Evaluation of the Stability Behavior of an Agricultural Unmanned Ground Vehicle
Round 1
Reviewer 1 Report
Introduction:
The introduction is well articulated. However, references could be added regarding the role of UGVs in smart farming and why these vehicles are increasingly taking place. Their increase in use could be due to the flexibility of operation in different environments and therefore an advantage is also addressed to the economic level.
Experimental evaluation:
Fig. 3: only one configuration of the UGV is depicted. Could the other configurations be added as well? It will improve the comprehension of the evaluation performed.
Theoretical Model:
Eq 3: all equations refer to polar coordinates. It is advisable to represent also eq. 3 in polar coordinates.
Validation:
Fig. 7: figure too dispersive and difficult to understand the trends. I recommend superimposing the trends of the different test configurations to relate only to two graphs, one for the lateral test and one for the longitudinal test. In addition, why some tests fail to reach the zero-force value?
Experimental evaluation / Discussion:
lines 207-243: this section describes the tipping tests but it never refers to the friction of the tracks on the floor and to the potential consequence on the vehicle slipping. It is advisable being more critical and to include a description of the acions adopted to maintain the UGV in the stability condition; in the discussion section focus on this simplification is advisable.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
1. Why did you not applied the ISO 16231-2 standard to the stability assessment?
2. Please, include the dynamic stability considerations in the Discussion, since it is far more significant in vehicle operation.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Dear author(s):
The abstract is lacking a brief introduction and a justification for the research. In lines 10-11, you mention “The peculiarity of the machine is in the driving part moving autonomously in the field…”. You could improve that by being more specific. For instance, does it have a steering control system with path-following navigation?
The Introduction of the manuscript is poorly written and would greatly benefit from an English language revision. There are many semantic and syntax errors throughout the text, which makes it difficult to read and understand.
I would suggest improving the introduction’s objectivity. You start mentioning the study’s justification in the last two paragraphs, but you could use the first two paragraphs to do that. In addition, your introduction is lacking some background information on research related to your topic. For instance, is there any other study on testing UGV stability?
The justification of the study needs improvement. You mentioned in lines 97-100 that “…Often the unmanned ground vehicles are seen as machines susceptible to replace the ride on tractors on very sloped areas, where dedicated cultivations are of interest, such as vineyards on extremely sloped areas on the hills and mountains.”. Although it makes sense that a vehicle with a higher center of gravity (CG), such as a tractor, is more unstable than UGVs designed to have a lower CG, you still need to clarify some points:
· Are vineyards on mountainous terrains a common practice locally? Or is it the same across the globe?
· What is being currently used to work on those vineyards? Tractors, manual labor…?
· You mentioned in lines 93-94 that “…The stability of highly automated machines is a very important issue if the operation in agriculture is considered.”, but the importance is not clear. Why do you need to study UGV stability, since there’s no human operator involved?
· In summary, you need to make it clear how is your study relevant.
You mentioned in lines 91-92 that “…In the standardised procedure a reference to the stability performance of these automated vehicles is done but currently the subject has still to be developed.”. However, it’s not clear the procedures for testing the stability of those vehicles and also why it needs to be developed.
Further, it is not clear the novelty of the study. You mentioned you evaluated the stability of a UGV but what’s the innovation in that? What are you doing differently from other similar research and/or the current standard?
Similar to the previous sections, the experimental evaluation section of the manuscript would greatly benefit from an English language revision. In addition, some sentences are not appropriate in scientific writing or require appropriate scientific terminology. For instance:
· “Naked Agricultural UGV” (line 115): Maybe “UGV in unladen weight condition” would be better?
· “Agricultural UGV linked to an air-assisted sprayer” (line 116): Maybe “Agricultural UGV fitted with an air-assisted sprayer” would be better?
In the section “2.3.1 Centre of gravity position determination”, you mentioned CoG was determined using an oscillating platform. Make sure to detail how you can determine CoG using this method and the mathematical formulas you used.
