this does not work yet

steering.ino

/*
 * Raceing car steering
 * - receives commands from the '/racer/driving' topic from ROS on a Raspberry PI through serial port
 * - translates throttle and steering commands into servo control
 * - publishes actions in the '/racer/driving_status' channel
 */

#include <stdio.h>
#include <ros.h>
#include <geometry_msgs/Twist.h>
#include <Servo.h>
#include <algorithm.h>
#include <string.h>

#define BAUD_RATE 115200

#define STEERING_PIN 9
#define ESC_PIN 10

#define STEERING_LEFT -1
#define STEERING_CENTER 0
#define STEERING_RIGHT 1

#define SPEED_FULL_REVERSE -1
#define SPEED_NEUTRAL 0
#define SPEED_FULL_FORWARD 1

const std::string driving_topic = "/racer/driving";
const std::string driving_status_topic = "/racer/driving_status";

double fmap(double value, double in_min, double in_max, double out_min, double out_max);
void drive_callback(const geometry_msgs::Twist& twist_msg);

ros::NodeHandle node_handle;

std_msgs::String status_msg;

ros::Publisher driving_status(driving_status_topic, &status_msg);
ros::Subscriber<geom> driving(driving_topic, &drive_callback);

Servo steering_servo;
Servo esc_throttle; // The ESC works like a Servo

void setup() {
  Serial.begin(BAUD_RATE));

  node_handle.initNode();
  node_handle.advertise(driving_status);
  node_handle.subscribe(driving);  

  steering_servo.attach(STEERING_PIN);
  esc_servo.attach(ESC_PIN);

  steering_servo.write(STEERING_CENTER) ;
  esc_servo.write(SPEED_NEUTRAL);
}

void loop() {
  node_handle.loopOnce();
  delay(1);
}

void drive_callback(const geometry_msgs::Twist& twist_msg) {
  int steering_angle = fmap(twist_msg.angular.z, 0.0, 1.0, STEERING_LEFT, STEERING_RIGHT);
  int throttle = fmap(twist_msg.liner.xm, 0.0, 1.0, SPEED_FULL_REVERSE, SPEED_FULL_FORWARD);

  steerring_servo.write(steering_angle);
  esc_servo.write(throttle);
}

double fmap(double value, double in_min, double in_max, double out_min, double out_max) {
  double mapped_value = (value - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
  return std::clamp(mapped_value, out_min, out_max);
}