While I was chasing some Motor Drivers, I ran across Pololu's balancing robot.
They have a video showing that it can stand up.
You buy the motors and wheels separately and they recommend a 80 x 10mm wheel
There are three motors and then there are 5 different ratios in the geabox
Perhaps the most annoying part is not knowing which is the best option.
Surely stability is better with X and higher speed with some stability is better with Y.
The Assembly went relatively well.
I would suggest tinning the motor connections before getting them anywhere near the control board.
There are a few SMD IC's right below the brush connections, and one solder blob is all it takes ....
I did have issues with the bearings and shafts.
Some of the bearings slide over the shaft, and others were so tight they required some persuasion.
So I would trial fit and juggle where to fit the tight bearings.
The assembly is not something that you could give to a small child without the possibility of damaging something.
There are various parts that would suit them, and others that are just too delicate.
The Controller is based on an ATmega32U4 and the board includes the motor drivers, quadrature detectors, and various other interfaces.
It includes a LSM6DS33 gyro and accelerometer as well as a LIS3MDL 3 axis magnetometer.
They make the comment in the notes about interference and reference the forum on a solution.
A Raspberry Pi header is provided and the 5v regulator capable of supplying 2A powers the RPi.
The integrated level converters allow connection to the I2C on the RPi.
They have even provided an 4096 byte ID EEPROM that connects to the Pi ID_SD and ID_SC pins.
I can see the Pi Zero being put to use later maybe.
They provide some nifty arms to help prevent damage.
They are adjustable for angles, which is interesting given that it seems to be able to stand up from horizontal.
So for now that's about it.
I'm not sure what it will get used for.
I am going to chase down an 8x2 LCD as it should provide some useful feedback.
In theory this could be included in the Open Arduino ... but that is hardly fair.