root / demos / hunter_prey / lib / src / libdragonfly / odometry.c @ 1828
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#include "odometry.h" 

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#include "encoders.h" 
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#include <math.h> 
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#include <avr/interrupt.h> 
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#include "time.h" 
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#include "serial.h" 
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long lround(double d); 
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int encoder_ltm1, encoder_rtm1;

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//Measure mm displacement in x and y from starting position. (+x:theta=0 +y:theta=M_PI/2)

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long diff_x,diff_y, velocity;

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//Measures radian angle displacement from starting position. (initially 0)

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double angle;

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/**

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* Retrieve the estimated x position. [millimeters]

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*/

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long odometry_dx(void){ 
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return diff_x;

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} 
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/**

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* Retrieve the estimated y position. [millimeters]

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*/

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long odometry_dy(void){ 
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return diff_y;

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} 
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/**

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* Retrieve the estimated angle [radians]

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*/

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double odometry_angle(void){ 
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return angle;

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} 
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long odometry_velocity(void){ 
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return velocity;

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} 
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/**

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* Initializes odometry to run on timer 2.

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* Also resets all values so that the center of the robot is

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* considered to be at the origin facing the x direction.

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*/

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void odometry_init(void){ 
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encoders_init(); 
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delay_ms(100);

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odometry_reset(); 
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//CTC Mode. CLK / 1024

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TCCR2 = 0; // (Fully disconnected) 
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TCCR2 = _BV(WGM21)  _BV(CS22)  _BV(CS20); //CLK/1024 , CTC Mode.

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TIMSK = _BV(OCIE2); 
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OCR2 = ODOMETRY_CLK; 
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} 
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/**

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* Resets all values so that the center of the robot is

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* considered to be at the origin facing the x direction.

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*/

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void odometry_reset(void){ 
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diff_x = 0;

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diff_y = 0;

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encoder_ltm1 = encoder_read(LEFT); 
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encoder_rtm1 = encoder_read(RIGHT); 
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angle = 0.0; 
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} 
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void odometry_run(void){ 
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//Angle swept through in a time step CCW

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double theta, rl, dc;

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long dr,dl;

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//Get the change in wheel positions

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{ 
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int encoder_right = encoder_read(RIGHT);

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int encoder_left = encoder_read(LEFT);

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dl = encoder_left  encoder_ltm1; 
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dr = encoder_right  encoder_rtm1; 
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//No motion.

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if(dl == 0 && dr == 0) return; 
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encoder_ltm1 = encoder_left; 
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encoder_rtm1 = encoder_right; 
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// Try to avoid over/underflow.

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dl = dl > 512 ? dl  1024 :dl; 
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dl = dl < 512 ? dl + 1024 :dl; 
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dr = dr > 512 ? dr  1024 :dr; 
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dr = dr < 512 ? dr + 1024 :dr; 
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//Convert "clicks" to um

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dl *= CLICK_DISTANCE_UM; //um

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dr *= CLICK_DISTANCE_UM; 
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} 
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if(dl == dr){

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diff_x += lround(dl*cos(angle)/1000.0); //mm 
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diff_y += lround(dl*sin(angle)/1000.0); //mm 
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velocity = lround((dl * 1000.0)/(ODOMETRY_CLK*TIME_SCALE)); //um / ms = mm/s 
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usb_puts("dc: ");

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usb_puti(dl); 
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usb_puts("um, velocity: ");

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usb_puti(velocity); 
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usb_puts("\r\n mm/s");

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return;

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} 
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//Call the left wheel 0, clockwise positive.

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rl = ((double)(ROBOT_WIDTH_UM*dl))/((double)(dl  dr)); //um 
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theta = ((double)(dl  dr))/((double)ROBOT_WIDTH_UM); //rad 
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//Distance the center has traveled.

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dc = (theta * (rl  ROBOT_WIDTH_UM)) / 2.0; //um 
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velocity = lround( dc * 1000 /(ODOMETRY_CLK*TIME_SCALE));

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usb_puts("dc: ");

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usb_puti(dl); 
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usb_puts("um, velocity: ");

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usb_puti(velocity); 
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usb_puts("\r\n mm/s");

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//angle is necessarily CCW+, so subtract.

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angle = ANGLE_SCALE * theta; 
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//Change state variables. Probably lose all measurements less then a mm.

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diff_x += lround((DISTANCE_SCALE * dc * cos(angle))/1000.0); //mm 
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diff_y += lround((DISTANCE_SCALE * dc * sin(angle))/1000.0); //mm 
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} 
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ISR(TIMER2_COMP_vect){ 
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odometry_run(); 
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} 
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long lround(double d){ 
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double f = floor(d);

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return (long)(d  f > 0.5 ? f + 1 : f); 
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} 
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