Scalybot: A Snake-Inspired Robot With Active Control of Friction

Abstract

Snakes are one of the world’s most versatile locomotors, at ease slithering through rubble or ratcheting up vertical tree trunks. Their adaptations for movement across complex dry terrain thus serve naturally as inspirations for search-and-rescue robotics. In this combined experimental and theoretical study, we perform experiments on inclined surfaces to show a snake’s scales are critical anatomical features that enable climbing. We find corn snakes actively change their scale angle of attack by contracting their ventral muscles and lifting their bodies. We use this novel paradigm to design Scalybot, a two-link limbless robot with individually controlled sets of belly scales. The robot ascends styrofoam plates inclined up to 45°, demonstrating a climbing ability comparable to that of a corn snake in the same conditions. The robot uses individual servos to provide a spatial and temporal dependence of its belly friction, effectively anchoring the stationary part of its body while reducing frictional drag of its sliding section. The ability to actively modulate friction increases both the robot’s efficiency over horizontal surfaces and the limiting angles of inclination it can ascend.

Enhanced Locomotion Efficiency of a Bio-inspired Walking Robot using Contact Surfaces with Frictional Anisotropy

“…This makes our solution simple and cheap. Our approach is also different from other developments which require complex motion control or/and special robot structures (e.g., active scales) to achieve frictional anisotropy for efficient locomotion263738.…”

“…On the other hand, having strong mechanical interlocking in both directions (i.e., frictional isotropy) will also allow the robot to grip to the surface but it will have difficulty releasing itself from the surface. Based on these concepts of frictional anisotropy and mechanical interlocking, Marvi et al 26. developed active scales and their control to generate the frictional anisotropy for the snake-inspired robot Scalybot; thereby allowing it to climb inclines up to 45°.…”

Friction enhancement in concertina locomotion of snakes

“…We have implemented static friction in a model for Scalybot, a two-segment snake robot [14]. We are currently working on a generalized static friction model for nodes of higher order using equation (3.5).…”

“…This material was employed because its roughness was greater than the corn snake scale thickness of 45 mm. In this regime, friction coefficients m st are significantly affected by scale angle of attack, as shown in Marvi et al [14]. Static friction coefficients of the snake's ventral surface were measured using the inclined plane method on a 90 Â 30 cm styrofoam plank [13].…”

Incorporating frictional anisotropy in the design of a robotic snake through the exploitation of scales

“…Scalibot [8] is an example of such a two-link robot that has scales attached to its underbelly. This design uses prismatic joints to actuate the robot, essentially anchoring the back link to move forward.…”