Please have a look at this youtube video.
When this mobile robot operates, the rack (which is said to weight up to 450 kg) can have its Center Of Mass (COM) distributed at any location. For example, this COM can be located 5 or 10 cm off from the center of the robot. Because of this, when the robot revolves, the center of rotation will not be at the center of the robot anymore. However as you see in the video, it can still rotate many circles perfectly around its up-right axis.
So what do you think about this? Is this possible by mechanical design only? Or did they use some kind of advanced feedback control system to counter the effect of the off-center COM?