A robotic crawler exploiting directional frictional interactions:   experiments, numerics, and derivation of a reduced model
  We present experimental and numerical results for a model crawler which is able to extract net positional changes from reciprocal shape changes, i.e. 'breathing-like' deformations, thanks to directional, frictional interactions with a textured solid substrate, mediated by flexible inclined feet. We also present a simple reduced model that captures the essential features of the kinematics and energetics of the gait, and compare its predictions with the results from experiments and from numerical simulations. 
Giovanni Noselli and Antonio DeSimone
cond-mat.soft