Multi-rotor air resistance coefficient calibration method, device and computer-readable storage medium

Abstract

The present invention discloses a method, device and computer-readable storage medium for calibrating the drag coefficient of a multi-rotor. The method includes: performing flight tests at multiple set airspeeds along a straight and level flight route in a windless environment and a windy environment, and recording flight control logs according to a measurement sequence composed of airspeed, inclination angle and acceleration during the flight tests; combining each flight control log, respectively selecting corresponding measurement combinations according to the acceleration, endurance and acceleration corresponding stages; taking the least square solution obtained from a preset number of the measurement combinations as the calibration result, and applying the calibration result to a preset real-time airspeed estimation algorithm to obtain an estimation result. The present invention realizes a low-cost experimental calibration algorithm, efficiently and accurately calculates the multi-rotor drag coefficient function, and effectively verifies the accuracy of the calibration result and the estimation algorithm.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned aerial vehicles, and particularly to a method, device and computer-readable storage medium for calibrating the drag coefficient of a multi-rotor Background Art

[0002] Currently, the functional model between the drag coefficient and the inclination angle is a prerequisite for a multi-rotor aircraft to calculate the airspeed based on the principles of dynamics. Generally, the drag coefficient model of a multi-rotor can be theoretically established through aerodynamic analysis and computer aerodynamic simulation.

[0003] However, due to the complex aerodynamic characteristics of multi-rotor aircraft, it is difficult to theoretically give the analytical formula of the functional relationship between the drag coefficient and the inclination angle.

[0004] Existing computer simulations can give approximate solutions. However, limited by the model accuracy and computer computing power, the simulation method has a high cost and the accuracy cannot be guaranteed.

[0005] Based on this, how to effectively calibrate the multi-rotor drag coefficient function has become a technical problem to be solved urgently at present. Summary of the Invention

[0006] In order to solve the above technical defects in the prior art, the present invention proposes a method for calibrating the drag coefficient of a multi-rotor, which includes:

[0007] Performing flight tests at multiple set airspeeds according to a straight and level flight route in a windless environment and a windy environment, and recording flight control logs according to a measurement sequence composed of airspeed, inclination angle, and acceleration during the flight tests;

[0008] Combining each flight control log, respectively selecting corresponding measurement combinations according to the acceleration, endurance, and acceleration corresponding stages;

[0009] Taking the least squares solution obtained from a preset number of the measurement combinations as the calibration result, and applying the calibration result to a preset real-time airspeed estimation algorithm to obtain an estimation result;

[0010] Comparing the estimation result with the measurement result obtained by an airspeed meter during the flight test, and verifying the accuracy of the calibration result and the real-time airspeed estimation algorithm according to the comparison result.

[0011] Optionally, the method further includes:

[0012] Establishing an airspeed calculation mathematical model according to the principles of dynamics and in combination with the control laws of multi-rotor attitude augmentation, altitude holding, and position tracking:

[0013] , as Formula 1;

[0014] Convert the formula 1 into a calibration form:

[0015] , as formula 2;

[0016] where the first-order air resistance coefficient function , the second-order air resistance coefficient function and the third-order air resistance coefficient function are all undetermined functions with unknown analytical forms, the inclination angle and the acceleration are measured by an attitude sensor and an acceleration sensor, and the airspeed is measured by the pneumatic airspeed indicator.

[0017] Optionally, the method further includes:

[0018] Perform a fifth-order Taylor expansion on the first-order air resistance coefficient function , the second-order air resistance coefficient function and the third-order air resistance coefficient function :

[0019] , as formula 3;

[0020] Through the formula 3, the calibration of the first-order air resistance coefficient function , the second-order air resistance coefficient function and the third-order air resistance coefficient function is converted into the calibration of the constant coefficients .

[0021] Optionally, the method further includes:

[0022] By substituting the formula 3 into the formula 2 and converting it into a matrix form, a calibration constraint equation is obtained:

[0023] , as formula 4.

