Each motor remembers which CLASS it has been assigned. You may have one motor assigned to FOCUS, and another assigned to ZOOM. Or, you may have two motors assigned to FOCUS.
You can easily change which CLASS a motor is assigned to. Enter the MENU on the Controller.
MENU - MOTORS - SET CLASS
Then select the SERIAL# of the motor you which to re-assign. (The serial number is laser etched onto the back of the motor body)
Once changed, the motor will immediately begin to respond to commands on its new Class.
The motor will remember its Class through power cycles.
After changing the motor class you might need to change the axis control. You can do this in the menu of the MK3.1 Controller. Example below,
MENU - INPUTS - AXIS - FOCUS - KNOB