Hygrobot: Hydrogen-Powered Mobile Robotic Platform for Rough Terrain: Electro-Mechanical Design, Physical Implementation, and Experimental Testing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The presented research is very interesting and promising. I congratulate the authors on the results achieved. However, I have a few comments.

The description of the structure is too detailed, it is not a target structure - it is just a testbed

There is no description of the design assumptions (empty weight, payload, speed, maximal slop) for UGVs and no estimation of the average and peak load of engines (drive system), which should be the basis for the motor selection.

There is no description of the expected conditions of use (motion resistance and speed) and no estimate of the necessary power on wheels.

Volume should be expressed in dm³

Pressure should be expressed in MPa or kPa

No description of the surface on which the test was conducted – type of surface and its inclination, etc.

No description of brake efficiency – what accelerations occur during braking or what is the permissible slope of the terrain for which the brakes are sufficient

The assessment of driving force is carried out by relating the driving force to the vehicle's weight or by specifying the maximum gradient of the hill - not the moment at the wheels.

 

Author Response

Dear Editor-in-chief and Reviewer

On April, 1^st 2025, we received the decision from your prestigious journal regarding our article applsci-3558007. Editor invited us revise the manuscript found at the above link according to the reviewers' comments and upload the revised file with deadline 18th April.

The authors are grateful for the opportunity to resubmit the article and have carefully followed all the reviewers’ recommendations.

In the attached response letter , we provide our responses to the reviewers’ comments. Each comment is first numbered, followed by the authors' response (in blue colour). If applicable, we also include a separate paragraph detailing the changes made in the revised version of the manuscript.

All modifications resulting from the reviewers’ comments are highlighted in the revised manuscript.

Sincerely,

The Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The Authors have prepared a fascinating manuscript entitled " Hygrobot: hydrogen-powered mobile robotic platform for rough terrains. Electro-mechanical design, physical implementation and experimental testing." Regardless, please refer to the comment from the Reviewer for improvement.

Major

1. Please highlight the important parameter of hydrogen utilization in the abstract. For example, the longest distance, operation duration, hydrogen consumption efficiency, and other theoretical to implementation metrics were achieved from the hydrogen system. So that it aligns with the manuscript title that highlights the hydrogen-powered mobile robotic platform.
2. Please elaborate more in the introduction section in regard to:
   1. Why should the author integrate the use of a battery with the PEMFC in the design?
   2. What is the reason for selecting the LiPo battery compared to other battery types?
   3. What is the reason for selecting the PEMFC compared to other fuel cell types?
3. What are the anticipated lifetime, durability, and key performance metrics of expected outcomes of the design created by the Authors? This is not yet reflected in the data presented.
4. In relation to Table 5. Please elaborate more information such as the type of battery, power density of the battery, charging power density (W/cm³), and charging capacity, including delivery from the battery and hydrogen fuel cell, so that it can be directly compared with the same scientific perspective of the respective cited reference. Please also add more reference comparisons if there are any publications that use a hybrid of battery and fuel cell in a similar manner as what the Authors did.
5. In relation to Table 5, please also elaborate on cost efficiency and performance efficiency. For example, distance/kWh, LCOE of electricity, etc., to show the strength or weakness of the compared system.
6. What is the design of the drivetrain that is used in the Author’s design, and why is it designed in such a way? Please elaborate also in the context of hydrogen utilization. Drivetrain examples are FWD, RWD, 4WD, AWD, or others that can be explained by the Authors.
7. Is there any specific reason for the author to select IP50, as stated in Table 5, for the designed Hygrobot: hydrogen-powered mobile robotic platform? Is it a minimum requirement or just a capability in the current state of the art? Please elaborate more in the manuscript.

Minor

1. Please check the consistency of the unit throughout the manuscript. I.e., on page 14. The hydrogen consumption values measured by FT-01 range from 3.78 L/min to 4.36 L/min, while the average hydrogen consumption by the ground robotic platform is 𝑉_{𝐻2𝑐𝑜n𝑠𝑢𝑝𝑡𝑖𝑜𝑛} = 4.05 l/min. It should be l/min or L/min; L or l for liters?

 

Comments on the Quality of English Language

It seems good

Author Response

Dear Editor-in-chief and Reviewer,

On April, 1^st 2025, we received the decision from your prestigious journal regarding our article applsci-3558007. You invited us revise the manuscript found at the above link according to the reviewers' comments and upload the revised file with deadline 18th april.

The authors are grateful for the opportunity to resubmit the article and have carefully followed all the reviewers’ recommendations.

We provide our responses to the reviewers’ comments in attached letter. Each comment is first numbered, followed by the authors' response (in blue colour). If applicable, we also include a separate paragraph detailing the changes made in the revised version of the manuscript.

All modifications resulting from the reviewers’ comments are highlighted in the revised manuscript.

Sincerely,

The Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study presents a hydrogen-battery hybrid mobile robotic platform (Hygrobot) with a focus on rough terrain mobility and energy management. The mechanical design, hybrid power integration, and safety protocols demonstrate engineering practicality. However, revisions are required to strengthen innovation claims, experimental rigor, and contextual relevance.

