# Category Archives: aeromodelling research

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## Arduino Tutorial: Digital scale

In the previous post has been written about the calibration of load cell sensor for measuring the thrust ofpropeller and the motor/engine. In a posting has been found a constant magnitude of the sensor output voltage per gram about 0.267012014. So every 1 gram increase in weight of load will raise the output voltage of the sensor about 0.267012014 mV.

In my project, this output voltage must be converted into digital numbers using the ADC on the Arduino Nano. Henceforth, the data is sent serially to the PC to be displayed in the monitor. PC programs used in visual basic 6. As a development, in terms of measuring the thrust, required the measurement results are presented in graphical form.

## What about the working principle of the Arduino program ?

1. At just the Arduino turn on, will assume the load is 0.
2. Arduino will sent periodically value of ADC to the PC every 200mS.

As written in previous posting, I will design and make a test equipment to measure the thrust of propeller and the motor/engine in aeromodelling parts. This measure will help to design rc model, such as fixed wing and multicopter. Before designing a total airframe, need to know first the characteristics of the motor/engine and matching propeller size. I used the load cell with specifications was written on this posting. My load cell is 15Kg of full scale with output voltage about 2mV/V. I used the amplifier capable to gained up to 1000x with source 5V for load cell reference voltage. This mean will give output about 10mV in full scale of 15Kg load.

## How to a simple calibrate  ?

Since I do not have the standard weight of high-priced, this way is simple to use a digital scale which has an accuracy of about 0.1gram and can measure up to 1Kg. Next, weigh any load with digital scale, record the result. Then move to the load cell and measuring with a digital voltmeter on the load cell amplifier output voltage.

 Photo of digital scale Photo of Load cell 362.2 gram 105.1 Volt 528.5 gram 151.8 Volt 63.5 gram 19.8 volt 275.9 gram 80.7 volt 34.1 gram 11.7 volt 14.7 gram 6.1 volt 30.2 gram 10.6 volt 130.2 gram 39.1 volt 40.4 gram 13.2 volt 101.2 gram 30.7 volt

Plot data using SCILAB

The commands to plot the datas using SCILAB as follow:

->weight = [362.2,528.5,	63.5,275.9,34.1,	14.7,30.2,130.2,	40.4,101.2]
weight  =

362.2    528.5    63.5    275.9    34.1    14.7    30.2    130.2    40.4    101.2

->volt=[105.1,151.8,19.8,80.7,11.7,6.1,10.6,39.1,13.2,30.7]
volt  =

105.1    151.8    19.8    80.7    11.7    6.1    10.6    39.1    13.2    30.7

->size(weight)
ans  =

1.    10.

->size(volt)
ans  =

1.    10.

->plot(weight,volt,'ro-.')

->xgrid

->ylabel("Loadcell amplifier output (mV)")

Will result a graph as follow:

## How much’s the output voltage of amplifier at zero load ?

On zero load output voltage at zero load is 2.8mV. My amplifier can not adjust to 0.0 volt, because there null offset voltage. On arduino using 10bit adc with 5V ref, will convert into (2.8/5000)*1024 =  0.57344 less than 1, or will known as 0 decimal.

## How to calculate voltage per Kg or mV/Kg ?

From the above data, I would find the average value using Microsoft Excel, will be obtained as follows:

So output voltage of amplifier will be: 0.267012014 mV/gram or 267.012014 mV/Kg.

The output amplifier according to specifications from 0 up to 4.3 volts. So that the maximum load that can be read are: 4300/267.012014 = 16.104Kg, near specification of loadcell about 15Kg.

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## An easy way to see the responses of ENC-03 gyro chip

Chip Gyro of ENC-03 is often used as a sensor to stabilize the aircraft or multicopter using RC. To learn seriously need to know the workings and characteristics of this chip. Data sheet for this sensor can be downloaded here. Chip is famous for its resistance to vibration and is easy to use because it has an analog output.

The sensor works because of the angular velocity, analog output voltage will depend on the angular velocity applied to the sensor.  Sensor output voltage will follow the following equation:

$V_{out}=&space;V_0+S_v\cdot&space;\omega$

V0 is the static output voltage at angular velocity = 0 deg/s. $V_0=&space;V_{ref}&space;\pm&space;0.6&space;V$

From datasheet $\small&space;V_{ref}=1.35V$. Thus the magnitude $\small&space;V_o=1.21V&space;-&space;1.41V$. Sv is scale factor in mV/deg/S = 0.67V. And $\tiny&space;\omega=-90&space;to&space;90deg/S$.

## Schematic

This circuit is the simplest. Voltage source connected to the RC tap, 100 ohms and 47uF to eliminate the ripple in the voltage source.

Gyro output voltage tap connected to the RC, 6.8KOhm and 0.68uF, serves as a simple lowpass filter to eliminate the output voltage caused by vibration.

Vref is the output that generates a voltage as a reference that may be required by the circuit on the outside.

At Vref is necessary to add capacitors of 4.7uF.

## Microcontroller

To read the response of the output voltage of the gyro, so easy to do I use nano Arduino board. This board contains a microcontroller type ATMega 328p. Because it already has an internal ADC, it will be easy to record responses.

In my Arduino programming using A0 as the ADC to convert the voltage output come from the gyro into digital numbers. Hereinafter ADC conversion result is sent serially to be recorded by using hyperterminal on windows.  I decided to process the data and plotted using Scilab.

## Board of ENC-03 Gyro

I got this gyro board by removing the yaw gyro on kkboard. However, it should be added 100ohm resistor and 47uF capacitor on the power supply VCC. And 0.68uF capacitor also needs to be added to the gyro output.

