These are sumo shields I created for the Boise Code Camp robotics competition.
If you print them upside down, the design is self-supporting. The holes on the front shield allow an HC-SR04 ultrasonic sensor to be mounted in the shield.
I've posted an updated version with some minor improvements to make printing easier. You'll want to check your infill settings - printing with more than 20% infill may take a while.
Flip them over.
There's a lot of straight lines in this print, so I enabled acceleration limits in Slic3r and increased my maximum print speed. The acceleration limit prevents jarring the print loose, and let me double my usual maximum print speed. Overall, the print completed in about 66% of the time without the acceleration & speed adjustments, and I had fewer failed prints.