How Servo Motor Works:
How servo motors work and how to control servos using Arduino and SG90 PWM driver. There are many types of servo motors and their main feature is the ability to precisely control the position of their shaft. A servo motor is a closed-loop system that uses position feedback to control its motion and final position.
Industrial type servo motors the position feedback sensor is usually a high precision encoder, while in the smaller RC or hobby servos the position sensor is usually a simple potentiometer. The actual position captured by these devices is fed back to the error detector where it is compared to the target position. Then according to the error the controller corrects the actual position of the motor to match with the target position.
Servo motor with Arduino:
Hobby servos are small in size actuators used for controlling RC toys cars, boats, airplanes etc. They are also used by engineering students for prototyping in robotics, creating robotic arms, biologically inspired robots, humanoid robots and so on.
How Servo Work:
Inside a hobby servo there are four main components, a DC motor, a gearbox, a potentiometer and a control circuit. The DC motor is high speed and low torque but the gearbox reduces the speed to around 60 RPM and at the same time increases the torque.
The potentiometer is attached on the final gear or the output shaft, so as the motor rotates the potentiometer rotates as well, thus producing a voltage that is related to the absolute angle of the output shaft. In the control circuit, this potentiometer voltage is compared to the voltage coming from the signal line. If needed, the controller activates an integrated H-Bridge which enables the motor to rotate in either direction until the two signals reach a difference of zero.
A servo motor is controlled by sending a series of pulses through the signal line. The frequency of the control signal should be 50Hz or a pulse should occur every 20ms. The width of pulse determines angular position of the servo and these type of servos can usually rotate 180 degrees.
Generally pulses with 1ms duration correspond to 0 degrees position, 1.5ms duration to 90 degrees and 2ms to 180 degrees. Though the minimum and maximum duration of the pulses can sometimes vary with different brands and they can be 0.5ms for 0 degrees and 2.5ms for 180 degrees position.
Arduino Servo Motor Control:
Let’s put the above said to test and make a practical example of controlling a hobby servo using Arduino.Here SG90 which is a high-torque servo featuring metal gearing with stall torque of 3 kg-cm. The high torque comes at a price and that’s the stall current of the servo which is 500mA. The running current is from 500mA to 900mA and the operating voltage is from 4.8 to 7.2V.
The current ratings indicate that we cannot directly connect this servo to the Arduino, but we must use a separate power supply for it. We simply need to connect the control pin of the servo to any digital pin of the Arduino board 9th pin, connect the Ground and the positive wires to the external 5V power supply, and also connect the Arduino ground to the servo ground.
