[GeoffP]

if skid steering is used (2 left wheels in-line and driven 1 speed, 2 right wheels in-line and driven another speed), and the side robot is up against the wall where wheels on one side are on carpet and the wheels on the other are on the slippery field, then will the robot be able to away from the wall?another method would be flywheel steering where the one side is pushed up or down to turn the bot with the forces from the torque produced from trying to tilt the axis. that may not get you away from the wall either though.
i think articulated steering is necessary.