Passively Adapting Enclosed Tip Mount

• The paper introduces a passively adapting enclosed tip mount that dynamically adjusts clamp force to maintain distal payload placement and reduce propulsion losses in soft growing vine robots.
• It employs a 3D printed Onyx clamp with elastic bands and a high-friction silicone sheet to achieve state-dependent friction through passive mechanical adaptation.
• Experimental validations in a pipe-inspection setup demonstrate that the adaptive design outperforms constant-force mounts by minimizing drag and enhancing payload transport efficiency.

Searching arXiv for the specified paper and closely related tip-mount work on vine/eversion robots. arxiv_search(query="^^^^^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^^^^^"A Hermetic, Transparent Soft Growing Vine Robot System for Pipe Inspection\"^^^^^^^^2 OR \2^^^^^^^^"passively adapting enclosed tip mount\"", max_results=5)

Passively adapting enclosed tip mount denotes an enclosed payload-transport mechanism for soft growing vine robots that automatically changes its clamp force as it approaches the everting tip, allowing sensing and communication hardware to remain near the distal inspection front while reducing propulsion losses (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). In the 2^^^^2(Heap et al., 30 Oct 2025) OR \22^^^^5 pipe-inspection system in which the concept is introduced, the mount operates inside a hermetic, transparent vine robot body and is designed to solve a specific eversion kinematics problem: because the robot grows from the tip and the tail travels at twice the speed of the tip, an internal payload attached to the tail would otherwise be left behind unless it is continuously transported forward (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The mechanism therefore occupies a distinct place within the broader literature on vine-robot tip hardware, differing both from external textile caps that rely on distributed friction over the body surface (Suulker et al., 2023, Suulker et al., 2024) and from roller-based internal mounts optimized for high-speed growth on high-friction bodies (Valdivia et al., 4 Jun 2026).

^^^^2 OR \2^^^^. Concept and problem formulation

The passively adapting enclosed tip mount was introduced in the context of a hermetic and transparent vine robot system for visual condition assessment and mapping within non-branching pipes (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). Its function is to keep the cameras, MCU, IMU, PoE splitter, and cable tether near the robot’s growing tip while all components remain enclosed inside the soft, airtight, and transparent body. This requirement arises because the payload cannot simply be rigidly fixed to the robot body: in an everting robot, the tip is not a static end-effector but a moving growth front.

The relevant locomotion principle is eversion. Pressurizing an inverted LDPE tube causes the body to extend from the tip, and the paper states that the tail travels at twice the speed of the tip (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). This kinematic asymmetry creates a transport problem internal to the robot: a load attached to the tail is dragged relative to the body as growth proceeds. The passively adapting enclosed tip mount is intended to maintain distal payload placement without incurring the major propulsion losses that would result from a clamp with approximately fixed friction.

The paper distinguishes two enclosed transport concepts. The first is the constant-force enclosed tip mount, which clamps the tail with roughly fixed friction. The second is the passively adapting enclosed tip mount, whose clamp force changes automatically depending on where the mount is relative to the robot tip (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The latter is reported as preferable because it reduces the force lost to drag while still keeping the payload at the tip.

2. Mechanical architecture and passive adaptation principle

Mechanically, the mount is a 3D printed Onyx part with a scissor-like, two-arm clamp (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). Elastic bands provide the closing force, and a high-friction silicone sheet (Dycem) forms the gripping surface against the vine robot tail. The payload and the mount are attached to the tail, so as the robot grows, the tail is pulled forward and the mount is carried along with it.

Its defining feature is not continuous low friction, but state-dependent friction. While the mount remains behind the true tip, it stays clamped tightly enough to remain attached to the tail. Once it reaches the growing tip, the geometry of the everting tail pushes the two clamp arms apart, reducing the effective clamping force (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). This reduction in clamping force lowers the frictional resistance to tail motion. The mount is therefore described as passively adapting because no actuator, sensor, or active control is required; the clamp force changes automatically through interaction between clamp geometry, tail, and everting body.

The paper’s qualitative interpretation is that the mount is designed to be sufficiently gripping while it is transported forward, but to become easier to slide once it arrives at the tip (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). This is the central contrast with fixed-friction designs, which must be tuned conservatively to avoid slipping and therefore dissipate more of the available growth force.

