Unknown System Dynamics Estimator-Based Anti-Disturbance Attitude Funnel Control for Quadrotors with Experimental Verifications
Round 1
Reviewer 1 Report
The paper presents an unknown system dynamics estimator-based anti-disturbance funnel control for quadrotor attitude dynamics, ensuring tracking performance experiencing parametric uncertainties and external perturbations. The results are validated both through simulation and experimental. The paper is well written, and the issues are well described.
However, I have a few recommendations for improving the manuscript:
-Regarding the control structure, a figure/scheme describing the strategy would be useful.
-The conclusions should be a little extended, highlighting the contributions of the proposed control strategy.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
In the paper the authors present disturbance-rejection based control method for quadrotors, verified by means of experiments. In the introductory part of the paper, various deployments of quadrotors are presented, and related to the references, what gives rise to presentation of different control approaches. The authors focus on tracking subject to predetermined performance requirements, by means of defining a funnel.
At first, the standard UAV model is presented in vertical motion. Secondly, for the introduced dynamics estimator, and the defined envelope describing the funnel, a control policy is defined.
Finally, the stability analysis is performed. This seems a very promising solution, with just a single assumption that error dynamics constants are bounded. This is not a conservative requirement.
The solution is verified by means of experiment with the UAV grabbed in a frame to test changes in variables. The question which need to be addressed in the paper is what is the impact of control signal constraint on the overall performance of the system, showing the results from simulations, and potentially describing the impact on the performed stability analysis.
Secondly - what are the bounds on the funnel to be satisfied? What if its dynamics in transient state overperform the dynamics of the UAV itself?
Finally, what if the UAV model is very far from the initially estimated one? As in the case of a carried load when the initial model does not include it?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The article is interesting and a good candidate for publication. However, some issues must be addressed before publication. The detailed comments are presented below:
1. Some formal aspects must be revised. Some citations are incorrect. For instance, line 49 «in [13], by regulating…» the author is part of the sentence, as such must appear the name and then [13].
2. The introduction must be more clear about the importance of the study, specially from the theoretical point of view. Otherwise the document appears to be a technical experiment. The problem also occurs in the conclusions, which, at this point is just a simple recapitulation.
3. The method seems adequate and well explained, but my concern is the link to the theory, which is totally missing.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Please find the comments referring to the paper as an attachment.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Thank you for incorporating the requested changes and addressing the issue of constraints. I find the paper acceptable in its current form.
Reviewer 3 Report
Congrats on the revision.
Reviewer 4 Report
All comments of the reviewer have been included in the revised version of the paper. I recommend publication this paper in its present form.
