Pages: [1]   Go Down
Author Topic: Quadrotor prj using Angular Rate Sensors (ENC Series) --- Murata  (Read 1122 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 6
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi every one, i am a last year student in Vietnam and i have my term project is ” Building a quadrotor”.
I  have something confuse about my project and i really need your help.
The hardware which i use to build my quadroto is “kk multicoter controller black board v5.5”, in this board there are 3 angular rate sensors and the main uController is atmega168pa, and here is the datasheets.

1.Kk_board datasheet: http://www.kkmulticopter.com/downloads/resources/KKmulticontroller%20v.5.5.pdf

2.The angular rate sensor use in kk board: (ENC series) http://www.murata.com/products/catalog/pdf/s42e.pdf

I follow the way to calculate the value of three angular rate sensors in these website:
http://arduino.cc/forum/index.php?topic=58048.0
and
http://www.starlino.com/imu_guide.html

My code is C++ for atmega168pa and i know this forum is about adruino, but i think my code is very cleary and easy to understand. Here is it:

Code:
/************************************************************************/
/*  MAIN FUNTION                                                       */
/************************************************************************/
int main(void)
{
CLKPR=0x80;
CLKPR=0x00;

//----------- system init --------------------
sei();
usart_init();
adc_sensor_init();
led_init();
motor_control_init();
motor_start();
DDRB|=(1<<PINB3);// measure loop time for cheking
//-----------------------------------------------------------
//---------- update the zero value ---------
adc_sensor_get_value();
roll_zero=roll_adc;//~=824
yaw_zero=yaw_adc;//~=816
pitch_zero=pitch_adc;//~=846
roll_angle=360;
yaw_angle=360;
pitch_angle=360;
//----------------------------------------------------------
timer2_start();//start measure system time by timer2
_delay_ms(2000);
led_on();
while(1)
    {
//--------------   get value in 3 sensors -----------------------
PORTB^=(1<<PINB3);// toogle this pin per main loop
adc_sensor_get_value();//

//-------- just process roll gyro--------------------------------------------------------------
if(roll_adc<roll_zero)
{
roll_rate=(roll_zero-roll_adc)/sensitivity;//tinh toc do goc theo phuong roll [degree/s]
roll_angle-=roll_rate*dtime/1000;//tra ve gia tri degree theo phuong roll [degree]
}

if(roll_adc>roll_zero)
{
roll_rate=(roll_adc-roll_zero)/sensitivity;//tinh toc do goc theo phuong roll [degree/s]
roll_angle+=roll_rate*dtime/1000;//tra ve gia tri degree theo phuong roll [degree]
}
//---------------------------------------------------------------------------------------------

usart_clr();
usart_print_nb(roll_angle);//print roll_angle to computer screen

//----------------------- creat fixed_loop_time= 25ms per loop---------------------------------
loop_usefull_time=sys_time-last_time;
if(loop_usefull_time<fixed_loop_time)
{
for(i=0;i<(fixed_loop_time-loop_usefull_time);i++)
{
_delay_ms(1);
}
}
dtime=sys_time-last_time;//dtime=time per main loop (ms)
last_time=sys_time;//update the last_time value for the next loop
//------------------------------------------------------------------------------------------
    }
}

ISR(TIMER2_OVF_vect)//when the timer2 over flow we have: sys_time=sys_time +1(ms)
{ // so we can caculate the dtime( time per main loop)
sys_time+=1; 
TCNT2=130;
}

I recognize that: the response of the angular rate sensor is 50Hz (according to the sensor datasheet) , it means that: in 1 second the sensor just can output the value 50 times ( true or false ???? ), so my fixed_loop_time is 25ms per loop =>per 1 second i read the adc value 40 times < 50 times.
I think i do it almost correct like the guide  but my result is not true as the real angular. So i make the video for you to see my problems.

As you see in my video, the angle when the board in balance point is 360 degrees, when it rolls left the angle will increase and when it rolls right the angle will decrease. And after all, when the board comes back to the zero spot, the angular must be 360 degrees, but no. So i think that may be the sensitivity when it rolls left is different than when it rolls right although in one sensor.

Now i really need all off your help, please give me any ideal to solve this problem. Many thank to you.
P/s: I’m so sorry about my English !
Logged

Dubuque, Iowa, USA
Offline Offline
Faraday Member
**
Karma: 46
Posts: 2502
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

This is referred to as "gyro drift". I'm going to skip an explanation because I'd assuredly explain it poorly, but some Google searching will explain why you're seeing what you're seeing.

Also, the "50Hz" response means it takes 1/50th of a second to respond to the angular rate change -- it's the time it takes for the analog output voltage to match the angular rate of rotation. Or as another example, your fingers respond to heat at about 5Hz -- it takes you about a fifth of a second to realize what you're touching is hot smiley-wink
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 6
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Oh, your explains are very cleary and so funny at the last. Many thanks to you.  smiley
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 6
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

This is referred to as "gyro drift". I'm going to skip an explanation because I'd assuredly explain it poorly, but some Google searching will explain why you're seeing what you're seeing.

Also, the "50Hz" response means it takes 1/50th of a second to respond to the angular rate change -- it's the time it takes for the analog output voltage to match the angular rate of rotation. Or as another example, your fingers respond to heat at about 5Hz -- it takes you about a fifth of a second to realize what you're touching is hot smiley-wink


Dear Chagrin,

I just known that i have to use the Kalman filter or something like that to receive the true values. But in this board just only have the gyro sensors and none of accelerometer sensor. So can i use the Kalman filter without the value of accelerometer sensors ?
Logged

Dubuque, Iowa, USA
Offline Offline
Faraday Member
**
Karma: 46
Posts: 2502
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

No, you're going to need a board with both an accelerometer and gyro. The accelerometer is there so, via force of gravity, you can always get a zero point reference as to which direction is "down". If you need a zero point reference for yaw then you would also need a magnetometer.

Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 6
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I don't know how they can make the quad flied just using 3 gyro sensors in this board. I read the asm code, which they write for this board, but can't learn anything.
Logged

Pages: [1]   Go Up
Jump to: