Design method for efficient driving system of ornithopter

Abstract

The invention provides a design method of an efficient driving system of a flapping wing aircraft, which comprises the following steps: firstly, determining design parameters of a flapping wing driving system, determining an optimal flapping law of a flapping wing, and calculating the torque and power of a flapping wing rocker arm in a cruising state; the design method comprises the following steps of: determining the parameters of a flapping mechanism, performing motor type selection and testing and battery and electronic speed controller type selection on the basis of determining the parameters of the flapping mechanism, checking a take-off state, and designing a speed reducer if the checking meets requirements, thereby finishing the design of the driving system of the flapping-wing aircraft. According to the requirements of a flapping wing driving system, the characteristics and interface relations of a battery, an electronic speed controller, a motor, a speed reducer and a flapping mechanism are comprehensively considered, and the forward design of the system is achieved. By means of the method, the efficient design requirement of the system can be met, and the take-off function requirement is considered.

Description

Technical Field

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

[0002] The flapping-wing aircraft drive system provides power for each component of the flapping-wing aircraft to maintain its flight and the normal operation of the onboard equipment. It directly affects the flight performance of the aircraft and the normal operation of the onboard equipment. At present, for flapping-wing aircraft with a certain degree of practicality, the drive system mainly adopts the energy power form of "battery + electric control + motor + reducer + flapping mechanism".

[0003] For the design method of flapping-wing aircraft drive system, existing research mainly focuses on how to design flapping mechanisms to achieve complex motion forms. The parameter matching method between the components basically follows the design method of the "motor + propeller" power system, that is, assuming that the load torque is a constant value, and designing the motor and propeller according to the assumed load torque requirements.

[0004] However, the bionic characteristics of flapping-wing aircraft result in periodic and violent fluctuations in load torque. This periodic and violent fluctuation in load torque causes the efficiency of the drive system to fluctuate within a certain range. Therefore, it is necessary to consider the law of efficiency changes within a flapping cycle during the design process. In addition, there is a strong coupling relationship between the various components that make up the drive system, such as batteries, electric regulators, motors, reducers, and flapping mechanisms. Due to the characteristics of flapping-wing aircraft, the traditional flapping-wing aircraft drive system design method can no longer meet the design requirements of high-performance flapping-wing aircraft. How to design an efficient drive system solution has become the key to whether flapping-wing aircraft can fly efficiently. Summary of the invention

[0005] In view of the problems existing in the traditional flapping-wing aircraft drive system design method, the present invention proposes a flapping-wing aircraft drive system design method, starting from the flapping-wing drive system requirements, comprehensively considering the characteristics and interface relationships of the battery, electric regulator, motor, reducer, and flapping mechanism, and realizing the forward design of the system. Through this method, the high-efficiency design requirements of the system can be achieved, while taking into account the take-off function 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: According to 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 laws for the flapping wings in takeoff and cruising states, including:

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

[0012] Take-off state: flapping frequency f t , take-off angle of attack, average take-off 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 law 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 of a 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 system 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 The bending moment around the rocker arm axis, θ is the flapping angle of the 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 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 ; and according to the estimated lift L(t) and thrust T(t) variation law in a flapping cycle, 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 ;

[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 arm 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 required by the setting;

[0051] Step 3.2: Use a dynamometer to test the working characteristics of the selected micro brushless motor, and fit the following functional relationship through 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 reducer reduction ratio i, where T m,high The motor output torque corresponding to the high efficiency point determined according to the motor test data; 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 m ; Then, according to the ESC used in the motor test, the battery output voltage and the motor equivalent input voltage U are adjusted 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: According to the battery output voltage U obtained in step 3.3, select the number of battery cells S connected in series; select the battery capacity according to the mission endurance requirement;

[0062] Step 5: Select the ESC according to the voltage range of the battery selected in step 4. The minimum operating voltage of the ESC must be lower than the cut-off voltage of the battery, and the maximum operating voltage must be higher than the maximum voltage of the battery.

