Using Continuous Servos to drive Obstacle Avoidance rover

tadashi-hamada · June 8, 2022, 5:02pm

Hi there,

I am trying to drive an obstacle avoidance robot (using a regular ultrasonic distance sensor) using 4 continuous rotation servos.
Is this possible? and if so how?

Thanks

anon73444976 · June 8, 2022, 5:04pm

Why four?
Those things are notoriously difficult to drive at a given speed.

johnwasser · June 8, 2022, 5:33pm

Yes. You drive it like any four-wheel-drive skid-steer object-avoiding car that uses DC gear motors except you use the Servo library to drive the motors instead of four H-Bridge drivers.

https://create.arduino.cc/projecthub/jojessegaming/4-wheeled-obstacle-avoiding-car-87f494

https://create.arduino.cc/projecthub/adam/obstacle-avoiding-car-a192d9

tadashi-hamada · June 9, 2022, 5:15am

Thank you for the reply but I am a noob to Arduino so if it would be possible for you or someone to explain it briefly and what I would have to change in the regular code I will be grateful. I also do not have a motor driver and have to make the project without it.

tadashi-hamada · June 9, 2022, 5:17am

I was thinking of making one of those skid steers with an ESP 32 too so two things in one I guess.

johnwasser · June 9, 2022, 3:03pm

Then:

tadashi-hamada · June 9, 2022, 4:04pm

I see but when I modify the code to suit my needs I get an error regarding the distance sensor(I am using a grove Ultrasonic Distance Sensor.
Here is my code:

#include <Servo.h>        //add Servo Motor library            
#include <Ultrasonic.h>      //add Ultrasonic sensor library

Ultrasonic ultrasonic(7);
#define MAX_DISTANCE 300 // sets maximum useable sensor measuring distance to 300cm
#define MAX_SPEED 160 // sets speed of DC traction motors to 150/250 or about 70% of full speed - to get power drain down.
#define MAX_SPEED_OFFSET 40 // this sets offset to allow for differences between the two DC traction motors
#define COLL_DIST 30 // sets distance at which robot stops and reverses to 30cm
#define TURN_DIST COLL_DIST+20 // sets distance at which robot veers away from object


Servo M1;
Servo M2;
Servo M3;
Servo M4;
Servo Sense;

const int FORWARD = 180;
const int BACKWARD = 0;
const int RELEASE = 90;

int leftDistance, rightDistance; //distances on either side
int curDist = 0;
String motorSet = "";
int speedSet = 0;

//-------------------------------------------- SETUP LOOP ----------------------------------------------------------------------------
void setup() {
  Sense.attach(7);
  M1.attach(10);  // attaches the servo on pin 10 (SERVO_1 on the Motor Drive Shield to the servo object 
  M2.attach(10);
  M3.attach(10);
  M4.attach(10);
  ultrasonic = ultrasonic.MeasureInCentimeters();
 }
//------------------------------------------------------------------------------------------------------------------------------------

//---------------------------------------------MAIN LOOP ------------------------------------------------------------------------------
void loop() {
  Sense.write(90);  // move eyes forward
  curDist = digitalRead(7);   // read distance
  if (curDist < COLL_DIST) {changePath();}  // if forward is blocked change direction
  moveForward();  // move forward
  delay(500);
 }
//-------------------------------------------------------------------------------------------------------------------------------------

void changePath() {
  moveStop();   // stop forward movement
  Sense.write(36);  // check distance to the right
    delay(500);
    rightDistance = readPing(); //set right distance
    delay(500);
    Sense.write(144);  // check distace to the left
    delay(700);
    leftDistance = readPing(); //set left distance
    delay(500);
    Sense.write(90); //return to center
    delay(100);
    compareDistance();
  }

  
void compareDistance()   // find the longest distance
{
  if (leftDistance>rightDistance) //if left is less obstructed 
  {
    turnLeft();
  }
  else if (rightDistance>leftDistance) //if right is less obstructed
  {
    turnRight();
  }
   else //if they are equally obstructed
  {
    turnAround();
  }
}