In the section “2.3.2 Lateral tipping test”, you mentioned that “A load cell was positioned under the right track to predict the limit stability angle of the different UGV configurations.”. That sentence is confusing. How does the load cell was used to predict the limit stability angle?
· Line 284: “…moreover, the root-mean-square error (RMSE) was clearly”. What did you mean by that?
· Lines 315-317: “In the longitudinal test the variability was greater demonstrating that the stability angle is influenced by the implement more in the longitudinal stability behaviour than in the lateral one.” That’s a great point! However, how can you translate the findings on the stability angles to practical recommendations? For instance, for UGVs operation, does it mean that changing the geometry of the implements would be a good alternative to decrease its instability? Also, is there any parameter (angle threshold) defined by an ISO that regulates if a UGV stability angle is acceptable (considered safe)?
You tested the UGV fitted with a full and empty sprayer tank. I understand that both scenarios result in different CoG positions compared to the other attachment. However, is it a representative situation? Rather than testing the UGV fitted with a full and empty sprayer tank, I would recommend testing it in extreme conditions, in which the tank’s volume is associated with higher liquid shift and sloshing levels.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 4 Report
This paper explains about “Evaluation of the stability behavior of an agricultural Unmanned Ground Vehicle”. The topic of the paper draws interest. However, the reviewer views the manuscript needs a significant effort to improve its quality to ensure publication in Sustainability. The reviewer recommends further major revision of the paper. Below are some comments to help the authors to improve the paper.
1. Reviewer thinks that the abstract should be written in concise, consists of background, reason or objectives of the study, methodology, focus on the key points of the results and writing in one paragraph. The reviewer suggests the author to include the key results in the form of numbers or percentages in the abstract. Please revise it.
2. The introduction section should address the novelty/gap between this study and the current research trend clearly. Please give statement in the end of introduction section about the objective of this study simply and clearly.
3. I think you need to expand the explanation regarding the results and discussion. The explanation is too simple. Please be added with the reinforcement from other references.
4. The reviewers see that there are still a lot of old references, please replace them and or add them with newer ones.
5. In the conclusion section, please add further studies to be carried out.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments to the authors:
Dear author(s):
1- The abstract is lacking a brief introduction and a justification for the research. Also, in lines 10-11, you mention “The peculiarity of the machine is in the driving part moving autonomously in the field…”. You could improve that by being more specific. For instance, does it have a steering control system with path-following navigation?
2- Again, I need to emphasize that the manuscript needs an English language revision. There are many semantic and syntax errors throughout the text, which makes it difficult to read and understand.
3- The introduction is unnecessarily long, and I would suggest improving its objectivity. You start mentioning the study’s justification in the last two paragraphs, but you could use the first paragraphs to do that. You could modify the intro so that the first two (or even the first) paragraphs can give the reader a general idea of what the paper is about.
4- I would suggest improving the justification of your manuscript by mentioning that UGVs are expensive assets for farmers, thus, it’s important to improve their stability during operation.
5- In the section “2.3.2 Lateral tipping test”, you mentioned that “A load cell was positioned under the right track to measure the upstream side force of the different UGV configurations. A digital level was used for monitoring in real-time the angle of inclination of the UGV.”. How does the load cell interact with the level to predict the limit stability angle? You need to give more details on how you got the tilt angle measurements.
6- How do the results in table 3 translate to practice? Although I understood that the unladen UGV is more stable than the UGV fitted with a sprayer tank, it’s missing a discussion about “what do these numbers represent in practice?”. For instance, what do 49 degrees of lateral tipping angle mean? Is it safe? Try to link that discussion with existing standards for agricultural vehicles that proposes a limit of tipping angles. For example, if the safe limit for a tractor is 30 degrees and you got higher tipping angles for your UGV, does it mean that your UGV is safe to operate on farms? Also, since you mentioned UGVs will possibly be operated in hilly areas, what should be a good estimate for the inclination in those areas?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Based on the explanations and improvements that have been made by the author, the reviewers recommend accepting and publishing this paper in the sustainability journal.
Author Response
Thank you for the revision.