[0024] Optionally, the method further includes:

[0025] Define the vectors , and the scalar , where:

[0026] , as formula 5;

[0027] , as formula 6;

[0028] , as formula 7;

[0029] Abbreviate the calibration constraint equation as:

[0030] , as Formula 8.

[0031] Optionally, the method further includes:

[0032] During the flight test, take n groups of different measurement sequences:

[0033] , as Formula 9;

[0034] wherein, the measurement combination of the measurement sequence is taken from the actual straight and level flight process.

[0035] Optionally, the method further includes:

[0036] Determine that the measurement combination satisfies the Formula 8 based on straight and level flight;

[0037] Substitute the n groups of measurement combinations into the Formula 5 and the Formula 7 to obtain n groups of 、 ;

[0038] Substitute the n groups of 、 into the Formula 8 to obtain n groups of measurement equations:

[0039] , as Formula 10.

[0040] Optionally, the method further includes:

[0041] When n>18, obtain the least squares solution of from the n groups of measurement equations;

[0042] Complete the calibration of the constant coefficients through the least squares solution, that is, as the calibration of the first-order drag coefficient function 、the second-order drag coefficient function and the third-order drag coefficient function .

[0043] The present invention also proposes a multi-rotor drag coefficient calibration device, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the computer program is executed by the processor, the steps of the multi-rotor drag coefficient calibration method described in any one of the above are implemented.

[0044] The present invention also provides a computer-readable storage medium, on which a multi-rotor air resistance coefficient calibration program is stored. When the multi-rotor air resistance coefficient calibration program is executed by a processor, the steps of the multi-rotor air resistance coefficient calibration method described in any one of the above are implemented.

[0045] Implementing the multi-rotor air resistance coefficient calibration method, device and computer-readable storage medium of the present invention, by performing flight tests at multiple set airspeeds along a straight and level flight route in a windless environment and a windy environment, and recording flight control logs according to a measurement sequence composed of airspeed, inclination angle, and acceleration during the flight tests; combining each flight control log, respectively selecting corresponding measurement combinations according to the acceleration, endurance, and acceleration phases; taking the least squares solution obtained from a preset number of the measurement combinations as the calibration result, and applying the calibration result to a preset real-time airspeed estimation algorithm to obtain an estimation result; comparing the estimation result with the measurement result obtained by an airspeed meter during the flight tests, and verifying the accuracy of the calibration result and the real-time airspeed estimation algorithm according to the comparison result. An experimental calibration algorithm with low cost is realized, making full use of airspeed measurement, attitude measurement, and acceleration measurement during the flight test calibration process, efficiently and accurately calculating the multi-rotor air resistance coefficient function, and effectively verifying the accuracy of the calibration result and the estimation algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0047] Figure 1 is a flowchart of the multi-rotor air resistance coefficient calibration method of the present invention;

[0048] Figure 2 is a coordinate system definition diagram of the multi-rotor air resistance coefficient calibration method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0050] In the following description, suffixes such as "module", "component", or "unit" used to represent elements are only for the convenience of description of the present invention and have no specific meaning in themselves. Therefore, "module", "component", or "unit" can be used interchangeably.

[0051] Figure 1 is a flowchart of the multi-rotor air resistance coefficient calibration method of the present invention. This embodiment provides a multi-rotor air resistance coefficient calibration method, which includes:

[0052] S1. Conduct flight tests at multiple set airspeeds along a straight and level flight path in a windless environment and a windy environment, and record flight control logs according to a measurement sequence composed of airspeed, inclination, and acceleration during the flight tests;

[0053] S2. Combine each flight control log and select corresponding measurement combinations according to the acceleration, endurance, and acceleration - corresponding phases respectively;

[0054] S3. Take the least - squares solution obtained from a preset number of the measurement combinations as the calibration result, and apply the calibration result to a preset real - time airspeed estimation algorithm to obtain an estimation result;

[0055] S4. Compare the estimation result with the measurement result obtained by an airspeed indicator during the flight tests, and verify the accuracy of the calibration result and the real - time airspeed estimation algorithm according to the comparison result.

