The designs of the main printed circuit board are available in the code repository. You will need Fritzing software to open them and export as whatever format is required for fabricating it.
Arduino Pro Mini is used for the brains of the robot. It is connected directly to the servo signals and to the battery. There is also a 1000µF electrolytic capacitor connected across the battery to avoid brown-outs. An optional voltage divider of two 47kΩ resistors, with a 47nF capacitor for noise reduction is used to monitor the battery voltage and shut down the robot when it drops too low. The battery is any light 1S, 3.7V LiPo cell. Other kinds of batteries can be used, as long as they are light enough and provide enough power. Remote control is done using a VS1838B infra-red sensor, but other sensors can be used.
Several pins of the Arduino are free, including the I²C pins, allowing for connecting more sensors.
The prototype also has an optional LiPo charging/protection module attached, for convenience, although the battery can be charged by any suitable charger.