The lion kingdom discovered RC with a zip zap micro toy someone brought into the day job.  It could almost go the length of a hallway on a charge, some 350ft based on a goog earth photo of the building.  It was quite addictive to discover how far something that small could be made to go.  Then came the even more addictive picco Z in 2006.  The addiction to that was from achieving the most stable flight with the least controls.

Something about the micro toys seemed addictive in ways none of the larger vehicles were.  It might have been trying to get the maximum ratio of range to size.  Lions just outgrew the toy problem & transitioned to using RC parts to solve bigger problems after 2006.  Then there was a home made toy that was self propelled but not RC.

The whole thing got lions pondering what the smallest possible RC thing would be.  Below a certain size, wheels aren't practical & solenoid driven jumping becomes more practical.  Habayusa 2 used hopping rovers.  It takes lions back to the photovore craze.   The minimum system would be a big solenoid actuator & a weight shift mechanism. 

The free flight craze came along & revealed the minimum solenoid actuator.  There was no practical linear actuator.  3D printing made these infinitely easier to make.  There could be 2 rotating actuators forming a linear motion but it would be big. 

Suspect the material that it travels on is just going to be limited by the size & it's just going to be 2 big solenoid plungers for motion, a battery, & a brain. 

It's a pretty tough problem, since you're trying to create the most reaction force in the smallest space.  Early biological machines used thousands of hairs. 

https://www.newsdirectory3.com/japans-first-lunar-rover-to-be-sold-to-the-public/

This might be the smallest moving thing currently made. 

It's got the full phone app, camera, collapsing ability but something that just drives around could be a couple pager motors.  A good old commutator is still smaller than a solid state motor controller.