Lesson 10 · Changing Speed

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Suggested Time: 60-75 minutes

Lesson Plan

Overview

In this section we will be programming our Barnabas Rover to change speeds.

Changing Speed

So what happens if you want to change the speed of your motor? Well the answer here is that we need to switch our thinking from digital to analog. Until now we’ve been controlling our DC drive control pins (8,11,10,12) by either turning them fully on (HIGH) or fully off (LOW). This results in either full speed (HIGH) or not moving at all (LOW). To set the speed in between these two values, we need to use something called analog control. The table below shows how digital and analog relate to one another when coding

You can see that analog value of 255 is the same as HIGH, and analog value of 0 is the same as LOW. Using analog value 128 will allow you to set the pin to be half on (Note: 128 is half of 255) This is something that you can’t do with digital.

See the updated motor control tables for both motor A and motor B using analog control.

Note: In the table below, only pins 8 and 11 can be controlled via analog so pins 8 and 12 can still only be HIGH or LOW.

Motor A Control Table Using Analog

Motor B Control Table Using Analog

Motor A Control Table Using Analog

Motor B Control Table Using analog

int motb_pin1 = 3;
int motb_pin2 = 11;

int mota_pin1 = 9;
int mota_pin2 = 10;

int button_pin = 2;

void setup() {
  
  //-Control Motor B
  pinMode(motb_pin1,OUTPUT);
  pinMode(motb_pin2,OUTPUT);
  
  //-Control Motor A
  pinMode(mota_pin1,OUTPUT);
  pinMode(mota_pin2,OUTPUT);
  
  //- button
  pinMode(button_pin,INPUT_PULLUP);
  
}

//- turn 90 degrees
void turnRight() {
  
}

void turnLeft() {
  
}

void stop() {
  //- motor a
  analogWrite(mota_pin1,255);
  analogWrite(mota_pin2,255);
  
  //- motor b
  analogWrite(motb_pin1,255);
  analogWrite(motb_pin2,255);
}

void moveForward(int speed) {
  
  //- motor a
  analogWrite(mota_pin1,speed);
  analogWrite(mota_pin2,0);
  
  //- motor b
  analogWrite(motb_pin1,0);
  analogWrite(motb_pin2,speed);
  
}

void moveBackward(int speed) {
  
  //- motor a
  analogWrite(mota_pin1,0);
  analogWrite(mota_pin2,speed);
  
  //- motor b
  analogWrite(motb_pin1,speed);
  analogWrite(motb_pin2,0);
  
}

void loop() {
  
  if (digitalRead(button_pin)==LOW) {
    for (int i=255;i>0;i--) {
      moveForward(i);
      delay(100);
    }
  }
  else {
    stop();
  }

}

Additional Resources