An Ultra-Fast Rolling Double-Helical Robot Driven by Constant Humidity

Abstract

Untethered soft robots made of stimuli-responsive materials hold great application potential in various fields. However, most robots of this type require artificial modulation of the stimuli to actuate, while it is a great challenge to achieve fast periodic locomotion under a constant external environment. Here, a double-helical robot constructed with humidity-sensitive agarose (AG) films, referred to as the Dualicalbot is proposed, which can rapidly roll under a constant humid environment by making two helices alternately bend by absorbing humidity to actuate the robot in two half-cycles. A theoretical model is built to unveil the periodic deformation of the robot as well as the correlation between the design parameters and the motion speed, based on which the Dualicalbot can reach a maximum rolling speed of 5.8 BL s^-1. Moreover, it is capable of carrying a payload up to 100% of self-weight and detecting the acid environment it rolls through. This work is envisaged, and more generally the structural design and theoretical modeling principle, will open a new avenue for the development of advanced soft robotics with diverse functionalities.

Keywords: constant humidity; double‐helical structure; rolling locomotion; soft robot; stimuli‐responsive materials.

Figure 1

Structural design of the Dualicalbot. A) The Dualicalbot is assembled by two helical strips A₁A₂ and A₃A₄, and two semicircular strips A₁A₄ and A₂A₃. PET plates are placed on both sides of each strip, and six tapes P1 – P6 are attached to the strips at prespecified positions. B) The specific positions of the tapes with respect to the reference planes Γ and Ψ, which are parallel to the xoz and yoz coordinate planes, respectively, and intersecting the geometric center of the robot. i) is the first half cycle, and ii) is the second half cycle after rolling 180°.

Figure 2

Theoretical modeling and experimental validation of the Dualicalbot. A) Geometric parameters of the Dualicalbot. The corrugated strip is a flattened double‐helical structure by cutting at the point A₄. The colors of the four segments correspond to Figure 1A. B) Theoretical configurations of the right‐handed helix A₁A₂ projected on the xoy plane during the first half cycle. C) The configurations comparison and deviation of helix A₁A₂ at the end of the startup stage and at 0.5T, which are obtained from the theoretical model. D) The side view and top view snapshots of the Dualicalbot captured from Movie S2 (Supporting Information) in the startup stage and the first rolling cycle. E) The speed (BL s^{‐ 1}) versus time (s) of the Dualicalbot in the first four locomotion cycles in Movie S2 (Supporting Information). F‐G) Comparison of the experimental and theoretical configurations at the end of the startup stage and at 0.5T, respectively, and the shaded bands are the experimental results of three tests.

Figure 3

Parametric analysis of the Dualicalbot. A–C) The theoretical predictions of the speed vary with different values of geometric parameters. A) is the effect of the strip length a and width b on speed, B) is of the helical angle γ and the strip thickness μ, and C) is of the tape width c and the tape position e. D‐L) The experimental validation of the theoretical results. D–F) show the relationships between the rolling speed and a, and G‐L) are the relationships between the rolling speed and b, γ, μ, c, e, and RH, respectively. The red lines are the theoretical results, and the blue lines are obtained from experiments, which contain the error bars of at least four measurements.

Figure 4

Performance demonstrations of the Dualicalbot. A) Ashby plot of the maximum locomotion speed (BL s⁻¹) versus the body length (mm) in the reported untethered soft robots made from stimuli‐responsive materials. B) The relationship between rolling speed and payload of the Dualicalbot with optimal geometric and environmental parameters (scale bar: 6 mm). C) Experimental snapshots of the acid environment detection robot rolling over the humid and acid area, and then discoloring in the dry and neutral area.