//-------------------------------------------------------------------------------------------------------------------------------------

int readPing() { // read the ultrasonic sensor distance
  
  delay(70);   
  unsigned int uS = ultrasonic();
  return cm;
}
//-------------------------------------------------------------------------------------------------------------------------------------
void moveStop() {M1.write(RELEASE); M2.write(RELEASE); M3.write(RELEASE); M4.write(RELEASE);}  // stop the motors.
//-------------------------------------------------------------------------------------------------------------------------------------
void moveForward() {
    motorSet = "FORWARD";
    M1.write(FORWARD);      // turn it on going forward
    M2.write(FORWARD);      // turn it on going forward
    M3.write(FORWARD);     // turn it on going forward
    M4.write(FORWARD);     // turn it on going forward
  for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the speed up to avoid loading down the batteries too quickly
  {
    M1.write(speedSet);
    M2.write(speedSet);
    M3.write(speedSet); 
    M4.write(speedSet);
    delay(5);
  }
}
//-------------------------------------------------------------------------------------------------------------------------------------
void moveBackward() {
    motorSet = "BACKWARD";
    M1.write(BACKWARD);     // turn it on going backward
    M2.write(BACKWARD);     // turn it on going backward
    M3.write(BACKWARD);    // turn it on going backward
    M4.write(BACKWARD);    // turn it on going backward
  for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the speed up to avoid loading down the batteries too quickly
  {
    M1.write(speedSet);
    M2.write(speedSet);
    M3.write(speedSet); 
    M4.write(speedSet); 
    delay(5);
  }
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnRight() {
  motorSet = "RIGHT";
  M1.write(FORWARD);      // turn motor 1 forward
  M2.write(FORWARD);      // turn motor 2 forward
  M3.write(BACKWARD);    // turn motor 3 backward
  M4.write(BACKWARD);    // turn motor 4 backward
  M3.write(speedSet+MAX_SPEED_OFFSET);      
  M4.write(speedSet+MAX_SPEED_OFFSET);     
  delay(1500); // write motors this way for 1500        
  motorSet = "FORWARD";
  M1.write(FORWARD);      // set both motors back to forward
  M2.write(FORWARD);
  M3.write(FORWARD);
  M4.write(FORWARD);      
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnLeft() {
  motorSet = "LEFT";
  M1.write(BACKWARD);      // turn motor 1 backward
  M2.write(BACKWARD);      // turn motor 2 backward
  M1.write(speedSet+MAX_SPEED_OFFSET);     
  M2.write(speedSet+MAX_SPEED_OFFSET);    
  M3.write(FORWARD);     // turn motor 3 forward
  M4.write(FORWARD);     // turn motor 4 forward
  delay(1500); // write motors this way for 1500  
  motorSet = "FORWARD";
  M1.write(FORWARD);      // turn it on going forward
  M2.write(FORWARD);      // turn it on going forward
  M3.write(FORWARD);     // turn it on going forward
  M4.write(FORWARD);     // turn it on going forward
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnAround() {
  motorSet = "RIGHT";
  M1.write(FORWARD);      // turn motor 1 forward
  M2.write(FORWARD);      // turn motor 2 forward
  M3.write(BACKWARD);    // turn motor 3 backward
  M4.write(BACKWARD);    // turn motor 4 backward
  M3.write(speedSet+MAX_SPEED_OFFSET);      
  M4.write(speedSet+MAX_SPEED_OFFSET);
  delay(1700); // write motors this way for 1700
  motorSet = "FORWARD";
  M1.write(FORWARD);      // set both motors back to forward
  M2.write(FORWARD);
  M3.write(FORWARD);
  M4.write(FORWARD);      
}```

I am getting the error: no match for call to '(Ultrasonic) ()' and: 'cm' was not declared in this scope
return cm;

johnwasser · June 9, 2022, 4:27pm

To figure out how to use the Ultrasonic library, look at the UltrasonicSimple example that came with the library: File > Examples -> Ultrasonic -> UltrasonicSimple

tadashi-hamada · June 9, 2022, 5:16pm

Thank you, could you please review this code?

#include <Servo.h>        //add Servo Motor library            
#include <Ultrasonic.h>      //add Ultrasonic sensor library

Ultrasonic ultrasonic(7);
#define MAX_DISTANCE 300 // sets maximum useable sensor measuring distance to 300cm
#define MAX_SPEED 180// sets speed of DC traction motors to 150/250 or about 70% of full speed - to get power drain down.
#define MAX_SPEED_OFFSET 40 // this sets offset to allow for differences between the two DC traction motors
#define COLL_DIST 30 // sets distance at which robot stops and reverses to 30cm
#define TURN_DIST COLL_DIST+20 // sets distance at which robot veers away from object


Servo M1;
Servo M2;
Servo M3;
Servo M4;
Servo Sense;

const int FORWARD = 180;
const int BACKWARD = 0;
const int RELEASE = 90;

int leftDistance, rightDistance; //distances on either side
int curDist = 0;
String motorSet = "";
int speedSet = 0;