[0063] Step 6: Takeoff status verification:

[0064] Recalculate the torque and power in the take-off state according to the flapping frequency and take-off overload in the take-off state; check whether the motor can meet the load torque and speed when the rocker arm power is maximum and the rocker arm torque is maximum respectively; check whether the motor meets the take-off requirements according to the motor test results; if it meets the take-off requirements, proceed to the next step; if not, return to step 3 and reselect the motor;

[0065] Step 7: Use a two-stage reducer and design the reducer parameters, including the reduction ratios i1 and i2 of each stage, the gear pressure angle α, and the number of teeth z of 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 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 in 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 in a flapping cycle;

[0072] If the variation law of lift L(t) with time is unknown, then according to the total weight of the aircraft W T By 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] In a further preferred embodiment, 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 in a flapping cycle in cruise state cmin and the maximum value L cmax ; Where L(t) is the lift force varying with time in 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 in 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 in 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 flutter 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 in one flapping cycle in cruise state c , where T i is the thrust sampling value, N c is the number of samples of thrust 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 in 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 , at the end of the downward and upward phases, the thrust minimum value T is generated cmin ;

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

[0092]

[0093] Calculate the minimum thrust T in a 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 finding functions respectively, and the second and third parameters are the range of flapping cycles for finding extreme values;

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

[0095]

[0096] Estimated thrust first peak value 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 by the hinge during the initial design, and assume that the additional space Δ required by the gear and the hinge is 0. 2-2 After that, we get Δ=R 2-2 -l q, re-estimate 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] In a further preferred embodiment, 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 circuit resistance, 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 modulus 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 stress of material bending fatigue.

[0118] Beneficial Effects

[0119] The design method of the flapping-wing aircraft high-efficiency drive system proposed in the present invention starts from the requirements of the flapping-wing drive system, comprehensively considers the characteristics and interface relationships of the battery, electric regulator, motor, reducer, and flapping mechanism, and realizes the forward design of the system. Through this method, the high-efficiency design requirements of the system can be achieved, while taking into account the take-off function requirements.

[0120] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through 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 easily understood from the description of the embodiments in conjunction with the following drawings, in which:

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

[0123] Figure 2 It is a schematic diagram of 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] Fig. 9 It is the characteristic curve diagram of the alternative motor;

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

[0132] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not 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, and the equivalent voltage transmitted to the motor is controlled by an electric regulator to adjust the motor speed. The motor reduces speed and increases torque through a reducer, and drives the flapping wing through a flapping mechanism to achieve a predetermined motion form. The specific flapping wing drive system design method flow 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: According to the performance indicators and overall design requirements of the flapping-wing aircraft, determine the overall design parameters, including the total weight W 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 = 10.0 m / s, cruising flight angle 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 law of the flapping wing in takeoff and cruising states by using methods such as scale rate or wind tunnel test, including:

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

[0139] Take-off state: flapping frequency f t , take-off angle of attack, average take-off 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 take-off state t and maximum load torque M tmax The demand determines the maximum power of the drive system.

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

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

[0143] Step 3: Calculation of 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 of lift generated in one flapping cycle, Ns;

[0149] Icd ,I cu are the impulses generated by 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 in a flapping cycle, N respectively.

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

[0154]

[0155] Where: L(t) is the lift force that varies with time in 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 lift L(t) are known (e.g., obtained through wind tunnel tests), the average lift 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 law 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 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 phases 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 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 varies with time in a flapping cycle, N;

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

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

[0175] If the variation law 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 minimum lift force L is estimated according to the sinusoidal curve of 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 the negative lift have amplitudes L cmax and L cmin The minimum lift value L is estimated according to formula (6) cmin and the maximum value L cmax .

[0178]

[0179] (3) Calculation of average thrust.

[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 thrust that changes with time in a flapping cycle, N;

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

[0184] If the time-sampling values ​​of thrust T(t) are known (e.g. obtained through wind tunnel tests), the average thrust can be solved by 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 change law of thrust T(t) with time 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 of the aircraft 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) with time is unknown, the average thrust is obtained by formula (9).

[0191]

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

[0193] In 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 (i.e., negative thrust extreme value) is generated at the end of the downward flapping stage and the upward flapping stage.

