Top view, wheels straight. Each colour represents a different set of structural members, gray is chassis, red is input, green are connecting rods, blue are supporting arms, yellow are bearings.
Main view, wheels turned.
Top view, wheels turned. The multiple pivots connecting the wheels means that the point they rotate around is inside the wheel, not the chassis. This reduces friction with the ground when turning, and the amount of space the wheels take up because they don't need to swing back and forth as much.
Just an example of the calculation (calculation=pain) involved in building something like this in a CAD program. Too many angles. Blah.