Design method of high-efficiency driving system for ornithopter

Abstract

The application provides a design method of an efficient driving system of a flapping-wing aircraft. First, design parameters of a flapping-wing driving system are determined, and an optimal flapping law of a flapping wing is determined, and a rocking arm torque and power of the flapping wing in a cruising state are calculated. Then, flapping mechanism parameters are determined, and motor selection and testing, battery and electronic speed controller selection are carried out on the basis of the determination of the flapping mechanism parameters, and a reducer is designed, so as to complete the design of the driving system of the flapping-wing aircraft. The application starts from the demand of the flapping-wing driving system, and comprehensively considers the characteristics and interface relationship of the battery, the electronic speed controller, the motor, the reducer and the flapping mechanism, and realizes the forward design of the system. Through the method, the efficient design requirement of the system can be realized, and the take-off function requirement is also considered.

Description

Technical Field

[0001] The present invention relates to the field of flapping-wing aircraft drive system design, in particular to a flapping-wing aircraft high-efficiency drive system design method. Background Art

[0002] The propulsion system of a flapping-wing aircraft provides power to its various components, maintaining flight and the normal operation of its onboard equipment. It directly impacts the aircraft's flight performance and the proper functioning of its onboard equipment. Currently, the propulsion system for flapping-wing aircraft with a certain degree of practicality primarily utilizes a "battery + electronic speed controller + motor + reducer + flapping mechanism" energy source.

[0003] Existing research on flapping-wing aircraft drive system design focuses on designing flapping mechanisms to achieve complex motion patterns. The parameter matching between the various components essentially follows the design method of a "motor + propeller" power system, assuming a constant load torque and designing the motor and propeller based on the assumed load torque requirement.

[0004] However, the biomimetic nature of flapping-wing aircraft results in periodic and dramatic fluctuations in load torque. This periodic fluctuation causes the drive system's efficiency to fluctuate within a certain range, necessitating consideration of the efficiency variations within a flapping cycle during the design process. Furthermore, the drive system's components, including the battery, electronic speed controller, motor, reducer, and flapping mechanism, are strongly coupled. Due to these characteristics, traditional drive system design methods are no longer sufficient for high-performance flapping-wing aircraft. Designing an efficient drive system is crucial to ensuring the efficient flight of flapping-wing aircraft. Summary of the Invention

[0005] To address the challenges of traditional flapping-wing aircraft drive system design, this paper proposes a design method for flapping-wing aircraft drive systems. Starting from the requirements of the flapping-wing drive system, this method comprehensively considers the characteristics and interface relationships of the battery, electronic speed controller, motor, speed reducer, and flapping mechanism to achieve forward system design. This method achieves high-efficiency design requirements while also taking into account takeoff requirements.

[0006] The technical solution of the present invention is:

[0007] A method for designing an efficient drive system for a flapping-wing aircraft comprises the following steps:

[0008] Step 1: Determine the design requirements for the flapping-wing drive system:

[0009] Step 1.1: Based on the set flapping-wing aircraft performance indicators and overall design requirements, determine the overall design parameters, including the total weight W T, cruising speed V c , cruise state angle of attack α, wingspan B T , flapping wing length l T , flapping mechanism height limit H m ;

[0010] Step 1.2: Determine the optimal flapping patterns for the flapping wing during takeoff and cruise, including:

[0011] Cruise state: lift-to-drag ratio or thrust-to-weight ratio Flapping frequency f c , flapping amplitude Φ c Or the variation of flapping wing flapping angle Θ with time Θ = g c (Φ c ,f c ,t);

[0012] Takeoff state: flapping frequency f t , takeoff angle of attack, average takeoff overload n t ;

[0013] Step 1.3: Calculate the torque and power of the flapping wing rocker arm in cruise state;

[0014] The cruise state flapping wing rocker torque is calculated by the following process:

[0015] If the variation of lift L(t) and thrust T(t) in a flapping cycle is known, then according to the formula

[0016]

[0017] Calculate the torque M at the swing arm shaft on one side of the flapping-wing aircraft x 、M xmin 、M xmax and M z 、M zmin 、M zmax , where F x (t) is the x-direction force under the axis of the flapping wing body, F z (t) is the z-direction force under the axis of the flapping wing body, M x is the body axial force F z Torque around the rocker arm shaft, M z is the body axial force F z Bending moment around the rocker axis, Θ is the flapping angle of the flapping wing, l T is the length of one side wing;

[0018] If the variation law of lift L(t) and thrust T(t) in a flapping cycle is unknown, then according to the formula

[0019]

[0020] Estimate the variation law of lift force L(t); according to the formula

[0021]

[0022] Estimate the change law of thrust T(t); where L cmin and L cmax is a flapping cycle in the cruise state [0,t c ] Minimum and maximum values ​​of internal lift; f c is the flapping frequency, t c is the duration of a flapping cycle, T c1max and T c2max is a flapping cycle in the cruise state [0,t c ]The first peak value and the second peak value of the internal thrust. The thrust T(t) produces the first peak value T when it reaches the maximum angular velocity during the flapping phase. c1max , the second peak value T is generated when the maximum angular velocity is reached during the upward phase c2max ; According to the estimated lift L(t) and thrust T(t) in a flapping cycle, calculate the torque M at the swing arm shaft on one side of the flapping aircraft x 、M xmin 、M xmax and M z 、M zmin 、M zmax ;

[0023] The cruise state flapping wing rocker power is calculated by the following process:

[0024] According to the formula

[0025]

[0026] Calculate the flapping wing rocker power P x and the maximum value P xmax and the minimum value P xmin , where ω Θ is the flapping angular velocity,

[0027] Step 2: Based on the wingspan B determined in step 1 T , flapping wing length l T , flapping mechanism height limit H m and flapping amplitude Φ c , design the flapping mechanism scheme:

[0028] The flapping mechanism of the flapping wing drive system adopts a single crank double rocker mechanism; with the crank rotation center as the origin of the coordinate system, the flapping mechanism scheme includes the rocker length l y , crank length l q, connecting rod length l k , rocker arm shaft position (y y ,z y ):

[0029] Step 2.1: According to the wingspan B T and flapping wing length l T Parameters, according to the formula

[0030]

[0031] Determine the lateral position y of the rocker arm shaft y ;

[0032] Step 2.2: According to the formula

[0033]

[0034] Determine the rocker arm length l y ;

[0035] Step 2.3: According to the formula

[0036]

[0037] Estimated crank length l q ;

[0038] Step 2.4: According to the formula

[0039] z y ≈H m -l q -l y -Δ

[0040] Estimate the longitudinal position z of the rocker arm shaft y , where Δ is the additional space required for the gears and hinges;

[0041] Step 2.5: According to the formula

[0042]

[0043] Determine the connecting rod length l k , establish a flapping mechanism with symmetrical flapping characteristics;

[0044] Or according to the formula

[0045]

[0046] Determine the connecting rod length l k , establish a flapping mechanism with asymmetric flapping characteristics;

[0047] Step 3: The flapping wing rocker power P determined in step 1 x and the range of variation [Pxmin ,P xmax ], select the motor and determine the characteristic parameters:

[0048] Step 31: According to the formula

[0049]

[0050] Calculate the required motor rated power P e , where η trans is the mechanical transmission efficiency; select the rated power and P e The difference is less than the micro brushless motor of the set requirement;

[0051] Step 3.2: Use a dynamometer to test the operating characteristics of the selected micro brushless motor, and fit the following functional relationship to the test data:

[0052]

[0053] Where T m is the motor output torque, I m is the current in the circuit, U is the battery output voltage, n m is the motor speed;

[0054] Step 3.3: According to the formula

[0055]

[0056] Calculate the reduction ratio i of the reducer, where T m,high The motor output torque corresponding to the high efficiency point determined according to the motor test data is obtained; and the motor speed under the current flapping frequency reduction ratio i is obtained

[0057] n m,i =60if c

[0058] And calculate the motor torque T m,high and the speed is n m,i The battery output voltage U and the current I in the motor circuit when m Then, according to the ESC used in the motor test, the battery output voltage and the motor equivalent input voltage U are calculated at different throttles Th. rms The conversion relationship can be used to obtain the equivalent voltage coefficient σ under different throttle states.

