How does the centipede coordinate the movement of its legs?

The movement of animals (terrestrial, aerial and aquatic) has always attracted the attention of scientists and, in general, of the vulgar. Furthermore, this attraction has had important practical consequences, both for man (locomotor corrections, prostheses, etc.) and for the creation of machines, robots, etc., and even for the current three-dimensional virtual museums. Today we look at land animals with legs. Of these, for those with up to six legs, there are different realistic models that allow the complete movements to be replicated.

However, the problem becomes more complex, and biomechanical models more sophisticated, when the number of pairs of legs increases. Complexity that increases when these animals, as usual, move on an irregular surface. Today we make a brief description of centipedes. By the way, they are one of the 13,000 species of myriapods. Also, let's not forget that its number of legs ranges from tens to hundreds, distributed over an elongated and segmented body structure. Lastly, they have a pair of sensory antennae and two tail filaments. Due to its unusual structure and unique locomotion system it is an interesting subject of study for physics, robotics and graphic research.

A model to describe the movement of a centipede must meet at least the following requirements: it must describe the physical realism of a deformable body, the contact of the legs with the surfaces and what is called the wave pattern of the legs that , on a surface, including irregular ones, moves the whole body.

Drawing taken from an article by Fang, Jiang, and Terzopoulos.

In this introduction we focus our attention on one such model. The figure that accompanies the text shows a centipede model that includes: rigid segments with legs with rotation in the rigid segment and two joints, deformable segments, deformable antennae and tail. The color of each leg indicates its status: swinging forward, swinging back, adjusting, and supporting. These are the four common situations on uneven surfaces. The deformable nature of myriapods is emulated by means of a fast and elastically robust simulation method. The decentralized and distributed system of leg control allows simulating their biological movement on any type of surface.

In order for the animation to be realistic, in real time, the model uses a hybrid simulation method that incorporates both body states, kinematic and dynamic. The pattern bears some similarity to the Dragon Dance that is performed during the spring festival in Chinese culture. It is performed by between 9 and 15 dancers and the first of them is the one who decides the locomotion. That is equivalent to saying that the high-level locomotion decision is made by the centipede brain. Once the model has been defined, with the appropriate equations, the problem becomes a computer simulation. A job that requires knowledge of physics, robotics and programming.

What has been described above can be considered a simple model that, based on identical leg controllers, describes the behavior of the centipede on uneven terrain as well as when it encounters obstacles on the surface. In the model, the antennae are sensory organs for detecting food and obstacles. Evidently increasing the complexity of this and other models, researchers are getting closer to simulating the real behavior of these complex animals.