//-------------------------------------------- SETUP LOOP ----------------------------------------------------------------------------
void setup() {
  Sense.attach(11);
  M1.attach(10);  // attaches the servo on pin 10 (SERVO_1 on the Motor Drive Shield to the servo object 
  M2.attach(9);
  M3.attach(6);
  M4.attach(5);
  ultrasonic = ultrasonic.MeasureInCentimeters();
 }
//------------------------------------------------------------------------------------------------------------------------------------

//---------------------------------------------MAIN LOOP ------------------------------------------------------------------------------
void loop() {
  Sense.write(90);  // move eyes forward
  curDist = digitalRead(7);   // read distance
  if (curDist < COLL_DIST) {changePath();}  // if forward is blocked change direction
  moveForward();  // move forward
  delay(500);
 }
//-------------------------------------------------------------------------------------------------------------------------------------

void changePath() {
  moveStop();   // stop forward movement
  Sense.write(36);  // check distance to the right
    delay(500);
    rightDistance = readPing(); //set right distance
    delay(500);
    Sense.write(144);  // check distace to the left
    delay(700);
    leftDistance = readPing(); //set left distance
    delay(500);
    Sense.write(90); //return to center
    delay(100);
    compareDistance();
  }

  
void compareDistance()   // find the longest distance
{
  if (leftDistance>rightDistance) //if left is less obstructed 
  {
    turnLeft();
  }
  else if (rightDistance>leftDistance) //if right is less obstructed
  {
    turnRight();
  }
   else //if they are equally obstructed
  {
    turnAround();
  }
}


//-------------------------------------------------------------------------------------------------------------------------------------

int readPing() { // read the ultrasonic sensor distance
  delay(70);   
  unsigned int uS =  ultrasonic.MeasureInCentimeters();
  int cm = uS;
  return cm;
}
//-------------------------------------------------------------------------------------------------------------------------------------
void moveStop() {M1.write(RELEASE); M2.write(RELEASE); M3.write(RELEASE); M4.write(RELEASE);}  // stop the motors.
//-------------------------------------------------------------------------------------------------------------------------------------
void moveForward() {
    motorSet = "FORWARD";
    M1.write(FORWARD);      // turn it on going forward
    M2.write(FORWARD);      // turn it on going forward
    M3.write(FORWARD);     // turn it on going forward
    M4.write(FORWARD);     // turn it on going forward
  for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the speed up to avoid loading down the batteries too quickly
  {
    M1.write(speedSet);
    M2.write(speedSet);
    M3.write(speedSet); 
    M4.write(speedSet);
    delay(5);
  }
}
//-------------------------------------------------------------------------------------------------------------------------------------
void moveBackward() {
    motorSet = "BACKWARD";
    M1.write(BACKWARD);     // turn it on going backward
    M2.write(BACKWARD);     // turn it on going backward
    M3.write(BACKWARD);    // turn it on going backward
    M4.write(BACKWARD);    // turn it on going backward
  for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the speed up to avoid loading down the batteries too quickly
  {
    M1.write(speedSet);
    M2.write(speedSet);
    M3.write(speedSet); 
    M4.write(speedSet); 
    delay(5);
  }
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnRight() {
  motorSet = "RIGHT";
  M1.write(FORWARD);      // turn motor 1 forward
  M2.write(FORWARD);      // turn motor 2 forward
  M3.write(BACKWARD);    // turn motor 3 backward
  M4.write(BACKWARD);    // turn motor 4 backward
  M3.write(speedSet+MAX_SPEED_OFFSET);      
  M4.write(speedSet+MAX_SPEED_OFFSET);     
  delay(1500); // write motors this way for 1500        
  motorSet = "FORWARD";
  M1.write(FORWARD);      // set both motors back to forward
  M2.write(FORWARD);
  M3.write(FORWARD);
  M4.write(FORWARD);      
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnLeft() {
  motorSet = "LEFT";
  M1.write(BACKWARD);      // turn motor 1 backward
  M2.write(BACKWARD);      // turn motor 2 backward
  M1.write(speedSet+MAX_SPEED_OFFSET);     
  M2.write(speedSet+MAX_SPEED_OFFSET);    
  M3.write(FORWARD);     // turn motor 3 forward
  M4.write(FORWARD);     // turn motor 4 forward
  delay(1500); // write motors this way for 1500  
  motorSet = "FORWARD";
  M1.write(FORWARD);      // turn it on going forward
  M2.write(FORWARD);      // turn it on going forward
  M3.write(FORWARD);     // turn it on going forward
  M4.write(FORWARD);     // turn it on going forward
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnAround() {
  motorSet = "RIGHT";
  M1.write(FORWARD);      // turn motor 1 forward
  M2.write(FORWARD);      // turn motor 2 forward
  M3.write(BACKWARD);    // turn motor 3 backward
  M4.write(BACKWARD);    // turn motor 4 backward
  M3.write(speedSet+MAX_SPEED_OFFSET);      
  M4.write(speedSet+MAX_SPEED_OFFSET);
  delay(1700); // write motors this way for 1700
  motorSet = "FORWARD";
  M1.write(FORWARD);      // set both motors back to forward
  M2.write(FORWARD);
  M3.write(FORWARD);
  M4.write(FORWARD);      
}  ```

