After finding the 4tronix RoboHat was not powerful enough for the motors we were using, we decided to switch to the PiBorg ThunderBorg
This would also leave more GPIO pins exposed for the kicker / shooter mechanism control - and anything else we may want to add.
Setting up the ThunderBorg was fairly straightforward - except that their provided python code only works in Python 2. Even using 2to3 to convert to Python 3 doesn't make it work because of some subtlety in the I2C messaging. (The code runs - but can't find any ThunderBorg boards on the I2C bus).
I found a Python 3 version at http://forum.piborg.org/downloads/thunderborg/ThunderBorg3.py.txt
This worked perfectly.