[EricH]

I've never seen that on an FRC robot, but I have seen blocks of multiple mecanums working together.

However, I suspect that you won't see improved traction. Mecanum rollers don't really get down to microscale interactions like treaded wheels, so I suspect that while a doubled traction wheel will show an increase in traction due to "interesting" stuff happening where we can't see, a doubled mecanum probably won't.

If I might make a suggestion, search for "octocanum" here on Chief Delphi, and see if you think it will work. Octocanum pairs each mecanum wheel with a traction wheel and switches wheels depending on whether traction or maneuverability is desired.