Turning with 4 kit wheels

[Racer26]

Skid steering is actually quite different from differentials in cars.

The problem has more to do with a high lateral coefficient of friction between the carpet and your wheels (meaning how hard is it to push the wheels across the carpet perpendicular to the wheels plane of rotation). A high lateral coefficient of friction, plus a wheelbase that is longer than its track width makes for a robot that doesn't turn.

Building a long orientation bot with 6wd, dropping the center set of wheels by 1/8" has the effect of creating two stable 4wd configurations with a short wheelbase.

[cmrnpizzo14]

This white paper covers what you want to know pretty thoroughly.