Holonomic Drive

[kresty]

If you look closely, you'll see a bar running across the middle of the bottom with a couple blocks.  I couldn't figure out why a block and bar was just sitting there, but figured it had to do something:

Underside of Sentry Droid

So, I asked The bar is for uneven floors, apparently it is so that each pair of omnis on the sides can pivot so that all 4 wheels might stay in contact on slightly uneven surfaces!