Positive traction system for vehicles

Claim 1

A GROUND TRAVERSING VEHICLE COMPRISING A FIRST FRONT CHASSIS SECTION AND A SECOND REAR CHASSIS SECTION PIVOTED TOGETHER AT A CENTER JOINT FOR LIMITED RELATIVE ROTATION IN A HORIZONTAL PLANE ABOUT A VERTICAL AXIS AND FOR LIMITED RELATIVE ROTATION ABOUT A LONGITUDINALLY ALIGNED HORIZONTAL AXIS BUT RESTRAINED AGAINST RELATIVE ROTATION ABOUT A TRANSVERSE HORIZONTAL AXIS, WHEELS CARRIED BY EACH CHASSIS SECTION AND MOUNTED FOR ROTATION ABOUT AXES TRANSVERSE TO THE LONGITUDINALLY ALIGNED HORISONTAL AXIS TO MAINTAIN THE VEHICLE UPON THE GROUND TO BE TRAVERSED, MEANS ASSOCIATED WITH AT LEAST ONE CHASSIS SECTION AND COMPRISING ELEMENT HAVING A GROUND ENGAGING PORTION WHICH IS VERTICALLY MOVABLE INTO AND OUT OF ENGAGEMENT WITH THE GROUND THROUGH THE AXIS OF THE ADJACENT WHEEL CARRIED BY THE CHASSIS SECTION TO SELECTIVELY FIX ONE OF AT LEAST TWO POINTS EQUALLY SPACED FROM THE LONGITUDINALLY ALIGNED HORIZONTAL AXIS AND EQUALLY SPACED FROM THE CENTER JOINT ON OPPOSITE SIDES OF THE SAID AT LEAST ONE CHASSIS SECTION RELATIVE TO THE GROUND TO BE TRAVERSED, AND MEANS TO ARTICULATE THE VEHICLE ABOUT ITS CENTER JOINT FOR THE OTHER OF SAID TWO POINTS TO MOVE IN AN ARC ABOUT THE SAID ONE POINT.