[Nuttyman54]

Austin can give a more accurate answer than I, but I believe we are running a version of "Cheesy Drive"

At high speeds, your rate of turn is very sensitive to small disturbances in drive side speeds, so holding a good line with tank sticks gets increasingly difficult as your drive speed goes up. By letting the computer take care of the exact speeds and feeding the system a turning radius and speed, high speed control becomes much easier. It also allows you to scale the steering response based on your throttle level, although I don't know if we do that or not.

The quick-turn button allows a more traditional steering scheme for in-place turns. We've been using a steering wheel setup since 2006 and it's served us really well. It's just the wheel and a joystick for throttle control, as Jared surmised.