OK, we dig bristle bots, and got a set of HexBugs as a gift. They're a blast.
Now, since building the SHR, we view all things as potential robot bodies. At Target, they were selling kitchen scrubbers for a buck. (US$1). The rubber top made a great spot for a switch or could have been a light, or even a propeller.
The clear body looked like a great spot for a flashing LED for night time use.
Love the switch we found for this. Fit's perfectly in the rubber top.
So used a breadboard to figure out the basics, but when it went together, fit was an issue. It didn't. That's why you see holds drilled through the bottom. The idea was to nestle/mount the battery within the bristles. Figured this would help bring the center of gravity down as well.