[0059] U rms =U×σ

[0060] Recalculate the battery output voltage U in the cruise state;

[0061] Step 4: Based on the battery output voltage U obtained in step 3.3, select the number of battery cells S in series; select the battery capacity based on the mission endurance requirements;

[0062] Step 5: Select the ESC based on the battery voltage range selected in step 4. The ESC's minimum operating voltage must be lower than the battery's cutoff voltage, and its maximum operating voltage must be higher than the battery's maximum voltage.

[0063] Step 6: Takeoff status verification:

[0064] Recalculate the takeoff torque and power based on the flapping frequency and takeoff overload. Verify the motor's load torque and speed at maximum rocker arm power and maximum rocker arm torque. Verify the motor's takeoff requirements based on the motor test results. If so, proceed to the next step. If not, return to step 3 and reselect a motor.

[0065] Step 7: Use a two-stage reducer and design the reducer parameters, including the reduction ratios i1 and i2 at each stage, the gear pressure angle α, and the number of teeth z at each stage. i , gear modules m1 and m2 at each level.

[0066] Further preferred solution: In step 1.3, if the variation law of lift force L(t) with time is known, then according to the formula

[0067]

[0068] Calculate the average lift L during the positive lift phase cd and the average lift L in the negative lift phase cu , where L(t) is the lift force that varies with time during a flapping cycle; t d1 , t d2 are the start time and end time of the positive lift phase in a flapping cycle respectively; t u1 , t u2 are the starting time and ending time of the negative lift phase in a flapping cycle, respectively;

[0069] If the lift force L(t) is sampled over time, then according to the formula

[0070]

[0071] Calculate the average lift L during the positive lift phase cd and the average lift L in the negative lift phase cu , where L i is the lift sampling value; N d is the number of samples in the positive lift phase within a flapping cycle; N u is the number of samples in the negative lift phase within a flapping cycle;

[0072] If the variation of lift force L(t) with time is unknown, then according to the total weight of the aircraft W T According to the formula

[0073]

[0074] Estimate the average lift L during the positive lift phase cd and the average lift L in the negative lift phase cu , where n cd is the average overload in the positive lift phase. cu is the load coefficient of the negative lift phase relative to the positive lift phase.

[0075] A further preferred solution is that in step 1.3, if the variation law of lift force L(t) with time is known, then according to the formula

[0076]

[0077] Calculate the minimum lift value L during a flapping cycle in the cruise state cmin and the maximum value L cmax ; where L(t) is the lift force that varies with time during a flapping cycle;

[0078] If the variation law of lift force L(t) with time is unknown, then according to the formula

[0079]

[0080] Estimate the minimum lift value L during a flapping cycle in cruise state cmin and the maximum value L cmax , where n cd is the average overload in the positive lift phase. cu is the load coefficient of the negative lift phase relative to the positive lift phase.

[0081] Further preferred solution: In step 1.3, if the change law of thrust T(t) over time is known, then according to the formula

[0082]

[0083] Calculate the average thrust T during one flapping cycle in cruise state c , where T(t) is the time-varying thrust in a flapping cycle, t c is the duration of a flapping cycle;

[0084] If the thrust T(t) sampling value over time is known, then according to the formula

[0085]

[0086] Calculate the average thrust T during one flapping cycle in cruise state c , where T i is the thrust sampling value, N c is the number of thrust samples in one flapping cycle;

[0087] If the change law of thrust T(t) with time is unknown, then according to the formula

[0088]

[0089] Calculate the average thrust T during one flapping cycle in cruise state c .

[0090] Further preferred solution: In step 1.3, the thrust T(t) generates the first peak value T when it reaches the maximum angular velocity during the flapping phase. c1max , the second peak value T is generated when the maximum angular velocity is reached during the upward phase c2max , the minimum thrust T is generated at the end of the downward and upward stages cmin ;

[0091] If the law of change of thrust T(t) with time is known, then according to the formula

[0092]

[0093] Calculate the minimum thrust T in one flapping cycle in cruise state cmin , the first peak value T c1max and the second peak value T c2max , where MIN(·,·,·) and MAX(·,·,·) are the minimum and maximum value obtaining functions respectively, and the second and third parameters are the flapping period ranges for obtaining extreme values;

[0094] If the change law of thrust T(t) with time is unknown, then according to the formula

[0095]

[0096] Estimated first peak value of thrust T c1max , the second peak value T c2max and the minimum thrust T cmin , where n cf is the ratio coefficient of the second highest peak value to the first highest peak value.

[0097] A further preferred solution is to ignore the hinge and the additional space required for the hinge during the initial design, and assume that the additional space Δ required for the gear and hinge is 0. 2-2 Then, we get Δ=R 2-2 -l q, when re-estimating the longitudinal position z of the rocker arm shaft y .

[0098] In a further preferred embodiment, the mechanical transmission efficiency η trans =η link η gear , where η link is the flapping mechanism efficiency, η gear is the reducer efficiency.

[0099] A further preferred solution is that in step 3.2, if there is a lack of test data, the motor characteristic parameters are obtained by using the first-order equivalent model of the brushless DC motor, according to the formula

[0100]

[0101] Calculate, where U m is the motor input voltage, K V is the speed constant, R m is the total resistance of the loop, and I0 is the no-load current of the motor.

[0102] A further preferred solution is that in step 3.3, if the motor test data is missing, the motor efficiency formula is used.

[0103]

[0104] Taking the derivative of the reduction ratio i, we get the efficiency η m The maximum value point, and then solve the reduction ratio i and motor input voltage U m , and then solve for the battery output voltage U.

[0105] Furthermore, the reducer parameter design process is:

[0106] (1) According to the formula

[0107]

[0108] Calculate the reduction ratio at each level, where i 总 is the total transmission ratio;

[0109] (2) According to the formula

[0110]

[0111] z1=z min ,z3=z min

[0112] z2=z min i1

[0113] z4=z min i2

[0114] Determine the number of teeth on each gear; where a is the gear pressure angle, z min The minimum number of teeth allowed for the gear to not produce undercutting. is the tooth addendum coefficient;

[0115] (3) According to the formula

[0116]

[0117] Calculate the torque and module on each level of pinion, where T i is the torque on the pinion shafts at each level, K is the load factor, are tooth shape coefficient and stress correction coefficient respectively, [σ F ] is the allowable bending fatigue stress of the material.

