Skip to end of metadata
Go to start of metadata

You are viewing an old version of this page. View the current version.

Compare with Current View Version History

« Previous Version 14 Next »

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.

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

SG90 Micro Servo

  • 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 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


C++Blocks
#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 */

]] ></ac:plain-text-body></ac:structured-macro></div></td><td><div class="content-wrapper"><p><ac:image ac:thumbnail="true" ac:width="300"><ri:attachment ri:filename="image2020-1-20_17-58-31.png" /></ac:image></p></div></td></tr></tbody></table><p><br /></p><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>
  • No labels