Patent ID: 7188568

Claim:
A self-propelled vehicle for movement within a tubular member comprising: a core element; propulsion mechanisms distributed about a perimeter of said core element, each of said propulsion mechanisms including: a drive belt having an outer side and an inner side; a drive pulley encompassed by said drive belt for engaging said inner side of said drive belt; a driven pulley encompassed by said drive belt for engaging said inner side of said drive belt, said drive belt extending longitudinally between said driven pulley and said drive pulley; and means, encompassed by said drive belt, for providing outwardly-directed force to an underlying portion of said drive belt to press said outer side of said drive belt against an inner wall of said tubular member, said providing means comprising a spring loaded mid-roller assembly interposed between said drive pulley and said driven pulley, wherein: a first one of said propulsion mechanisms is located at a first position substantially above said core element; and a second one of said propulsion mechanisms is located at a second position substantially below said core element, and said mid-roller assembly of said second propulsion mechanism exhibits greater spring force than said mid-roller assembly of said first propulsion mechanism; and a motor arrangement in communication with said each of said propulsion mechanisms for actuating said drive pulley to rotate said drive belt in contact with said inner wall of said tubular member thereby moving said vehicle.