Small legged robot can run on the water surface because of scaling effect. While the reaction from the water surface is proportional to the leg area, (length squared) the weight is proportional to the volume (length cubed). Therefore the small object is difficult to sink. It seems that basilisk lizards less than 200g can run on the water surface. Water striders do not even sink due to the surface tension. The surface tension is proportional to the length. We are developing a cm-scale on-water running robot with legs.
Four legged robot with tail (Otsuka model 2011):
Four legged robot without a tail (Otani model 2014):
On-water locomotion simulation by FSI:
Under analyzing…..