The UART port has been used to control the Bluetooth device. So the Gertbot will not work as a addon board. To resolve this you must complete two steps:
Using sudo nano - add to the /boot/config.txt file: dtoverlay=pi3-disable-bt enable_uart=1
Using sudo nano - remove "console=serial0,115200 console=tty1" from the /boot/cmdline.txt file
Now you can install the Gertbot GUI for testing the board. The picture above shows the board wired to 4 brushed motors and two 9 volt batteries.
You can also control the Gertbot with a simple python program.