[0118] Beneficial effects

[0119] The proposed method for designing an efficient flapping-wing aircraft drive system takes into account the requirements of the flapping-wing drive system and comprehensively considers the characteristics and interface relationships of the battery, electronic speed controller, motor, speed reducer, and flapping mechanism to achieve forward system design. This method achieves the system's high efficiency design requirements while also taking into account takeoff performance requirements.

[0120] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0121] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0122] Figure 1 It is a flowchart of the drive system design method;

[0123] Figure 2 is a schematic diagram of the average lift and lift range;

[0124] Figure 3 It is a schematic diagram of average thrust and thrust range;

[0125] Figure 4 It is the conversion and synthesis diagram of lift and thrust;

[0126] Figure 5 It is a schematic diagram of rocker arm torque;

[0127] Figure 6 It is a schematic diagram of the flapping mechanism scheme;

[0128] Figure 7 It is the motor characteristic curve diagram;

[0129] Figure 8It is a schematic diagram of the transmission form of the reducer;

[0130] Figure 9 It is the characteristic curve diagram of the alternative motor;

[0131] Figure 10 This is the ESC test result chart. DETAILED DESCRIPTION

[0132] The following describes in detail embodiments of the present invention. The embodiments are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0133] The flapping wing drive system of the flapping wing aircraft in this embodiment is powered by a lithium battery. The equivalent voltage transmitted to the motor is controlled by an electronic regulator, thereby adjusting the motor speed. The motor is reduced in speed and increased in torque through a reducer, and the flapping mechanism drives the flapping wings to achieve a predetermined motion form. The specific flapping wing drive system design method is shown in the attached figure. Figure 1 As shown, the following steps are included:

[0134] Step 1: Determine the design requirements for the flapping-wing drive system.

[0135] Step 1.1: Determine the overall design parameters, including the gross weight W, based on the performance indicators and overall design requirements of the flapping-wing aircraft. T , cruising speed V c , angle of attack α, wingspan B T , flapping wing length l T , flapping mechanism height limit H m .

[0136] In this embodiment, the total weight W T =2.0N, cruising speed V T c=10.0m / s, cruising flight angle of attack α=12°, wingspan B T =0.625m, flapping wing length l T =0.3m, flapping mechanism height limit H m =60mm.

[0137] Step 1.2: Determine the optimal flapping patterns for the flapping wing in takeoff and cruising states using methods such as scaling or wind tunnel testing, including:

[0138] Cruise state: lift-to-drag ratio or thrust-to-weight ratio Flapping frequency f c , flapping amplitude Φ c Or the variation of flapping wing flapping angle Θ with time Θ = g c (Φ c ,f c ,t);

[0139] Takeoff state: flapping frequency f t , takeoff angle of attack, average takeoff overload n t .

[0140] The flapping amplitude of the flapping wing in the cruise state Φ c , frequency f c and flapping load torque range [M xmin ,M xmax ] The demand determines the optimal working point and efficiency of the drive system, and the flapping frequency f in the takeoff state t and maximum load torque M tmax The demand determines the maximum power of the drive system.

[0141] In this embodiment, in cruise state: lift-to-drag ratio Flapping frequency f c =8Hz, flapping amplitude Φ c =60°, no sweep;

[0142] Takeoff state: flapping frequency f t =10Hz, takeoff flight angle of attack α=20°, average takeoff overload n t =1.1.

[0143] Step 3: Calculate the torque and power of the flapping wing rocker arm in cruise state.

[0144] 1) Calculation of flapping wing rocker torque in cruise state:

[0145] (1) Calculation of average lift.

[0146] The average lift L generated by the flapping wing is in a state of constant straight and level flight during cruising. c Equal to the total weight of the aircraft W T , that is, the positive mean lift L cd The impulse I cd =L cd t d With negative average negative lift L cu The impulse I cu =L cu t u The sum should be equal to the total weight of the aircraft W T The impulse I in one flapping cycle c =W T t c .

[0147]

[0148] Where: I c is the total impulse generated by lift in one flapping cycle, Ns;

[0149] Icd , I cu are the impulses generated by the positive lift and negative lift in one flapping cycle, Ns;

[0150] t d , t u are the durations of the positive lift phase and the negative lift phase in a flapping cycle, s;

[0151] t c is the duration of a flapping cycle, s;

[0152] L cd , L cu are the average lift in the positive lift phase and the average lift in the negative lift phase within a flapping cycle, N.

[0153] If the variation law of lift force L(t) with time is known, the average lift force can be solved by formula (2).

[0154]

[0155] Where: L(t) is the lift force that changes with time during a flapping cycle, N;

[0156] t d1 , t d2 are the start time and end time of the positive lift phase in a flapping cycle, s;

[0157] t u1 , t u2 are the start time and end time of the negative lift phase in a flapping cycle, s.

[0158] If the time-varying sample values ​​of the lift force L(t) are known (e.g., obtained through wind tunnel testing), the average lift force can be solved using formula (3).

[0159]

[0160] Where: L i is the lift sampling value, N;

[0161] N d is the number of samples in the positive lift phase within a flapping cycle;

[0162] N u is the number of samples in the negative lift phase within a flapping cycle.

[0163] If the variation of lift force L(t) with time is unknown, we can assume that t d =2 / 3t c and t u =1 / 3t c , and according to the total weight of the aircraft WT Estimate the average lift during the downward and upward phases using formula (4).

[0164]

[0165] Where: n cd is the average overload in the positive lift stage. According to the statistical results of the test data, n can be preliminarily taken as cd =2.0;

[0166] n cu is the load coefficient of the negative lift stage relative to the positive lift stage, which can be preliminarily taken as n cu =-0.5.

[0167] In this embodiment, since the variation law of lift force L(t) with time is unknown, we take n cd =2.0, n cu =-0.5, and the average lift in the downward and upward stages is estimated according to formula (4).

[0168]

[0169] (2) Calculation of lift variation range.

[0170] If the variation law of lift force L(t) with time is known, the minimum value of lift force L in a flapping cycle can be obtained by formula (5): cmin and the maximum value L cmax .

[0171]

[0172] Where: L(t) is the lift force that changes with time during a flapping cycle, N;

[0173] L cmin , L cmax are the minimum and maximum values ​​of lift force in one flapping cycle, N;

[0174] MIN() and MAX() are functions for finding the minimum and maximum values ​​respectively;

[0175] If the variation of lift force L(t) with time is unknown, it can be assumed that the positive lift and negative lift have amplitudes L cmax and L cmin The sinusoidal curve changes, and the minimum lift value L is estimated according to formula (6) cmin and the maximum value L cmax The meaning of each parameter is as shown in the attached Figure 2 shown.

[0176]

[0177] In this embodiment, it is assumed that the positive lift and negative lift have amplitudes L cmax and L cmin The sinusoidal curve changes, and the minimum lift value L is estimated according to formula (6) cmin and the maximum value L cmax .

[0178]

[0179] (3) Average thrust calculation.

[0180] If the variation law of thrust T(t) with time is known, the average thrust can be solved by formula (7).

[0181]

[0182] Where: T(t) is the time-varying thrust in a flapping cycle, N;

[0183] t c is the duration of a flapping cycle, s.

[0184] If the time-varying sample values ​​of the thrust T(t) are known (e.g., obtained through wind tunnel testing), the average thrust can be solved using formula (8).

[0185]

[0186] Where: T i is the thrust sampling value, N;

[0187] N c is the number of thrust samples in one flapping cycle.

