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Generation of Propulsive Force via Vertical Undulations in Snakes


Jurestovsky, Derek; Usher, Logan; Astley, Henry (2021), Generation of Propulsive Force via Vertical Undulations in Snakes, Dryad, Dataset,


Lateral undulation is the most widespread mode of terrestrial vertebrate limbless locomotion, in which posteriorly propagating horizontal waves press against environmental asperities (e.g. grass, rocks) and generate propulsive reaction forces. We hypothesized that snakes can generate propulsion using a similar mechanism of posteriorly propagating vertical waves pressing against suitably oriented environmental asperities. Using an array of horizontally oriented cylinders, one of which was equipped with force sensors, and a motion capture system, we found snakes generated substantial propulsive force and propulsive impulse with minimal contribution from lateral undulation. Additional tests showed that snakes could propel themselves via vertical undulations from a single suitable contact point, and this mechanism was replicated in a robotic model. Vertical undulations can provide snakes a valuable locomotor tool for taking advantage of vertical asperities in a variety of habitats, potentially in combination with lateral undulation,  to fully exploit the 3D structure of the habitat.


This dataset was collected using a 248 cm long trackway with eleven horizontal oak dowels with one dowel equipped with two six-axis force sensors on either end. Four corn snakes (Pantherophis guttatus) were encouraged to traverse the trackway with six motion capture cameras set up to track their progress and obtain kinematics. Data was analyzed using a custom-written script in MATLAB. An ANOVA and Tukey's post-hoc statistical tests were carried out also using custom-written scripts in MATLAB. Two additional tests were conducted with an 8° (insufficient angle for vertical undulation) and 30º (sufficient angle for verticl undulation) sloped wedge to determine whether the snake could traverse a tunnel using vertical undulation. Finally, a snake-like robot, made of 3D printed parts and servo motors, was used to confirm whether vertical undulation alone can propel a snake-like robot through our experimental setup.


University of Akron