Experimental Study on the Longitudinal Motion Performance of a Spherical Robot Rolling on Sandy Terrain
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis study presents and evaluates an improved mathematical model of rolling and slipping of a spherical robot over sandy terrain. The paper is reasonably well-written and explains the theoratical and practical aspects of the model in detail. The data collection is noisy and should be improved by better sensor placement to obtain improved estimates of position.
1. The meaning of 'passing' in the paper title is not clear. Suggest use another phrase instead.
2. Use only the last name in citing references in text (line 55).
3. Double-check the phrase 'sand bearing capacity' (line 63). Do you mean 'load bearing capacity?'
4. Suggest use another phrase for 'passibility performance' (line 83).
5. Please add comments about paper contributions and paper structure at the end of the Introduction section.
6. Remove indent from all lines strating with 'where...' (e.g., line 106).
7. Define 'sinkage coefficient' (line 120).
8. Change 'multiplied by twice' to 'multiplied by two' (line 129).
9. Eqn (8) defines Rf as a quadratic function of s. Shouldn't the exponent of s term in (8) also estimated experimentally?
10. Should the rhs in (11) be T instead of tau?
11. Change 'acceleration of gravity' to 'acceleration due to gravity' (line 164).
12. Correct the phrase 'linear rolling' (line 174) as eqn (11) has nonlinear terms in it.
13. Rephrase the title of Sec. 3.1 to make it clear. The terms 'passes performance' and 'passibility' should be either clearly defined or replaced.
14. Suggest replace 'This paper uses..' with 'This study varies..' (line 228).
15. Explain the S-N-K model refered on line 233.
16. Use standard units velocity and acceleration in Table 2.
17. Explain the blank column appearig in Table 3.
18. Use more informative captions for Tables 2,3 &4.
19. Explain '9th orthogonal experiment' (line 245).
20. Change 'difference terrain' to 'different terrain' (line 261).
21. The plots in Fig. 4 shows that experimental data collection wasn't carefully done. This could be due to loose or improper sensor placement.
22. Mention the modeling equations (line 288).
23. Change 'Firstly,' to 'First,' (line 294).
24. Be consistent in using active or passive voice in the last paragraph on page 10.
25. Shouldn't F1 and F2 independently varied in Table 5?
26. What is the percentage error observed with respect to Theory 1 and Theory 2 in Fig. 9?
27. Explain the 'alternative strategies for extrication' mentioned on line 395.
Comments on the Quality of English Language
Some key phrases used in the paper are not clearly defined.
Author Response
We would like to thank you for your valuable comments, which have greatly improved the readability of the manuscript. Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
The paper presents the experimental research results on spherical robots' slip effect while rolling on sandy terrain. This research provides an in-depth analysis of how the slip effect interferes with the motion of spherical robots on sandy terrain, where the robots can sink, and create a high ledge for the robot to overcome.
The presented research results are very interesting and have a good possibility of being used in real scenarios that require spherical robots.
Please correct the following:
1. On line 48, there are too many grouped references [3-8]. Please split them into several citing enumerations of the most used or important "drive structure, control methods, and motion planning" methods. Otherwise, please reduce the number of references at this location, using the most important and prominent ones.
As an exception, you should not group more than three references. Usually, one or two references should be used at one location.
2. On line 54, please split the reference group [10-15] as the same rule as above should be used.
3. Equation 11 is barely visible. Please increase the font size to the one required by the MDPI formats. If the equation is too large for a single line, you can split it into multiple lines.
4. How does the equation from line 102 [ s=(Rw-v)/(Rw) ] relate to the equation on line 35, [ v = Rw ]? Does it lead to a division by zero (singularity point)?
5. Please correct the phrase on lines 106-107. I am referring to "is not less than zero," knowing that s = [0,1]. If it is correct, then please explain what you mean by it.
6. Please update Table 2 by using rot/s^2. Example: replace 39076 with the result of 39076/130254, etc.
7. Please correct the column header in Table 3 (Blank column).
8. As a suggestion, you can merge Tables 2 and 3 by replacing all 1,2,3 values with the actual ones (use the rot/s^2 converted value). The values should fit well in the table. This update will increase the reader's understanding of what you want to convey.
9. Please update Table 4. Update the column "index" according to the SNK Newman–Keuls method.
10. Please do not number the conclusions in the Conclusions section.
Best regards.
Comments on the Quality of English LanguageEnglish corrections:
1. On line 88, please replace the semicolon ':' with a period '.' or correct the phrases.
2. Please correct the English on line 202.
Author Response
We would like to thank you for your valuable comments, which have greatly improved the readability of the manuscript. Your comments have been responded to point by point. Please see the attachment and the updated text.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper primarily investigates the key factors influencing the passability performance of spherical robots and constructs a mechanical interaction model between spherical robots and dry loose sand. The model is validated through experiments. However, several points need to be improved.
1. The introduction is not sufficient to describe the research background and research status. And it should use the correct reference format.
2. Please use the same format for formulas in your manuscript. For example, the format of formula 11 on page 5 is different from that of other formulas.
3. The manuscript uses the wrong language structure, for example, when describing the formula, "where" explains the meaning of some symbols in the formula and should not be re-segmented.
4. To use a formula, table or picture in the text, it needs to use cross references.
5. The analysis of experimental results is not sufficient. For example, how to draw experimental conclusions through orthogonal experiment and range analysis on page 7.
Author Response
We would like to thank you for your valuable comments, which have greatly improved the readability of the manuscript. Your comments have been responded to point by point. Please see the attachment and the updated text.
Author Response File: Author Response.pdf
