[AustinSchuh]

When you say it doesn't turn, what are the symptoms? Do the motors stall? Do the wheels spin? Is your battery voltage above 10 volts or so when trying to turn?

Also, it might help if you provided a picture of your robot so we can look for potentially other problems.

Last time I ran the numbers, 6 ft/sec with 4 CIMS and roughtop (I think I used a coefficient of friction of 1.5) should be able to spin tires while drawing only about 40 amps per motor. We've also used 6wd long for a couple years, with a dropped center wheel, and not had trouble turning. So, I'm having trouble visualizing what's going wrong with your setup.