1. Insufficient Novelty Clarification

• Issue: Prior works (e.g., Dudek et al., 2023) have explored PEMFC in mobile robots, but differentiation in mechanical design (e.g., suspension) or energy management is not adequately justified.
• Suggestion: Compare with recent platforms (e.g., Ibericadron XAG R150 V2) to highlight unique contributions.

2. Incomplete Experimental Validation

• Issue: Lack of long-term durability tests (>500 hours) and extreme environment (temperature/humidity) performance data limits generalizability.
• Suggestion:
  • Add tests under -10°C to 50°C to evaluate fuel cell efficiency and battery degradation.
  • Include terrain adaptability metrics (e.g., mud/sand traversal efficiency).

3. Data Interpretation and Literature Gaps

• Issue: Fixed PEMFC power (170 W) in Figure 13 lacks dynamic load-matching analysis; outdated references (pre-2023) weaken context.
• Suggestion:
  • Describe dynamic power allocation algorithms for fuel cell-battery synergy.
  • Cite recent works (e.g., Aziz, 2021 on hydrogen storage) to update background.

4. Language and Formatting

• Grammar: Correct “higher than 8 h” to “over 8 hours”; define “rejuvenation procedure” (e.g., membrane rehydration protocol).
• Consistency: Standardize acronyms (e.g., “BoP” as Balance of Plant); improve figure annotations (Figure 1 component labels).

Comments on the Quality of English Language

Language and Formatting

• Grammar: Correct “higher than 8 h” to “over 8 hours”; define “rejuvenation procedure” (e.g., membrane rehydration protocol).
• Consistency: Standardize acronyms (e.g., “BoP” as Balance of Plant); improve figure annotations (Figure 1 component labels).

Author Response

Dear Editor-in-chief and Reviewer,

On April, 1^st 2025, we received the decision from your prestigious journal regarding our article applsci-3558007. You invited us revise the manuscript found at the above link according to the reviewers' comments and upload the revised file with deadline 18th april.

The authors are grateful for the opportunity to resubmit the article and have carefully followed all the reviewers’ recommendations.

We provide our responses to the reviewers’ comments in attached letter. Each comment is first numbered, followed by the authors' response (in blue colour). If applicable, we also include a separate paragraph detailing the changes made in the revised version of the manuscript.

All modifications resulting from the reviewers’ comments are highlighted in the revised manuscript.

Sincerely,

The Authors

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The Authors have prepared a revised manuscript entitled " Hygrobot: hydrogen-powered mobile robotic platform for rough terrains. Electro-mechanical design, physical implementation and experimental testing." Regardless, please refer to the comment from the Reviewer for improvement.

Major

1. Please elaborate. If the hydrogen tank is almost empty or already empty, what will happen? Is there a sensor that can detect it? How about battery performance in this case, etc.? Please also relate this to the hydrogen supply failure test.
2. Please also elaborate on the impact of vibration and hitting, especially due to the terrain surface, such as a hole or pit. Are there any safety measures in place to prevent failures in the hydrogen and electricity systems?
3. Is IP50 implemented enough to maintain performance in high humidity, under rainy or after-rainy conditions, especially related to terrain as shown in Table 2? What if Hygrobot is partially or fully submerged due to an accident? Please elaborate more on this matter. Please also address whether this condition will become a functional limitation of the Hygrobot with also consideration of remote control performance.

Minor

4. Please check whether the mass unit of bar stated in line 492 is correct or not. “The bar had a mass of 0.58 g, …” as well as the value of “bar mass = 0.08 kg” in line 498.
5. Please check the consistency of the “space” between the value and its unit. For example,
   1. in line 228, discharge rate of 1.5C but in line 281 of 1.5 C. including C-rate in Table 8. Please check throughout the manuscript.
   2. Converter 12V in table 5 or 12 V in line 163 including in the figure as well.
6. What is the meaning of the ”battery sybsystem” in line 162? Does it mean battery subsystem or what?

Author Response

Dear Editor-in-chief and Reviewers,

On April, 20^th  2025, we received the decision from your prestigious journal regarding our article applsci-3558007. You invited us to revise the manuscript found at the above link according to the reviewers' comments and upload the revised file within 5 days.

The authors are grateful for the opportunity to resubmit the article and have carefully followed all the reviewers’ recommendations.

Below, we provide our responses to the reviewers’ comments. Each comment is first numbered, followed by the authors' response (in blue colour). If applicable, we also include a separate paragraph detailing the changes made in the revised version of the manuscript.

All modifications resulting from the reviewers’ comments are highlighted in the revised manuscript.

Sincerely,

The Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 the manuscript is now in satisfactory condition.

Author Response

Dear Editor-in-chief and Reviewers,

On April, 20^th  2025, we received the decision from your prestigious journal regarding our article applsci-3558007. You invited us to revise the manuscript found at the above link according to the reviewers' comments and upload the revised file within 5 days.

The authors are grateful for the opportunity to resubmit the article and have carefully followed all the reviewers’ recommendations.

Below, we provide our responses to the reviewers’ comments. Each comment is first numbered, followed by the authors' response (in blue colour). If applicable, we also include a separate paragraph detailing the changes made in the revised version of the manuscript.

All modifications resulting from the reviewers’ comments are highlighted in the revised manuscript.

Sincerely,

The Authors

Author Response File: Author Response.pdf