Using the transferability approach, the robot first explores how it can moves (is using the wheels OK? how to walk?) then it can exploits its discovery to move.
In this video, it quickly discovers that the best way to move on a flat surface is to use its wheels. When the wheels are inefficient (e.g. on a grid), it discovers how to walk.
Koos, S. and Mouret, J-B. (2011). Online Discovery of Locomotion Modes for Wheel-Legged Hybrid Robots: a Transferability-based Approach.
Proceedings of CLAWAR, World Scientific Publishing Co., publisher. Pages 70-77.