[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 thrust within a flapping cycle, N respectively; MIN(·,·,·) and MAX(·,·,·) are the minimum and maximum value obtaining functions respectively, and the second and third parameters are the flapping cycle range for obtaining 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 preliminarily 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 cruising 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 in the flapping wing, the bending moment M z It does not do work, but it will affect 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 attached 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 law of lift L(t) and thrust T(t) in one flapping cycle is unknown, according to the previous assumption, lift and thrust vary along sinusoidal curves with different amplitudes in one flapping cycle.

[0210] If the time-varying pattern of the flapping angle Θ of the flapping wing is unknown, it can be assumed that the flapping angle Θ changes with time sinusoidally 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 , the lift reaches the minimum value L when the flapping angle reaches 0 degrees during the upward phase 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 in two cycles 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 the sine wave, 5t c / 8≤t <t c Stage T cmin The amplitude varies 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] 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, according to the flapping frequency f 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 change according to a sinusoidal curve. The lift change 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 up and down flapping without forward and backward sweeping, ignoring the bending moment M formed by the rocker axis. z , calculate the M of the single-side 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 variation law of the flapping angle Θ of the flapping wing realized by the flapping mechanism over time 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 law of the flapping angle Θ of the flapping wing is unknown, it can be assumed that the flapping angle Θ changes with time sinusoidally according to formula (14). The angular velocity is calculated according to formula (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), calculate the total power change P of the rocker arms on both sides 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 within a 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 the 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 in the figure, 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 To ensure the phase difference of the rocker arms on both sides is as small as possible under the range requirements, the rocker arm length l y Horizontal position y with rocker arm shaft y The constraints 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 and approximately satisfies the constraint 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 flapping mechanism height limit H m , that is, the height limit in the z-axis direction, the longitudinal position z of the rocker arm shaft 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 limit and the lower limit 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 characteristics of asymmetric flapping.

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

[0269]

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

[0271]

[0272] In the flapping amplitude Φ c Under the requirement, the transmission angle of the mechanism within the motion cycle is maximized, and δ u =δ d , the length of the rocker arm, crank, connecting rod and the position of the rocker arm shaft must satisfy 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] Rocker arm shaft lateral position y y and the 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) Flap 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 its 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 The efficiency of the flapping mechanism is about 90% to 95% if a crank rocker mechanism is used;

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

[0297] Then 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 the single-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 initially 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 19W. A flapping mechanism of a two-stage gear reducer is selected. The efficiency of the flapping mechanism is assumed to be 0.95, the efficiency of the single-stage gear reducer is assumed to be 0.97, and 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] According to formula (31), the output power and range of the motor of the flapping-wing aircraft in the cruising state are calculated.

[0309]

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

[0311]

[0312] According to formula (33), the rated power P of the selected motor is estimated e

[0313]

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

[0315] Table 1- Motor parameters

[0316]

[0317] Step 3.2: Determine the 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. 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 there is no motor test data, 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), and the inductance of the brushless DC motor is usually in the mH range. 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: 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 obtained by testing with an LCR tester. If this is not possible, you can also check the motor internal resistance characteristics provided by the manufacturer. Back EMF constant K e and K t The numerical value is close, and K is often used in engineering applications. e =K t However, in many cases, the brushless motor constant is not clearly given, but only the motor's K 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 taken as an example to match the flapping wing motion parameters with the power system. The motor is tested for characteristics using a dynamometer. The throttle state is 100%. The dynamometer is used to obtain characteristic relationship curves of the candidate motors under a series of voltages, as shown in the attached figure. Fig. 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] The torque of the motor is amplified after passing through the reducer, and the output speed is reduced. The speed and torque output by the reducer are transmitted through the flapping mechanism to drive the flapping wing to achieve the expected flapping. Therefore, the output end of the flapping mechanism needs to meet two constraints at the same time: reaching the desired flapping frequency; the output torque that can be provided is not less than the load torque requirement of the flapping wing.

[0339] After determining the speed reducer ratio and battery voltage, the above two constraints need to be tested, and the motor can be checked to see if it can meet the load torque and speed when the rocker arm power is maximum and the rocker arm torque is maximum. The takeoff state can be checked directly in step 6. If the motor can meet the takeoff state requirements, it can meet the cruise state 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 under different throttles Th are calculated. rms The conversion relationship 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 the 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 speed 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 10mNm, 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 10mNm and the speed is 12432rpm.

