On Steerability Factors for Growing Vine Robots

TL;DR

The paper addresses how design and control parameters influence 3D steerability of pneumatically steered vine robots carrying tip payloads. It conducts systematic experiments in self-supporting 3D and ground-supported planar settings, comparing exterior versus integrated pouch designs and varying pressure ratios to quantify steerability. Key findings show steerability declines with increasing tip load, peaks at moderate chamber pressure, increases with length, and is largely insensitive to diameter; exterior pouches bend at lower pressure ratios but saturate, while integrated pouches require higher ratios yet achieve higher curvature. These results yield practical guidelines for task-specific vine robot design and control, while also highlighting hysteresis and the need for strategies to coordinate growth and steering in real-world deployments.

Abstract

Vine robots extend their tubular bodies by everting material from the tip, enabling navigation in complex environments with a minimalist soft body. Despite their promise for field applications, especially in the urban search and rescue domain, performance is constrained by the weight of attached sensors or tools, as well as other design and control choices. This work investigates how tip load, pressure, length, diameter, and fabrication method shape vine robot steerability--the ability to maneuver with controlled curvature--for robots that steer with series pouch motor-style pneumatic actuators. We conduct two groups of experiments: (1) studying tip load, chamber pressure, length, and diameter in a robot supporting itself against gravity, and (2) studying fabrication method and ratio of actuator to chamber pressure in a robot supported on the ground. Results show that steerability decreases with increasing tip load, is best at moderate chamber pressure, increases with length, and is largely unaffected by diameter. Robots with actuators attached on their exterior begin curving at low pressure ratios, but curvature saturates at high pressure ratios; those with actuators integrated into the robot body require higher pressure ratios to begin curving but achieve higher curvature overall. We demonstrate that robots optimized with these principles outperform those with ad hoc parameters in a mobility task that involves maximizing upward and horizontal curvatures.

Figures (8)

• Figure 1: Recommendations for robot operation. Our research shows that steerability is higher when a robot has lower tip weight, a moderate chamber pressure relative to its actuators, and a longer length. Diameter has minimal impact, while the ideal fabrication method depends on what pressure ratios the robot will operate at. A robot with uninformed parameters steers to lower curvatures than a robot with informed parameters.
• Figure 2: Experimental setup and points of interest for self-supporting 3D steerability experiments. (a) The robot is placed on a table with support only underneath the base section. Tracking the base LED, tip LED, and coordinate axis allows us to align the data with a reference frame fixed to the table. (b) The order in which the robot tip visits the six via points is shown in blue. The convex hull area of those points is shown in red. The square root of the convex hull area is the characteristic length, which is plotted in Fig. \ref{['key experiments']}, along with the horizontal and vertical range.
• Figure 3: Results of self-supporting 3D steerability experiments. For all parameters, we plot the average characteristic length and its standard deviation, along with the horizontal and vertical range for each trial. (a) Increasing tip load significantly decreases characteristic length, horizontal range, and vertical range. (b) Increasing pressure initially increases and then decreases characteristic length; it significantly decreases horizontal range and changes vertical range erratically. (c) Increasing robot length increases characteristic length and significantly increases horizontal range, while decreasing vertical range. (d) As long as the robot is not collapsed (leftmost data point), varying diameter does not significantly impact characteristic length, horizontal range, or vertical range.
• Figure 4: Cross-section diagram of robot body fabrication methods. (a) Exterior pouches: series pouch motor actuators are heat sealed separately and taped to the outside of the main chamber tube. (b) Integrated pouches: pouch chambers are heat sealed directly to the main chamber tube. Both designs use thermoplastic polyurethane-coated ripstop nylon.
• Figure 5: Experimental setup for supported planar steerability experiments. The robot (1.75 m long) is entirely supported on the floor as it curves due to changing actuator and chamber pressure. Motion capture markers are placed along the centerline at 25 cm intervals to capture the robot shape and tip position.