Snake robots can traverse complex environments with limbless locomotion, but maneuvering in low-clearance environments remains challenging because a gait must maintain a small swept height while also providing planar steering. Existing rolling gaits preserve a low swept height body configuration but generally provide limited steering, whereas steering gaits often introduce vertical undulation and require additional clearance. With that in mind, this paper develops S-rolling, a steerable rolling gait that combines low swept height locomotion with planar maneuverability for twistable snake robots. S-rolling is designed using an S-shaped planar backbone curve, whose head and tail segments roll with independently controlled angular velocities, producing different motion modes. We derive its joint space gait equation, in which a central twist joint realizes the relative rotation between the two segments. We also develop a quasi-static kinematic model relating the segment rolling speeds to the linear and angular velocities of the robot. Real-robot experiments demonstrate the various motion modes, traversal through a 10 cm clearance test track, and maneuvering tasks beneath a large workpiece and a car chassis. In these low-clearance scenarios, S-rolling successfully performs approximately 90∘ and 180∘ heading changes, whereas the baseline rolling arc gait cannot change the robot heading.
Figures & tables
Fig. 1: The T-Snake uses S-rolling to conduct the tests under a car chassis. (a) The joint arrangement of a T-Snake module, and the bottom view of the T-Snake traversing under the chassis. (b) Task sequence: 1) entering beneath the vehicle; 2) turning 180∘ in place to reorient its head; and 3) exiting from beneath the vehicle. (d) The proposed S-rolling gait realizes 180∘ heading change, while (c) the baseline gait, rolling arc, cannot perform.
Fig. 2: Overview of the dorsal reference curve. (a) The dorsal reference frames along the curve c(s) . (b) The relative rotation angle ϕij from frame Di to frame Dj .
Fig. 3: Develop S-rolling using backbone curve method. (a) The backbone curve consists of two tangential circular arcs. A bellows frame Dr is defined along the curve. We add geometric constraints to determine the unique configuration of the curve. (b) The curve is divided into two segments, and the rolling of each segment is controlled by a different rotation angle. After rotating e^ar , it forms e^ah in frame Dh and e^at in frame Dt .
Fig. 4: Illustration of the discrete mechanism of T-Snake.
Fig. 5: Illustration of the kinematic model of S-rolling on the T-Snake.
Fig. 6: S-rolling locomotion tests under laboratory conditions. (a)-(d) Different motion modes of S-rolling on the T-Snake hardware. (e) Trajectory of the T-Snake traversing the test track.
Fig. 7: Illustration of the T-Snake tests under a large workpiece. (a) The rolling arc gait cannot reach the target exit, while (b) the proposed S-rolling gait completes the task successfully. (c) The bottom view of the T-Snake traversing under the workpiece.