Robust Collision-Free Guidance and Control for Underactuated Multirotor Aerial Vehicles
Round 1
Reviewer 1 Report
The article titled “Robust Collision-Free Guidance and Control for underactuated multirotor aerial vehicles”, relates to my area of interest that’s why I recommend some points which may help in order to improve the readability as well as overall structure of this manuscript. The following are my suggestions, recommendations and questions for this article which may help to improve the quality of this manuscript are as follows.
Robust Collision-Free Guidance and Control for Underactuated Multirotor Aerial Vehicles
1. Title statement is not accurate. It must be rewritten.
2. Abstract
· Background of the area must be elaborated more
· By using the given study, how can you relate that your proposed method is better than the other ones.
3. Introduction (Minor revision is required in this section)
· Put some more pictures of your relevant work
· Related work of the proposed area must be elaborated further
4. Methodology (Minor revision is required in this section)
· Describe your proposed method "sufficiently" detailed such that others can redo your work.
· Proposed work needs to be compared more with other related techniques to further discuss the effectiveness of your study.
5. Results
· Validation part in this section also needs to be added
· Comparison with some other experiments may be added too
6. Discussions
· Must include this part before conclusion
· Define the potential application of the findings and limitations in this part
7. References
Check all the references carefully. Some of the related references written below must be cited and added in this section to further strengthen this work
General Comments
· Title statement is not proper. It must be rewritten
· Minor observations in the introduction part as I reflect it on point number 3 so kindly incorporate all those points accordingly.
· In methodology part, your proposed study must be sufficient enough so that others can redo your experiments. Also reflect effectiveness of your proposed work with proper details.
· Validation and comparison part are missing in the result section in your study.
· Check all the references carefully and incorporate the above mentioned papers in your reference list.
The article titled “Robust Collision-Free Guidance and Control for underactuated multirotor aerial vehicles”, relates to my area of interest that’s why I recommend some points which may help in order to improve the readability as well as overall structure of this manuscript. The following are my suggestions, recommendations and questions for this article which may help to improve the quality of this manuscript are as follows.
Robust Collision-Free Guidance and Control for Underactuated Multirotor Aerial Vehicles
1. Title statement is not accurate. It must be rewritten.
2. Abstract
· Background of the area must be elaborated more
· By using the given study, how can you relate that your proposed method is better than the other ones.
3. Introduction (Minor revision is required in this section)
· Put some more pictures of your relevant work
· Related work of the proposed area must be elaborated further
4. Methodology (Minor revision is required in this section)
· Describe your proposed method "sufficiently" detailed such that others can redo your work.
· Proposed work needs to be compared more with other related techniques to further discuss the effectiveness of your study.
5. Results
· Validation part in this section also needs to be added
· Comparison with some other experiments may be added too
6. Discussions
· Must include this part before conclusion
· Define the potential application of the findings and limitations in this part
7. References
Check all the references carefully. Some of the related references written below must be cited and added in this section to further strengthen this work
General Comments
· Title statement is not proper. It must be rewritten
· Minor observations in the introduction part as I reflect it on point number 3 so kindly incorporate all those points accordingly.
· In methodology part, your proposed study must be sufficient enough so that others can redo your experiments. Also reflect effectiveness of your proposed work with proper details.
· Validation and comparison part are missing in the result section in your study.
· Check all the references carefully and incorporate the above mentioned papers in your reference list.
Author Response
Answer: Dear Reviewer, thank you for all your comments that helped us to improve the paper. Besides answering all your comments (highlighted in blue in the new version of the manuscript), we have thoroughly revised the entire manuscript to improve its clarity. As follows, we have done our best to address each one of your comments.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The topic of the paper is highly topical. The reviewed paper proposed a robust guidance and control architecture for underactuated MAVs equipped with fixed rotors. The proposed guidance method outperformed the original Continuous Control Obstacles ( CCO [30]) in avoiding collisions with moving objects. The article represents a valuable contribution to the development of new methods in the field of robust guidance and control architecture for underactuated MAVs. I consider the presentation of the proposed method to be exemplary.
My comment on the article concerns the absence of a smaller practical experiment with the application of the proposed method and an evaluation of the requirements for the computing power of the devices on which the proposed method would be implemented.
