An official website of the United States government
Soft robotic snakes made of compliant materials can continuously deform their bodies and, therefore, mimic the biological snakes' flexible and agile locomotion gaits better than their rigid-bodied counterparts. Without wheel support, to date, soft robotic snakes are limited to emulating planar locomotion gaits, which are derived via kinematic modeling and tested on robotic prototypes. Given that the snake locomotion results from the reaction forces due to the distributed contact between their skin and the ground, it is essential to investigate the locomotion gaits through efficient dynamic models capable of accommodating distributed contact forces. We present a complete spatial dynamic model that utilizes a floating-base kinematic model with distributed contact dynamics for a pneumatically powered soft robotic snake. We numerically evaluate the feasibility of the planar and spatial rolling gaits utilizing the proposed model and experimentally validate the corresponding locomotion gait trajectories on a soft robotic snake prototype. We qualitatively and quantitatively compare the numerical and experimental results which confirm the validity of the proposed dynamic model.
more »
« less
This content will become publicly available on January 1, 2027
Rolling Locomotion in Soft Robotic Snakes: Modeling, Control, and Experimental Validation
Soft robotic snakes, characterized by continuous body deformation, offer a superior platform for investigating the fundamentals of efficient biological locomotion. This paper introduces a mathematical framework for modeling and analyzing the planar rolling gait of these soft robotic snakes. We leverage principles of continuous deformation and distributed contact dynamics to derive an analytical relationship between the joint parameters of the robot and its resulting rolling velocity. To validate the model and enable practical application, we develop a configuration-space closed-loop controller for accurate trajectory tracking. The stability of the proposed controller is formally confirmed using the input-to-state stability criteria. Simulations and experimental validation demonstrate that the controller achieves accurate trajectory tracking and confirm that the measured rolling speed adheres to the theoretical prediction. These results affirm the effectiveness and accuracy of our gait modeling and control strategy for enhancing the locomotion performance and fundamental understanding of soft robotic snakes. Note to Practitioners—Soft robotic snakes offer unique advantages for applications requiring navigation in cluttered or confined environments, yet their highly compliant bodies and non-linear pneumatic actuation have historically made reliable motion control a significant barrier to deployment. This work addresses that practical need by providing an engineering framework that allows practitioners to command the snake robot to roll at a predictable speed and in a predictable direction, overcoming the unreliability of open-loop actuation. The presented geometric model can be used to estimate forward speed based on desired snake parameters, while the core practical contribution is the closed-loop controller that actively compensates for real-world issues. This controller maintains consistent body curvature despite common challenges like sensor noise, fabrication imperfections, material stiffness variations, and pneumatic delays, all of which typically undermine performance on physical hardware. Validation confirms this approach delivers improved trajectory tracking and more repeatable rolling behavior than current methods. Engineers deploying this framework should note its assumption of planar rolling on relatively uniform terrain and reliance on standard IMU sensing and pneumatic actuation, which may limit performance on highly irregular surfaces or when extreme speed in pressure dynamics is required. This foundation is essential for extending soft snake capabilities toward future, complex behaviors like autonomous navigation and obstacle-aware gaits.
more »
« less
- PAR ID:
- 10713688
- Publisher / Repository:
- IEEE
- Date Published:
- Journal Name:
- IEEE Transactions on Automation Science and Engineering
- Volume:
- 23
- ISSN:
- 1545-5955
- Page Range / eLocation ID:
- 12537 to 12549
- Subject(s) / Keyword(s):
- Soft robotic snake, rolling locomotion, closed-loop control
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Snake robotics is an important research topic with a wide range of applications, including inspection in confined spaces, search-and-rescue, and disaster response. Snake robots are well-suited to these applications because of their versatility and adaptability to unstructured and constrained environments. In this paper, we introduce a soft pneumatic robotic snake that can imitate the capabilities of biological snakes, its soft body can provide flexibility and adaptability to the environment. This paper combines soft mobile robot modeling, proprioceptive feedback control, and motion planning to pave the way for functional soft robotic snake autonomy. We propose a pressure-operated soft robotic snake with a high degree of modularity that makes use of customized embedded flexible curvature sensing. On this platform, we introduce the use of iterative learning control using feedback from the on-board curvature sensors to enable the snake to automatically correct its gait for superior locomotion. We also present a motion planning and trajectory tracking algorithm using an adaptive bounding box, which allows for efficient motion planning that still takes into account the kinematic state of the soft robotic snake. We test this algorithm experimentally, and demonstrate its performance in obstacle avoidance scenarios.more » « less
-
Snakes are a remarkable evolutionary success story. Numerous snake-inspired robots have been proposed over the years. Soft robotic snakes (SRS), with their continuous and smooth bending capability, can better mimic their biological counterparts' unique characteristics. Prior SRSs are limited to planar operation with a limited number of planar gaits. We propose a novel SRS with spatial bending ability and investigate snake locomotion gaits beyond the planar gaits of the state-of-the-art systems. We derive a complete floating-base kinematic model of the SRS and use the model to derive joint-space trajectories for serpentine and inward/outward rolling locomotion gaits. These gaits are experimentally validated under varying frequency and amplitude of gait cycles. The results qualitatively and quantitatively validate the proposed SRSs' ability to leverage spatial bending to achieve locomotion gaits not possible with current SRS designs.more » « less
-
null (Ed.)In this paper, we present a new locomotion control method for soft robot snakes. Inspired by biological snakes, our control architecture is composed of two key modules: A reinforcement learning (RL) module for achieving adaptive goal-tracking behaviors with changing goals, and a central pattern generator (CPG) system with Matsuoka oscillators for generating stable and diverse locomotion patterns. The two modules are interconnected into a closed-loop system: The RL module, analogizing the locomotion region located in the midbrain of vertebrate animals, regulates the input to the CPG system given state feedback from the robot. The output of the CPG system is then translated into pressure inputs to the pneumatic actuators of the soft snake robot. Based on the fact that the oscillation frequency and wave amplitude of the Matsuoka oscillator can be independently controlled under different time scales, we further adapt the option-critic framework to improve the learning performance measured by optimality and data efficiency. The performance of the proposed controller is experimentally validated with both simulated and real soft snake robots.more » « less
-
Soft robotic snakes (SRSs) have a unique combination of continuous and compliant properties that allow them to imitate the complex movements of biological snakes. Despite the previous attempts to develop SRSs, many have been limited to planar movements or use wheels to achieve locomotion, which restricts their ability to imitate the full range of biological snake movements. We propose a new design for the SRSs that is wheelless and powered by pneumatics, relying solely on spatial bending to achieve its movements. We derive a kinematic model of the proposed SRS and utilize it to achieve two snake locomotion trajectories, namely side winding and helical rolling. These movements are experimentally evaluated under different gait parameters on our SRS prototype. The results demonstrate that the SRS can successfully mimic the proposed spatial locomotion trajectories. This is a significant improvement over the previous designs, which were either limited to planar movements or relied on wheels for locomotion. The ability of the SRS to effectively mimic the complex movements of biological snakes opens up new possibilities for its use in various applications.more » « less
