This is a pretty sweet autonomous robot that employs pencil erasers as bumpers. It’s called No. 2, Champion Autonomous Mini-Sumo Robot (a name that just rolls off the tongue, no?)
You can see a really quick video of this robot vs. a block of wood (?!?!?!) below:
Of course, the sadist in me wants to flip those pencils around and sharpen them to a point to make it a more stabby robot, but that would be more offensive than defensive, I suppose.