If i understand what your asking correctly i think your talking about a holonomic drive which looks like
this
except on FRC not vex, which i believe can be done with the Andy mark trick wheels. they do more or less the same thing as mechanum wheels except with different methods, the only differences in function being that they are A) much easier to find and buy but are B) a possible disadvantage in this years game due to the issue of getting up the ramp with them(if i remember properly their was a thread on this issue) an issues that doesn't exist with mechanums.
my understanding of the basic idea behind them is that just like with mechanums they are designed to slip at certain angles which allows for lateral and diagonal movement of the robot. In actuality you are only pushing in the diagonal direction with a pair of wheels but the slip created by those rollers on them allows this to be converted into other directions