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REVIEW 2 major objections 38 references

Polymander II: an amphibious salamander-inspired robot with contact and flow sensors

T0 review · 2 major / 0 minor · reviewed 2026-06-30 · grok-4.3

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Pith's one-line read A salamander-inspired robot uses Hall-effect sensors to measure both foot contact forces on land and lateral hydrodynamic forces in water.

desk verdict Polymander II integrates Hall-effect sensors for dual land-water force sensing on an existing salamander platform with some practical details, but the performance claims rest on unshown test data. read the letter →

arxiv 2605.24465 v2 pith:A22LQ7MM submitted 2026-05-23 cs.RO

Qiyuan Fu , Sudong Lee , Andrea Grillo , Jonathan Arreguit , Louis Gevers , Josie Hughes , Auke J. Ijspeert This is my paper · ORCID
classification cs.RO
keywords amphibiousrobotHall-effectsensorsalamander-inspiredcontactforcehydrodynamiclocomotioncontrolexteroceptivesensingfeedback
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper presents Polymander II, an amphibious robot inspired by salamanders, that integrates Hall-effect sensors at multiple body positions to capture exteroceptive data. These sensors detect ground contacts during terrestrial movement and water flow forces during aquatic movement while also acquiring joint positions and loads. The system supports simultaneous high-rate sensing above 500 Hz for forces and 100 Hz for proprioception, with compact design that simplifies waterproofing. This addresses the limitation that few amphibious robots can sense interactions in both environments. A sympathetic reader would care because such sensing could enable more robust transitions between terrains and coordinated body movements.

What carries the argument

Hall-effect sensors that infer forces from magnetic field changes and can be placed separately from the measured object, enabling easy embedding and waterproofing while delivering high sensitivity to small forces.

What would settle it

Tests showing consistently noisy or inaccurate force readings from the sensors during combined land-water locomotion trials, or the robot failing to maintain stable gaits when sensor data is used for control adjustments.

Watch

Extended reading notes

Core claim

Hall-effect sensors embedded in the robot provide accurate measurements of foot contact forces and lateral hydrodynamic forces across terrestrial and aquatic conditions, allowing the robot to traverse amphibious environments and opening the possibility of feedback control for complex locomotion tasks.

Load-bearing premise

The Hall-effect sensors deliver accurate low-noise force measurements in both land and water without needing extensive calibration for each new deployment or environment.

Editorial extensions

If this is right

  • The robot can traverse mixed amphibious environments using the combined sensor data.
  • Feedback control becomes feasible for handling more complex locomotion tasks across terrain changes.
  • Simultaneous high-frequency exteroceptive and proprioceptive data supports real-time body coordination.
  • Compact sensor placement at multiple positions scales to other robot designs needing dual-environment sensing.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The same sensor approach might extend to robots that must handle additional transitions such as mud or ice without redesigning the sensing hardware.
  • Force data could be used to automatically adjust leg stiffness or body posture at the moment of entering or exiting water.
  • Integration with existing joint load sensors may allow closed-loop gait optimization that reduces energy use during environment switches.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 0 minor

Summary. The manuscript presents Polymander II, a salamander-inspired amphibious robot that embeds Hall-effect sensors to measure foot contact forces and lateral hydrodynamic forces. The design uses two bus lines to acquire exteroceptive data at >500 Hz alongside proprioceptive joint data at 100 Hz. The sensors are described as compact, sensitive to small forces, and easy to waterproof. The authors state that tests demonstrate the robot's traversal of amphibious environments and the potential for feedback control in complex locomotion tasks.

Significance. If substantiated, the sensor integration approach could provide a practical route for amphibious robots to obtain multi-modal force feedback without heavy per-deployment calibration, supporting more adaptive bio-inspired locomotion. The emphasis on embedding multiple compact sensors while maintaining high sampling rates and waterproofing offers engineering value for similar platforms. The current absence of quantitative validation, however, limits the work to a design description rather than a demonstrated advance.

major comments (2)
  1. [Abstract] Abstract: the claim that 'Our tests demonstrate the robot's capabilities in traversing amphibious environments and its potential in using feedback control for more complex locomotion tasks' supplies no quantitative results, error analysis, sensor calibration data, or control-loop details, leaving the central claim unsupported by visible evidence.
  2. [Abstract] Abstract / sensor description: the assertion that Hall-effect sensors embedded at multiple positions deliver accurate, low-noise measurements of both contact and hydrodynamic forces across terrestrial and aquatic conditions without requiring extensive per-deployment calibration is presented without supporting calibration curves, noise spectra, or cross-environment accuracy metrics.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on our manuscript. We agree that the abstract contains claims that exceed the quantitative evidence presented and will revise it accordingly to align with the design-focused content of the paper.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the claim that 'Our tests demonstrate the robot's capabilities in traversing amphibious environments and its potential in using feedback control for more complex locomotion tasks' supplies no quantitative results, error analysis, sensor calibration data, or control-loop details, leaving the central claim unsupported by visible evidence.

