Carol Wong: C.1 Source Acquisition


I chose to explore the concept of serpentine or undulatory locomotion, wave like movements that generate fluidity in motion. Such locomotion allows the robot to maneuver through confined spaces to previously inaccessible areas, providing many opportunities in the medical field, such as navigating blood vessels.

In conceiving a topic of interest for this assignment, I realized that I did not know much about the robotics field as it currently stands. I searched for some inspiration from biological models that exhibit extraordinary capabilities, starting my search there and then returning to the literature to determine if such capabilities have or have not already been integrated into robotic systems. An inspiration came from the C. elegans worm, a very simple organism with a fully developed nervous system that confers fine motor control. It is a very well studied organism, whose biological under-wirings have been fully mapped. The fact that such a simplistic neuronal architecture, consisting of only several hundreds of neurons, could confer such a high level of motor control to the worm motivated me to inquire further.

The overarching question I pose is: “How do certain animals achieve wave-like locomotion patterns? How can such mechanisms be applied to achieve that locomotion in robots?”

C.1.0) Source

I started my search on Scopus, in order to identify the articles that have contributed the most to the topic of interest, peripherally determining the impact of each by number of citations and validity by journal. I tried various key search words, with combinations of “serpentine”, “serpent*”, *motion, “undulatory”, “robot*”. Inputting “serpentine locomotion” in the search bar, I received 26 hits, 12 of which have been cited by other papers. To get a sense of where the field stood, I started by looking at the highest cited source [1]; albeit published in 2002 it is so widely cited (85 citations to date) that the information it presents must have significantly contributed to and shaped the field. I further broadened my search my typing in “serpent* *motion robots”. This increased the hits to 87, and I was able to find [2] and [3] this way. Further search in ISI, specifically using “undulatory” and “robot” generated additional results, namely [4].

[1] reported on how they created a wheel-less robot that achieved serpentine motion, incorporating control feedback to delegate efficiency of movement.

As [1] quotes: “A mathematical framework is established for modeling, analysis, and synthesis of the serpentine gait, but the tremendous adaptability of the snakelike mechanism to rugged environments has not yet been fully exploited. Studies of other gaits remain to be done…” This suggested to me the importance of the environment, and thus I narrowed my focus to navigation through fluids.

To satisfy to requirement of identifying one recent paper on bio-inspired robots, I selected [2]. The paper reports on how snake-like locomotion was achieved by mimicking the mechanisms of tadpole tail propulsion. The authors effectively controlled the motion of a tad-pole robot through a wireless, electromechanical system, specifically, “improving the thrust of the tadpole robot developed, the biomimetic undulatory tadpole locomotion is investigated.” A new composite formed actuator is used to confer greater control over movement.

C.1.1) Venue

This paper is published in Smart Materials and Structures, a journal dedicated to “technical advances in smart materials, systems and structures, including materials, sensing and actuation, optics and electromagnetics, structures, control and information processing.” It seems a valid portal through which to publish a paper in robotics, specifically when the design incorporates an element that uses a material composite not previously used. In this case, an ionic polymer–metal composite is the material for the actuator that detects the ‘fin’ ( a polymer film) of the tad-pole robot moving.

Looking at ISI ratings, this journal has an impact rating of 1.749 and a Scopus rating of SJR (2009): 0.093 and SNIP (2009): 1.890.

C.1.2) Authors’ Qualification

The primary author is affiliated with the Korea Aerospace University. It is unclear how so, but the assumption is that he is a professor. Scopus reports a h-index of 19 for him. Looking at a list of his publications, he has presented at IEEE International Conferences, published in analytical chemistry, actuator, mechatronic systems, mechanical engineering, neurology, and a whole array of different fields, demonstrating that although Smart Materials and Structures may not be the ideal venue for a robotics based paper, the author still holds expertise in his field. The second author has an h-index of 32, works at a research institute, and has an extensive history of affiliations with many universities and research institutions. The third and last authors have an h-index of 17 and are affiliated with Korean universities. The first, third, and last authors have been actively contributing to the literature for more than ten years; the second for more than 35 years.

