Paddle trajectory generation for accessing soft terrain by an ePaddle locomotion mechanism

The use of rescue robots in disaster response has become increasingly common, but few of them can operate on harsh amphibious terrain, especially on soft terrain. To access such challenging environments, we have proposed a novel eccentric paddle mechanism (ePaddle) which exhibits high environmental adaptability and can achieve six major types of gait, such as wheel-like rolling, two legged walking gaits, wheel-paddle-integrated rolling, and aquatic paddling gaits. In this paper, we present the details of the paddle trajectory generation method for ePaddle to access soft terrain. On such conditions, the paddle can operate as a lug to generate additional pull and lift forces that improve traction performance and prevent wheel sinkage than using wheel-like rolling. We adopt the passive pressure theory to model the pull and lift forces acting on the paddle; these forces are determined by soil parameters and the inclination angle, sinkage length, and moving direction angle of the paddle. Based on this model, we propose a motion planning strategy to control the inclination angle and protruded length of the paddle to generate required pull and lift forces and weaken any fluctuations in them. Then, we verify the effectiveness of our proposed method by using simulations.