The Gertbot is a daughter board and I decided to use the Raspberry Pi 3 instead of the Raspberry Pi 2. I am using the Stretch image. 

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.

I  downloaded Gertbot Debug GUI (.tgz) from here. This is a executable for the Raspberry Pi. I used FileZilla to transfer the file to the Raspberry Pi.

You can also control the Gertbot with a simple python program.