[0363]

[0364] Test the ESC. The test results are as attached. Fig.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 with respect to i, we get the efficiency η m The maximum point of is:

[0380] Take the no-load current of 0.7A and the internal resistance of 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 in the 80% throttle cruising state.

[0386]

[0387] Step 4: Battery Selection

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

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

[0390]

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

[0392] Step 5: ESC Selection

[0393] According to the battery voltage range in step 4, the ESC is selected. The lowest operating voltage of the ESC must be lower than the battery cut-off voltage, and the highest operating voltage must be higher than the maximum voltage of the battery. In this embodiment, the electronic speed regulator model selected is DSHOT BULLET30A brushless ESC. The voltage range is 2S to 4S, and the continuous operating current is 30A.

[0394] Step 6: Takeoff status check

[0395] Take-off state: flapping frequency f t , take-off angle of attack, average take-off overload n t .

[0396] Recalculate the torque and power in the takeoff state according to the flapping frequency and takeoff overload in the takeoff state. Verify whether the motor can meet the load torque and speed when the rocker arm power is maximum and the rocker arm torque is maximum. Verify whether the motor meets the takeoff requirements according to the motor test results.

[0397] In this embodiment:

[0398] Take-off 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 take-off 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 14.3mNm and the speed is 16432rpm.

[0408]

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

[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 17.6mNm and the speed is 11461rpm.

[0413]

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

[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. When 8 < i ≤ 50, a two-stage reducer is selected. At present, most flapping-wing aircraft choose two-stage reducers. As shown in Figure 8 the figure, gear 1 is connected to the motor, gear 2 and gear 3 are integrated, 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 without root cutting 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 And 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 take-off state is larger, a safety factor n0 should be multiplied on the basis of the cruise state. According to experience, the value can be taken as 2). Then, the modulus 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 modulus value is calculated, it can be appropriately rounded according to the standard modulus 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 shafts 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 the composite tooth form coefficient. For small number of teeth gear (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 it is recommended to select materials with bending fatigue strength greater than 360 MPa);

[0436] The ratio of 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 module of each level of reduction gear is calculated by 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 is to be understood that the above embodiments are exemplary 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 intent of the present invention.

Claims

1. A method for designing an efficient drive system for a flapping-wing aircraft, characterized in that: 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 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 ; Step 1.2: Determine the optimal flapping laws for the flapping wings in takeoff and cruising states, including: Cruise state: lift-to-drag ratio or thrust-to-weight ratio Flap frequency f c , flapping amplitude Φ c Or the variation law of flapping angle Θ of flapping wing with time Θ=g c (φ c ,f c ,t); Take-off state: flapping frequency f t , take-off angle of attack, average take-off overload n t ; 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 variation law of lift L(t) and thrust T(t) in a flapping cycle is known, then according to the formula Calculate the torque M at the swing arm shaft of a 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 system 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 The bending moment around the rocker arm axis, θ is the flapping angle of the wing, l T is the length of one side wing; If the variation law of lift L(t) and thrust T(t) in a flapping cycle is unknown, then according to the formula Estimate the variation law of lift L(t); according to the formula 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 ; and according to the estimated lift L(t) and thrust T(t) variation law in a flapping cycle, 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 ; The cruise state flapping wing rocker power is calculated by the following process: According to the formula 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, 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: 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 l y , crank length l q , connecting rod length l k , rocker arm shaft position (y y ,z y ): Step 2.1: According to the wingspan B T and flapping wing length l T Parameters, according to the formula Determine the lateral position y of the rocker arm shaft y ; Step 2.2: According to the formula Determine the rocker arm length ly; Step 2.3: According to the formula Estimate the crank length lq; Step 2.4: According to the formula z y ≈H m -L q -L y -Δ Estimate the longitudinal position z of the rocker arm shaft y , where Δ is the additional space required for the gears and hinges; Step 2.5: According to the formula Determine the connecting rod length l k , establish a flapping mechanism with symmetrical flapping characteristics; Or according to the formula Determine the connecting rod length l k , establish a flapping mechanism with asymmetric flapping characteristics; Step 3: The flapping wing rocker power P determined in step 1 x And the range of variation [P xmin ,P xmax ], select the motor and determine the characteristic parameters: Step 3.1: According to the formula 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 required by the setting; Step 3.2: Use a dynamometer to test the working characteristics of the selected micro brushless motor, and fit the following functional relationship through the test data: 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; Step 3.3: According to the formula Calculate the reducer reduction ratio i, where T m,high The motor output torque corresponding to the high efficiency point determined according to the motor test data; and the motor speed under the current flapping frequency reduction ratio i is obtained n m,i =60if c 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 m ; Then, according to the ESC used in the motor test, the battery output voltage and the motor equivalent input voltage U are adjusted at different throttles Th. rms The conversion relationship can be used to obtain the equivalent voltage coefficient σ under different throttle states. IN rms =U×σ Recalculate the battery output voltage U in the cruise state; Step 4: According to the battery output voltage U obtained in step 3.3, select the number of battery cells S connected in series; select the battery capacity according to the mission endurance requirement; Step 5: Select the ESC according to the voltage range of the battery selected in step 4. The minimum operating voltage of the ESC must be lower than the cut-off voltage of the battery, and the maximum operating voltage must be higher than the maximum voltage of the battery. Step 6: Takeoff status verification: Recalculate the torque and power in the take-off state according to the flapping frequency and take-off overload in the take-off state; check whether the motor can meet the load torque and speed when the rocker arm power is maximum and the rocker arm torque is maximum respectively; check whether the motor meets the take-off requirements according to the motor test results; if it meets the take-off requirements, proceed to the next step; if not, return to step 3 and reselect the motor; Step 7: Use a two-stage reducer and design the reducer parameters, including the reduction ratios i1 and i2 of each stage, the gear pressure angle α, and the number of teeth z of each stage. i , gear modules m1 and m2 at each level.

