You need to be somewhat judicious in selecting motor ports for the functions of your robot.
The cortex has 2 PTC (circuit breakers) - ports 1-5 and ports 6-10. You can divide your motors between these two halves and split the load.
If you have a power expander, that has its own PTC for its 4 ports that it powers. The expander uses its own power lines rather than the power lines in the cortex, thus further freeing the cortex. The expander only uses the signal lines from the cortex.
So, in total, you have 3 PTCs that can each support 4 amps of current. You need to divide your loads across these ports/PTCs so none are overloaded.
We have had many discussions with the girls on motors and power this year. After these discussions and testing, they divided up the heavy load motors across the 3 total PTCs in the system. This is how we have things mapped right now (I think):
Cortex ports 1, 2,3 are connected to motors and can support a total of 4 amps across those ports with its PTC. If memory serves, they have the left side drive motors on ports 2 and 3. Port 1 is for another function.
cortex ports 4, 5, 6, 7 all go to an expander for other functions and can support a total of 4 amps on the epander PTC. I think our shooter is here with 2 of those motors (high torque from rubber bands, but short duration). and the other 2 are for other functions
Cortex ports 8, 9, 10 are connected to motors and can support a total of 4 amps across those ports with the second cortex PTC. I believe ports 8 and 9 are the right side drive motors.
The girls created a mapping sheet showing a cortex in the center of the page and sections around the perimeter for motors, analog io, digital IO and such (picture attached). They keep this updated and in their engineering notebook for reference when explaining how the robot is programmed and to make sure they reconnect things correctly after rebulids.
Hope this helps.