Frequency modulation of body waves to improve performance of sidewinding robots

Abstract

Sidewinding is a form of locomotion executed by certain snakes and has been reconstructed in limbless robots; the gait is beneficial because it is effective in diverse terrestrial environments. Sidewinding gaits are generated by coordination of horizontal and vertical traveling waves of body undulation: the horizontal wave largely sets the direction of sidewinding with respect to the body frame while the vertical traveling wave largely determines the contact pattern between the body and the environment. When the locomotor’s center of mass leaves the supporting polygon formed by the contact pattern, undesirable locomotor behaviors (such as unwanted turning or unstable oscillation of the body) can occur. In this article, we develop an approach to generate desired translation and turning by modulating the vertical wave. These modulations alter the distribution of body–environment contact patches and can stabilize configurations that were previously statically unstable. The approach first identifies the spatial frequency of the vertical wave that statically stabilizes the locomotor for a given horizontal wave. Then, using geometric mechanics tools, we design the coordination between body waves that produces the desired translation or rotation. We demonstrate the effectiveness of our technique in numerical simulations and on experiments with a 16-joint limbless robot locomoting on flat hard ground. Our scheme broadens the range of movements and behaviors accessible to sidewinding locomotors at low speeds, which can lead to limbless systems capable of traversing diverse terrain stably and/or rapidly.

Mechanical intelligence simplifies control in terrestrial limbless locomotion

“…Finally, the bilateral actuation scheme suggests a design and control paradigm for limbless robots. Contrasting the lack of mechanical intelligence in limbless robots to date, the bilateral actuation mechanism offloads complex sensorimotor controls for handling bodyenvironment interactions to mechanical intelligence, improving locomotion efficiency and freeing up onboard hardware and computational bandwidth for advanced sensing and motion planning techniques (37,45,70,(81)(82)(83)(84)(85)(86)(87). This represents a paradigm shift in limbless robotics that could pave the way for the future development of more agile, intelligent, and capable limbless robots that fulfill their promised potential of maneuverability in extremely complex environments, finding diverse applications such as search and rescue, industrial inspection, agricultural management, and planetary exploration.…”

Multilegged matter transport: A framework for locomotion on noisy landscapes

“…From the Shannon scheme for signal transmission, it is reasonable to anticipate improved performance with more elaborate coding schemes, which we define in matter transport as designing the terradynamic interaction profile of bacs (e.g., the instantaneous thrust function f ( t ) and thrust-velocity relationship). One straightforward method to modulate the bac-interaction profile is to change the body wave amplitude ( 27 ) or the number of waves on the body ( 33 ), which alters the temporal and spatial distribution of bacs and the associated body postures. To illustrate the potential of appropriate coding, we show one example of gait design modulation.…”

Optimizing contact patterns for robot locomotion via geometric mechanics

“…In previous work (Astley et al, 2015;Chong et al, 2021c), the sidewinding gait for limbless robots was decomposed into two waves, one in the horizontal plane and one in the vertical plane. In this way, the formulas of shape changes are prescribed as follows:…”

“…As expected, the displacement decreased as the number of motors decreased until N = 10. Turning behavior emerged at N < 10, which can be caused by the unstable configurations in the gaits (Chong et al, 2021c). These unstable turning behaviors led to high variability in speed.…”