MPU-6050's Linear Acceleration is Way Off

[georgelue321]

Hello!

 

I have installed Jeff Rowberg's i2cdevlib library which I can use for my MPU-6050 to make it interact with Arduino.

 

However, I have an odd problem with one of its functions.

 

It's got a function to turn the accelerometer & gyroscope readings into linear acceleration. This is the definition of the function:

 

uint8_t MPU6050::dmpGetLinearAccel(VectorInt16 *v, VectorInt16 *vRaw, VectorFloat *gravity) {
    // get rid of the gravity component (+1g = +8192 in standard DMP FIFO packet, sensitivity is 2g)
    v -> x = vRaw -> x - gravity -> x*8192;
    v -> y = vRaw -> y - gravity -> y*8192;
    v -> z = vRaw -> z - gravity -> z*8192;
    return 0;
}

 

 

However, whenever the function is called in the example code:

 

           // display real acceleration, adjusted to remove gravity
            mpu.dmpGetQuaternion(&q, fifoBuffer);
            mpu.dmpGetAccel(&aa, fifoBuffer);
            mpu.dmpGetGravity(&gravity, &q);
            mpu.dmpGetLinearAccel(&aaReal, &aa, &gravity);
            Serial.print("areal\t");
            Serial.print(aaReal.x);
            Serial.print("\t");
            Serial.print(aaReal.y);
            Serial.print("\t");
            Serial.println(aaReal.z);

 

I get values way off, when I'm not even moving my MPU-6050!

 

These are a few of the values I get:

 

areal -473 423 -425
areal -460 400 -450
areal -471 522 -458
areal -322 276 -582

 

Do you know how I can fix this? 

Thanks!

-George

 

[Jeff Rowberg]

Hi George,

 

Given that these values are relatively close to 0 on the scale of 1g (~5% of 8192), this is most likely due to calibration offsets in that specific sensor. You can overcome these with manual offsets in your own code, or with the various OFFSET registers in the MPU.

[shajia ikram]

Hi Jeff!!

I wanted to ask some questions regarding aaReal Readings in MPU-6050 dmp6 file.

--> How do we find the sensitivity of acceleration readings (what specific values did you choose?). This is because I have to divide acceleration by sensitivity factor.

--> How exactly did you calculate GRAVITY VECTOR for gravity compensation??

Kindly reply ASAP..

Regards..