> For the complete documentation index, see [llms.txt](https://monasheng.gitbook.io/zerotohero/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://monasheng.gitbook.io/zerotohero/arduino-zero-to-hero/advanced-skills/servos.md). # Servos ## Fundamentals Servo motors are like miniaturised DC motors with built-in motor controllers. Unlike DC motors however, Servo motors are designed for *position control*, rather than speed control. Consequently, servos are typically used for precision positioning, rather than locomotion - e.g. for controlling robotic arms, joints, etc.

A typically hobby-grade servo motor. From wikimedia commons: https://commons.wikimedia.org/wiki/File:Servo_Motor.jpg

Servo motors are normally packaged on with a flange for mounting and with splined shaft for interfacing with accessories. They take a fixed input voltage (usually $$5;\text{V}$$) and come rated to a maximum torque (often in given in kg-cm). Many cheaper servo motors have plastic gears, though metal-gear variants (which are more expensive) can usually bear larger torques at the expense of drawing more current in operation. ## Servo Motor Control Most servo motors take only 3 inputs: 1. A fixed supply voltage, (usually $$5;\text{V}$$, though many are tolerant to higher voltages), 2. A `GND` reference, and, 3. A PWM\* input, ordinarily provided by an MCU. {% hint style="danger" %} :zap: **Warning:** Like DC motors, servos can draw high currents in operation. They should not be powered directly from an MCU, but rather some external source (e.g. a battery, or power supply). Consult the datasheet for the loaded-current rating of a servo before integrating it! **The only connection between a servo motor and your MCU should be the PWM position signal.** {% endhint %}

## Complete Sample Code Servo motors can be controlled one of two ways: 1. By directly writing a PWM signal to their input line, or, 2. By using the `` library. ### Direct PWM Servo Control Driving a servo directly with PWM can be challenging. You need to map and understand how the PWM output range (`0-255`) maps to an equivalent output voltage, and how this maps to an angle on the servo. For rudimentary or simple applications, however, this may be feasible. ```arduino void setup() { // Set PIN 3 as an output. pinMode(3, OUTPUT); // Setup the Serial Monitor for later Serial.begin(9600); } void loop() { // Increment the PWM of Pin 3 for(int i=0; i<=255; i=i+25) { analogWrite(3,i); Serial.print("Current PWM = "); Serial.println(i); // Wait for 0.5 seconds delay(500); } } ```

Driving a servo using `analogWrite()`. Note that an external supply is being used to provide power to the servo, and only the PWM signal is suppled by the Arduino. Importantly, a /pages/bo0pJxx7asGilJAZeEav#common-gndis tied between the Arduino and supply.

### `` Library Control Arduino has a built-in servo control library to make precise position of servo motors easily achievable. {% embed url="" %} {% embed url="" %} In short, to use this library, you must: 1. `#include` the library at the beginning of your script, as with any other [Arduino C](/zerotohero/arduino-zero-to-hero/arduino-programming/arduino-c.md#library-inclusions), 2. declare a variable to represent your servo using the built-in `Servo` type provided by the library, 3. tell the library which pin the servo variable is to apply to, via the `attach` method provided by the library ( analogous to setting a `pinMode()`), 4. write a target angle to the servo object, which tells the library to do any math necessary and output an appropriate PWM signal to the attached pin. ```arduino // Include the Servo Library #include // Define a global servo variable Servo myServoVariable; void setup() { // Attach the servo variable to PIN 3 myServoVariable.attach(3); // Setup the Serial Monitor for later Serial.begin(9600); } void loop() { // Increment the servo angle of Pin 3 for(int i=0; i<=180; i=i+10) { myServoVariable.write(i); Serial.print("Current Angle = "); Serial.println(i); // Wait for 0.5 seconds delay(500); } } ```