I picked up a Hexbug Nano V2 toy http://www.hexbug.com/v2 the other day. It moves by vibrating the body and the flexible legs only let it move forward. The motion is pretty random, kind of like a big bug. It needed something extra so I made a small truncated icosahedron in Cheetah3D and printed a bunch. These "eggs" provide some obstacles for it as it moves around it's environment. Here's a short video of them in action: https://vimeo.com/77012228

Have fun!

UPDATE: The "eggs" seem to jam less often if they are scaled to 95% before printing.

I used ReplicatorG to prepare the file, a MakerBot Replicator2 with the Replicator 2 slicing defaults and the following settings with white MakerBot PLA to do the printing:

Infill = 10%
Layer Height = 0.200
Shells = 1
Feedrate = 40
Travel Feed = 55
Temperature = 220

I used a raft with full support. It only takes 10 minutes to print one of these 15 mm diameter things and the support structure snaps right off.