Dynamic Vertical Climbing Mechanism of Chinese Dragon-Li Cats Based on the Linear Inverted Pendulum Model

Humans have long desired but never achieved the capacity to climb walls. The fundamental reason is that human hands and feet cannot climb vertical walls like geckos and bees. Animals lacking an adhesive structure can use the body’s dynamic effect to climb walls. Here we investigated the dynamic wall climbing behavior of individuals who cannot remain stationary on the vertical wall. Taking the domestic cat as the experimental object, we constructed an experimental platform as the obstacle for the cat to climb the wall. Our research indicated that domestic cats must meet the following physical conditions to do dynamic vertical wall climbing: vertical obstacles must have nonvertical surfaces, a horizontal run-up, and contact with nonvertical surfaces before the vertical speed reduces to zero. Here we proposed a dynamic vertical wall climbing model with three contact states based on an investigation of domestic cats’ dynamic wall climbing behavior and the LIP model. The motion range of the LIP model’s generalized angular coordinates varies depending on the contact state. The horizontal run-up action can improve the jumping height and obtain horizontal speed. When making contact with the vertical surface of the obstacle, the motion inertia in the horizontal direction can produce a reaction force on the contact surface, which can compensate for the influence of some gravity. This alternating contact strategy lets cats switch different initial and end contact angles. This investigation clarifies the essential process underlying animals’ dynamic vertical wall climbing and establishes the theoretical foundation for the legged robot to do dynamic vertical wall climbing.