While I have to say that, that is an amazing ball caster your sporting there it seems like it would have been a lot less work to get one of these:
Just a thought…
How does it handle, it looks like it would be really squirly and turn way too fast to be easily controlled. Then again that just my experience with two wheeled bots.
On Carpet those are champ. On pavement & sidewalks & other surfaces those are very unhappy.