I took the Nano controller that I used with the small train from my SuperRobot and just reconnected it to the battery and DC motors on my DCMotorMobot. This is all connected outside the 3D printed shell so is just dragged or pushed along but I wanted to make sure that the motor driver H bridge PCB that I was using would work with these motors, as it didn't work very well with my SuperRobot. As you can see from the video below, it all worked fine.
I have purchased some Arduino Nano's without the connector pins installed which arrived very quickly so that it will fit into the base compartment of my robot chassis, along with a dual DC motor driver PCB. Unfortunately, at present, the Nano will not upload a programme. I'm not sure why as I have a driver for the CH340 installed and I have selected Nano so it should work. I'll have another look at this sometime tomorrow or later.