Robot base

What is considered the robot base? Is it the 4 wheels with the motors attached or would it include any extensions with small wheels attached to the extensions without ant motor?

The definition of the mobile robotic base that makes up Subsystem 1, can be found in the VEX IQ Challenge Highrise Game Appendix. It is as follows

So any extensions with wheels that that are used to help the robot move about the field would be considered part of the mobile robotic base for the purposes of <R2>