More Like this

1. Moving sidewinding forward: optimizing contact patterns for limbless robots via geometric mechanics

   https://doi.org/10.15607/RSS.2021.XVII.031  

   Chong, Baxi; Wang, Tianyu; Lin, Bo; Li, Shengkai; Choset, Howie; Blekherman, Grigoriy; Goldman, Daniel (July 2021, Robotics: Science and Systems)

   Chong, Baxi; Wang, Tianyu; Lin, Bo; Li, Shengkai; Choset, Howie; Blekherman, Grigoriy; Goldman, Daniel (Ed.)

   Abstract—Contact planning is crucial to the locomotion per-formance of limbless robots. Typically, the pattern by which contact is made and broken between the mechanism and its environment determines the motion of the robot. The design of these patterns, often called contact patterns, is a difficult problem. In previous work, the prescription of contact patterns was derived from observations of biological systems or determined empirically from black-box optimization algorithms. However, such contact pattern prescription is only applicable to specific mechanisms, and is challenging to generalize. For example, the stable and effective contact pattern prescribed for a 12-link limbless robot can be neither stable nor effective for a 6-link limbless robot. In this paper, using a geometric motion planning scheme, we develop a framework to design, optimize, and analyze contact patterns to generate effective motion in the desired directions. Inspired by prior work in geometric mechanics, we separate the configuration space into a shape space (the internal joint angles), a contact state space, and a position space; then we optimize the function that couples the contact state space and the shape space. Our framework provides physical insights into the contact pattern design and reveals principles of empirically derived contact pattern prescriptions. Applying this framework, we can not only control the direction of motion of a 12-link limbless robot by modulating the contact patterns, but also design effective sidewinding gaits for robots with fewer motors (e.g., a 6-link robot). We test our designed gaits by robophysical experiments and obtain excellent agreement. We expect our scheme can be broadly applicable to robots which make/break contact. 

   more » « less
2. Central pattern generator with inertial feedback for stable locomotion and climbing in unstructured terrain.

   Guillaume Sartoretti, Samuel Shaw (May 2018, IEEE International Conference on Robotics and Automation)

   : Inspired by the locomotor nervous system of vertebrates, central pattern generator (CPG) models can be used to design gaits for articulated robots, such as crawling, swimming or legged robots. Incorporating sensory feedback for gait adaptation in these models can improve the locomotive performance of such robots in challenging terrain. However, many CPG models to date have been developed exclusively for open-loop gait generation for traversing level terrain. In this paper, we present a novel approach for incorporating inertial feedback into the CPG framework for the control of body posture during legged locomotion on steep, unstructured terrain. That is, we adapt the limit cycle of each leg of the robot with time to simultaneously produce locomotion and body posture control. We experimentally validate our approach on a hexapod robot, locomoting in a variety of steep, challenging terrains (grass, rocky slide, stairs). We show how our approach can be used to level the robot's body, allowing it to locomote at a relatively constant speed, even as terrain steepness and complexity prevents the use of an open-loop control strategy. 

   more » « less
3. Soft Robotic Snake Locomotion: Modeling and Experimental Assessment

   https://doi.org/10.1109/CASE49439.2021.9551398  

   Arachchige, Dimuthu D.; Chen, Yue; Godage, Isuru S. (August 2021, IEEE 17th International Conference on Automation Science and Engineering)

   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
4. An obstacle disturbance selection framework: emergent robot steady states under repeated collisions

   https://doi.org/10.1177/0278364920935514  

   Qian, Feifei; Koditschek, Daniel E (July 2020, The International Journal of Robotics Research)

   Natural environments are often filled with obstacles and disturbances. Traditional navigation and planning approaches normally depend on finding a traversable “free space” for robots to avoid unexpected contact or collision. We hypothesize that with a better understanding of the robot–obstacle interactions, these collisions and disturbances can be exploited as opportunities to improve robot locomotion in complex environments. In this article, we propose a novel obstacle disturbance selection (ODS) framework with the aim of allowing robots to actively select disturbances to achieve environment-aided locomotion. Using an empirically characterized relationship between leg–obstacle contact position and robot trajectory deviation, we simplify the representation of the obstacle-filled physical environment to a horizontal-plane disturbance force field. We then treat each robot leg as a “disturbance force selector” for prediction of obstacle-modulated robot dynamics. Combining the two representations provides analytical insights into the effects of gaits on legged traversal in cluttered environments. We illustrate the predictive power of the ODS framework by studying the horizontal-plane dynamics of a quadrupedal robot traversing an array of evenly-spaced cylindrical obstacles with both bounding and trotting gaits. Experiments corroborate numerical simulations that reveal the emergence of a stable equilibrium orientation in the face of repeated obstacle disturbances. The ODS reduction yields closed-form analytical predictions of the equilibrium position for different robot body aspect ratios, gait patterns, and obstacle spacings. We conclude with speculative remarks bearing on the prospects for novel ODS-based gait control schemes for shaping robot navigation in perturbation-rich environments. 

   more » « less
5. Dynamic Modeling and Validation of Soft Robotic Snake Locomotion

   https://doi.org/10.1109/ICCAR57134.2023.10151763  

   Arachchige, Dimuthu D.; Mallikarachchi, Sanjaya; Kanj, Iyad; Perera, Dulanjana M.; Chen, Yue; Gilbert, Hunter B.; Godage, Isuru S. (April 2023, 2023 9th International Conference on Control, Automation and Robotics (ICCAR))

   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