Robot Class - Check my Code Please

Processing Coding Questions
1

Hello Geniuses,

This code is for a Differential Drive Mobile Robot Class.
The robot should change each of its left and right wheel velocity from [-1.0 to 1.0] .
// I used nested for loop for this.

In each specific velocity value for left and right wheel, the robot will go in a circular trajectory.
I need to calculate the diameter of this circle by calculating the distance between the first point and current point of its trajectory (then stop at the longest distance).

I have wrote the code – but it doesn’t work.

class Robot {
  
  float diameter;
  float distance;
  int   index = 1;  //index for number of outputs
  int condition;       //if (Nl == Nr or Nl = -Nr) = 0; 
  
  float [] velocityLeft  = {1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0, -0.1, -0.2, -0.3, -0.4, -0.5, -0.6, -0.7, -0.8, -0.9, -1.0};
  float [] velocityRight = {1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0, -0.1, -0.2, -0.3, -0.4, -0.5, -0.6, -0.7, -0.8, -0.9, -1.0};
  
  
  float Nl;    //Right wheel velocity
  float Nr;    //Left  wheel velocity
  float theta = radians(0); //Angle with -x-axis
  
  ArrayList<Float> positionX = new ArrayList<Float>();
  ArrayList<Float> positionY = new ArrayList<Float>();
  
  float radius = 3;  //DDMR wheel radius
  float L = 6;       //Distance between two wheels
  
  float vx;
  float vy;
  PVector velocity = new PVector(vx, vy); //linear velocity
  PVector location; //DDMR current location
  float omega;      //Angular velocity
  
  float initialX;
  float initialY;
  
  Robot (){
    initialX = 300;
    initialY = 300;
    location = new PVector (initialX, initialY); // Initialize the location.
  }
  
  

  void display(){
    
    for (int iterationLeft = 0; iterationLeft < velocityLeft.length; iterationLeft ++)
    {
      for (int iterationRight = 0; iterationRight < velocityRight.length; iterationRight ++)
      {
        condition = 1;
        diameter  = 0;
        distance  = 0;
        
        Nl = velocityLeft[iterationLeft];
        Nr = velocityRight[iterationRight];
        velocity.x = (radius/2)*cos(theta)*(Nr + Nl);
        velocity.y = (radius/2)*sin(theta)*(Nr + Nl);
        omega = radians((radius/(2*L))*(Nl-Nr));
        
        
        if (positionX.size() > 0){
         for (int iterationDelete = 0; iterationDelete < positionX.size(); iterationDelete ++)
                {
                  positionX.remove(iterationDelete);
                  positionY.remove(iterationDelete);
                }//end (for) iterationDelete 
        }//end (if) statement
        
        if (Nl == Nr) 
          {
            condition = 0;
            print (index + ": Diameter = Infinity - Straight Movement - " + "Left Speed = " + Nl + " - Right Speed = " + Nr + "\n");
            index ++;
          } else if (Nl + Nr == 0) 
          {
            condition = 0;
            print (index + ": Diameter = 0 - In place turning " + "Left Speed = " + Nl + " - Right Speed = " + Nr + "\n");
            index ++;
          } 
          
        while (condition == 1) 
        {
        
          //Save the all location values of x and y in an ArrayList
          positionX.add(location.x);
          positionY.add(location.y);
          
          location.add(velocity);
          theta = theta + omega;
        
          //Calculate the distance between the current position and the first position
          int lastIndex = positionX.size()-1;
          distance = dist(positionX.get(0), positionY.get(0), positionX.get(lastIndex), positionY.get(lastIndex));
        
          if (diameter <= distance)
            {
              diameter = distance;
            }//end of (if) statement 
          
          if (diameter > distance)  
            {
              print(index + ": Diameter= " + diameter + " - Left Speed = " + Nl + " - Right Speed = " + Nr + "\n");
              condition = 0;
              index++;
            }//end of (if) Statement 
            
        }//end of (While) Loop 
      }//end (for) iterationRight loop
    }//end (for) iterationLeft loop  
  }//end void Display()
}//end class Robot
2

Can you please be more specific? What do you mean when you say it doesn’t work? Have you tried debugging your code? Which line of code is behaving differently from what you expected?

1 Like
3

The first line in (while) loop

positionX.add(location.x);

crashed in event thread due to null
java.lang.NullPointerException
	at processing.mode.java.runner.Runner$2.run(Runner.java:590)

I got also the following message

An OutOfMemoryError means that your code is either using up too much memory
because of a bug (e.g. creating an array that's too large, or unintentionally
loading thousands of images), or that your sketch may need more memory to run.
If your sketch uses a lot of memory (for instance if it loads a lot of data files)
you can increase the memory available to your sketch using the Preferences window.
4

Well, your error message says it all: it sounds like you’re creating an array that’s too large. The ArrayList class uses an array internally, so my guess is you’re adding too many elements to your ArrayList. Try printing out the size of that ArrayList just before that line. What do you expect the size to be? What is the size actually?

5

I got it thanks.
So, if i want to remove all the elements from the ArrayList in the way that ArrayList will add new elements from the index[0]
I was using

//Remove Elements
ArrayList.remove(index);
//Add Elements
ArryList.add(newElement);

ArrayList becomes larger and larger !!!

6

Then you want myList.clear()

From the ArrayList reference page

…follow the link to the Java reference:

https://docs.oracle.com/javase/1.5.0/docs/api/java/util/ArrayList.html#clear()

and it is here:

public void clear ()

Removes all of the elements from this list. The list will be empty after this call returns.

1 Like