Servo Motors

Standard servos are used to maintain a certain angle, not meant for full rotation
Uses closed loop feedback control
Servos are used in applications requiring high torque, accurate rotation within a limited angle such as Robotic arms, valve control, rudder control etc.

Courtesy : https://howtomechatronics.com/how-it-works/how-servo-motors-work-how-to-control-servos-using-arduino/

SG90 is a servo motor which operates based on PWM control signals
The servo maintains a certain angle (position) based on the width of the pulse fed in through a signal input
Some technical specifications
Weight: 9 g
Dimension: 22.2 x 11.8 x 31 mm approx.
Stall torque: 1.8 kgf·cm
Operating speed: 0.1 s/60 degree
Operating voltage: 4.8 V (~5V)
PWM frequency = 50Hz
Pin configuration: Yellow / Light Orange / White (Signal), Red / Dark Orange (+5V), Brown/Black (Ground)

Note : The pulse width in the image does not correspond to SG90, for illustration of the concept only.

Image courtesy: Stefan Tauner

544 – 1500 – 2400 us

0° – 90° – 180°

Continuous Rotation Servos

Continuous rotation servos are normal servos modified to perform open loop speed control (instead of closed loop position control)
Rotation speed and direction are controlled through PWM signals (pulse width) for continuous rotation servos, just like how position is controlled for standard servos
Effectively, continuous servos are DC motors with integrated motor drivers and reduction gears in a compact, inexpensive package
FS90R continuous rotation operating speed: 110RPM (4.8V); 130RPM (6V)
Can continuous rotation servos be used to achieve accurate positioning without any additional hardware?

Servo Library

This library allows an Arduino board to control servo motors.
Standard servos allow the shaft to be positioned at various angles, usually between 0° and 180°. Continuous rotation servos allow the rotation of the shaft to be set to various speeds
Any digital pin on UNO can be used, not necessarily those supporting PWM. However, note that using Servo library disables analogWrite() functionality on pins 9 and 10
attach(int) - attach a servo to an I/O pin, e.g., servo.attach(pin), servo.attach(pin, min, max)

servo: a variable of type Servo, pin: pin number, default values: min = 544 ms, max = 2400 ms

write(int) - write a value to the servo to control its shaft accordingly

Standard servo - set the angle of the shaft

Continuous rotation servo - set the speed of the servo

(0: full speed in a direction, 180: full speed in the other, and around 90: no movement)

e.g., servo.write(angle), angle = 0 to 180

detach() - stop an attached Servo from pulsing its I/O pin

http://arduino.cc/en/Reference/Servo

#include <Servo.h>
 
Servo servo_7;
 
void setup()
{
  servo_7.attach(7);
}
 
void loop()
{
  servo_7.write(45);
  delay(10); 
}
/* servo connected to pin 7 will maintain an angle of 45o */

]] ></ac:plain-text-body></ac:structured-macro><p><br /></p><p><br /></p><p><ac:image ac:height="250"><ri:attachment ri:filename="image2019-12-28_18-47-48.png" /></ac:image></p><p>Caution : Do not overload the servo. The servo and your battery / power source could be damaged if servo is overloaded.</p><p>Do not power the servo from a 9V battery. Most servos can&rsquo;t take &gt; 6V.</p><p><br /></p><p><strong>Exercise 6</strong></p><ul><li>Create a program to sweep the servo back and forth between 0o and 180o gradually such that it takes a total of 18 seconds to complete a back and forth sweep</li></ul><p>Hint :</p><ul><li>Increment and decrement by 1o, with a 50 milliseconds delay at each step</li></ul><p><br /></p><ac:structured-macro ac:name="code" ac:schema-version="1" ac:macro-id="41ef3738-d59b-4b15-8e05-4a8f467ff94c"><ac:parameter ac:name="language">cpp</ac:parameter><ac:plain-text-body><![CDATA[#include <Servo.h> 
 
Servo myservo; 
int pos = 0;    
// variable to store the servo position 

void setup() 
{ 
  myservo.attach(7);  
} 

void loop() 
{ 
  for(pos = 0; pos <= 180; pos++)
  {                                
    myservo.write(pos);            
    delay(50);                     
  } 
  for(pos = 180; pos >= 0; pos--)   
  {                                
    myservo.write(pos);            
    delay(50);                     
  } 
}


]] ></ac:plain-text-body></ac:structured-macro>