[0188] If the time-varying law of thrust T(t) is unknown, the average thrust T generated by the flapping wing in the straight and level flight state is c Equal to the drag D when the aircraft is flying at cruising speed c , according to the lift-to-drag ratio or thrust-to-weight ratio The average thrust can be obtained by formula (9).

[0189]

[0190] In this embodiment, since the variation pattern of the thrust T(t) over time is unknown, the average thrust is obtained by formula (9).

[0191]

[0192] (4) Calculation of thrust variation range.

[0193] During a flapping cycle, the thrust T(t) generally has two peaks. The first peak value (positive thrust extreme value) is generated when the maximum angular velocity is reached in the downward flapping stage, and the second peak value is generated when the maximum angular velocity is reached in the upward flapping stage. The minimum thrust value (i.e., negative thrust extreme value) is generated at the end of the downward and upward flapping stages.

[0194] If the variation law of thrust T(t) with time is known, a flapping period [0,t c ]Minimum value of internal thrust T cmin , the first peak value T c1max and the second peak value T c2max .

[0195]

[0196] Where: T cmin 、T c1max 、T c2max are the minimum, first peak and second peak values ​​of the thrust within a flapping cycle, N; MIN(·,·,·) and MAX(·,·,·) are the minimum and maximum value calculation functions, respectively. The second and third parameters are the flapping cycle range for calculating the extreme values.

[0197] If the variation law of thrust T(t) with time is unknown, it can be assumed that the first peak value, the second peak value and the minimum thrust value are T c1max 、T c2max =n cf T c1max and T cmin =-n cf T cmax The sinusoidal curve changes, the time of each phase is equal, and the first peak value T of the thrust is estimated according to formula (11): c1max , the second peak value T c2max and the minimum thrust T cmin The meaning of each parameter is as shown in the attached Figure 3 As shown. Among them, n cf is the ratio coefficient of the second peak value to the first peak value, which can be initially taken as n cf =0.5.

[0198]

[0199] In this embodiment, take n cf =0.5, assuming that the first peak value, the second peak value and the minimum thrust are T c1max 、T c2max =n cf T c1max and T cmin =-n cf T cmaxThe sinusoidal curve changes, the time of each phase is equal, and the first peak value T of the thrust is estimated according to formula (11): c1max , the second peak value T c2max and the minimum thrust T cmin .

[0200]

[0201] (5) Calculation of torque variation range.

[0202] Before calculating the torque generated at the rocker arm shaft, it is necessary to convert the lift L(t) and thrust T(t) from the wind axis to the body axis, as shown in the following figure. Figure 4 shown.

[0203] If the variation patterns of lift L(t) and thrust T(t) within a flapping cycle are known, the body axis force can be calculated according to formula (12).

[0204]

[0205] Where: α is the flight angle of attack of the aircraft in cruise state, °.

[0206] The torque generated at the rocker arm shaft includes the body axial force F z Torque M around the rocker arm axis (x-axis) x The bending moment M formed by the rocker arm axis z If there is no forward and backward sweeping motion during the flapping process, the bending moment M z It does not do work, but it affects the contact pressure of the rocker arm shaft, thereby increasing the friction at the rocker arm shaft. In the initial design, only the torque M around the rocker arm shaft can be considered. x , assuming that the flapping wing force point is located at 1 / 2 of the wing length, as shown in the following Figure 5 As shown. Calculate the torque M at the single-side rocker arm shaft according to formula (13): x 、M xmin 、M xmax and M z 、M zmin 、M zmax .

[0207]

[0208] Where: l T is the length of one side wing (the distance from the rocker arm shaft to the wing tip), m.

[0209] If the variation patterns of lift L(t) and thrust T(t) within a flapping cycle are unknown, according to the previous assumptions, lift and thrust vary along sinusoidal curves of different amplitudes within a flapping cycle.

[0210] If the temporal variation pattern of the flapping angle Θ of the flapping wing is unknown, it can be assumed that the flapping angle Θ changes sinusoidally with time according to formula (14).

[0211]

[0212] Where: Φ c is the flapping amplitude of the flapping wing, °;

[0213] f c is the flapping frequency, f c =1 / t c .

[0214] During the downward phase, the lift reaches its maximum value L when the flapping angle reaches 0 degrees. cmax , when the flapping angle reaches 0 degrees during the upward phase, the lift reaches its minimum value L cmin The lift variation law is estimated according to formula (15).

[0215]

[0216] The lift variation law is expressed by the flapping angle Θ, which can be approximately estimated according to formula (16).

[0217]

[0218] Where: is the flapping angular velocity of the flapping wing, rad / s.

[0219] The thrust occurs for two periods in one flapping cycle, 0≤t<3t c / 8 stage with T c2max =-T cmin The amplitude changes sinusoidally, 3t c / 8≤t<5t c / 8 stage with T c1max The amplitude changes according to the positive half cycle of sine wave, 5t c / 8≤t <t c Stage T cmin The amplitude changes sinusoidally.

[0220] The thrust variation law is estimated according to formula (17).

[0221]

[0222] The thrust variation law is expressed by the flapping angle Θ, which can be approximately estimated according to formula (18).

[0223]

[0224] Then, according to the expressions of lift L(t) and thrust T(t), use formulas (12) and (13) to calculate the torque M of the single-side rocker arm shaft:x 、M xmin 、M xmax and M z 、M zmin 、M zmax .

[0225] In this embodiment, since the flapping angle Θ of the flapping wing changes with time, the flapping frequency f is unknown. c =8Hz requirement, assuming that the flapping angle Θ changes sinusoidally with time according to formula (14) within one cycle.

[0226]

[0227] Assume that lift and thrust vary according to a sinusoidal curve. The lift variation law is estimated according to formula (15).

[0228]

[0229] The thrust variation law is estimated according to formula (17).

[0230]

[0231] Calculate the body axis force according to formula (12).

[0232]

[0233] According to the optimal flapping law of the flapping wing, the flapping mechanism adopts the up-and-down flapping mode without forward and backward sweeping, and ignores the bending moment M formed by the rocker axis. z , calculate the M of the single-sided rocker arm according to formula (13) x 、M xmin and M xmax .

[0234]

[0235] Among them, M xmin and M xmax The specific values ​​are

[0236]

[0237] 2) Power calculation.

[0238] If the time-varying law of the flapping angle Θ of the flapping wing realized by the flapping mechanism is known, Θ=g c (Φ c ,f c ,t), differentiate both sides of the formula to obtain the flapping angular velocity ω within one cycle Θ Changes over time The total power change and the maximum and minimum values ​​of the rocker arms on both sides are calculated according to formula (19).

[0239]

[0240] If the time-varying pattern of the flapping wing's flapping angle Θ is unknown, it can be assumed that the flapping angle Θ varies sinusoidally with time according to Equation (14). The angular velocity is calculated using Equation (20) (note the unit conversion).

[0241] ω Θ =πf c Φ c cos(2πf c t) 0≤t≤t c (20)

[0242] According to formula (19), the total power change P of the rocker arms on both sides is calculated x and the maximum value P xmax and the minimum value P xmin .

[0243] In this embodiment, it is assumed that the flapping angle Θ changes with time in a sinusoidal curve according to formula (14). Θ The change pattern over time is calculated according to formula (20).

[0244]

[0245] The power required at the rocker arm shaft and its range during one flapping cycle are calculated according to formula (19).

