ros arduino motor control

requires: rosserial, rosserial_arduino

Install requirements:

sudo apt-get install ros-melodic-rosserial-arduino
sudo apt-get install ros-melodic-rosserial

Arduino script

ros_l298n_pwm.ino

//* Ahmed A. Radwan (author)
//* Maisa Jazba 

#include <ArduinoHardware.h>
#include <ros.h>
#include <geometry_msgs/Twist.h>


#define EN_L 6
#define IN1_L 50
#define IN2_L 51

#define EN_R 7
#define IN1_R 52
#define IN2_R 53


double w_r=0, w_l=0;

//wheel_rad is the wheel radius ,wheel_sep is
double wheel_rad = 0.0325, wheel_sep = 0.295;


ros::NodeHandle nh;
int lowSpeed = 200;
int highSpeed = 50;
double speed_ang=0, speed_lin=0;

void messageCb( const geometry_msgs::Twist& msg){
speed_ang = msg.angular.z;
speed_lin = msg.linear.x;
w_r = (speed_lin/wheel_rad) + ((speed_ang*wheel_sep)/(2.0*wheel_rad));
w_l = (speed_lin/wheel_rad) - ((speed_ang*wheel_sep)/(2.0*wheel_rad));
}

ros::Subscriber<geometry_msgs::Twist> sub("cmd_vel", &messageCb );
void Motors_init();
void MotorL(int Pulse_Width1);
void MotorR(int Pulse_Width2);

void setup(){
Motors_init();
nh.initNode();
nh.subscribe(sub);
}


void loop(){
MotorL(w_l*10);
MotorR(w_r*10);
nh.spinOnce();
}


void Motors_init(){
pinMode(EN_L, OUTPUT);
pinMode(EN_R, OUTPUT);
pinMode(IN1_L, OUTPUT);
pinMode(IN2_L, OUTPUT);
pinMode(IN1_R, OUTPUT);
pinMode(IN2_R, OUTPUT);
digitalWrite(EN_L, LOW);
digitalWrite(EN_R, LOW);
digitalWrite(IN1_L, LOW);
digitalWrite(IN2_L, LOW);
digitalWrite(IN1_R, LOW);
digitalWrite(IN2_R, LOW);
}

void MotorL(int Pulse_Width1){
if (Pulse_Width1 > 0){
analogWrite(EN_L, Pulse_Width1);
digitalWrite(IN1_L, HIGH);
digitalWrite(IN2_L, LOW);
}

if (Pulse_Width1 < 0){
Pulse_Width1=abs(Pulse_Width1);
analogWrite(EN_L, Pulse_Width1);
digitalWrite(IN1_L, LOW);
digitalWrite(IN2_L, HIGH);
}

if (Pulse_Width1 == 0){
analogWrite(EN_L, Pulse_Width1);
digitalWrite(IN1_L, LOW);
digitalWrite(IN2_L, LOW);
}
}


void MotorR(int Pulse_Width2){

if (Pulse_Width2 > 0){
analogWrite(EN_R, Pulse_Width2);
digitalWrite(IN1_R, LOW);
digitalWrite(IN2_R, HIGH);
}

if (Pulse_Width2 < 0){
Pulse_Width2=abs(Pulse_Width2);
analogWrite(EN_R, Pulse_Width2);
digitalWrite(IN1_R, HIGH);
digitalWrite(IN2_R, LOW);
}

if (Pulse_Width2 == 0){
analogWrite(EN_R, Pulse_Width2);
digitalWrite(IN1_R, LOW);
digitalWrite(IN2_R, LOW);
}

}

On ros host

terminal 1:

roscore

terminal 2:

rosrun rosserial_python serial_node.py /dev/ttyUSB0

terminal 3:

Run forward

rostopic pub /cmd_vel geometry_msgs/Twist “{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0,y: 0.0, z: 0.0}}” –once

Stop

rostopic pub /cmd_vel geometry_msgs/Twist “{linear: {x: 0.0, y: 0.0, z: 0.0}, angular: {x: 0.0,y: 0.0, z: 0.0}}” –once

Rotate

rostopic pub /cmd_vel geometry_msgs/Twist “{linear: {x: 0.0, y: 0.0, z: 0.0}, angular: {x: 0.0,y: 0.0, z: 2.0}}” –once