comm-arduino-serial.py

import serial

ser = serial.Serial('<USB tty>', 9600)

"""
`Forward` is constant 85 to `Acceleration Servo` value
`Backward` is constant 103 to `Acceleration Servo` value
`Stop` is constant 90 to `Acceleration Servo` value

Before moving `Forward` or `Backward`, the `Acceleration Servo` is `Stop`ped for 1 second
to reduce the problems with the car locking up. 

Right is +5 to the `Steering Servo` value
Left is -5 to `Steering Servo` value
"""

ser.write('F')  # Forward
ser.write('L')  # Left 
ser.write('B')  # Backward
ser.write('S')  # Stop
ser.write('R')  # Right

# these can be combined
ser.write('FRRR') # forward with 3 rights 

listener.ino

#include <Servo.h> 
 
Servo steering_servo; 
Servo acceleration_servo;

// PIN CONSTANTS: 
int TURNING_PIN = 8;
int ACCELERATION_PIN = 9; 

// STEERING CONSTANTS:
// Steering servo has range of MAX_LEFT - MAX_RIGHT
int MAX_RIGHT = 110;
int MAX_LEFT = 40; 
int TURN_RADIUS = 5;

// ACCELERATION CONSTANTS:
int ACCELERATION = 83; 

// INIT VARS:
int turning_angle = 75; // steering mid-point
int message;
int pos = 0;    

void setup() 
{ 
  Serial.begin(9600);
  
  steering_servo.attach(TURNING_PIN);
  steering_servo.write(turning_angle); 

  acceleration_servo.attach(ACCELERATION_PIN); 
  acceleration_servo.write(ACCELERATION); 
} 

int turn(int dir){
  int curr_angle = turning_angle; 
  int curr_angle_prime = curr_angle + (TURN_RADIUS * dir); 

  if(curr_angle_prime > MAX_LEFT && curr_angle_prime < MAX_RIGHT){  
     int pos = curr_angle; 
      while(pos!=curr_angle_prime){
         steering_servo.write(pos);
         pos+=dir;  
         delay(5);
       }
       curr_angle = curr_angle_prime;
    } 

    
    return curr_angle; 
}

int accel(int a){
  acceleration_servo.write(a); 
}

void loop() 
{ 
   if( Serial.available() > 0 ) {
        message = Serial.read();
        Serial.flush();
        Serial.println( "ACK" );
        Serial.flush();

        // Left turn 
        if( message == 'L' ) {
          turning_angle = turn(-1);
        }
        
        // Right turn
         if( message == 'R' ) {
           turning_angle = turn(1);
        }
        
        // Forwards
         if( message == 'F' ) {
           accel(90); // stop or the car brakes and must be reset
           delay(1000);
           accel(85); 
        }
        
        // Backwards
         if( message == 'B' ) {
           accel(90);
           delay(1000);
           accel(103); 
        }
        
        // Stop
         if( message == 'S' ) {
          accel(90); 
        }

        
        // Explore 
        if( message == 'E' ) {
           // NOTHING; 
        }
    }
    
}