[0246]

[0247] Among them, P xmin and P xmax The specific values ​​are

[0248]

[0249] Step 2: Based on wingspan B T , flapping wing length l T , flapping mechanism height limit H m and flapping amplitude Φ c , design a flapping mechanism scheme.

[0250] The flapping mechanism scheme can adopt a single crank double rocker mechanism, a double crank double rocker mechanism, a crank slider mechanism, etc. Different schemes have different advantages and disadvantages. In order to achieve high-efficiency flapping in a limited space, this embodiment adopts a single crank double rocker mechanism. Figure 6 As shown, assuming that the crank rotation center is the origin of the coordinate system, the height limit H m Under the constraints, it is necessary to determine the rocker arm length l y , crank length lq , connecting rod length l k , rocker arm shaft position (y y ,z y ), the specific design process is as follows:

[0251] Step 2.1: Determine the lateral position y of the rocker arm shaft y .

[0252] According to the wingspan B T and flapping wing length l T Parameters, according to formula (21) determine the lateral position y of the rocker arm shaft y .

[0253]

[0254] Step 2.2: Determine the rocker arm length l y .

[0255] At a certain flapping amplitude Φ c Under the range requirements, in order to ensure that the phase difference of the rocker arms on both sides is as small as possible, the rocker arm length l y Horizontal position y with rocker arm shaft y The constraint of formula (22) must be satisfied between them, and the rocker arm length l can be determined by this formula y .

[0256]

[0257] Step 2.3: Determine the crank length l q .

[0258] Crank length l q and rocker arm length l y The relationship between the two approximately satisfies the constraints of formula (23), and the crank length l can be determined by this formula. q .

[0259]

[0260] Step 2.4: Determine the longitudinal position z of the rocker arm shaft y .

[0261] According to the height limit H of the flapping mechanism m , that is, the height limit in the z-axis direction, the longitudinal position of the rocker shaft z y Calculate according to formula (24).

[0262] z y ≈H m -l q -l y -Δ (24)

[0263] Where: Δ is the additional space required for the gear and hinge. The additional space required for the hinge can be ignored in the preliminary design. The additional space for the gear is assumed to be 0. 2-2 Then, we can get Δ=R 2-2 -l q , then return to this step to recalculate and update the mechanism dimensions.

[0264] Step 2.5: Determine the connecting rod length l k .

[0265] There are two ways to determine the length of the connecting rod. The first method assumes that when the crank rotates to the upper and lower limits respectively, the rocker reaches the swing limit position accordingly. The mechanism established in this way has symmetrical flapping characteristics. The geometric constraint relationship in the form of formula (25) can be established, and the connecting rod length l can be determined based on this formula. k .

[0266]

[0267] The second method uses the maximum transmission angle as a constraint to establish a solution formula. The mechanism established in this way has the characteristic of asymmetric flapping.

[0268] Transmission angle when the rocker swings upward to the extreme position (wing flapping) (crank and frame overlap and are collinear)

[0269]

[0270] Transmission angle when the rocker swings downward to the extreme position (wing flapping) (the crank and the frame are straightened and collinear)

[0271]

[0272] In the flapping amplitude Φ c Under the requirement of maximizing the transmission angle of the mechanism within the motion cycle, let δ u =δ d , the length of the rocker arm, crank, connecting rod and the position of the rocker arm shaft must meet the constraints of formula (28). According to this formula, the connecting rod length l can be calculated k .

[0273]

[0274] In addition, the rack length l is determined j .

[0275] Horizontal position y of rocker arm shaft y and longitudinal position z y After determination, the rack length l can be obtained by formula (29) j .

[0276]

[0277] In this embodiment:

[0278] (1) Flapping wing span B T is 625mm, and the flapping wing length is l T is 300 mm, and the lateral position y of the rocker arm shaft is determined according to formula (21): y .

[0279]

[0280] (2) Flutter amplitude Φ c is 60°, and the rocker arm length l is determined according to formula (22) y .

[0281]

[0282] (3) Determine the crank length l according to formula (23) q .

[0283]

[0284] (4) Flapping mechanism height limit H m =60mm, assuming that the additional space Δ required by the gear and hinge is 0, the longitudinal position z of the rocker arm shaft is determined according to formula (24): y .

[0285] z y ≈H m -l q -l y -Δ=60-6.7-13.4=39.9mm

[0286] (5) Determine the connecting rod length l according to formula (28) k , to maximize the transmission angle of the mechanism within the motion cycle.

[0287]

[0288] (6) Determine the rack length l according to formula (29) j .

[0289]

[0290] Finally, determine the rocker arm length l y =13.4mm, crank length l q =6.7mm, connecting rod length l k =40.2mm, rack length l j =41.8mm, rocker arm shaft position (12.5mm, 39.9mm).

[0291] Step 3: Based on the total power P of the rocker arms on both sides determined in step 1 x and the range of variation [P xmin ,P xmax ] to select the motor and determine the characteristic parameters.

[0292] Step 3.1: Motor selection

[0293] The flapping mechanism is connected to the motor through a reducer, and the mechanical transmission efficiency of the drive system is η trans It can be expressed as:

[0294] η trans =η link η gear (30)

[0295] Where: η link For the efficiency of the flapping mechanism, if a crank rocker mechanism is used, the transmission efficiency is about 90% to 95%;

[0296] η gear The transmission efficiency is related to the number of reducer stages. The transmission efficiency of a single-stage gear pair is about 95% to 98%.

[0297] The output power requirement of the motor of the flapping-wing aircraft in the cruising state is

[0298]

[0299] The load transfer ratio of the flapping mechanism can be approximately determined by the ratio of the rocker arm and the crank length. The motor torque T m Torque M transmitted to one-side rocker shaft x It can be expressed as formula (32).

[0300]

[0301] According to the torque M of the single-sided rocker arm shaft x , we can calculate M x Absolute value of period average torque use and the flapping frequency f c Estimate the rated power P of the selected motor e

[0302]

[0303] According to the rated power of the motor, a power approximately equal to P is preliminarily selected. e Alternative micro brushless motor.

[0304] In this embodiment, the total power variation range of the flapping wings on both sides obtained in step 1 is -3.96 to 19 W. A flapping mechanism of a two-stage gear reducer is selected. The efficiency of the flapping mechanism is assumed to be 0.95, and the efficiency of the single-stage gear reducer is assumed to be 0.97. The total efficiency of the two-stage gear reducer is:

[0305] η gear =0.97×0.97=0.941

[0306] The mechanical efficiency of the drive system is calculated according to formula (30).

[0307] η trans =η link η gear =0.95×0.941=0.89

[0308] The output power and range of the motor of the flapping-wing aircraft in the cruising state are calculated according to formula (31).

[0309]

[0310] Among them, P mmax The specific value is

[0311]

[0312] Estimate the rated power P of the selected motor according to formula (33) e

[0313]

[0314] According to P e Select an alternative micro brushless motor with a rated power that meets the flapping wing drive power requirements. The motor models shown in Table 1 are initially selected to meet the requirements.

[0315] Table 1- Motor parameters

[0316]

[0317] Step 3.2: Determine motor characteristic parameters

[0318] In order to achieve a good matching design effect for the flapping-wing drive system, it is first necessary to know the working characteristics of the selected micro brushless motor.

[0319] For example, a dynamometer can be used to test the working characteristics of the motor, as shown in the attached Figure 7 As shown. The following functional relationship can be obtained by fitting the experimental data:

[0320]

[0321] Where: T mis the motor output torque, Nm; I m is the current in the circuit, A; U is the battery output voltage, V; n m is the motor speed, rpm.

