The Goal:

Create a robot that moves forward until it reaches a wall and stop before colliding.

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We’ll do this by adding motors to what we’ve built in tutorials 1 and 2.

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Motors

DC Motor

2 Wires

Bidirectional if attached backwards

Cannot be supplied with sufficient power from an Arduino or Pi

Watch this to learn how a DC motor works

Motor Driver

Controlled by signals sent from Arduino

Powered by a separate battery source

Can do variable motor speed

robotshop.com

amazon.com

Motor Controller (L298N)

Motor Controller

• This is the motor controller that we use in the lab
• It is not available in TinkerCad, so we’ll use a different but similar motor controller

fut-electronics.com

Start with our circuit from last week

Available here if you don’t have it:

https://www.tinkercad.com/things/gGnORvqfupr

Add battery and motor controller

5 V Power

9 V Power

Ground

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Connect Motor 1

Define pins for motor 1

Add this before the setup() function:

// Define pins for motor controller

const int MOTOR1_FORWARD = 12; // Input 1

const int MOTOR1_BACKWARD = 11; // Input 2

const int MOTOR1_SPEED = 5; // Enable 1 & 2

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Do the same thing for motor 2

Define pins for motor 2

// Define pins for motor controller

const int MOTOR1_FORWARD = 12; // Input 1

const int MOTOR1_BACKWARD = 11; // Input 2

const int MOTOR1_SPEED = 5; // Enable 1 & 2

const int MOTOR2_FORWARD = 3; // Input 3

const int MOTOR2_BACKWARD = 2; // Input 4

const int MOTOR2_SPEED = 6; // Enable 3 & 4

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Final Circuit

Write the code: Setup Function

Add this to our setup() function:

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// Set speed for both motors

digitalWrite(MOTOR1_SPEED, HIGH);

digitalWrite(MOTOR2_SPEED, HIGH);

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Write the code: Loop Function

Add the bolded lines to our loop() function:

if (distance < 20) { // If the distance is < 20cm:

// Turn on the LED

digitalWrite(LED_PIN, HIGH);

// Turn off motor 1 by setting both pins to low

digitalWrite(MOTOR1_FORWARD, LOW);

digitalWrite(MOTOR1_BACKWARD, LOW);

// Do the same for motor 2

digitalWrite(MOTOR2_FORWARD, LOW);

digitalWrite(MOTOR2_BACKWARD, LOW);

} else { // If the distance is not < 20cm

// Turn off the LED

digitalWrite(LED_PIN, LOW);

// Setting the forward pin to high and backward to low will make the motors rotate forward.

digitalWrite(MOTOR1_FORWARD, HIGH);

digitalWrite(MOTOR1_BACKWARD, LOW);

// Do the same for the right motor.

digitalWrite(MOTOR2_FORWARD, HIGH);

digitalWrite(MOTOR2_BACKWARD, LOW);

}

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Your robot is complete!

• This is all the code and electronics necessary to create a robot that can detect a wall and stop before colliding with it
• The only remaining step would be to build the hardware
• If we were to build this in real life, it would look like the robot to the right

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PWM Control

• But what if the robot is moving too fast?
• We can adjust the speed of the motors using PWM (Pulse Width Modulation) control

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• Digital pins can only be set to two voltages. In the case of the Arduino, these are 0 V (low) or 5 V (high)
• However, we can send more complicated data with digital pins by turning them on and off really quickly

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PWM Control

• When the signal is in the up position we provide power to the motor and when it's down we turn off the power.
• The higher the percentage of the duty cycle the longer the signal is in the on state. If the signal is on for longer then so is the motor.
• This is called Pulse-Width-Modulation or PWM, we are changing the "width" of the on signal to increase or decrease the motor speed.

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PWM Control in Arduino

• On the Arduino, pins marked with a ~ symbol are capable of PWM
• Rather than setting these pins to HIGH and LOW with digitalWrite(), we can set them to any integer value from 0 to 255 with analogWrite()
• 0 is completely off
• 255 is completely on
• For example, 128 would give us a duty cycle of about 50%

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Slowing down the motors

To slow down the motors, replace the code in setup() where we set the motor speeds with:

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// Set speed for both motors

analogWrite(MOTOR1_SPEED, 128);

analogWrite(MOTOR2_SPEED, 128);

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Questions?

• Don’t hesitate to ask me or any officer!
• In meetings or via GroupMe direct message
• You can find my finished circuit and code here:
• https://www.tinkercad.com/things/i6hUzUrIFYT
• If you’re looking for a recap, check out the write-up of these tutorials by Dhruv Sringari:
• https://github.com/Penn-State-Robotics-Club/tutorials
• Note: These tutorials were designed for use in person, so the type of motor controller and the code for the motor controller and distance sensors differ.

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