At home with just the kids, used the SBrick for a RC micro rover:
It’s very fragile but I’m certain it is possible to make it even smaller and sturdy, just a matter of time and skill.
[actualized on the next day]
A slightly better version witj less friction at the connection between the weels and the micro-motors. Also tried 3 CR2430 lithium batteries to supply 9 Volt. The batteries behave better than expected.
Almost out of nowhere I now have a table robot with great potential for Snap!
[new actualization]
Robot consumption with 3 fresh CR2430 batteries goes from 60 mA (moving forward) to 90 mA (rotating over itself).