[0322] If motor test data is lacking, the first-order equivalent model of the brushless DC motor can be used to obtain the motor characteristic parameters. The voltage division of each part of the motor can be written as formula (35).

[0323]

[0324] Where: L is the total inductance of the loop, H; U m is the motor input voltage, V.

[0325] Under the action of the alternating aerodynamic load of the flapping wings, the motor current fluctuates at the same frequency as the flapping frequency (usually less than 10 Hz). The inductance of the brushless DC motor is usually in the order of mH. The voltage division effect of the motor inductance in Equation (35) due to this part of the current fluctuation can be ignored. Therefore, Equation (35) can be simplified to the first-order form shown in Equation (37).

[0326]

[0327] Formula (36) can be rearranged to obtain:

[0328]

[0329] Where: ω m is the motor speed, rad / s; R m is the total resistance of the loop, Ω; E a is the induced voltage, V; K e is the back electromotive force constant, V / (rad / s); K t is the torque constant, Nm / A; K V is the speed constant, rpm / V; I0 is the no-load current of the motor, A.

[0330] The motor internal resistance can be measured by an LCR meter. If this is not possible, you can also check the motor internal resistance characteristics provided by the manufacturer. Back electromotive force constant K e and K t The values ​​are close, and K is often used in engineering applications. e =K t However, in many cases, the brushless motor constant is not clearly given, and only the motor's K is given. V value, then we can use the induced electromotive force in formula (38) to combine ω m and n m The unit conversion relationship between the two motor speeds derives K V The relationship between the value and the back electromotive force constant.

[0331]

[0332] Substituting into formula (37) we can get

[0333]

[0334] In this embodiment, the MN1804 (2400KV) motor is used as an example to match the flapping wing motion parameters with the power system. The motor characteristics are tested using a dynamometer. The throttle state is 100%. The dynamometer is used to obtain the characteristic relationship curves of the candidate motors under a series of voltages, as shown in the attached figure. Figure 9 shown.

[0335] The following functional relationship can be obtained by fitting the experimental data.

[0336]

[0337] Step 3.3: Determine the reducer ratio

[0338] After passing through the reducer, the motor's torque is amplified while the output speed is reduced. The speed and torque output by the reducer are transmitted through the flapping mechanism to drive the flapping wings to achieve the desired flapping motion. Therefore, the output end of the flapping mechanism needs to meet two constraints at the same time: achieving the desired flapping frequency and providing an output torque that is no less than the load torque requirement of the flapping wings.

[0339] After determining the reducer ratio and battery voltage, the two constraints above need to be verified. Verify that the motor can meet the load torque and speed requirements at maximum rocker arm power and maximum rocker arm torque, respectively. You can directly verify the takeoff state in step 6. If the motor can meet the takeoff requirements, it can also meet the cruise requirements.

[0340] If you already have motor test data:

[0341] The reduction ratio i is calculated based on the motor output torque at the high efficiency point and the cycle average load torque.

[0342]

[0343] Calculate the motor speed at the current flapping frequency reduction ratio i

[0344] n m =60if c (41)

[0345] Combine equations (32) and (34) to calculate the battery output voltage U and the current I in the motor circuit that can meet the required flapping frequency. m .

[0346] During the motor test, the throttle state is 100%. In order to leave a margin of control power, the throttle state is 80% in the cruise state. It is necessary to recalculate the battery output voltage U in the cruise state. According to the ESC used in the motor test, the battery output voltage and the motor equivalent input voltage U are calculated at different throttles Th. rms The conversion relationship between σ and σ can be used to obtain the equivalent voltage coefficient σ under different throttle states.

[0347] U rms =U×σ (42)

[0348] Recalculate the battery output voltage U in cruise state.

[0349] If motor test data is missing:

[0350] Motor efficiency η m for

[0351]

[0352]

[0353] n m =60if c (45)

[0354]

[0355] The combined formula (39)(43)(44)(45)(46) gives

[0356]

[0357] Motor efficiency η m It is a function of the reduction ratio i. Taking the derivative with respect to i, we get the efficiency η m The maximum value point of the reduction ratio i and the motor input voltage U can be solved m , and then solve for the battery output voltage U.

[0358] In this embodiment, according to the motor test data, the selected motor has a higher efficiency when the output torque is around 10 mNm, and the reduction ratio is calculated according to formula (40).

[0359]

[0360] Calculate the motor speed required at this time.

[0361] n m =60if c =60×25.9×8=12432rpm

[0362] Calculate the battery output voltage and the current in the motor circuit when the motor torque is 10 mNm and the speed is 12432 rpm.

[0363]

[0364] Test the ESC. The test results are as follows: Figure 10 As shown. The following functional relationship can be obtained by fitting the experimental data:

[0365] σ=0.67Th 0.5 +0.032

[0366] During the motor test, the throttle state is 100%. Calculate the equivalent input voltage of the motor at this time.

[0367] U rms =U×σ=5.88×(0.67+0.032)=4.13V

[0368] Take the throttle in the cruise state as 80% and recalculate the battery output voltage U in the cruise state.

[0369]

[0370] Motor output power P m for

[0371]

[0372] Input power P min for

[0373]

[0374] Calculate the motor efficiency at this time

[0375]

[0376] If motor test data is missing:

[0377] According to formula (47), the motor efficiency expression is:

[0378]

[0379] Taking the derivative of i, we get the efficiency η m The maximum point of is:

[0380] Take the no-load current as 0.7A and the internal resistance as 0.23Ω. When i=27.7, ηmmax=69.24%.

[0381] At this time, the input voltage of the motor

[0382]

[0383] Calculate motor input power

[0384] P min =U m I m =6.3×3.27=20.6W

[0385] Estimate the battery output voltage U at 80% throttle cruising state.

[0386]

[0387] Step 4: Battery Selection

[0388] Based on the battery output voltage U obtained in step 3, select the appropriate number of battery cells in series S. Select the battery capacity based on the mission requirements (endurance).

[0389] In this embodiment, when the motor test data is available, a battery with 2S cells in series is selected based on the battery output voltage U obtained in the cruise state in step S3-3. min and the flight time requirement of the flapping-wing aircraft, calculate the watt-hours WH of the required battery, and choose the flight time as 50 minutes.

[0390]

[0391] Where: t is the flight time of the flapping-wing aircraft, h.

[0392] Step 5: ESC Selection

[0393] Select the ESC based on the battery voltage range in step 4. The ESC's minimum operating voltage must be lower than the battery's cutoff voltage, and its maximum operating voltage must be higher than the battery's maximum voltage. In this example, the selected electronic speed controller is the DSHOT BULLET30A brushless ESC. Its voltage range is 2s to 4s, and its continuous operating current is 30A.

[0394] Step 6: Takeoff status check

[0395] Takeoff state: flapping frequency f t , takeoff angle of attack, average takeoff overload n t .

[0396] Recalculate takeoff torque and power based on the flapping frequency and takeoff overload. Verify the motor's ability to meet load torque and speed requirements at both maximum rocker arm power and maximum rocker arm torque. Verify the motor meets takeoff requirements based on the motor test results.

[0397] In this embodiment:

[0398] Takeoff state: flapping frequency f t =10Hz, average takeoff overload n t =1.1.