[0056] Optionally, in this embodiment, an additional airspeed indicator is installed on the multi - rotor aircraft, and this airspeed indicator is only used for the above - mentioned flight tests.

[0057] Optionally, in this embodiment, the above - mentioned airspeed indicator is installed on the top of the cockpit away from the interference of the propeller airflow, and this airspeed indicator is a pressure - type airspeed indicator.

[0058] Optionally, in this embodiment, the measurement data of this airspeed indicator is transmitted to the flight control system of the multi - rotor aircraft through the data bus of the multi - rotor aircraft, and the flight control system calibrates and records the above - mentioned measurement data.

[0059] Optionally, in this embodiment, for the above - mentioned flight tests, in order to ensure the robustness of the calibration result, flight tests under multiple different working conditions are designed.

[0060] Optionally, in this embodiment, a flight test under one working condition is that, in a windless environment, along a straight and level flight path, the airspeeds are set to 5m / s, 10m / s, 15m / s, 20m / s, 25m / s, 30m / s respectively, where the actual observed airspeed is taken as the standard.

[0061] Optionally, in this embodiment, a flight test under another working condition is that, in a windy environment, along a straight and level flight path, the airspeeds are set to 5m / s, 10m / s, 15m / s, 20m / s, 25m / s, 30m / s respectively, where the actual observed airspeed is taken as the standard.

[0062] Optionally, for the above data acquisition and subsequent result calibration, in the process of the above flight test, the measured sequence of "airspeed / tilt angle / acceleration" generated is handed over to the flight control log for recording and the time reference is unified; further, for each flight log, different measurement combinations are selected from the "acceleration", "cruise", and "deceleration" stages respectively ; further, a total of 200 groups of measurement combinations are taken, and the least-squares solutions of 200 groups of measurement equations are obtained using the mathematical tool MATLAB to complete the calibration; further, the calibration results calculated above are applied to the real-time airspeed estimation algorithm, and through the above flight test, the measurement results of the airspeed meter are compared to verify the accuracy of the calibration results and the estimation algorithm.

[0063] Based on the above calibration steps, the specific calibration principle will be described below.

[0064] First, please refer to Figure 2 the coordinate system definition diagram of the multi-rotor air resistance coefficient calibration method of the present invention shown. In this embodiment, the following coordinate system definitions are determined: one is the ground coordinate system ; the second is the body coordinate system ; the third is the body horizontal coordinate system (i.e., the custom coordinate system) where the origin O is set at the center of mass of the body, OX is set in the body symmetry plane, horizontally pointing forward of the body, OZ vertically downward, OY follows the right-hand rule and horizontally points to the right side of the body.

[0065] Secondly, the following conventions are made for multiple common symbols: is the total mass of the whole machine, is the linear acceleration of the center of mass, is the gravitational acceleration, V is the airspeed, is the body horizontal tilt angle (it can be understood that for longitudinal motion, it is the pitch angle), is the first-order air resistance coefficient function, is the second-order air resistance coefficient function, is the third-order air resistance coefficient function. Among them, the first-order air resistance coefficient function , the second-order air resistance coefficient function and the third-order air resistance coefficient function are all mainly dynamically related to the horizontal tilt angle. Further, it is agreed that the subscripts of the above physical quantities x, y, z represent the three-axis projections or components corresponding to the body horizontal coordinate system, and the subscript represents the three-axis projections or components in the corresponding body coordinate system (ground coordinate system).

[0066] Based on the above coordinate system definition and symbol convention, the following is the principle for calibrating the drag coefficient of a multi-rotor aircraft.

[0067] In this embodiment, according to the dynamic principle and combined with the control laws of multi-rotor attitude augmentation stability, altitude holding, and position tracking, an airspeed calculation mathematical model is established: , as Formula 1;

[0068] Convert the said Formula 1 into a calibration form:

[0069] , as Formula 2;

[0070] Among them, the first-order drag coefficient function , the second-order drag coefficient function and the third-order drag coefficient function are all undetermined functions with unknown analytical forms. The inclination angle and the acceleration are measured by an attitude sensor and an acceleration sensor, and the airspeed is measured by the said airspeed meter of the pneumatic type.

