Experimental Verification of Thrust Model Blower

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For lift and movement of hovercraft were selected blowers of type GWS 40B 6000KV, which have a built-in three-phase brushless motor with revolution KV=6000 (6000 revolutions per minute to 1V). The engine belongs between the inrunners, because the rotor spins inside. This brushless motor was preferred before DC motor and it's mainly due to the performance and service life. DC battery voltage is to be transformed into a three alternating voltage with phase displacement 120°, which will be fed into the blower. This transformation of the DC voltage to AC voltage allows us regulators of brushless engines. For our blowers were selected regulators Xcontroller XC22-L, we can see in Figure 2 ^[1].

Figure 2. Testing bench for blowers via deformation of spring [1]

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2. Testing of the Maximum Thrust Via Deformation of the Spring

This procedure of testing consists of measurement deformation spring of constructed dynamometer, which deforms in dependence on size of the thrust blower and using relation is this deformation recalculated on the thrust.

The blower is stored in PVC coupling with a diameter 50 mm. This PVC coupling is anchored by two adducent tapes on thin-walled L profile. Profile with blower and dynamometer are anchored on laboratory stand with double clamps. Blower and dynamometer are connected each other by carbine, which is fixed to blower by three copper wires relabeling insulating tape, shown in Figure 3 ^[1].

Figure 3. Testing bench for blowers via deformation of spring [1]

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In the testing of the maximum thrust via deformation of the spring, microcontroller BasicATOM Pro 28-M is powered from laboratory source SP 150 and communicating with the PC needed for programming is secured using the RS232 interface, we can see in Figure 4. Resistive track of the potentiometer is powered from a 5V source SP 150 and regulator Xcontroller XC22-L is powered from laboratory source DIAMETRAL V130R50D. By moving the runner of potentiometer varies the size of the analog voltage to pine P0 of the microcomputer and from pin P4 is transmitted a modulated periodic signal with different impulse width, which is dependent on analog voltage. This dependence can be formulated by relation:

(1)

where: t_imp[μs] – is impulse width

U_an[V] – analog voltage

This signal with different impulse width enters to regulator and causes a change revolution of the blower and subsequent deformation of the spring. During the measurement on oscilloscopes Voltcraft DSO-6250S was watched the changing pulse width from the microcomputer and the frequency of a one phase motor of the blower ^{[1, 2, 3]}.

Program:

temp var word

a var sword

main

adin16 p0,temp

a=temp*2000/65472-1000

servo p4,a,10

goto main

Figure 4. Scheme engagement with laboratory source DIAMETRAL V130R50D [1]

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First, the maximum deflection of the spring was measured at the maximum of the pulse width, what we can see in Table 1. The biggest deformation caused the blower number 4, on which will be realized also further measurements ^[1].

Figure 5. View to measuring progress [1]

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Table 1. Maximum deformation of spring at the maximum impulse width [1]

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The measured values pulse width and frequency of one phase of the motor were read from Oscilloscopes and written into prepared table Table 2, from which was constructed graph, which we can see in Figure 6 ^[1].

Figure 6. Graph dependence frequency of phase motor on impulse width [1]

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On the previous graph we can see that the frequency phase of motor has logarithmic course with equation of reliability R²=0,879. Uncertainty of the measured values created due to from problematic reading, because the values of the frequency and impulse width constantly varied.

Then on the laboratory source Diametral V130R50D were read the values of the entering current to the controller of blower at different frequencies and these values are written in Table 3 ^[1].

Table 2. Frequency motor for different impulse width [1]

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Table 3. Entering currents to regulator of blower for different frequencies [1]

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From Table. 3 was constructed graph, shown in Figure 7, where the values of current obtained experimental varied according to the linear trend line with the equation of reliability R²=0,977. Displacements of values also are created due to the variation in frequency ^[1].