[0399] Calculate the power P required at the rocker arm shaft during the flapping cycle in the takeoff state x and torque M x .

[0400] Among them, P xmax and M xmax The specific value is

[0401] P xmax =2M x (0s)ω Θ (0s)=2×0.333Nm×32.9rad / s=21.9W

[0402] M xmax =M x (0.0625s) = 0.405Nm

[0403] P x (0.0625s) = 18.8W

[0404] 1) When the power is maximum, calculate the motor torque and speed at this time

[0405]

[0406]

[0407] Calculate the battery output voltage and the current in the motor circuit when the motor torque is 14.3 mNm and the speed is 16432 rpm.

[0408]

[0409] The battery voltage meets the takeoff voltage requirement.

[0410] 2) When the torque is maximum, calculate the motor torque and speed at this time

[0411]

[0412] Calculate the battery output voltage and the current in the motor circuit when the motor torque is 17.6 mNm and the speed is 11461 rpm.

[0413]

[0414] The battery voltage meets the takeoff voltage requirement.

[0415] Step 7: Reducer design

[0416] The reducer gear set is mainly used to transmit the rotational motion of the motor, and convert the rotational motion of the motor into the up-and-down flapping of the flapping wing through the linkage mechanism connected to the output end. The gear reducer can be divided into single-stage, two-stage, three-stage and multi-stage according to the number of reduction gears; different stages of reducers can be selected according to different reduction ratios. When the reduction ratio i ≤ 8, a single-stage reducer is selected, and when 8 < i ≤ 50, a two-stage reducer is selected. Most flapping-wing aircraft currently choose a two-stage reducer. As shown in Attachment Figure 8 Gear 1 is connected to the motor, gears 2 and 3 are an integral body, and gear 4 is connected to the crank.

[0417] Parameter Design of Reducer

[0418] To reduce the size of the aircraft and the mass of the prototype, it is necessary to design the parameters of the reduction mechanism. The parameters to be designed include the reduction ratios i1, i2 of each stage, select the appropriate gear pressure angle α and the number of teeth z of each stage of gears i (i = 1, 2, 3,...), the module m1, m2 of each stage of gears. The specific design method (assuming a two-stage reduction scheme) is as follows:

[0419] (1) Design of reduction ratio distribution for each stage.

[0420] According to the equal surface contact fatigue strength of the gears, the reduction ratios of each stage can be calculated by formula (48) under the condition of knowing the total transmission ratio i 总 .

[0421]

[0422] (2) Select the gear pressure angle a and determine the number of teeth of each gear.

[0423] The common values of the pressure angle are 20°, 22.5°, 25°, which can be selected according to the actual situation of the flapping wing. For example, considering the gear contact strength and bending strength and making the gear have fewer teeth, the pressure angle is selected as 25°. The minimum number of teeth z allowed for the gear not to generate undercut can be calculated by formula (49) and the selected pressure angle a min and the reduction ratios i1, i2 determined in the previous step, the number of teeth of each gear can be designed by formula (50).

[0424]

[0425]

[0426] In the formula: is the addendum coefficient, with a value of 1;

[0427] (3) Design of the module of each stage of gears in the reducer.

[0428] Through formula (51), the maximum torque M on one side of the rocker armxmax , rocker arm length l y and crank length l q The torque on each pinion is calculated based on the reduction ratio of each stage (note: the torque calculated here is the torque in the cruise state. Considering that the torque on the gear shaft in the takeoff state is larger, a safety factor n0 should be multiplied on the cruise state. According to experience, the value can be 2). Then, the module m1 and m2 of each stage of the reducer are designed and calculated according to the tooth heel bending strength design formula (52). After the module value is calculated, it can be rounded appropriately according to the standard module value or actual size requirements.

[0429]

[0430]

[0431] Where:

[0432] K is the load factor, which can be taken as 1 based on experience in the preliminary design stage;

[0433] T i is the torque on the pinion shaft at each level, N / mm; (Note: The torque on the low-speed shaft is based on the maximum torque M on the rocker shaft xmax and the ratio of rocker arm length to crank length);

[0434] They are tooth shape coefficient and stress correction coefficient respectively, and their product is is the composite tooth form coefficient. For small tooth number gears (11 to 17 teeth), the value can be 5.5. If the calculated number of teeth is greater than 17, the composite tooth form coefficient can be determined by referring to the gear design manual;

[0435] [σ F ] is the material bending fatigue allowable stress in MPa (considering the fluctuating load of flapping-wing aircraft, materials with higher bending fatigue allowable stress are usually selected, and materials with bending fatigue strength greater than 360 MPa are recommended);

[0436] The ratio can be taken as 0.015 in the preliminary design stage;

[0437] is the tooth width coefficient, which can be taken as 0.1 based on experience in the preliminary design stage.

[0438] In this embodiment:

[0439] (1) According to formula (48) and the reduction ratio of 25.9 calculated by S-3, the reduction ratios of each level are designed and calculated:

[0440]

[0441] (2) Select the pressure angle as 25° and calculate the number of teeth of each gear according to formula (49) and formula (50):

[0442]

[0443] (3) M calculated according to S1-3 xmax The length l of the rocker arm and crank calculated with S2 y 、l q The modules of the reduction gears at each level are calculated using formula (51) and formula (52):

[0444]

[0445] Finally, the reduction ratio of each stage of the reducer is determined to be i1=6.7, i2=3.86, the number of teeth of each gear is z1=11, z2=74, z3=11, z4=43, and the module of each gear is m1=0.4, m2=0.8.

[0446] Finally, the design of the flapping-wing drive system of the flapping-wing aircraft is completed.

