[jreneew2]

Hey there! Our team has run mecanums for a long time now and here are my recommendations:

Size: 6in wheels (nice in between size)
Vendor: Vex (they make really nice plastic wheels. We even had mecanums this year and didn't have have a single roller break ever. This included going over the Rock Wall full speed.)
Frame: modified kit chassis. We ran a modified kit chassis in 2014 and a modified version of that in 2015. You really want a square base for mecanums.
Gearbox: toughbox nano. These are really nice because they are easily moddable and easy to maintain. They also fit really nice on the kit chassis.