We built a pretty interesting drive-train this year, it was a 8 wheel, drop center, articulated tank drive. The articulation was what made it really interesting. One side of the drive-train (4 wheels-2 CIMs) was solidly fixed to the frame, but the other side was on a pivot underneath the frame. This meant that the sides of our drive-train could be in different planes at the same time. This was really effective at getting over the ramparts specifically because we could drive right up the middle and have both sides of our drive-train flat against both slopes of the ramparts.
https://www.thebluealliance.com/match/2016code_qm3
You can see in this video our robot really bounced back and forth, this was because it would rock on the pivot point due to it not being perfectly balanced.