In accordance with the data sheet, this board is placed upright and moved radially. Can also be placed upright and inverted, but the gyro output voltage changes will be reversed as well.

To be able to move freely in the radial, required a dish to put this gyro board. To connect with pin of the Arduino board, can be soldered directly  using  cables.

Additional compenents of resistor and capasitor can be soldered into header pins of this board.

## Dish

In order gyro board can be moved radially with ease, need a dish to put the gyro board. The dish is made using styrofoam plate. At the center of the dish, bamboo as a holder mounted to rotate the dish. Arduino board and gyro board placed on this dish.  Furthermore, the Arduino board is connected with usb cable to the computer to record the results of Gyro responses of the radial motions.

This method is the most inexpensive and easy to make because it uses materials easily obtained is styrofoam.

## Other Dish

Because I can do the job using mechanical equipment such as lathes, milling machines, drilling machines, welding machines and so forth. I prefer this dish using iron material, because it is more robust and stable during use.

## Basic Recording

The basis of recording the response of the gyro output is done by reading through the adc conversion. I am using the Arduino programming with nano board. Arduino program as follows:

void setup() {
Serial.begin(115200);
}

void loop() {
Serial.println(sensorValue);
delay(50);
}

#### Recording steps:

1. Turn on Arduino by plugging USB’s arduino board to the computer.
2. Open hyperterminal, set baud to 115200 baud, 8bit, No parity, 1 stop bit.
3. Connect communication by clicking “Call” icon. You must ensure that the serial channel selection is correct. You will see the data receive by hyperterminal
4. Rotate the dish, you’ll see a change of data in hyperterminal.
5. To record and stored in a file, select the “Transfer -> Capture Text”. Then asked to fill in your name and the file folder.
6. Turn the dish as the fourth step in accordance with your wishes.
7. Stop record by select the “Transfer->Capture Text->Stop”.

#### Processing of data

The file name of the data is capture5.txt. Further data will be read and processed using Scilab program. Use the console to process manually. Scilab commands as follow:

-->// read data file into sh matrix

// convert sh matrix string content into d matrix as numeric
-->d=evstr(sh);

// convert adc data (0-1024, 10bit) into analog voltage
-->analog=(d/1024)*5.0;

// how big is the size of data
-->size(analog)
ans  =

694.    1.

// make t matrix as time (axis plot) 0 to 693
-->t=0:693;

// plot data
-->plot2d(t,analog,style=2)

The results of the graph are shown as follows.

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## Engineering design of measuring instrument for testing propeller thrust

This mechanical design serves to measure the thrust generated by the propeller.  In the world of aeromodelling, to design a model aircraft  require  the performance datas of thrusts that generated by the propeller. This will find the suitability of the propeller for the type of aircraft.

Overall, the mechanical system can be divided into several parts:

1. Pole
Serves to hold the thrust by the propeller. At the bottom there is a weight load that does not shake.
2. Slider
Is a moving part which rests two linear bearings. This section is used to hold the motor / engine and propeller.
3. Motor/Engine and propeller mount
Serves to hold the motor/engine and propeller. This section will vary according to the motor/engine.
Sensors that work mechanically, driven by a slider that moves as result of thrust backward.

This mechanical system can be used to test the thrust by using electric motors or engines. Thus it will become easier to get the appropriate size of the propeller.

The data can be obtained by using a mechanical system are:

1. Relationship between the RPM with the generation of thrust.
2. The relationship between RPM and current/power which is absorbed.
3. The relationship between the current/power which is absorbed and thrust.

Point (1) The first can be used to obtain the performance of the propeller (the motor has more power), the second is used to obtain the size of the propeller in accordance with the motor / engine specific.

Point (2) can be used to calculate or test a long fly to the configuration of the motor, propeller and certain batery capacity (mAH).

Point (3) can be used to calculate the efficiency of the power absorbed by the thrust generated.

## How it works

The main principle of this mechanical is the Motor/Engine and propeller can move through the slider. In order to be a little friction, slider is associated in two linear bearings. The use of two linear bearings also serve for the motor does not rotate. If the wind direction toward the front, then there will be thrust to the rear. One end of the slider there is a “load cell pusher” that serves to suppress the load cell at the time when thrust generated. By adding a signal conditioner, the output voltage of load cell can be converted to digital by using the ADC.

## Motor/Engine Mount

In order to hold the motor/engine include propeller need mount that can joint to slider. This mount has a variety of forms according to the motor / engine that is used.

To measure the thrust with a direction to the rear, I use the sensor “load cell”.

1. CAPACITY:  15kg(30lb)
2. RATED OUTPUT:  2.0 ±0.1mv/v
3. ZERO BALANCE : ± 0.5 % F.S.
4. OUTPUT EFFECT ON ZERO: 0.03 %F.S. ( within 5 minutes)
5. CREEP: 0.030~0.05 %F.S. ( within 5 minutes)
6. NONLINEARITY ,HYSTERESIS AND REPEATABILITY: <± 0.03 % F.S.
7. INPUT IMPEDANCE: 395±5 Ohm
8. OUTPUT IMPEDANCE: 350±5 Ohm
9. TEMPERATURE EFFECT ON OUTPUT %OF APPLIED LOAD: ± 0.03, %F.S./10c°
10. TEMPERATURE EFFECT ON ZERO %OF RATED OUTPUT: ± 0.8,%F.S./10c°
11. EXCITATION VOLTAGE: 10 Volt
12. INSULATION RESISTANCE: 300M W