My teams bumpers were mentioned above. It was our teams alternative to what we considered disqualification magnent wedges.
They were parallelograms spring loaded down. When a robot hit us they would dig into the cushioned side and push the bumpers up, pulling their front wheels off the ground and shifting some of their weight onto us. In theory they worked well but they had a couple issues. First was weight, to cover all 4 sides weighed about 12 pounds plus a 5 pound powered lifting mechanism which we removed. The other issue was that they just didn't work as well as wedges. We were rarely pushing other robots and while they didn't have the danger of tipping other robots we just didn't need that.