An apparatus for climbing and descending stairs or other obstacles has three flexibly connected sections and a pair of crawler belt systems on opposite sides of the unit. Each of the crawler belt systems comprised of three crawler belts are driven by one of a pair of motors that directly drives a pinion that engages two of the crawler belts, one of which then drives the last crawler belt through another pinion. The stair-climbing apparatus also includes a mounting platform for coupling a carrier device such as a wheelchair or a box. In order to provide cushioning and stability for movements from a horizontal surface to an inclined surface and vice versa, shock absorbers are provided between the three sections. A linear actuator is also provided to provide stabilization as well as the ability to raise and lower both the stair-climbing crawler unit as well as the wheelchair, providing three modes of operation including manually wheel driven mode, motor wheel driven mode, and motor crawler driven mode.