Figure 7. Graph dependence entering current to regulator on frequency phase motor

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On determination the thrust of blowers is necessary to determine the stiffness spring of dynamometer. By means of double clamp, dynamometer is clamped to a laboratory stand and on its end are gradually added weights. With the increasing weight is watched size deformation of spring and these values are recorded in Table 4 together with the calculated gravity force according to the relation ^{[4, 6]}:

(2)

where: F_g[N] – is the gravity force acting on weights

m[kg] – the mass of weight

g[m.s^-2] – the gravity acceleration

Figure 8. View to measuring progress [1]

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Table 4. Values needed to determine stiffness of spring [1]

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Figure 9. Graph dependence gravity force on deformation of spring [1]

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From the graph, shown in Figure 9, after application of the linear trend line we get the prescription of function-stiffness of the springs with the equation of reliability R²=0,9987.

From equilibrium of forces, shown in Figure 10, by neglecting friction between the contact surfaces of the blower and the inner cylindrical surface PVC coupling, we get the relation ^{[7, 8, 9]}:

(3)

After substituting the thrust force of blower:

(4)

acting force on the spring:

(5)

and the stiffness into equation (3) and its adjustment we get the relation to calculate the thrust of blower:

(6)

where: m_t[g] – is the thrust of blower

k[N.m^-1] – the stiffness of spring

Δ[m] – the deformation of spring

Figure 10. Principled scheme engagement of blower with spring

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Values of deformation from Table 1 we will substitute into equation (6) and we will get thrust of blowers added into following table ^[1].

Table 5. Table of maximum deformation, which is added about thrust [1]

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Figure 11. Column diagram of thrust blowers via the deformation of spring [1]

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3. Testing of the Maximum Thrust Via Wood Beam in the Shape Letter L

The advantage of this method lies in the possibility of obtaining the values of the thrust blower directly without any calculations.

In this method of testing was used test bench consisting of wood beam in the shape of the letter L, which is stored in the bearings 6001 in wood supports, we can see in Figure 10. At the top of the beam is hole with a diameter 43 mm, which is created for mounting tested blower using insulation tape wrapped around a plastic cylindrical part of the blower, which prevents unwanted movement. At the bottom is the rubber foot attached using screw connection ^{[1, 2, 3]}.

Figure 12. Test bench for blowers in SolidWorks2011 [1]

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Distance between the axis of the hole for the blower and the joint must be the same as the distance between the joint and the axis of the rubber foot due to that thrust force of blower transfer through the rubber foot on digital weight SALTER 1066 in the ratio of 1: 1, shown in Figure 13. Calibration of digital weight has been confirmed by the manufacturer stated accuracy 1 g.

The scheme engagement and the program are the same as in the previous method of measurement. In this method of measurement is addition source Diametral in order to compare the values of the thrust also used Li-Polymer battery, we can see in Figure 14 ^[1].

Figure 13. Principled scheme of test bench [1]

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On blowers was measured their maximum thrust. They were powered from source Diametral V130R50D and also from Li-polymer battery, shown in Table 6. Thrust of blowers, which were powered from laboratory source, is lower, because the entering current to the blower at voltages 11V is until 16A and power supply has a current limit to 10A. For blower number 4 again was the biggest thrust ^[1].

Figure 14. Scheme engagement with energy source Akku LiPol Xpower 2200-3S ES [1]

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Figure 15. View to measuring progress [1]

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Table 6. Tabuľka maximálnych ťahov [1]

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Figure 16. Column diagram of thrust blowers via the wood beam in the shape letter L [1]

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Then was selected blower No.3 powered from laboratory source and was measured the frequency phase of motor and thrust at varying voltages, we can see in Table 7 ^[1].

Table 7. Table of frequencies and thrusts for different values of current [1]

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In the previous table, we can see, that until at the voltage 7.4 V, the propeller of blower started to spin.

Figure 17. Graph of dependence thrust blowers on frequency phase motor [1]

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Figure 18. Graph of dependence thrust of blower on current [1]

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The previous graphs show the dependences thrust of blower on frequency phase motor, electric current and voltage, which have linear course with the competent equations reliability R²=0,996, R²=0,999 and R²=0,997. In Figure 19 we can see how at the voltage 10,5 V has not already increased thrust of blower, what is caused by current limit of laboratory source ^[1].

Figure 19. Graph of dependence thrust of blower on voltage [1]

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