Snails employ a distinctive crawling mechanism in which the pedal waves travel along the foot and interact with the mucus to promote efficient movement on various substrates. Inspired by the concavities on the pedal wave, we develop a new bionic snail robot that introduces transverse patterns in a longitudinal wave to periodically change the friction. The poroelastic foam serves as flexible constraint and fills the robot's internal cavity. It contributes to the bending action, and maintains the thinness and softness of the robot. Then, the model of the robot's single segment is built utilizing the Euler-Bernoulli beam theory. The model aligns well with the experimental data, thereby confirming the effectiveness of soft constraints. The evaluation of pedal wave is conducted, which further guides the optimization of the control sequence. The experiments demonstrated the robot performing retrograde wave locomotion on dry substrates. Notably, shear-thickening fluids were found to be suitable for this particular crawling pattern compared with other mucus simulants, resulting in direct wave locomotion with a 49% increase in speed and a 33% reduction in energy usage. The load capacity of the soft snail robot was also enhanced, enabling it to carry loads up to 2.84 times its own weight. The use of mucus in crawling also brings valuable insights for the enhancement of other biomimetic robots.
Keywords: direct and retrograde waves; mucus simulant; poroelastic foams; shear-thickening liquids; snail robot.