How a Servo Motor Works and How to Control It with Arduino

Overview

This video explains what a servo motor is, how it achieves precise control using a closed-loop gear train and internal electronics, and how to program one with an Arduino. It covers the differences between open-loop and closed-loop servos, the role of a potentiometer for position feedback, and how a PWM signal determines the final position.

The tutorial then guides you through a practical circuit: connecting a servo, a potentiometer, and an Arduino on a breadboard, and wiring them to a PC to run simple code. The goal is to map an analog input to a servo angle, demonstrating how to implement servo control in real hardware projects.

Introduction to Servo Motors

The video begins with a description of what a servo motor is and why it is used in precision engineering. Unlike a basic DC motor that spins continuously, a servo receives targeted position commands, typically within a limited angular range, and uses feedback to maintain the commanded position. The content emphasizes the closed-loop nature of most hobby servos, which utilize internal electronics and a potentiometer for position sensing.

Internal Structure and Torque

Inside a servo, a DC motor drives a compact compound gear train that converts high speed to high torque. The video walks through the typical arrangement: a small input gear (pinion) meshing with a larger gear train that reduces speed and increases torque. Torque is described as the motor's output capability, often specified as weight at a given lever arm, such as 25 kg-cm for a larger unit. The data sheet relationship between voltage and torque is explained, noting that higher voltage increases torque up to the device’s limits, after which stalling may occur and current rises dramatically.

Position Sensing and Feedback

Position sensing is achieved with a potentiometer attached to the output gear. As the output turns, the potentiometer’s resistance changes, providing a voltage that the servo’s controller uses as a feedback signal. This feedback is compared to the control signal from the external controller to minimize error and hold the motor at the desired position.

Control Signals and PWM

A servo is commanded by a pulse width modulation (PWM) signal delivered to the dedicated signal wire. Pulses are sent roughly every 20 milliseconds (~50 Hz). The width of each pulse determines the target position: wider pulses move the output to one extreme, narrow pulses to the opposite, with intermediate widths yielding intermediate angles. The servo maintains the selected position as long as the pulse width remains constant, changing when the input signal changes.

Electrical Interface and Driving Circuit

The video describes how the PWM signal is read by the servo’s internal circuit, converted to a voltage, and processed by a comparator and motor driver. The motor driver uses an H-bridge arrangement to control rotation direction. The discussion includes how adjusting power supply voltage affects speed and torque, and how the control system ensures the output gear and potentiometer stay synchronized with the input command.

Hands-on Arduino Project

The core of the project is to control a servo using an Arduino and a potentiometer. The required parts are listed: Arduino, a servo, a potentiometer, a breadboard, wires, and a suitable power supply. The assembly steps are described: connect 5V and ground rails on the breadboard, wire the potentiometer across 5V and ground with the center pin to analog input A0, connect the servo 5V and ground, and connect the servo signal wire to Arduino pin 9. The video notes that this arrangement allows a potentiometer’s angle to be read by the Arduino, which then translates the reading into a servo position using a pre-existing servo library.

Programming the Arduino

The Arduino code is explained at a high level. It begins with including the Servo library and creating a Servo object, for example named servo1, and attaching it to pin 9. The potentiometer input is linked to an analog pin (A0). The code reads the analog value (0 to 1023), maps it to a 0 to 180-degree scale, and writes that angle to the servo. The result is a manual, intuitive control of the servo position via the potentiometer, illustrating how analog signals can be converted into precise rotational movement.

Extensions and Further Learning

The video closes by inviting viewers to explore more advanced circuits and to check additional content for related motor types such as stepper motors and DC motors. It emphasizes that with this foundational setup, you can design more complex servo-enabled systems, integrate multiple sensors, or add additional servos for multi-axis control in robotics and automation projects.