Figure 9. Viscous friction (presence of lubricant) between snake robot segment and surface

From

Experimental Analysis of Friction Effects Affecting the Snake Robot Segment during Rectilinear Locomotion

Ivan Virgala, Alexander Gmiterko, Peter Frankovský

American Journal of Mechanical Engineering. 2013, 1(7), 412-416 doi:10.12691/ajme-1-7-52