Controlling a Servo Motor with RAMPS Shield and a Potentiometer

Servo motor are fundamental motor in robotics and mechanical electronics circuits. We have illustrated number of ways to control a servo motors. In the Hobby Servo Motor control with L293D Motor Shield, we showed how to use L293D motor driver shield along with Arduino Uno to control a servo motor. In the tutorial Servo Motor control using Simulink and Arduino we showed another way of controlling a servo motor which is using Matlab/Simulink.

In this post, we'll explore how to use the RAMPS (RepRap Arduino Mega Pololu Shield) to control a servo motor by reading an analog signal from a potentiometer. We'll walk through the setup and provide an example code to demonstrate the process.

Introduction

The RAMPS shield is widely known for its application in 3D printing, but its utility extends beyond that. It can be used in various projects requiring motor control, such as robotics. In this tutorial, we'll see how the RAMPS shield can help control a servo motor based on the position of a potentiometer.

What You Need

• Arduino Mega
• RAMPS Shield
• Servo Motor
• Potentiometer
• Connecting Wires

Setting Up

The following picture shows servo motor connected to the Arduino Mega RAMPS Shield and the potentiometer.

See the following video of operation of the servo motor control with the Arduino Mega's RAMPS shield.

1. Hardware Connections:

   • Connect the potentiometer to the RAMPS shield. The middle pin of the potentiometer goes to the analog input pin (A13), and the other two pins go to 5V and GND.
   • Attach the servo motor to the servo pin (D11) on the RAMPS shield.

2. Code Explanation:

   • The servo motor is controlled by the Servo library.
   • The potentiometer's analog input is read and mapped to a corresponding servo position.
   • A threshold is used to avoid small fluctuations causing rapid movements of the servo.

The Code

Here's the code to control the servo motor using the RAMPS shield and a potentiometer:

#include <SPI.h>
#include <Servo.h>

#define T0                         13    // Analog Input
#define SERVO0                     11   // Servo Pin

Servo myservo;                            // create servo object to control a servo
int pos;
int prevPos;                        // variable to hold servo position
const int threshold = 2;                  // Threshold to avoid small changes causing servo movement

void setup() {
  Serial.begin(9600);  // Initialize serial port for debugging.
  Serial.println("Testing Servo Motor");
  pinMode(T0, INPUT_PULLUP);      // configure RAMPS TEMP_0_PIN for reading thermistor (MEGA pin 13 from pin_map.h)
  myservo.attach(SERVO0);             // attach servo object to the servo on SERVO0_PIN (MEGA pin 11 from pin_map.h)

  // Sweep servo to test range
  for (pos = 0; pos <= 180; pos += 1) {
    myservo.write(pos);
    delay(15);
  }
  for (pos = 180; pos >= 0; pos -= 1) {
    myservo.write(pos);
    delay(15);
  }
}

void loop() {
  int sensorValue = analogRead(T0);  // read temperature from thermistor

  Serial.print("sensorValue: ");
  Serial.print(sensorValue);

  int mappedPos = map(sensorValue, 0, 1023, 180, 0);  // map deg C 0-100 to servo degrees 0-180

  // Apply hysteresis to prevent small changes from causing rapid servo movements
  if (abs(mappedPos - prevPos) >= threshold) {
    myservo.write(mappedPos);
    prevPos = mappedPos;  // Update prevPos only when the servo moves
  }

  delay(500); // Delay for a short period before the next reading
}

How It Works

1. Setup Phase:

   • The setup() function initializes the serial communication for debugging and configures the analog input pin for the potentiometer.
   • The servo motor is attached to the specified pin, and it performs a sweep to test its range.

2. Main Loop:

   • The loop() function continuously reads the analog value from the potentiometer.
   • The analog value is mapped to a corresponding servo position.
   • A threshold mechanism ensures the servo only moves if the change in position is significant, preventing unnecessary movements and jerks.

Conclusion

Using the RAMPS shield to control a servo motor with a potentiometer is a straightforward process. This setup can be used in various applications where precise control of a servo motor is required based on analog inputs. With a few components and the provided code, you can easily integrate this into your projects.

Feel free to modify the code and experiment with different sensors and motors to expand the functionality of your RAMPS shield! This blog post should give readers a clear understanding of how to control a servo motor using the RAMPS shield and a potentiometer, complete with example code and explanations.