Alright, so I will connect the H-Bridges to the Arduino, and the batteries and motors to the H-Bridge?
Great! This is more information than I have found anywhere. Thanks a lot!
Also - you may want to rethink just driving two wheels on a side - you'll likely have much better luck running all three wheels at once on a side...
Not sure how to make the H-Bridge, though. Buy it. H-bridge controllers are widely available and reasonably priced.Make sure you leave headroom on the voltage and current specs.