If you have never seen the amazing MorpHex hexapod robot in action then you need to see this video. If you have seen it then look again because now MorpHex can transform itself into a ball that rolls under its own power.
Now we have a video that shows the ball unfolding and walking and then closing back up and rolling by pushing with each of its segments.
At the moment, control of direction isn't perfect and the ball tends to roll in a curve. Zenta, or Kåre Halvorsen to give him his full name, thinks that it is due to an asymmetry in the design which he has plans to fix in the future.