Snake Robot – The future of agile motion

By | March 26, 2015

              Crawling movement as a motive mode seen in nature of some animals such as snakes possesses a specific syntactic and dynamic analysis. A snake robot or serpentine robot designed by inspiration from nature and snakes crawling motion is regarded as a crawling robot. In this article, a snake robot with spiral motion model will be analyzed. The purpose of this analysis is to calculate the vertical and tangential forces along snake’s body and to determine the parameters affecting these forces. A snake-like device that could slide, glide and slither could open up many applications in exploration, hazardous environments inspection, and medical interventions. 


                Biological snakes are pervasive across the planet; their diverse locomotion modes and Physiology make them supremely adapted for the wide variety of terrains, environments, and climates that they inhabit. A snake-like device that could slide, glide and slither could open up many applications in exploration, hazardous environments, inspection and medical interventions.

One of the fundamental issues is understanding their locomotion. A wheel turns the vehicle moves. A leg pushes the vehicle moves. How a snake moves is not so evident. A worthwhile snake robot has the ability to wriggle into confined areas and traverse terrain that would pose problems for traditional wheeled or legged robots. The design and implementation of a snake robot is the confluence of several technologies: actuation, form and structure, electronics, control, sensing, etcetera.

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Why Serpentine Locomotion?

For centuries, people have created a menagerie of machines whose appearance and movement have mirrored animals to an astonishing degree. The general motivations for serpentine locomotors are environments where traditional machines are precluded due to size or shape. For example, environments include tight spaces, long narrow interior traverses, and travel over loose materials and terrains. Wheels offer smooth and efficient locomotion but often require modifications to terrains for best use. Integration is complicated, even intractable if individual areas are not thought of in the whole.

Flowchart for Snake Robot design

Flowchart for Snake Robot design

Configuration and Design

The challenge of configuration is determining the form of a robot. The challenge of actuation is determining the technology that drives the mechanism. The questions are sometimes mundane but essential to answer: How long should segments be? What angle should they subtend? Are there actuation techniques that can provide smoother curves? Determining both the result and implications of each decision is a challenge.

Configuration and Design for snake robot

Infrastructure and Electronics

Supplying and routing power and signals in complex robots is often underestimated as a design task. Serpentine robots must be compact and small to accrue the advantages shown in the previous section. Small size burdens the tasks of wire routing and actuation support.

Control and Sensing

Finally, the greatest challenge: how to learn to control such a device? A larger issue is determining the process, method and framework to achieve this.

Carnegie Mellon’s snake robot

Carnegie Mellon’s snake robot  PC-Techcrunch

Advantages of Snake Robots

Stability: Unless a serpentine robot purposefully slithers off a cliff, it cant fall over. In contrast, stability is of great concern to wheeled and legged machines in rough terrain; they can fall over. Terrain contacts in vehicles form a constellation of points on the terrain; if the center of gravity moves beyond the bounds of the convex polygon formed by these points, it tips over. In a serpentine robot, the potential energy remains low in most situations; therefore there are few concerns for stability and no need for the support
polygons formed by wheel or leg contact points.

Terrainability: Terrainability is the ability of a vehicle to traverse rough terrain. Terrain roughness is often measured by scale of features, power spectral density, distribution of obstacles such as rocks and geographic forms or even its fractal dimension A serpentine mechanism holds the promise of climbing heights many times its own girth; this feature can enable passage through terrain that would encumber or defeat similarly scaled wheeled and legged machines.

Traction: Traction is the force that can be applied to propel a vehicle. Traction is usually limited to the product of the vehicle weight and the coefficient of friction. The distribution of the snake mass over such a large area, in comparison to mass equivalent legged or wheeled vehicles, results in forces that can be below the thresholds of the plastic deformation of the soil. In comparison, load concentration resulting from most wheels or leg designs results in soil work. Because of the large contact area, serpentine vehicles may result in little or no soil work. Limbless locomotion may prove superior in marginal or soft terrains where plowing and shearing actions restrict wheel mobility.

