Archivi tag: drone

Sulla calibrazione dell’IMU

I’d like to put here some consideration about the imu calibration, that means how it is mounted the imu on the drone respect the propeller plane. This information is fundamental to garanty a perfect hover position without lateral mevement of the drone.

In other words, if I set roll=0 and pitch=0 I want that the prop plane is aligned with the world, evenif the sensor can be not perfectly aligned with the world (and also with the propeller plane).

In this pictures you can see this case: the world (blue) , the sensor (red) and the prop plane ( orange).

IMU_cal1 IMU_cal2

In the next picture let’s put some manes to the angles:

IMU_cal3

Important: Note that gamma is the angle measured by the accelerometer.

The most important information I need to know is the angle beta : the offset between the sensor and the prop plane . this is the error generated to the mechanical installation of the imu.

This value is used to compensate the measured value from the accelerometer.

alpha and beta are the 2 unknowns so I need 2 equations to solve this problem.

I decide to use this simple method to calibrate imu:

1) Take a reference plane ( my kitchen table) . It does not metter if it is not perfect alingned to the world, it is just enough it is stable.

2)Place from behind the prop plane on the “table roof”.

IMU_cal3b

3) Measure the angles of the accelerometer (gamma1).

4)turn the drone 180 degree respect yaw and place it again on the table roof.

5)Measure the angles again ( gamma2) .

6)consider that, in those 2 measurements, the alpha angle is constant ( i do not move the table…) , while the angle beta is equal but inverted ( due to the rotation of the drone).So the result is:

IMU_cal4

 

In order to manage this method in a easy way I added in the code the option called “fine calibration” .

The last version is now on github.

Just run the myQrc.py , move to the new mode “IMU” and follow the instructions.

 

 

 

 

myQrc Rilasciata

I just upload the last and final version of the myQ release candidate on github

DSC_6918

All the software has been debugged and tested.

All the functionalities are now stable.

I tested in different options (debug mode, netscan activated, sensor log) and the result is that I can run the main loop every 10 ms and get sensor data every 6 ms.

It can happen to have a delay on the sensor data loop when a log is added ( 2/3 ms).

 

I removed the webserver from the list of test to do, so it is not supported in this version of the software. The main reason is an instability when runnin gon raspberry. I have to investigate a more robust way to manage the comunication via browser.

 

Next time I will write a post the drone will be just landed…(after its first flight!!!)