My old Sante Fe engine quit, so I bought 3 NOS ones on line.  One is the F7 style with the heavy chassis, but has no rubber wheels.  The other ones are like my old one, and have rubber wheels.  The new one just sits and spins the wheels with no cars connected.  I don]t get it.  He offered to send me another new one of the same style, but has no rubber wheels either.  I don't understand how they run if they cannot get traction.  The other two new ones run great.