Calculating Vibrational frequency with MPU 6050

Hello I am trying to calculate the vibrational frequency of a motor. I am using an arduino to power a motor, 10mm Vibration Motor - 3mm Type Model: 310-122 by percision microdriver. Using a duty cycle of .54 i epxect a vibrational frequency of 190hz but when i plot it i only get to 40hz i beleive. My current script uses the ardunio and mpu 6050 library to loop reading the values then storing them into an array. I plot acceleration vs time and use the fft to get magnitude vs frequency. Is it my sampling frequency that may be wrong? I have based my code off other examples I have seen on MathWorks. Also would it be better if i recorded the data to an excel then read that in a different script? I have seen a lot of examples that read from excel and then fft.

clear all
close all

a = arduino('COM3', 'Uno', 'Libraries', 'I2C');
imu = mpu6050(a);
%pause on
writePWMDutyCycle(a,'D3', .24);
format shortg
tic
for i = 1:1000
    %c = clock
    acc = readAcceleration(imu);
    x(i) = (acc(1)/9.80665);
    y(i) = (acc(2)/9.80665);
    z(i) = (acc(3)/9.80665);
    toc
    time(i) = toc;
    %pause(0.1);
end
%toc

f1 = figure;
f2 = figure;
f3 = figure;
f4 = figure;
f5 = figure;
f6 = figure;

plot(time,x,'.-')
ylabel('y,Acceleration (g)')
xlabel('x,Time (MilliSeconds)')
title('X Accel')

figure(f5)

plot(time,y,'.-')
ylabel('y,Acceleration (g)')
xlabel('x,Time (MilliSeconds)')
title('Y Accel')

figure(f4)

plot(time,z,'.-')
ylabel('y,Acceleration (g)')
xlabel('x,Time (MilliSeconds)')
title('Z Accel')

%0.015

t = (time)*1E-1;       % time to miliseconds, maybe no conversion?
v = x;          % accel values of x axis (g)
L = length(t); 
Ts = mean(diff(t));
Fs = 1/Ts;
Fn = Fs/2;

vc = v - mean(v);

FTv = fft(vc)/L;                                        % Fourier Transform
Fv = linspace(0, 1, fix(L/2)+1)*Fn;                     % Frequency Vector (Hz)
Iv = 1:length(Fv);                                      % Index Vector
figure(f3)
plot(Fv, abs(FTv(Iv))*2)
grid
xlabel('Frequency (Hz)')
ylabel('Amplitude (g)')
title('X Frequency')


v2 = y;
vc2 = v2 - mean(v2); 

FTv2 = fft(vc2)/L;                                        % Fourier Transform
Fv2 = linspace(0, 1, fix(L/2)+1)*Fn;                     % Frequency Vector (Hz)
Iv2 = 1:length(Fv2);                                      % Index Vector
figure(f2)
plot(Fv2, abs(FTv2(Iv2))*2)
grid
xlabel('Frequency (Hz)')
ylabel('Amplitude (g)')
title('Y Frequency')

v3 = z;
vc3 = v3 - mean(v3); 

FTv3 = fft(vc3)/L;                                        % Fourier Transform
Fv3 = linspace(0, 1, fix(L/2)+1)*Fn;                     % Frequency Vector (Hz)
Iv3 = 1:length(Fv3);                                      % Index Vector
figure(f1)
plot(Fv3, abs(FTv3(Iv3))*2)
grid
xlabel('Frequency (Hz)')
ylabel('Amplitude (g)')
title('Z Frequency')

writePWMDutyCycle(a,'D3', 0);

[pvsk Reddy]

Hello Mr. Alexander,

Are able to sort this out? by chance.

Answer 1

[Gayatri Menon]

Hi,

Could you try setting the SampleRate of the imu object and use read()

>> imu = mpu9250(a,"SampleRate",190);
>> tt = imu.read
>> tt.Acceleration

Please use the below links for more information

https://www.mathworks.com/help/supportpkg/arduinoio/ref/mpu9250.read.html

Hope this helps

Thanks

Gayatri