2. 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 variation law of lift force L(t) with time is known, then according to the formula 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 in 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; If the lift force L(t) is sampled over time, then according to the formula 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 in a flapping cycle; If the variation law of lift L(t) with time is unknown, then according to the total weight of the aircraft W T By formula 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, n cu 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 variation law of lift force L(t) with time is known, then according to the formula Calculate the minimum lift value L in a flapping cycle in cruise state cmin and the maximum value L cmax ; Where L(t) is the lift force varying with time in a flapping cycle; If the variation law of lift force L(t) with time is unknown, then according to the formula Estimate the minimum lift value L in 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, n cu 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 change law of thrust T(t) with time is known, then according to the formula Calculate the average thrust T in 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; If the thrust T(t) sampling value over time is known, then according to the formula Calculate the average thrust T in one flapping cycle in cruise state c , where T i is the thrust sampling value, N c is the number of samples of thrust in one flapping cycle; If the law of change of thrust T(t) with time is unknown, then according to the formula Calculate the average thrust T in one flapping cycle in cruise state c .

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, 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 , at the end of the downward and upward phases, the thrust minimum value T is generated cmin ; If the change law of thrust T(t) with time is known, then according to the formula Calculate the minimum thrust T in a 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 finding functions respectively, and the second and third parameters are the range of flapping cycles for finding extreme values; If the law of change of thrust T(t) with time is unknown, then according to the formula Estimated thrust first peak value 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.

6. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 5, characterized in that: In the initial design, the hinge and the additional space required for the hinge are ignored, and the additional space Δ required for the gear and the hinge is assumed to be 0. 2-2 After that, we get Δ=R 2-2 -l q , re-estimate the longitudinal position z of the rocker arm shaft y .

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 η trans =η link η gear , where η link is the flapping mechanism efficiency, η gear is the reducer efficiency.

8. The method for designing a high-efficiency drive system for a flapping-wing aircraft according to claim 1, 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 U m is the motor input voltage, K V is the speed constant, R m is the total circuit resistance, and I0 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 1, characterized in that: In step 3.3, if there is no motor test data, use the motor efficiency formula 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.

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 at each level, where i 总 is the total transmission ratio; (2) According to the formula z1=z min ,z3=z min z2=z min i1 z4=z min and2 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; (3) According to the formula Calculate the torque and modulus 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 stress of material bending fatigue.

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