well will your driver be able to drive with the chosen drive train? Always make sure they get plenty of practice, even if it is just with a drive base.