Recently the chassis for the little robot arrived. We put it together, with my son (he screwed all the nuts by himself, after I showed him, how to do it). It looks like this:
Because I want a perfect cube for the robot, I will have to "trim" the acrylic chassis. Now, it's length is some 20cm, and width, at the wheels, 17cm. It means that I will cut some 3cm off of the chassis. It is much bigger, than I expected, so probably it won't run nicely with a one 18650 battery. But, this will be the job for the testing. I will probably wire up an ESP8266 with the motor driver, install Blynk on it, to test it, and to have my son playing with it, until I need it for the assembly.