Efficiency: Snakes achieve efficiencies and performance equivalent to biomechanisms of similar scale and mass. Reasons include reduced costs associated with less lifting of the center of gravity as compared to legged animals, elimination of the acceleration
or deceleration of limbs, and low cost for body support. The answer is that energy losses in snakes include greater frictional losses into the ground, lateral accelerations of the body that do not contribute to forward motion, and the cost of body
support for partial body elevations during movement.

Size: Depending on the mechanism design, the small frontal area of snake mechanisms allows penetration of smaller cross-sectional areas than mass-equivalent legged or wheeled vehicles. If the volume of a snake, a cylindrical form, is kept the same and the diameter is reduced by half, the length becomes four times greater. Cross-sectional area for mechanisms of similar density and mass may result in very long vehicles.

Redundancy: Candidate configurations for serpentine robots may employ many simple motion actuators in sequence. During operation, the loss of short segments would still permit mobility and maneuverability


Disadvantages of Snake Robots

Payload: Much locomotion has to do with work; the transport of materials from one place to another. There is no integral platform for attaching payloads.
Degrees of Freedom: To subtend the various curves needed for locomotion requires a larger number of actuators than most wheeled or legged vehicles. The number of DOFs in vehicles can range from two up to eighteen and even more for some walkers. A large number of DOFs may introduce reliability problems; numbers of units have a higher chance of having any unit fail.


Exploration: In unpredictable environments, there are zones of uncertainty and footing is insecure or unknown. A snake-like device can distribute its mass over a large area for support so that even if footing gives way, self-support between secure points enables continued operation. Such environments include planetary surfaces and extreme terrains with loose rubble and inclines near the slope of repose.

Inspection: Many inspection techniques in industry and medicine rely on fixed-base mechanisms such as borescopes, videoscopes, and fiberscopes. These devices are primarily used to inspect cavities that cannot be seen directly by the eye. Inspection applications include airline engine maintenance, quality control in manufacturing, and process monitoring and inspection in utilities and chemical plants. Simple direct-view borescopes have proven useful, but articulated self-advancing devices forming and following complex paths could open many more applications.

Medical: Snake-like devices have received attention as a potential medical technology. Minimally-invasive surgery reduces or eliminates the need to cut open large sections of skin and tissue. It is currently estimated that 35% of the 21,000,000 surgeries performed each year could be done with minimally invasive techniques]. There could be dramatic reductions in hospital stays, patient suffering, and costs. Laparoscopic devices, which are rigid tools inserted into the abdominal wall, and Endoscopic devices are used in these types of surgical procedures.

Hazardous Environments: Human activity is precluded in many areas where there are extremes of radiation, temperature, chemical toxicity, pressure or structural weakness. However, it is often necessary to explore and survey these areas to ensure safety and ascertain status. A variety of small tracked or wheeled machines have been constructed for such applications, but these have limitations in their ability to traverse and maneuver through hazardous terrain.
            A serpentine mechanism could fare better due to the advantages cited earlier. Other dangerous areas include those following disasters such as earthquakes, Explosions, cave-ins, hurricanes, fires etcetera. The search for survivors and removal of material is often thwarted by loose rubble that might be penetrable by a snake. Outfitted with sensors such as ammonia or pyroelectric IR detectors, a snake-like mechanism would enable sensing of humans in the rubble. These are applications that would eliminate life-endangering alternatives such as using heavy construction equipment to move loose material from accident sites.

Routing: Much effort in the wiring of existing structures requires routing of cables and lines through narrow passages behind existing walls and through pipes. A variety of manual tools for feeding the lines, such as fish tapes (metal bands) While some specialized devices have been designed for wire and cable routing they are not used in practice.


The basic purpose of the article was to introduce a new and upcoming subsection of hyper-redundant robots which are finding various uses in all fields. The future of snake robots with the amount of research and development being done is very bright. This article is trying to enlist the various types of snake robots emerging and the innumerable ways of achieving redundancy.

Author: Ravi Bandakkanavar

A Techie, Blogger, Web Designer, Programmer by passion who aspires to learn new Technologies every day. It has been 6 years since I have been publishing articles and enjoying every bit of it. I want to share knowledge and build a great community with people like you.

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One thought on “Snake Robot – The future of agile motion

  1. Dhana

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