Creating a simplified rolling cart using the new Rigidboy in 2.66

I’ve seen tutorials for using the “hinge” constraint to make objects rotate around a pivot point.
Can it be used the same way to create a spinning wheel for a simple cart?
I’ve attached a simple test where wheels are constrained to a box and the “hinge” is at the center of the wheel but it does not rotate; therefore, the cart does not roll down the slope.
Does anyone know if this is possible using the “hinge” constraint?
Does anyone know a better way?

File link to simplified cart:

As far as I understand the hinge constraint hinges around the Z-axis. In your file, in front view rotate the empties 90 degrees so that the Z-direction is along the axle and it should work.

That worked. Thanks.