3. Geometric and analytical model

The paper frames the adaptive behavior through a moment balance about the clamp pivot. Letting the spring force be PRESERVED_PLACEHOLDER_^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^, the authors write

PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^

where $d$ and $w$ are moment-arm lengths associated with the normal and friction components at the clamp, $\mu_s$ is the static friction coefficient, $f_{\text{coupling,max}$ is the maximum frictional coupling force between the mount and tail, and $\overrightarrow{F}_{va}$ and $\overrightarrow{F}_{vb}$ are reaction forces from the vine robot body acting to open the clamp (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

The paper’s qualitative conclusion from this relation is that $f_{\text{coupling,max}$ becomes a decreasing function of the opening forces generated by body-tail interaction. Thus, when the mount reaches the tip and the body geometry pushes on it more strongly, the clamp loosens automatically. The same section states that this sensitivity can be increased by making the force moment arms longer, decreasing $d$, or otherwise tuning the clamp geometry (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

The mount is also embedded in the standard vine-robot growth-force model. The baseline growth relation is given as

PRESERVED_PLACEHOLDER_^^^^2 OR \2(Heap et al., 30 Oct 2025) OR \2^^^^

and, for the robot in the paper, the authors later experimentally confirm

PRESERVED_PLACEHOLDER_^^^^2 OR \2 OR \2^^^^

with a measured value of ^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^.5^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^3, together with

PRESERVED_PLACEHOLDER_^^^^2 OR \22^^^^

(&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). When a load and tether are attached, the minimum pressure relation becomes

PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^3

where PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^4 includes frictional, gravitational, and base-station-induced forces from the tether and payload (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

For a constant-force enclosed tip mount, the paper modifies the growth condition to include

PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^5

and

PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^6

(&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). For the passively adapting design, the corresponding relations are

PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^7

and

PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^8

(&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The key distinction is that PRESERVED_PLACEHOLDER_^^^^2 OR \2^^^^9 now decreases as the mount is pushed open, lowering the interaction-force penalty. The paper states that, for a given maximum load, the passive mount introduces less propulsive force loss than a constant-force design (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

4. Fabrication and experimental validation

The mount is fabricated by 3D printing with Onyx on a Markforged printer; Dycem silicone sheet increases friction with the tail, and elastic bands serve as the spring element (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The design is explicitly characterized as simple, lightweight, and fully enclosed, so that it can operate inside the airtight body without exposing electronics to the pipe environment.

Experimental validation used a controlled growth setup. The procedure was to attach known masses to the vine robot tail or to the attached tip mount, seal an 88 mm diameter LDPE tube, ^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^.^^^^2 OR \2^^^^8 mm thick, to a pressure vessel using rubber gaskets and a hose clamp, increase internal pressure until growth was visually observed, repeat each condition for ^^^^2 OR \2(Heap et al., 30 Oct 2025) OR \2^^^^ trials, and measure pressure with a differential pressure gauge (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The robot grew vertically against gravity. The tail was approximated as 25 cm long with mass 9 g.

The no-tip-mount tests established the baseline system parameters, yielding $d$^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^ and $d$^^^^2 OR \2^^^^ (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The authors then tested constant-force and passively adapting mounts at nominal coupling strengths of ^^^^2 OR \22^^^^ N and 24 N, with clamp tuning checked using a force gauge and kept within ^^^^2 OR \2(Heap et al., 30 Oct 2025) OR \2^^^^% of the nominal value (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

The reported result is comparative rather than merely demonstrative. When the load is near the maximum coupling force, both designs approach the theoretical minimum growth pressure. As the load decreases, however, the constant-force design deviates strongly and requires nearly constant pressure, whereas the passively adapting design also deviates from the minimum but much less severely, because the clamp opens more easily as it reaches the tip (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The authors further note that practical operation should use a safety factor below maximum coupling friction so the mount is reliably transported; under that choice, the passive design clearly outperforms the constant-force design (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

