Hi!
With examples I found online I made an odometry publisher that generates odometry data (for gmapping) from encoder ticks. But When the robot is going straight forward, the odometry data gives the same translation in x en y direction.
Where are my mistakes? Here is the full publisher:
#include "ros/ros.h"
#include
#include
#include
#include "mastering_ros_demo_pkg/encoder_msg.h"
long _PreviousLeftEncoderCounts = 0;
long _PreviousRightEncoderCounts = 0;
ros::Time current_time_encoder, last_time_encoder;
//double DistancePerCount = (3.14159265 * 0.1524) / 200;
double DistancePerCount=1;
double x;
double y;
double th=0;
double W;
double V;
double vx;
double vy;
double vth;
double deltaLeft;
double deltaRight;
double d=50; //afstand tussen de wielen
int ticks_links;
int ticks_rechts;
//void WheelCallback(const geometry_msgs::Vector3::ConstPtr& ticks)
void WheelCallback(const mastering_ros_demo_pkg::encoder_msg::ConstPtr& msg)
{
//tijd van de meting
current_time_encoder = ros::Time::now();
//verschil in ticks tov vorige berekening
deltaLeft = msg->ticks_links - _PreviousLeftEncoderCounts;
deltaRight = msg->ticks_rechts - _PreviousRightEncoderCounts;
//snelheid links (x) en rechts (y)
vx = deltaLeft * DistancePerCount / (current_time_encoder - last_time_encoder).toSec();
vy = deltaRight * DistancePerCount / (current_time_encoder - last_time_encoder).toSec();
//als snelheid links = snelheid rechts -> snelheid = snelheid links en hoeksnelheid = 0
if (vx == vy)
{
V = vx;
W = 0;
}
else
{
// Assuming the robot is rotating about point A
// W = vel_left/r = vel_right/(r + d), see the image below for r and d
double r = (vx * d) / (vy - vx); // Anti Clockwise is positive
W = vx/r; // Rotational velocity of the robot
V = W * (r + d/2); // Translation velocity of the robot
}
//vth = hoeksnelheid
vth= W;
//aantal ticks onthouden
_PreviousLeftEncoderCounts = msg->ticks_links;
_PreviousRightEncoderCounts = msg->ticks_rechts;
//tijd van de laatste meting onthouden
last_time_encoder = current_time_encoder;
}
int main(int argc, char **argv)
{
ros::init(argc, argv, "odometry_publisher");
ros::NodeHandle n;
ros::Subscriber sub = n.subscribe("tick_topic", 100, WheelCallback);
//ros::Subscriber sub1 = n.subscribe("tick_topic", 100, ticks_topic_callback);
ros::Publisher odom_pub = n.advertise("odom", 50);
tf::TransformBroadcaster odom_broadcaster;
ros::Time current_time, last_time;
current_time = ros::Time::now();
last_time = ros::Time::now();
ros::Rate r(20.0);
while(n.ok()){
current_time = ros::Time::now();
//compute odometry in a typical way given the velocities of the robot
double dt = (current_time - last_time).toSec();
double delta_x = (vx * cos(th) - vy * sin(th)) * dt;
double delta_y = (vx * sin(th) + vy * cos(th)) * dt;
double delta_th = vth * dt;
x += delta_x;
y += delta_y;
th += delta_th;
//since all odometry is 6DOF we'll need a quaternion created from yaw
geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(th);
//first, we'll publish the transform over tf
geometry_msgs::TransformStamped odom_trans;
odom_trans.header.stamp = current_time;
odom_trans.header.frame_id = "odom";
odom_trans.child_frame_id = "base_link";
odom_trans.transform.translation.x = x;
odom_trans.transform.translation.y = y;
odom_trans.transform.translation.z = 0.0;
odom_trans.transform.rotation = odom_quat;
//send the transform
odom_broadcaster.sendTransform(odom_trans);
//next, we'll publish the odometry message over ROS
nav_msgs::Odometry odom;
odom.header.stamp = current_time;
odom.header.frame_id = "odom";
//set the position
odom.pose.pose.position.x = x;
odom.pose.pose.position.y = y;
odom.pose.pose.position.z = 0.0;
odom.pose.pose.orientation = odom_quat;
//set the velocity
odom.child_frame_id = "base_link";
odom.twist.twist.linear.x = vx;
odom.twist.twist.linear.y = vy;
odom.twist.twist.angular.z = vth;
//publish the message
odom_pub.publish(odom);
last_time = current_time;
ros::spinOnce();
r.sleep();
}
}
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