[0071] In this embodiment, take the fifth-order Taylor expansion for the said first-order drag coefficient function , the said second-order drag coefficient function and the said third-order drag coefficient function : , as Formula 3;

[0072] Through the said Formula 3, the calibration of the said first-order drag coefficient function , the said second-order drag coefficient function and the said third-order drag coefficient function is transformed into the calibration of the constant coefficients

[0073] .

[0074] In this embodiment, by substituting the said Formula 3 into the said Formula 2 and converting it into a matrix form, a calibration constraint equation is obtained:

[0075] , as Formula 4.

[0076] In this embodiment, define the vectors , and the scalar , where:

[0077] , as Formula 5;

[0078] , as Formula 6;

[0079] , as Formula 7;

[0080] Abbreviate the calibration constraint equation as:

[0081] , as Formula 8.

[0082] In this embodiment, during the flight test, take n groups of different measurement sequences:

[0083] , as Formula 9;

[0084] where the measurement combination of the measurement sequence is taken from the actual straight and level flight process.

[0085] Substitute the n groups of measurement combinations into the Formula 5 and the Formula 7 to obtain n groups of , ;

[0086] Substitute the n groups of , into the Formula 8 to obtain n groups of measurement equations:

[0087] , as Formula 10.

[0088] When n > 18, obtain the least squares solution of from the n groups of measurement equations;

[0089] Complete the calibration of the constant coefficient through the least squares solution, that is, as the calibration of the 1st - order aerodynamic drag coefficient function , the 2nd - order aerodynamic drag coefficient function and the 3rd - order aerodynamic drag coefficient function .

[0090] The beneficial effects of this embodiment are as follows: flight tests at multiple set airspeeds are performed along a straight and level flight route in a windless environment and a windy environment, and during the flight tests, flight control logs are recorded according to a measurement sequence composed of airspeed, inclination angle, and acceleration; in combination with each flight control log, corresponding measurement combinations are selected respectively according to the acceleration, endurance, and acceleration corresponding phases; the least squares solution obtained from a preset number of the measurement combinations is used as the calibration result, and the calibration result is applied to a preset real-time airspeed estimation algorithm to obtain an estimation result; the estimation result is compared with the measurement result obtained by an airspeed meter during the flight test, and the accuracy of the calibration result and the real-time airspeed estimation algorithm is verified according to the comparison result. A low-cost experimental calibration algorithm is realized, which makes full use of the airspeed meter measurement, attitude measurement, and acceleration measurement during the flight test calibration process, efficiently and accurately calculates the multi-rotor air resistance coefficient function, and effectively verifies the accuracy of the calibration result and the estimation algorithm.

[0091] Based on the above embodiment, the present invention further provides a multi-rotor air resistance coefficient calibration device, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the computer program is executed by the processor, the steps of the multi-rotor air resistance coefficient calibration method described in any one of the above are implemented.

[0092] It should be noted that the above device embodiment and method embodiment belong to the same concept. The specific implementation process is detailed in the method embodiment, and the technical features in the method embodiment are all correspondingly applicable in the device embodiment, so they will not be repeated here.

[0093] Based on the above embodiment, the present invention further provides a computer-readable storage medium, on which a multi-rotor air resistance coefficient calibration program is stored. When the multi-rotor air resistance coefficient calibration program is executed by a processor, the steps of the multi-rotor air resistance coefficient calibration method described in any one of the above are implemented.

[0094] It should be noted that the above medium embodiment and method embodiment belong to the same concept. The specific implementation process is detailed in the method embodiment, and the technical features in the method embodiment are all correspondingly applicable in the medium embodiment, so they will not be repeated here.

[0095] It should be noted that in this document, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising such element.

[0096] The serial numbers of the embodiments of the present invention described above are for description only and do not represent the superiority or inferiority of the embodiments.