    Authors: We accept this criticism. The manuscript emphasizes the sensor integration and robot design, with tests limited to qualitative demonstrations of amphibious traversal. No quantitative results, error analysis, or control-loop implementations for feedback are included. We will revise the abstract to remove the unsupported claim about feedback control potential and limit the statement to the observed traversal capabilities. revision: yes

  2. Referee: [Abstract] Abstract / sensor description: the assertion that Hall-effect sensors embedded at multiple positions deliver accurate, low-noise measurements of both contact and hydrodynamic forces across terrestrial and aquatic conditions without requiring extensive per-deployment calibration is presented without supporting calibration curves, noise spectra, or cross-environment accuracy metrics.

    Authors: The abstract statement summarizes the intended advantages of the Hall-effect sensor approach as described in the design section. However, we agree that the abstract itself provides no supporting quantitative data such as calibration curves or noise metrics. We will revise the abstract to qualify or remove this assertion, ensuring it does not overstate the evidence provided in the manuscript. revision: yes

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: hardware integration paper with no derivations or fitted predictions

full rationale

The paper is a description of robot hardware, sensor integration, and qualitative test demonstrations. It contains no equations, parameter fitting, predictions, or derivation chains. The central claims reduce to empirical observations of sensor performance and locomotion capability rather than any self-referential mathematical reduction. No load-bearing steps exist that could be circular by the enumerated patterns.

Assumptions & free parameters 0 free parameters · 1 assumptions · 0 invented entities

The central claim rests on standard domain assumptions about sensor behavior and robot mechanics rather than new free parameters or invented entities.

assumptions (1)
  • domain assumption Hall-effect sensors embedded in the robot structure can accurately transduce small contact and hydrodynamic forces in both air and water without significant structural interference or environmental noise.
    This premise is required for the claimed high-frequency exteroceptive sensing to be usable for locomotion control.

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Cite this review

Pith. "Pith review of Polymander II: an amphibious salamander-inspired robot with contact and flow sensors." pith.science (2026). https://pith.science/paper/A22LQ7MM

@misc{pith2026260524465,
  author       = {Pith},
  title        = {Pith review of: Polymander II: an amphibious salamander-inspired robot with contact and flow sensors},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/A22LQ7MM}},
  note         = {Machine review of arXiv:2605.24465}
}
read the original abstract

Robots benefit from sensory information to coordinate body movement, gain robustness against perturbations, and transition between different modes to adapt to various terrains. However, few amphibious robots can sense interactions with both terrestrial and aquatic environments. In this paper, we present a solution that uses Hall-effect sensors to sense foot contact forces and lateral hydrodynamic forces on a salamander-inspired amphibious robot. With two bus lines, the robot can simultaneously acquire this exteroceptive information at more than 500 Hz and proprioceptive information, such as joint positions and loads, at 100 Hz. The Hall-effect sensors used are compact, making them suitable for embedding in multiple positions within a robot, and exhibit high sensitivity to small forces. Moreover, because the sensor can be positioned separately from the measured object, waterproofing can be implemented with relative ease. Our tests demonstrate the robot's capabilities in traversing amphibious environments and its potential in using feedback control for more complex locomotion tasks.

Figures

Figures reproduced from arXiv: 2605.24465 by the authors.

Figure 1
Figure 1. Overview of Polymander II. (a) Major components. (b) Applications [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Design of the foot contact sensor. (a) (i) Assembled design and [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 4
Figure 4. Design of the flow sensor. (a) Assembled design and sensor [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
Figures from the paper (3 more)
Figure 5
Figure 5. Figure 5: Characterization results. (a) Linear relationship between the fin [PITH_FULL_IMAGE:figures/full_fig_p004_5.png]
Figure 6
Figure 6. Figure 6: Sealing mechanisms. (a) Sealing structure for the foot. (i) Hose [PITH_FULL_IMAGE:figures/full_fig_p005_6.png]
Figure 8
Figure 8. Figure 8: Walking with an open-loop CPG controller. (a) Snapshots of a [PITH_FULL_IMAGE:figures/full_fig_p007_8.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

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Pith tools

Reviewed June 30, 2026 · model on record in the stance chip above.