[EricH]

4WD often equals bouncy turns. It has to be done just right to eliminate that (usually omnis or casters, though the casters make it a 2WD). Almost the only easy way to eliminate this is to build a "wide" bot (the short side is front-to back), and then you have a tipping risk under normal driving. The most successful robot I have seen with 4 wheels is 69 in 2005. (At least, I remember them as having only 4.) They had very slick wheels, as I remember, so they slid a little bit.