C.1.3) Source Identification Methods

After consulting with Mr. Doug Mcgee, he recommended the following:

"I think you are off to a very good start here. You employed a thoughtful search strategy, starting with serpentine locomotion, you found synonyms that could help pull up other results like undulatory. You also employed truncation and identified parameters like the environment you are particularly interested in studying. At the same time, you kept your options open by discovering other sources of inspiration, like tadpoles, for your work. I saw one on your list, but don't forget to consider conference literature, as there is a lot of that in robotics. It can be harder to find external measures of quality, but you may still find quite a bit of good stuff there."

I did end up including more conference literature later on. He also recommended that:

"As you proceed, continue to keep track of keywords that can help refocus your searches. For example there may be specific aspects of your project that can serve as useful search terms such as terrain, materials selection, method of control, power source, weight, other components for your system such as actuators, sensors or the like, etc."

Because I wasn't delving deep into the literature, I did not find it necessary to utilize more specific keywords; this was meant to be a light exploration of what the field has to offer.

C.1.4) High Quality Bioinspired Robotics Contribution

As C.elegans was the inspiration for my topic of choice, I proceeded to search through the literature to find out more about its motor capabilities. Indeed, as one of the best and thoroughly studied organisms, the C.elegans motor system was well documented and I found a highly applicable paper [6].

The authors of [6] presented their findings on the turning mechanisms of C.elegans worm by studying the amplitude and period of the curvature of its body. A mathematical model led to the conclusion that the worm executes one of two mechanisms to make a smooth turn – either by increasing both amplitude and period of curvature, or decreasing both of them. The authors admit that the mechanism is not fully understood, but only modeled, and that future directions need to be taken. Once the mechanism is fully deciphered, it can be allow robots to make smoother turns. The mechanism is simply a matter of oscillatory behavior, which can be controlled electromechanically.

The primary author had an h-index of 0, having recently entered the field at the time. The remaining authors had indexes of 3, 16, and 9, respectively. It was presented at the 2008 International Conference on Control, Automation and Systems, ICCAS 2008.

C.1.5) General Robotics literature

It is clear that [5] and [3] are drawn from the robotics literature.

First source

[5] address how joint angle parameters for each link in a snake robot affect locomotion on land and in water. The authors found that “ [as] the frequency increases and the number of waves [decreases], the snake-like robot’s forward speed will also increase.” This demonstrates that the mechanisms of serpentine motion have been adapted and successfully applied to robotic systems.

This paper [5] was presented at the 2008 IEEE International Conference. This is the first publication of the primary author, who is a graduate student in China. The following three authors have h-indices of 9, 17, and 11, respectively. This article has not been cited, but as it is a publication stemming from a conference proceeding, explaining the relative lack of citations

Second Source

[3] present on active optimization of a snake-like robot. The authors note that “an important problem in the control of locomotion of robots with multiple degrees of freedom (e.g., biomimetic robots) is to adapt the locomotor patterns to the properties of the environment.” This demonstrates that locomotor patterns should respond to external stimuli. The authors optimize gait while the robot is moving, updating parameters in real-time. They report that optimal gaits were found to be significantly different from one terrain to another. This introduces the importance of feedback loops, demonstrating that there are challenges in directing controlled, snake-like locomotion that must be considered.

The primary author has an h-index of 7, the other 18, and the journal, IEEE Transactions on Robotics, has an impact factor of 2.035. [3] is a fairly reliable source.

C.1.6) Biology Literature

[8] and [4] are drawn from more traditional biology literature. They were found in Scopus and ISI during my initial search. I also looked into articles through PubMed. Each article recognizes, in some aspect, applications to bio-inspired robotics.

First Source

[8] introduces the salamander as an ideal model for gait studies. This amphibian’s has the ability to rapidly interchange between walking and swimming. While swimming, fast axial undulations are propagating from the salamander’s head to its tail, with its limbs folded back. This article provides insight into the distinctions between land and water maneuvering, presenting the magnitude of challenges in achieving robust, wave-like, movement. In presenting the distinctions, the authors capture the subtleties of swimming, a series of undulations that propel the salamander forward. The frequency of oscillatory centers in the body versus the leg allows for maneuvering in water and land.

