Sliding Mode Controller with Disturbance Observer for Quadcopters; Experiments with Dynamic Disturbances and in Turbulent Indoor Space
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors(A) Brief summary
The work described concerns the actual implementation of a control law described in a previous article. The authors briefly recall the elements concerning the control and its stability, as well as the mixing mechanism to find the forces to be applied to each propeller. The SMC parameter setting method is recalled. Despite the automatic PSO technique described, the setting must be adjusted by hand for the experimental UAV. The experimental test bench is described and interesting experimental results are given.
(B) Broad comments
1 - By doing a quick search on the net, one quickly finds more than ten bibliographical references whose title or abstract contain UAV and SMC. The paper cites no more than three articles that are not in the top ten. This could suggest that the authors want to minimize the extent of the state of the art on the subject.
2 - Today, no serious work on UAV control should be done by stabilizing Euler angles, especially if the objective is to test the robustness to violent disturbances. This representation is minimal but that is its only advantage. It is strongly nonlinear and has discontinuities. Moreover, it leads to errors of interpretation which will be discussed in part (C). It is a pity to make a lot of effort to adjust a command on a nonlinear model whereas a representation of the orientation in quaternions or with matrix in SO3 leads to "linear" models. Please read "Rotational Error Metrics for Quadrotor Control" (Alexander Spiter, Nathan Michael). You can also refer to the work of Mr. Pedro Castillo Garcia (not the reviewer) on the stability of aggressive quadcopter maneuvers.
The experimental results and the methodology are interesting but I think there is a flaw in the presented model between the controlled variables and the mixing process. It works because the angles (pitch, roll) stay small.
(C) Specific comments referring to line numbers, tables, or figures.
- page 7, equation 4: we can see that the control signal that control the yaw pitch and roll are directly given by the simply mixer structure. This is not true. Consider the following equation (see attached file for notations, sorry in french):
- page 10, line 2 : "camber" or "chamber" ?
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Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for Authors1. This research tested a sliding-mode surface controller (SMC) combined with disturbance observers to control a quadcopter, with automated initialization and tuning of control parameters. The SMC's performance was compared to a PSO-optimized PID controller, and its robustness was evaluated through extensive testing in a turbulent space with external disturbances. 2. To improve the SMC controller's performance, the authors could investigate alternative optimization algorithms for initializing and tuning the control parameters, and also compare it with other advanced control methods. Additionally, incorporating real-time obstacle detection and avoidance algorithms could make the SMC controller more practical in real-life scenarios.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsThe quadcopter experiment results are the focus of this paper and findings are validate. However, in my opinion, the paper has some shortcomings regarding the following concerns.
The novelty of this paper is unclear.
The author mentioned that they upgraded the proposed control theory. What are the differences in controller and disturbance observer design between your previous work [26] and current work?
System definition and control design are redundant in this paper and duplicate of the previous work in [26].
Since this work focus on quadcopter indoor experiment, a video link with experiment content can be attached.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThank you for your cover letter and the revision of the manuscript
Reviewer 3 Report
Comments and Suggestions for AuthorsThe Authors have addressed my concerns with the original manuscript. The revised manuscript is ready for publication.