[0097] From the description of the above embodiments, those skilled in the art can clearly understand that the above-described embodiment methods can be implemented by means of software plus a necessary general hardware platform. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions for causing a terminal (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in various embodiments of the present invention.

[0098] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention, and all of these are within the protection scope of the present invention.

Claims

1. A method for calibrating the drag coefficient of a multi-rotor, characterized in that, The method includes: Performing flight tests at multiple set airspeeds according to a straight and level flight route in a windless environment and a windy environment, and recording flight control logs according to a measurement sequence composed of airspeed, inclination angle, and acceleration during the flight tests; Combining each flight control log, respectively selecting corresponding measurement combinations according to the acceleration, endurance, and acceleration - corresponding stages; Taking the least - squares solution obtained from a preset number of the measurement combinations as the calibration result, and applying the calibration result to a preset real - time airspeed estimation algorithm to obtain an estimation result; Comparing the estimation result with the measurement result obtained by an airspeed meter during the flight test, and verifying the accuracy of the calibration result and the real - time airspeed estimation algorithm according to the comparison result; Wherein, According to the principle of dynamics, and combining the control laws of multi - rotor attitude stabilization, altitude holding, and position tracking, establish a mathematical model for airspeed calculation: , as Formula 1; Convert the formula 1 into a calibration form: , as Formula 2; Among them, is the overall machine mass, the first-order air resistance coefficient function , the second-order air resistance coefficient function and the third-order air resistance coefficient function are all to-be-determined functions with unknown analytical forms. The inclination angle and the acceleration are measured by an attitude sensor and an acceleration sensor, and the airspeed is measured by the pneumatic airspeed meter described above.

2. The multi-rotor air resistance coefficient calibration method according to claim 1, characterized in that The method further includes: For the first-order drag coefficient function 、the second-order drag coefficient function and the third-order drag coefficient function take the fifth-order Taylor expansion: , as Formula 3; Through the formula 3, the calibration of the first-order aerodynamic drag coefficient function , the second-order aerodynamic drag coefficient function and the third-order aerodynamic drag coefficient function is converted into the calibration of the constant coefficient .

3. The multi-rotor air resistance coefficient calibration method according to claim 2, wherein The method further includes: By substituting the formula 3 into the formula 2 and converting it into a matrix form, obtain a calibration constraint equation: , as Formula 4.

4. The multi-rotor air resistance coefficient calibration method according to claim 3, wherein The method further includes: Define vectors , and scalars , where: , as Formula 5; , as Formula 6; , as Formula 7; Abbreviate the calibration constraint equation as: , as Formula 8.

5. The multi-rotor air resistance coefficient calibration method according to claim 4, wherein The method further includes: During the flight test, take n groups of different measurement sequences: , as Formula 9; Among them, the measurement combination of the measurement sequence is taken from an actual straight and level flight process.

6. The multi-rotor air resistance coefficient calibration method according to claim 5, characterized in that The method further includes: Determine that the measurement combination satisfies the formula 8 based on straight and level flight; Substitute the measurement combinations of n groups into the formula 5 and the formula 7 to obtain n groups of and ; Substitute the , into the formula 8 to obtain n sets of measurement equations: , as Formula 10.

7. The multi-rotor air resistance coefficient calibration method according to claim 6, wherein The method further includes: When n > 18, the least-squares solution of is obtained from the n sets of the measurement equations; Calibration of the constant coefficients is completed through the least squares solution, that is, as the calibration of the first-order aerodynamic drag coefficient function , the second-order aerodynamic drag coefficient function and the third-order aerodynamic drag coefficient function .

8. A multi-rotor air resistance coefficient calibration device, characterized in that, The device includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the computer program is executed by the processor, it implements the steps of the multi - rotor wind resistance coefficient calibration method according to any one of claims 1 to 7.

9. A computer-readable storage medium, characterized in that, A multi - rotor wind resistance coefficient calibration program is stored on the computer - readable storage medium. When the multi - rotor wind resistance coefficient calibration program is executed by a processor, it implements the steps of the multi - rotor wind resistance coefficient calibration method according to any one of claims 1 to 7.

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