Bio-inspired robotic dog paddling: kinematic and hydro-dynamic analysis

Research on quadrupedal robots inspired by canids or felids have been widely reported and demonstrated. However, none of these legged robots can deal with difficult environments that include water, such as small lakes, streams, rain, mud, flooded terrain, etc. In this paper, we present for the first time a kinematic analysis and a hydrodynamic model of dog paddling motion in a robotic system. The quadrupedal paddling gait of dogs was first analyzed based on underwater video recording. Hydrodynamic drag force analysis in a paddling gait cycle was conducted for a prototype robotic dog. The prototype robotic dog was developed using four pre-charged pneumatics soft actuators with consideration of relative positions of CG (center of gravity) and CB (center of buoyancy) and their dynamic variation in paddling. It was found that such soft actuators have great potential in developing amphibious legged robots, because they are inherently water-tight, anti-rusty, simple in structural design, and have large hydrodynamic advantage due to their mostly hemi-cylindrical shape design. Trotting and paddling of the prototype robotic dog was also demonstrated. It is believed that our findings reported in this research will provide useful guidance in future development of amphibious robotic dogs.