[0447] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A method for designing an efficient drive system for a flapping-wing aircraft, characterized by: The following steps are involved: Step 1: Determine the design requirements for the flapping-wing drive system: Step 1.1: According to the set flapping-wing aircraft performance indicators and overall design requirements, determine the overall design parameters, including total weight , cruising speed , cruise state angle of attack ,span , flapping wing length , flapping mechanism height limit ; Step 1.2: Determine the optimal flapping patterns for the flapping wing during takeoff and cruise, including: Cruise state: lift-to-drag ratio or thrust-to-weight ratio , flapping frequency , flapping amplitude or flapping wing flapping angle Changes over time ; Takeoff state: flapping frequency , takeoff angle of attack, average takeoff overload ; Step 1.3: Calculate the torque and power of the flapping wing rocker arm in cruise state; The cruise state flapping wing rocker torque is calculated by the following process: If the lift is known and thrust The changing law within a flapping cycle is based on the formula Calculate the torque at the swing arm shaft of a flapping-wing aircraft 、 、 and 、 、 ,in is the x-direction force under the axis of the flapping-wing body, is the z-direction force under the axis of the flapping-wing body, Axial force The torque around the rocker arm axis, Axial force Bending moment about the rocker arm axis; 、 are the minimum and maximum value functions respectively; If the lift is unknown and thrust The changing law within a flapping cycle is based on the formula Estimating lift Law of change; according to the formula Estimated thrust Laws of change; and One flapping cycle for the cruise state Minimum and maximum values ​​of internal lift; is the duration of a flapping cycle, and One flapping cycle for the cruise state The first peak value and the second peak value of the internal thrust, thrust The first peak value is generated when the maximum angular velocity is reached during the flapping phase. , the second peak value is generated when the maximum angular velocity is reached during the upward phase ; and based on the estimated lift and thrust Calculate the torque at the swing arm shaft on one side of the flapping aircraft according to the changing law within a flapping cycle 、 、 and 、 、 ; The cruise state flapping wing rocker power is calculated by the following process: According to the formula Calculating flapping wing rocker power and the maximum value and minimum value ,in is the flapping angular velocity, ; Step 2: Based on the wingspan determined in step 1 , flapping wing length , flapping mechanism height limit and flapping amplitude , design the flapping mechanism scheme: The flapping mechanism of the flapping wing drive system adopts a single crank double rocker mechanism; with the crank rotation center as the origin of the coordinate system, the flapping mechanism scheme includes the rocker arm length , crank length , connecting rod length , rocker arm shaft position : Step 2.1: Based on the wingspan and flapping wing length Parameters, according to the formula Determine the lateral position of the rocker arm shaft ; Step 2.2: According to the formula Determine rocker arm length ; Step 2.3: According to the formula Estimating crank length ; Step 2.4: According to the formula Estimating the longitudinal position of the rocker arm shaft ,in Additional space required for gears and hinges; Step 2.5: According to the formula Determine the connecting rod length , establish a flapping mechanism with symmetrical flapping characteristics; Or according to the formula Determine the connecting rod length , establish a flapping mechanism with asymmetric flapping characteristics; Step 3: The flapping wing rocker power determined in step 1 and range of variation , select the motor and determine the characteristic parameters: Step 3.1: According to the formula Calculate the required motor power rating ,in is the mechanical transmission efficiency, for The cycle average value; select the rated power and The difference is less than the micro brushless motor of the set requirement; Step 3.2: Use a dynamometer to test the operating characteristics of the selected micro brushless motor, and fit the following functional relationship to the test data: in is the motor output torque, is the current in the motor circuit, is the battery output voltage, is the motor speed; Step 3.3: According to the formula Calculate the reduction ratio of the reducer ,in The motor output torque corresponding to the high efficiency point determined according to the motor test data; and the current flapping frequency reduction ratio Motor speed under And calculate the motor torque and the speed is Battery output voltage at and the current in the motor circuit ; Then, according to the ESC used in the motor test, The battery output voltage and motor equivalent input voltage are The conversion relationship is used to obtain the equivalent voltage coefficient under different throttle states. , using the formula Recalculate the battery output voltage in cruise state ; Step 4: Calculate the battery output voltage obtained in step 3.3 , select the number of battery cells in series; select the battery capacity according to the mission endurance requirements; Step 5: Select the ESC based on the battery voltage range selected in step 4. The ESC's minimum operating voltage must be lower than the battery's cutoff voltage, and its maximum operating voltage must be higher than the battery's maximum voltage. Step 6: Takeoff status verification: Recalculate the takeoff torque and power based on the flapping frequency and takeoff overload. Verify the motor's load torque and speed at maximum rocker arm power and maximum rocker arm torque. Verify the motor's takeoff requirements based on the motor test results. If so, proceed to the next step. If not, return to step 3 and reselect a motor. Step 7: Use a two-stage reducer and design the reducer parameters, including the reduction ratio of each stage. , gear pressure angle and the number of teeth on each gear , Gear modules at all levels .

2. The method for designing an efficient drive system for a flapping-wing aircraft according to claim 1, characterized in that: In step 1.3, if the lift force is known The law of change over time, according to the formula Calculate the average lift during the positive lift phase and the average lift in the negative lift phase ,in is the lift force varying with time within a flapping cycle; 、 are the starting time and ending time of the positive lift phase in a flapping cycle, respectively; 、 are the starting time and ending time of the negative lift phase in a flapping cycle, respectively; If the lift is known Sampling values ​​over time, then according to the formula Calculate the average lift during the positive lift phase and the average lift in the negative lift phase ,in is the lift sampling value; is the number of samples in the positive lift phase within a flapping cycle; is the number of samples in the negative lift phase within a flapping cycle; If the lift The law of change over time is unknown, then according to the total weight of the aircraft According to the formula Estimating the average lift during the positive lift phase and the average lift in the negative lift phase ,in is the average overload in the positive lift phase, is the load coefficient of the negative lift phase relative to the positive lift phase.

3. The method for designing an efficient drive system for a flapping-wing aircraft according to claim 1, characterized in that: In step 1.3, if the lift force is known The law of change over time, according to the formula Calculate the minimum lift force during a flapping cycle in cruise state and maximum value ;in is the lift force varying with time within a flapping cycle; If the lift If the law of change over time is unknown, then according to the formula Estimate the minimum lift force during a flapping cycle in cruise state and maximum value ,in is the average overload in the positive lift phase, is the load coefficient of the negative lift phase relative to the positive lift phase.

4. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 1, characterized in that: In step 1.3, if the thrust is known The law of change over time, according to the formula Calculate the average thrust in one flapping cycle in cruise state ,in is the time-varying thrust in one flapping cycle, is the duration of a flapping cycle; If the thrust is known Sampling values ​​over time, then according to the formula Calculate the average thrust in one flapping cycle in cruise state ,in is the thrust sampling value, is the number of thrust samples in one flapping cycle; If the thrust If the law of change over time is unknown, then according to the formula Calculate the average thrust in one flapping cycle in cruise state .

5. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 1, characterized in that: In step 1.3, thrust The first peak value is generated when the maximum angular velocity is reached during the flapping phase. , the second peak value is generated when the maximum angular velocity is reached during the upward phase , generating the minimum thrust at the end of the downward and upward phases ; If the thrust is known The law of change over time, according to the formula Calculate the minimum thrust in one flapping cycle in cruise state , the first peak and the second peak ,in 、 The functions are obtained for the minimum and maximum values, respectively, and the second and third parameters are the range of flapping periods for which the extreme values ​​are obtained; If the thrust If the law of change over time is unknown, then according to the formula Estimated first peak thrust , the second peak and minimum thrust ,in is the ratio coefficient of the second highest peak value to the first highest peak value.

6. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 5, characterized in that: When designing the initial solution, ignore the hinges and the additional space required for the hinges, and consider the additional space required for the gears and hinges as Assuming it is 0, when determining the maximum radius of the reduction gear After that, we get , when re-estimating the longitudinal position of the rocker arm shaft .

7. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 1, characterized in that: The mechanical transmission efficiency ,in is the flapping mechanism efficiency, is the reducer efficiency.

8. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 7, characterized in that: In step 3.2, if there is no test data, the first-order equivalent model of the brushless DC motor is used to obtain the motor characteristic parameters according to the formula Calculate, where is the motor input voltage, is the speed constant, is the total loop resistance, is the no-load current of the motor.

9. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 8, characterized in that: In step 3.3, if the motor test data is missing, use the motor efficiency formula Reduction ratio Derivative, get efficiency The maximum value point, and then solve the reduction ratio and motor input voltage , and then solve for the battery output voltage .

10. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 1, characterized in that: The reducer parameter design process is: (1) According to the formula Calculate the reduction ratio of each level, where is the total transmission ratio; (2) According to the formula Determine the number of teeth on each gear; is the gear pressure angle, The minimum number of teeth allowed for the gear to not produce undercutting. is the tooth addendum coefficient; (3) According to the formula Calculate the torque and module on each level of pinion, where is the torque on the pinion shafts of each level, is the load factor, are tooth shape coefficient and stress correction coefficient respectively, is the allowable stress of material bending fatigue, is the safety factor, is the tooth width coefficient.

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