An improved vehicle is provided that has an excellent obstacle overcoming ability, including stair climbing. The apparatus comprises a frame, and a pair of endless track units positioned on opposite sides. Each track unit has a plurality of telescoping rollers in contact with the inner track surface configured to guide the track around a track pathway, and move vertically when navigating over obstacles. Each track unit further comprises a drive assembly in contact with the track, and movable between a raised position and a lowered position, such that movement of the drive assembly also operates to provide track tension.
