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Difference between 180° vs 360° servo motors and how to control them with Arduino

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Topic starter

Hi everyone,

I'm working on a project that involves servo motors and I need some clarification on a few points. Specifically, I'm trying to understand the differences between 180-degree and 360-degree servo motors, and how to control each type using an Arduino. Here are my questions:

What are the key differences between 180-degree and 360-degree servo motors?

I know 180-degree servos rotate within a 180-degree range, but how does a 360-degree servo differ in terms of functionality and applications?
How do I control a 180-degree servo with an Arduino?

I would appreciate a simple example code and explanation on how to connect and control a 180-degree servo motor using an Arduino.
How do I control a 360-degree servo with an Arduino?

Is there a different method or code required for controlling a 360-degree servo compared to a 180-degree servo? If so, could you provide an example?

1 Answer
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The 180° servo is called a positional servo motor, meaning you can set them to a specific angle within their range i.e., from 0 to 180 degrees.

The 360° servo is called a continuous servo motor, meaning instead of setting a specific position, you control the speed and direction of rotation. As they can rotate continuously in either direction.

To control a servo using Arduino, you must first install the servo library. Yes, both types can be operated using this library. Then upload this code:

1) For positional servo first:

#include <Servo.h>

Servo myservo;  // create servo object to control a servo

void setup() {
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop() {
  myservo.write(90);  // sets the servo position to 90 degrees (middle)
  delay(1000);        // waits for a second
  myservo.write(0);   // sets the servo position to 0 degrees
  delay(1000);        // waits for a second
  myservo.write(180); // sets the servo position to 180 degrees
  delay(1000);        // waits for a second
}

In this case myservo.write(position) sets the servo at a particular angle bw 0 and 180° based on value of the position.

myservo.write(90) sets the servo to 90°
myservo.write(0) and myservo.write(180) sets the servo to 0 and then 180° respectively.

2) For continous servo upload the same code(the servo behaviour is different) :

#include <Servo.h>

Servo myservo;  // create servo object to control a servo

void setup() {
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop() {
  myservo.write(0);    // rotate at full speed in one direction
  delay(2000);         // let it rotate for 2 seconds
  myservo.write(90);   // stop the rotation
  delay(1000);         // wait for a second
  myservo.write(180);  // rotate at full speed in the other direction
  delay(2000);         // let it rotate for 2 seconds
  myservo.write(90);   // stop the rotation
  delay(1000);         // wait for a second
}

Here, the input for myservo.write(value) has a different meaning.

myservo.write(90) stops the servo.
myservo.write(0) and myservo.write(180) rotate the servo at full speed in opposite directions. Any value between this decreases the rotation speed.

Positional servo: where precise positioning is required, such as in robotic arms, control surfaces in RC vehicles, and pan/tilt mechanisms.

Continuous servo: where continuous rotation is needed, such as in wheels for mobile robots, winches, and conveyor belts.

 

Yvette Topic starter 08/07/2024 4:49 am

@amelia Thank you very much for the detailed explanation. I am curious though, what's the difference in their circuitry from the inside which makes one rotate continuously and the other just 180 degrees.

Admin Admin 09/07/2024 7:38 am

@Yvette Inside a standard servo motor, there's a potentiometer connected to the output shaft. This potentiometer provides feedback to the control circuitry about the current position of the shaft. The control circuit compares the desired position (set by the PWM signal) with the current position (measured by the potentiometer). It adjusts the motor's position to match the desired position, typically within a range of 0 to 180 degrees.
Continuous rotation servos do not have a potentiometer for position feedback. Instead, the feedback loop is removed or altered so that the motor can spin freely. The control circuitry is modified to interpret the PWM signal in terms of speed and direction rather than position. A neutral PWM signal typically stops the motor, while varying the PWM width in one direction causes forward rotation, and in the other direction, reverse rotation.

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