Self-propelled carriage suitable for moving in a cylindrical gallery

A self-propelled carriage suitable for moving in a gallery of substantially cylindrical shape that has no internal rail, the carriage comprising:

• a chassis comprising no more than two wheel sets, respectively a front set and a rear set;
• a skip;
• and
• a horizontal longitudinal support axis on which said skip is pivotally mounted in its length direction, each one of said two wheel sets being connected to a respective end of said support axis;
• each one of said two wheel sets comprising:
• two arms wherein each arm being a fixed length, a first end of each arm being pivotally mounted on one end of said support axis, said two arms lying in a common plane orthogonal to said support axis;
• means for maintaining the two arms at a constant angular separation;
• two rotary drive shafts, each drive shaft being pivotally mounted at a second end of the respective arm, said two drive shafts being orthogonal to said support axis;
• means for rotating said two drive shafts;
• and
• two wheels, each one of said two wheels comprising a hub secured to a corresponding rotary drive shaft, at least one circular disk secured to the hub such that the disk is perpendicular to the drive shaft, said disk having a periphery at which a plurality of rollers for co-operating with the cylindrical wall of said gallery, the two wheels of each of the two wheel sets being in sole contact with the cylindrical wall of the gallery, each roller being mounted to rotate freely about an axis that is orthogonal to the rotary drive shaft of the wheel.