Author Response
Answer: Dear Reviewer, thank you for all your comments and invaluable feedback regarding the paper. We agree that experiments are crucial for corroborating the results. In the conclusion section, we emphasized that an important and immediate future work can focus on an experimental validation using a mixed reality environment (for avoiding many crashes). However, it is worth emphasizing that the presented simulations (see Section 5) were performed in a high fidelity (soft) real-time simulator with a graphic interface. Please, see the link: https://youtu.be/d7K4e6Ytn8M.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper has a merit and well structured. However, the authors should address the follwoing:
1. The introduction section must be improved.
In the introduction section, the authors should focus on main issues here. Back ground, the problem statement, the motivations behind the work and its context, the main contributions and the outlines of the paper.
2. The related work still limited and the authors should cite some important references related to aerial vehicles applications such as:
Leader-follower control of unmanned aerial vehicles with state dependent switching
3. The authors should cite all Lemmas and remarks inside the text.
4. Some spaces should be added between the text and citation such as:
Using the Euler equation[34], the................
5. Some additional analysis should be added to the results.
6. Discussion section is necessary before the conclusion to interpret the results, discuss the challenges and limitations of the study.
7. More future directions should be added.
In general, the paper is interesting and I recommend the authors to address the previous comments
Author Response
Answer: Dear Reviewer, thank you for all your comments that helped us to improve the paper. Besides answering all your comments (highlighted in blue in the new version of the manuscript), we have thoroughly revised the entire manuscript to improve its clarity. As follows, we have done our best to address each one of your comments.
Author Response File: Author Response.pdf
Reviewer 4 Report
This paper makes a decent contribution to the UAV field. However, I have a few concerns:
1. How do you guarantee that inner loops objectives are always satisfied as instructed by outer loop? Are there any constraints on actuators that can violate this? What happens to time-scale separation in that case?
2. How do you account for size and shape of the obstacles? As per my understanding, the obstacles are considered as point mass, so collision is never going to happen? Please have a read at the paper to have a better understanding of my concern:
1. Dhal, Kashish, Abhishek Kashyap, and Animesh Chakravarthy. "Collision avoidance and rendezvous of quadric surfaces moving on planar environments." 2021 60th IEEE Conference on Decision and Control (CDC). IEEE, 2021.
2. Sunkara, Vishwamithra, Animesh Chakravarthy, and Debasish Ghose. "Collision avoidance of arbitrarily shaped deforming objects using collision cones." IEEE Robotics and Automation Letters 4.2 (2019): 2156-2163.
3. Quinlan, Sean. "Efficient distance computation between non-convex objects." Proceedings of the 1994 IEEE International Conference on Robotics and Automation. IEEE, 1994.
3. What is the time complexity of your algorithm and how do you compare it with other approaches? What are the main advantages of your approach.
English language is fine!
Author Response
Answer: Dear Reviewer, thank you for all your comments. Besides answering all your comments (highlighted in blue in the new version of the manuscript), we have thoroughly revised the entire manuscript to improve it in clarity. As follows, we have addressed each one of your comments.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Still I have some serious concern of this research. Authors define the two control problems but what are the solutions?. What is the merits of the controller previously many works are already done in this research domain. I did not find any novelty in it. As well as why only 2D based simulations are there. Its just a border line research having no novelty in it.
Its fine
Author Response
Answer: In the revised version of the manuscript, we have unified the two problems of the first submitted version. This unified problem is the one that this manuscript proposed new methods for solving. This unified problem is a nonlinear guidance and control problem of an underactuated UAV subject to disturbances and constraints, operating in a dynamic environment with multiple moving obstacles that can accelerate. This is a very challenging scenario that we succeeded in dealing with. To tackle this problem, we have adopted a hierarchical guidance and control architecture and proposed new guidance and control methods. To design the control laws, we proposed a new hierarchical sliding mode control scheme that enforces the time-scale separation without losing robustness; such an enforcement of TSS has not appeared in the literature yet. On the other hand, in the guidance, we have proposed a new method capable of robustly guarantee collision avoidance and the satisfaction of velocity and rotor thrust constraints for underactuated MAVs with uncertain dynamics. The guidance law is also carefully designed to provide sufficiently smooth commands for the inner loop does keep the sliding mode. Contrary to what Reviewer 1 said, the manuscript has clearly stated its novelties with respect to the state of the art, as detailed in the fifth paragraph of the introduction of the new manuscript version.
Additionally, contrary to what Reviewer 1 said, the proposed method is 3D, and we did not perform 2D based simulations. Please, see the simulation video in the following link, which is also cited in the manuscript: https://www.youtube.com/watch?v=d7K4e6Ytn8M [youtube.com].
Reviewer 3 Report
The authors addressed all required comments
The paper is ready to be accepted
Author Response
Thank you for your revision!
Reviewer 4 Report
Authors have addressed my concerns and I am happy with the publication.
English language quality is fine!
Author Response
Thank you for your revision!