5. Relation to textile soft caps and other tip-mount paradigms

The passively adapting enclosed tip mount belongs to a broader line of research on payload retention at the evolving tip of vine robots, but it addresses a different design regime from textile caps. The earlier soft cap literature describes a fully fabric-based cylindrical cap slipped over the tip “like a beanie,” with retention based on distributed friction and textile compliance rather than a pivoted clamp (Suulker et al., 2023). That design was proposed to preserve flexibility, squeezability, and navigability while carrying payloads such as a camera across long distances (Suulker et al., 2023). A closely related deformable tip mount is similarly described as a fabric-based, slip-on cap intended to preserve passage through narrow openings, permit eversion of protruding objects, and remain attached during body reorientation / navigation (Suulker et al., 2024).

These textile devices and the enclosed passive clamp share the feature of passive adaptation, but they solve different packaging problems. The textile caps are mounted externally over the everting tip, rely on circumferential friction, and are particularly suited to applications in which the payload may remain outside the main body while the cap deforms with the robot (Suulker et al., 2023, Suulker et al., 2024). By contrast, the passively adapting enclosed tip mount was developed for a hermetic architecture in which all electronics remain inside the airtight transparent body and the mount must both transport the payload forward and preserve the hermetic seal (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&).

Later work on high-speed vine robots presents yet another paradigm: a triangular roller tip mount that reduces internal resistance by rolling rather than sliding against the robot body, with performance benchmarked through tail tension (Valdivia et al., 4 Jun 2026). That design is also described as passively adapting, but its mechanism of adaptation differs. Its adaptation arises from geometric matching to the triangular body profile, compliant/rolling interfaces, and self-centering through internal bearing-like contact, rather than from a clamp whose friction force decreases when the everting tip pushes the arms open (Valdivia et al., 4 Jun 2026). This suggests that “passive adaptation” in vine-robot tip mounts is a broader class of design strategies rather than a single mechanism.

6. Operational significance, constraints, and unresolved issues

Within the 2^^^^2(Heap et al., 30 Oct 2025) OR \22^^^^5 pipe-inspection system, the passively adapting enclosed tip mount is the mechanism that makes the hermetic transparent architecture operationally viable (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). Because the payload remains near the inspection front, the robot can support condition assessment and mapping while keeping delicate electronics protected inside the body. The paper reports that, in the laboratory, the system traversed a 4.57 m pipe with three 9^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^° bends, reconstructing the path with less than 2.6° orientation deviation and less than ^^^^2 OR \2(Heap et al., 30 Oct 2025) OR \2^^^^ cm length deviation; in the field, it inspected a wastewater pipe and captured imagery of pipe damage and turns (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). The mount is presented as an enabling component in these demonstrations because it allows the payload to remain at the front without prohibitive growth resistance.

The design should not be conflated with a universally low-drag coupler. The paper explicitly emphasizes that the mount is not intended to exhibit low friction at all times; rather, it must be sufficiently gripping when transported forward and easier to slide only when it reaches the tip (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). A plausible implication is that the mount’s effectiveness depends on tuning for a specific load envelope and body geometry, since the same clamp must satisfy transport and release requirements under changing contact conditions.

The broader tip-mount literature identifies related constraints. In the textile-cap work, the friction-mobility balance is described as delicate: if the cap is too tight, friction becomes too large and blocks eversion; if it is too loose or too short, it can be pushed off the tip (Suulker et al., 2023). In the high-speed roller-mount work, the main performance metric $d$2 is treated as an aggregate measure of added resistance rather than a pure friction measurement (Valdivia et al., 4 Jun 2026). Taken together, these results indicate that tip-mount design for vine robots is governed by force-budget allocation as much as by attachment robustness.

The passively adapting enclosed tip mount therefore occupies an important intermediate position in the evolution of vine-robot end hardware. It retains the low-complexity, self-adjusting character associated with passive textile mounts, but translates that logic into an internal, hermetic, clamp-based mechanism tailored to enclosed payload transport (&&&^^^^2(Heap et al., 30 Oct 2025) OR \2^^^^&&&). Its primary significance lies in showing that a self-tuning frictional coupler can support distal sensing inside a sealed growing robot without the propulsion penalties associated with a conservatively tuned constant-force clamp.