johnwasser · June 9, 2022, 6:02pm

Does it compile for you? It doesn't for me.

sketch_may26b.ino: In function 'void setup()':
sketch_may26b:35:27: error: 'class Ultrasonic' has no member named 'MeasureInCentimeters'
   ultrasonic = ultrasonic.MeasureInCentimeters();
                           ^~~~~~~~~~~~~~~~~~~~
sketch_may26b.ino: In function 'int readPing()':
sketch_may26b:92:33: error: 'class Ultrasonic' has no member named 'MeasureInCentimeters'
   unsigned int uS =  ultrasonic.MeasureInCentimeters();
                                 ^~~~~~~~~~~~~~~~~~~~

I have the latest version of Ultrasonic (3.0.0) but the sketch uses a function that the current library doesn't have. The library instructions say to use:

ultrasonic.read()    // distance in CM
ultrasonic.read(CM)  // distance in CM
ultrasonic.read(INC) // distance in INCHES

Also, why are you calling a function that looks like it is supposed to return Centimeters and storing the result in a variable named 'uS' (microseconds).

tadashi-hamada · June 10, 2022, 3:44am

It does compile for me and I used the examples from the library as guidance for the code, and as for the uS most of the code was copied from other sources.

tadashi-hamada · June 10, 2022, 2:48pm

Edit: I've recompiled in the web editor and ran into the same issue above. I first compiled it using a windows IDE... a problem there? Here is the reviewed code:

#include <Servo.h>        //add Servo Motor library            
#include <Ultrasonic.h>      //add Ultrasonic sensor library

Ultrasonic ultrasonic(7);
#define MAX_DISTANCE 300 // sets maximum useable sensor measuring distance to 300cm
#define MAX_SPEED 180 // sets speed of DC traction motors to 150/250 or about 70% of full speed - to get power drain down.
#define MAX_SPEED_OFFSET 40 // this sets offset to allow for differences between the two DC traction motors
#define COLL_DIST 30 // sets distance at which robot stops and reverses to 30cm
#define TURN_DIST COLL_DIST+20 // sets distance at which robot veers away from object


Servo M1;
Servo M2;
Servo M3;
Servo M4;
Servo Sense;

const int FORWARD = 180;
const int BACKWARD = 0;
const int RELEASE = 90;

int leftDistance, rightDistance; //distances on either side
int curDist = 0;
String motorSet = "";
int speedSet = 0;

//-------------------------------------------- SETUP LOOP ----------------------------------------------------------------------------
void setup() {
  Sense.attach(11);
  M1.attach(10);  // attaches the servo on pin 10 (SERVO_1 on the Motor Drive Shield to the servo object 
  M2.attach(9);
  M3.attach(6);
  M4.attach(5);
  ultrasonic = ultrasonic.read(CM);
 }
//------------------------------------------------------------------------------------------------------------------------------------

//---------------------------------------------MAIN LOOP ------------------------------------------------------------------------------
void loop() {
  Sense.write(90);  // move eyes forward
  curDist = digitalRead(7);   // read distance
  if (curDist < COLL_DIST) {changePath();}  // if forward is blocked change direction
  moveForward();  // move forward
  delay(500);
 }
//-------------------------------------------------------------------------------------------------------------------------------------

void changePath() {
  moveStop();   // stop forward movement
  Sense.write(36);  // check distance to the right
    delay(500);
    rightDistance = readPing(); //set right distance
    delay(500);
    Sense.write(144);  // check distace to the left
    delay(700);
    leftDistance = readPing(); //set left distance
    delay(500);
    Sense.write(90); //return to center
    delay(100);
    compareDistance();
  }

  
void compareDistance()   // find the longest distance
{
  if (leftDistance>rightDistance) //if left is less obstructed 
  {
    turnLeft();
  }
  else if (rightDistance>leftDistance) //if right is less obstructed
  {
    turnRight();
  }
   else //if they are equally obstructed
  {
    turnAround();
  }
}


