Page Comparison

Servos

• 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.

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

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SG90 Micro Servo

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• 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)

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

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544 – 1500 – 2400 us

  0°  –   90° – 180°

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• 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

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• 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 us, max = 2400 us

• 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);
  // a variable can also be used instead of the constant (45)
  delay(10);

}
/* servo connected to pin 7 will maintain an angle of 45 degree */

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Caution : Do not overload the servo. The servo and your battery / power source could be damaged if the servo is overloaded.

Do not power the servo from a 9V battery. Most servos can’t take > 6V.

Continuous Rotation Servos

• Continuous rotation servos are standard 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 the position is controlled for standard servos

• Effectively, continuous servos are DC motors with integrated motor drivers and reduction gears in a compact, inexpensive package, rather than true 'servo' motors

• Continuous rotation servos allow the rotation of the shaft to be set to various speeds

  • Electrical connections are identical to that of a standard servo.

  • The original servo library can be used; e.g., servo.write(angle),  angle = 0 to 180  → 0: full speed in one direction, 180: full speed in the other, and around 90: no movement

• FS90R (also known as SG90 continuous / 360^o/ full rotation) operating speed: 110RPM (4.8V); 130RPM (6V)

Can continuous rotation servos be used to achieve accurate positioning without any additional hardware?