Pictures of one of our demo bots
top view and
corner view. We are in the process of developing a full set of twelve robots out of the VEXPro parts (twelve different styles of drivetrains with interchangeable manipulators). Each robot is 20" x 20" for portability and ease of use in small-ish spaces.
The mecanum one pictured was a summer day camp project for an 8th-9th grade group. 4" VEXPro wheels with clamping gearboxes. I think they are 11:72, but might be 12:72. Runs just fine on both tile and carpet and has been durable enough for demo purposes (we haven't specifically tried to break it). If we hadn't scavenged the control board for another project I'd show off the nice LED underglow too.