//-------------------------------------------------------------------------------------------------------------------------------------

int readPing() { // read the ultrasonic sensor distance
  delay(70);   
  unsigned int cm =  ultrasonic.read();
  return cm;
}
//-------------------------------------------------------------------------------------------------------------------------------------
void moveStop() {M1.write(RELEASE); M2.write(RELEASE); M3.write(RELEASE); M4.write(RELEASE);}  // stop the motors.
//-------------------------------------------------------------------------------------------------------------------------------------
void moveForward() {
    motorSet = "FORWARD";
    M1.write(FORWARD);      // turn it on going forward
    M2.write(FORWARD);      // turn it on going forward
    M3.write(FORWARD);     // turn it on going forward
    M4.write(FORWARD);     // turn it on going forward
  for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the speed up to avoid loading down the batteries too quickly
  {
    M1.write(speedSet);
    M2.write(speedSet);
    M3.write(speedSet); 
    M4.write(speedSet);
    delay(5);
  }
}
//-------------------------------------------------------------------------------------------------------------------------------------
void moveBackward() {
    motorSet = "BACKWARD";
    M1.write(BACKWARD);     // turn it on going backward
    M2.write(BACKWARD);     // turn it on going backward
    M3.write(BACKWARD);    // turn it on going backward
    M4.write(BACKWARD);    // turn it on going backward
  for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the speed up to avoid loading down the batteries too quickly
  {
    M1.write(speedSet);
    M2.write(speedSet);
    M3.write(speedSet); 
    M4.write(speedSet); 
    delay(5);
  }
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnRight() {
  motorSet = "RIGHT";
  M1.write(FORWARD);      // turn motor 1 forward
  M2.write(FORWARD);      // turn motor 2 forward
  M3.write(BACKWARD);    // turn motor 3 backward
  M4.write(BACKWARD);    // turn motor 4 backward
  M3.write(speedSet+MAX_SPEED_OFFSET);      
  M4.write(speedSet+MAX_SPEED_OFFSET);     
  delay(200); // write motors this way for 1500        
  motorSet = "FORWARD";
  M1.write(FORWARD);      // set both motors back to forward
  M2.write(FORWARD);
  M3.write(FORWARD);
  M4.write(FORWARD);      
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnLeft() {
  motorSet = "LEFT";
  M1.write(BACKWARD);      // turn motor 1 backward
  M2.write(BACKWARD);      // turn motor 2 backward
  M1.write(speedSet+MAX_SPEED_OFFSET);     
  M2.write(speedSet+MAX_SPEED_OFFSET);    
  M3.write(FORWARD);     // turn motor 3 forward
  M4.write(FORWARD);     // turn motor 4 forward
  delay(2000); // write motors this way for 1500  
  motorSet = "FORWARD";
  M1.write(FORWARD);      // turn it on going forward
  M2.write(FORWARD);      // turn it on going forward
  M3.write(FORWARD);     // turn it on going forward
  M4.write(FORWARD);     // turn it on going forward
}  
//-------------------------------------------------------------------------------------------------------------------------------------
void turnAround() {
  motorSet = "RIGHT";
  M1.write(FORWARD);      // turn motor 1 forward
  M2.write(FORWARD);      // turn motor 2 forward
  M3.write(BACKWARD);    // turn motor 3 backward
  M4.write(BACKWARD);    // turn motor 4 backward
  M3.write(speedSet+MAX_SPEED_OFFSET);      
  M4.write(speedSet+MAX_SPEED_OFFSET);
  delay(1700); // write motors this way for 1700
  motorSet = "FORWARD";
  M1.write(FORWARD);      // set both motors back to forward
  M2.write(FORWARD);
  M3.write(FORWARD);
  M4.write(FORWARD);      
}

system · December 7, 2022, 2:49pm

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.

Topic		Replies	Views
obstacle avoiding robot, help with code Robotics	22	69349	May 6, 2021
Obstacle Avoiding Robot Programming	29	194	July 6, 2025
Trying to write a unique obstacle avoiding car Programming	26	205	May 6, 2025
The Arduino robot and freshman Robotics	23	4759	May 6, 2021
Replicating an Obstacle Avoidance + Go-to-goal Rover General Guidance	5	231	August 21, 2024

Using Continuous Servos to drive Obstacle Avoidance rover

Related topics