A wheeled vehicle comprising a power-driven spider assembly for ascending and descending stairs. The vehicle includes an angular position sensor providing input to a controller operable to control a servo-motor to effectively lock the position of the spider relative to the frame, regardless of the hand truck's spatial orientation relative to a vertical plane, or any balancing of the hand truck. The angular position sensor provides input to the controller, which is programmed with predefined angular zones of instability, and causes the controller to accelerate rotation of the spiders through those zones when the wheeled vehicle is in the descent mode, to avoid instability of the hand truck. A hand truck may include a removable basket and/or a pivotable platform usable to transport loads.