First I want to discuss steering.

FreeRover has front wheel drive. Each of the two wheels is driven by a physically independent motor. The car has rack and pinion steering, steering is driven by a third NXT motor. Rack and pinion steering means that each wheel rotates around a different axis. Also, this gives the car a fixed wheel base, therefore it is very stable. In corners, the inner wheel rotates more slowly than the outer wheel. So the motors that drive the front wheels have to turn at different speeds. How much different? That can be calculated with a little math. It does make the software rather complex. A good software design is critical. These three aspects, car design, math and software will each be discussed in later posts.