Test-drove the robot last weekend with all equipment mounted and it was not great.
The wheeled base currently has two large wheels and a smaller caster in front that swivels freely (not motorized). The front wheel lets the whole system balance while letting the two primary wheels drive (rotate in the same direction) and turn (rotate in opposite directions). Great, right?
Unfortunately, the caster wheel that came with the base is deformable (squishes under pressure), has a really wide tire, and is high friction.
This means that when the robot tries to turn, the caster tries to rotate, but can't. It often gets caught in a bad position (see below) and the robot applies more power than it needs to in order to drive straight again. After enough build-up, the robot lurches forward and accelerates much faster than I designed the equipment to handle, so the whole robot wobbles a lot. Gah!
So why not replace the fancy tire with $10 office chair wheels? They have a much smaller radius, which lets them swivel easily, and they're much more slippery on carpet.
Some construction pictures (after milling blocks of aluminum, drilling holes, and tapping them):
And a video of the whole thing twirling with very small turn radius carrying a 200-pound load (comes out to about 50 pounds a caster). Silky smooth!