For my DCMotor Mobile Robot I have now 3D printed a small holder for the Nano and dual H bridge drive PCBs. I wanted to make this mobile robot as tidy and neat as I could so this is a good way of fixing in these two PCBs while at the same time making everything look neat. All it consists of is a flat plate that fits between the DC motor boxes in the bottom motor compartment of the mobile robot, which has the same spacing for the four holes so that it can be held securely with the existing screws. Then a small trough that is exactly the same length and width as the Nano and DC motor driver PCBs was added. Luckily the Nano and the motor driver PCB are exactly the same width which made things easier. I used PCBs without header pins soldered in as these would make it too high. The two PCBs fitted exactly and are held securely. The programming connector for the Nano just fits between the gap between the two side wheels. I did not design this it was just good fortune.
With everything fitted into the bottom compartment the rest of the mobile robot chassis can be re-installed and there is plenty (probably!) of space left in that bottom compartment for all the wires I will need to add. Fortunately there are not too many so I am hoping it will all fit together nicely. All that I need to do then is to connect the wires from the micro servo motor and LEDs/sensors that will be in the top dome into the bottom compartment and all the chassis and electronics will be finished. I will have to route these wires outside of the chassis as I cannot think of any way of routing them internally as the battery compartment gets in the way. Still, the head will only swing thorough an angle of 180 degrees so a small bunch of wires out of the back of the dome should not be too unsightly.
Then all that remains is to create some sort of useful programme.