Round 3
Reviewer 3 Report
Dear author(s):
Most of my comments are the same as my previous ones because all of them were disregarded for the manuscript’s review.
1- That’s the third time I’m mentioning that but I feel it is of utmost importance. I need to emphasize that the manuscript needs an English language revision. There are many semantic and syntax errors throughout the text, which makes it difficult to read and understand.
2- The introduction is unnecessarily long, and I would suggest improving its objectivity. You start mentioning the study’s justification in the last two paragraphs, but you could use the first paragraphs to do that. You could modify the intro so that the first two (or even the first) paragraphs can give the reader a general idea of what the paper is about.
3- I would suggest improving the justification of your manuscript by mentioning that UGVs are expensive assets for farmers, thus, it’s important to improve their stability during operation.
4- In the section “2.3.2 Lateral tipping test”, you mentioned that “A load cell was positioned under the right track to measure the upstream side force of the different UGV configurations. A digital level was used for monitoring in real-time the angle of inclination of the UGV.”. How does the load cell interact with the level to predict the limit stability angle? You need to give more details on how you got the tilt angle measurements.
Also, I noticed you added “…equivalent to the tilting platform angle.” at the end of that sentence, but still, it does not answer my question.
5- How do the results in table 3 translate to practice? Although I understood that the unladen UGV is more stable than the UGV fitted with a sprayer tank, it’s missing a discussion about “what do these numbers represent in practice?”. For instance, what do 49 degrees of lateral tipping angle mean? Is it safe? Try to link that discussion with existing standards for agricultural vehicles that proposes a limit of tipping angles. For example, if the safe limit for a tractor is 30 degrees and you got higher tipping angles for your UGV, does it mean that your UGV is safe to operate on farms? Also, since you mentioned UGVs will possibly be operated in hilly areas, what should be a good estimate for the inclination in those areas?
Author Response
Please find below our point-by-point responses:
1- That’s the third time I’m mentioning that but I feel it is of utmost importance. I need to emphasize that the manuscript needs an English language revision. There are many semantic and syntax errors throughout the text, which makes it difficult to read and understand.
Response: an English editing has been performed by MDPI service as evidenced by the attached certificate.
2- The introduction is unnecessarily long, and I would suggest improving its objectivity. You start mentioning the study’s justification in the last two paragraphs, but you could use the first paragraphs to do that. You could modify the intro so that the first two (or even the first) paragraphs can give the reader a general idea of what the paper is about.
Response: the first two paragraphs were revised accordingly.
3- I would suggest improving the justification of your manuscript by mentioning that UGVs are expensive assets for farmers, thus, it’s important to improve their stability during operation.
Response: already addressed previously.
4- In the section “2.3.2 Lateral tipping test”, you mentioned that “A load cell was positioned under the right track to measure the upstream side force of the different UGV configurations. A digital level was used for monitoring in real-time the angle of inclination of the UGV.”. How does the load cell interact with the level to predict the limit stability angle? You need to give more details on how you got the tilt angle measurements.
Also, I noticed you added “…equivalent to the tilting platform angle.” at the end of that sentence, but still, it does not answer my question.
Response: “2.3.2 Lateral tipping test” has been revised.
5- How do the results in table 3 translate to practice? Although I understood that the unladen UGV is more stable than the UGV fitted with a sprayer tank, it’s missing a discussion about “what do these numbers represent in practice?”. For instance, what do 49 degrees of lateral tipping angle mean? Is it safe? Try to link that discussion with existing standards for agricultural vehicles that proposes a limit of tipping angles. For example, if the safe limit for a tractor is 30 degrees and you got higher tipping angles for your UGV, does it mean that your UGV is safe to operate on farms? Also, since you mentioned UGVs will possibly be operated in hilly areas, what should be a good estimate for the inclination in those areas?.
Response: the aim of the paper is to study the stability of the DEDALO UGV and to evidence a methodological approach for the assessment. To define limits in the stability angles of autonomous vehicles is out of scope.
Author Response File: Author Response.pdf
