Odom Publisher by Subscribing Encoder Ticks for Differential Drive

asked 2019-01-12 19:09:03 -0500

akifozkanoglu gravatar image

I am trying to calculate odometry position and visualize in rviz. The movement can not be visualize properly although there is no syntax error

import math
from math import sin, cos, pi

import rospy
import tf
from nav_msgs.msg import Odometry
from geometry_msgs.msg import Point, Pose, Quaternion, Twist, Vector3
from odompackage.msg import EncoderTick




Left_Ticks=0
Right_Ticks=0

def tickcallback(msg):
    global Left_Ticks
    global Right_Ticks
    Left_Ticks = msg.left
    Right_Ticks = msg.right
    rospy.loginfo("I heard")

ex_Left_Ticks = 0
ex_Right_Ticks = 0




rospy.init_node('odometry_publisher')

odom_pub = rospy.Publisher("odom", Odometry, queue_size=50)
tick_sub =rospy.Subscriber("TicksPublisher",EncoderTick,tickcallback)
odom_broadcaster = tf.TransformBroadcaster()




current_time = rospy.Time.now()
last_time = rospy.Time.now()

r = rospy.Rate(10.0)




R = 0.0325        #//Wheel Radius
N = 40            #// Number of Ticks Per revolution
L = 0.125         #//Distance between left and right wheels

x = 0.0
y = 0.0
th = 0.0

vx =  0.0
vy =  0.0
vth =  0.0

dc = 0.0
dr = 0.0
dl = 0.0
dt = 0.0
dx = 0.0
dy = 0.0
dtheta = 0.0




while not rospy.is_shutdown():
    current_time = rospy.Time.now()

    L_delta_Tick = Left_Ticks - ex_Left_Ticks
    R_delta_Tick = Right_Ticks - ex_Right_Ticks
    dt = (current_time - last_time).to_sec()
    #rospy.loginfo(dt)
    #rospy.loginfo(Right_Ticks)
    #rospy.loginfo(Left_Ticks)

    dl = 2 * pi * R * L_delta_Tick / N
    dr = 2 * pi * R * R_delta_Tick / N
    dc = (dl + dr) / 2
    dtheta = (dr - dl) / L
    if dr==dl:
        dx=dr*cos(th)
        dy=dr*sin(th)
    else:
        radius=dc/dtheta
        iccX=x-radius*sin(th)
        iccY=y+radius*cos(th)
        dx=cos(dtheta)*(x-iccX)-sin(dtheta)*(y-iccY)+iccX-x
        dy=sin(dtheta)*(x-iccX)-cos(dtheta)*(y-iccY)+iccY-y
    x += dx  # delta_x
    y += dy #delta_y
    th =(th+dtheta)% (2 * pi) #delta_th
    odom_quat = tf.transformations.quaternion_from_euler(0, 0, th)

    # first, we'll publish the transform over tf
    odom_broadcaster.sendTransform(
       (x, y, 0.),
       odom_quat,
       current_time,
       "base_link",
       "odom"
    )

    # next, we'll publish the odometry message over ROS
    odom = Odometry()
    odom.header.stamp = current_time
    odom.header.frame_id = "odom"

    odom.pose.pose = Pose(Point(x, y, 0.), Quaternion(*odom_quat))
    vx=dx/dt
    vy=dy/dt
    vth=dtheta/dt
    odom.child_frame_id = "base_link"
    odom.twist.twist = Twist(Vector3(vx, vy, 0), Vector3(0, 0, vth))

    odom_pub.publish(odom)

    ex_Left_Ticks=Left_Ticks
    ex_Right_Ticks = Right_Ticks
    last_time = current_time
    r.sleep()

This is my encoder data publisher in arduino

#include <ros.h>
#include <odompackage/EncoderTick.h>

#define encoder_LF 7
#define encoder_RF 8

int Left_Ticks=0; 
int Right_Ticks=0;

ros::NodeHandle  nh;

odompackage::EncoderTick TicksMsg;
ros::Publisher TicksPub("TicksPublisher", &TicksMsg);

void pciSetup(byte pin)
{
    *digitalPinToPCMSK(pin) |= bit (digitalPinToPCMSKbit(pin));  // enable pin
    PCIFR  |= bit (digitalPinToPCICRbit(pin)); // clear any outstanding interrupt
    PCICR  |= bit (digitalPinToPCICRbit(pin)); // enable interrupt for the group
}

// Use one Routine to handle each group
ISR (PCINT2_vect) // handle pin change interrupt for D0 to D7 here
 {  
  if (digitalRead(encoder_LF)){   // read the input pin
  Left_Ticks +=1;}
 }  
ISR (PCINT0_vect) // handle pin change interrupt for D8 to D13 here
 {  
 if(digitalRead(encoder_RF)){  // read the input pin
  Right_Ticks += 1 ;}
 }



void setup()
{
  pciSetup(8);
  pciSetup(7);
  nh.initNode();
  nh.advertise(TicksPub);
}

void loop()
{
TicksMsg.left=Left_Ticks;
TicksMsg.right=Right_Ticks;
TicksPub.publish(&TicksMsg);
nh.spinOnce();
delay(100);
}
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Comments

Hi, did you find a solution for your issue ?

Shanika gravatar imageShanika ( 2019-06-20 02:56:34 -0500 )edit