The present invention discloses a travelling crab (1) adapted to travel along a supporting structure following a moving direction, comprising: a first set of wheels (2), each of said wheels having a first rotation axis orthogonal to the moving direction; and a second set of wheels (2'), each of said wheels having a second rotation axis orthogonal to the moving direction, said first and second set of wheels being attached to a crab body such that the moving direction is the same for the first and second set of wheels, wherein the wheels are attached to the crab body such that the first rotation axis and the second rotation axis are separated by an angle of at least 90 °. In particular, the axis of rotation of the first series of wheels (2) can be separated from the axis of rotation of the second series of wheels (2 ') by an angular separation of 120 °.