This is my entry, I call it "Blackout". Here is a bricksafe page with all WIP photos
It's based around a spinner that reaches in all directions. I had some problems with the weapon being too heavy (it's powered by a geared down RC motor).
I also wanted to make it driveable upside down, but it was unpractical and heavy, so I added a self-righting mechanism instead. It's powered by two PF Large motors with one linear actuator each. The body has a design so that the robot can't get stuck on it's side, if it would get flipped. The battery boxes are powered on by special "pull buttons" to make them impossible for another robot to switch off. Look at the end of the video to see how it works.