An apparatus for transporting a payload along the inside of a substantially horizontal pipe, which apparatus includes a pair of spaced apart, vertically aligned, relationally pivotably connected, rollable pipe tracking contactors, wherein pivoting of one of the pipe tracking contactors in a first direction results in pivoting of the other pipe tracking contactor in a direction opposite to the first direction. The apparatus further includes a control system which is used to maintain the vertical alignment of the pipe tracking contactors and which includes a two-dimensional tilt sensor that provides information to a controller regarding the orientation of the apparatus. Using the information from the sensor, the controller is able to correct both the lateral position and the speed of the contactors to bring the apparatus back into vertical alignment.