A robot has a robot body on a frame structure, the robot body having at least one enclosed space to hold at least one delivery item. At least one sensing device detects objects along a direction of motion of said robot. The robot has six wheels, where at least two wheels on a side of the frame are connected to each other. The axis of rotation of each wheel is substantially fixed with respect to the robot during forward, rearward, and turning motion of the robot. During transition, via a substantially vertical obstacle, from a first substantially horizontally surface to a second substantially horizontally surface higher than the first substantially horizontally surface, one of the connected wheels causes an upward or a downward force to be applied to the other connected wheel.