The REV Hubs are the core control units of a FIRST Tech Challenge robot.
A REV Control Hub combines a REV Expansion Hub with an embedded Android daughterboard connected to it. This means it is able to control all of the hardware components of your robot and also run your actual robot software. This is in contrast to the REV Expansion Hub which was only able to control hardware devices but is not able to to interpret and run the SDK.
A REV Expansion Hub is a hub that is used to control all of the hardware components of your robot.
It takes the commands your Android Device sends and actually makes it happen. If you want to move a motor,
an Expansion Hub is what takes the instruction of moving the motor and actually sends power to the motor in the
correct manner. It however does not know when to do this which is where the Android Device comes into play. This device
can either be a traditional Android Phone connected via USB or just the embedded device in a Control Hub. When using
more than one hub, these hubs can be connected via
RS485 or USB. More information can be found