It suggests the use of coupled oscillators to achieve the desired motion and again emphasizes how applicable biological models are to robotic systems. There are still challenges to overcome especially with serpentine robot locomotion, which demands many degrees of freedom for smooth, fluid motion.

As the authors so aptly point out: “There is currently no well-established methodology for controlling the locomotion of robots with multiple degrees of freedom, in particular for non–steady-state locomotion in complex environments.”

With the primary author having a Scopus h-index of 18 and the journal being Science, with an ISI reported impact factor of 29.747, this is certainly a reliable source of information.

Second Source:

[4] addresses the issue of control in locomotion, focusing on the aspect of undulatory motion. The authors quote: “Motion control is one of the most significant problems for emerging robotic applications dealing with locomotion in unstructured environments.”

The authors draw from the biological model of the polychaete annelid worm. This worm moves via undulations of its body, wave like motions that are achieved by the rowing action of many appendages, called parapodia, distributed along its body. Not only do these parapodia allow for undulatory motion, but they also allow for a multitude of functions like locomotion, transversing, and burrowing, all important capabilities when navigating an unstructured terrain. These motor activities are thought to originate from the worm’s central pattern generator (CPG) region, a neuronal network that produces regular, rhythmic motor patterns even with minimal external or internal stimuli is present.

Extending the neuromuscular control responsible for undulatory motion in worms to the realm of robots, the authors created a computation model of the worm’s CPG, hoping to apply it to robotic systems. This capitalizes on the crossover in the fields of robotics and biology, where biological mechanisms are deciphered and then extrapolated to create computation models, and eventually this biological mechanism is replicated by a robot.

This article appeared in Neurocomputing, and ISI indicates an impact rating of 1.440 and the authors both have Scopus h-indexes of 5. Though this is not too impressive, the topic is interesting enough that it has spurred 9 citations. Additional foray into the literature, particularly CPG applications in robotics, produced a review article on the mechanisms and use of CPG in robotic systems [7]. Cited over 69 times, with the author having a Scopus h-index of 18 (though this is a review article) and the journal, Neural Networks having an impact factor of 1.879, this is a pretty reliable review of CPG-based mechanisms of locomotion control, demonstrating that CPGs are important and researchers are interested in their applications.


[1] Saito, M., Fukaya, M., & Iwasaki, T. (2002). Serpentine locomotion with robotic snakes. IEEE Control Systems Magazine, 22(1), 64-81. Retrieved from
[2] Kim, B., Kim, D. -., Jung, J., & Park, J. -. (2005). A biomimetic undulatory tadpole robot using ionic polymer-metal composite actuators. Smart Materials and Structures, 14(6), 1579-1585. Retrieved from
[3] Crespi, A., & Ijspeert, A. J. (2008). Online optimization of swimming and crawling in an amphibious snake robot. IEEE Transactions on Robotics, 24(1), 75-87. Retrieved from
[4] Sfakiotakis, M., & Tsakiris, D. P. (2007). Neuromuscular control of reactive behaviors for undulatory robots. Neurocomputing, 70(10-12), 1907-1913. Retrieved from
[5] Zuo, Z., Wang, Z., Li, B., & Ma, S. (2008). Serpentine locomotion of a snake-like robot in water environment. Paper presented at the 2008 IEEE International Conference on Robotics and Biomimetics, ROBIO 2008 , art. no. 4912974, pp. 25-30. Retrieved from
[6] Kim, D., Hwang, H., Park, S., & Shin, J. H. (2008). Turning mechanism of a smooth body by amplitude and period control in curvature. Paper presented at the 2008 International Conference on Control, Automation and Systems, ICCAS 2008 , art. no. 4694515, 1765-1768. Retrieved from
[7] Ijspeert, A. J. (2008). Central pattern generators for locomotion control in animals and robots: A review. Neural Networks, 21(4), 642-653. Retrieved from
[8] Ijspeert, A. J., Crespi, A., Ryczko, D., & Cabelguen, J. -. (2007). From swimming to walking with a salamander robot driven by a spinal cord model. Science, 315(5817), 1416-1420. Retrieved from