Self-propelled vehicle for use in a conduit

A method of moving a conduit travelling vehicle, along a conduit, said method comprising the step of:

• with a conduit travelling vehicle, comprising
• an extensible body comprising a forward body portion and a rearward body portion,
• the forward body portion and the rearward body portion being separated by a powered telescoping connection of variable and controllable length, wherein the powered telescoping connection controllably alters a distance between said forward and rearward body portions;
• each of said forward body portion and rearward body portion including a wall-engaging mechanism;
• each wall engaging mechanism comprising a plurality of radially pivotable legs, each radially pivotable leg connected to one of said forward and rearward body portions at one end and having a wall-engaging foot at a distal end;
• for each wall engaging mechanism, all of the radially pivotable legs comprising wall engaging feet connecting to a common actuator, said common actuator controlling the radially extended position of said radially pivotable legs between retracted and extended positions;
• at least one of the wall engaging mechanism including at least one retractable wheel arrangement, said retractable wheel arrangement comprising a plurality of wall engageable wheel assemblies each coupled to a radially pivoting wheel bracket;
• said radially pivotable legs and said radially pivoting wheel brackets of said one wall engaging mechanism coupled with a coupling, the coupling preventing both of i) said radially pivotable legs and ii) said radially pivoting wheel brackets from being simultaneously in a fully radially extended position,
• alternately operating the common actuator of each wall engaging mechanism to radially extend the connected radially pivotable legs to an extended position, and successively extending and contracting the telescoping connection in synchronicity with operation of said common actuators, to alternately move the forward and rearward body portions when the respective legs of one of the forward and rearward body portions are in a retracted position, and the respective legs of the other one of the forward and rearward body portions body portions are not in the retracted position.