Several different servos in use (credit: Adafruit)

Servo Motor (Hobby or Standard)

These specialty motors have electronics, gears, and a motor to turn what is connected to them. Unlike other motors, servos have a limited range of rotation, usually half way around a circle (180 degrees). A servo can be told at what angle to turn to so movements can be controlled by the user.

A servo with an electronic servo controller is great for moving things in a very controlled fashion. Most robot joints along with robot car steering systems use servos. They can also be used to move something in and out a short distance dependent on the type of horn and connection to the horn.

Servo Sizes

Servos come in different sizes. They are often a "standard size" although when you buy one you should check the dimensions to make sure it is the size you want. Typical names for sizes are standard and micro although other terms like nano, ultra-nano, and giant might be used. 

robotics___cnc_155-03.jpg
Most servos are about this large, and are called 'standard size' servos
robotics___cnc_2201-03.jpg
Servos can be as small as a coin!

Inside of a Servo

Inside a servo is a continuous DC motor, control electronics, a variable resistor (potentiometer) and gears for the range of motion.

 

On the left is a nice photo we took of the internal gear-box of a servo!

 

Some servos come with metal gears, which are more rugged, but they may emit a bit more noise.

The gearbox means a servo is strong, and somewhat slow. It can only move back and forth about 180 degrees. The movement might be more limited on certain servos, perhaps 170 degrees on some, only 90 degrees on another.

There are three wires on a standard servo, two for DC power and one for control. A servo requires some other electronics to tell it what angle to turn to.... like a Crickit!

Servos come with various screw on pieces, called horns, to help you attach the servo to something else, making connections easier than with Continuous DC motors.

Horns & Accessories

One of the benefits of the servo form factor in general are the number of accessories available to mount on the shaft. Nearly all servo shafts have grooves so attachments fit in without spinning. The shaft also has a hole at the end to secure attachments.

The attachment items for servos are almost always called horns. Horns can come in various shapes to allow users to make various types of connections depending on their project. Most servos you buy will come with two or three horns that fit that specific servo but often you can mix or match other horns and shops have alternatives to the ones in the package.

Horns most often have holes in them to help make attachments, often screws or wires.

There are specialty accessories  for continuous rotation servos like wheels. For standard/hobby servos, a wheel would only turn 180 degrees, limiting the usefulness of a wheel.

Continuous Rotation Servo Wheel

PRODUCT ID: 167
Plastic wheel with a cutout specially designed to allow attachment to our larger continuous rotation servo. Makes it easy to get your...
$2.95
IN STOCK

Wheel for Micro Continuous Rotation FS90R Servo

PRODUCT ID: 2744
We're keepin' it wheel with this one!Need a great drive solution for your little robotic friends? This black plastic Micro Continuos...
$2.50
IN STOCK

As the cable of a servo has a connector on the end, there are extension cables available which extend the connection if your servo is not close to your controller board.

Servo Extension Cable - 50cm / 19.5" long

PRODUCT ID: 973
Stretch out your servo connections with this flexible servo extension cord. It has a 3 pin shrouded "male" connection to plug your servo into and then, 50cm later, a 3 pin...
$2.50
IN STOCK

Servo Extension Cable - 30cm / 12" long -

PRODUCT ID: 972
Stretch out your servo connections with this flexible servo extension cord. It has a 3 pin shrouded "male" connection to plug your servo into and then, 30cm later, a 3 pin...
$1.95
IN STOCK

Picking a Standard Servo

When looking for standard servo for your project, you will want to keep in mind these questions:

  1. What range of motion are you looking for? Most standard servos rotate in about a 180 degree arc but some have a smaller range (older or specialty models).
  2. What type of load are you trying to move? Cardboard and paper have different requirements than metal or other heavy loads. Look at the servo torque (rotational force) rating to see how much mechanical force the servo can handle safely. If your project needs more force, consider a larger servo or one with metal gears for more durability.
  3. How will you control the servo? Most often a servo is hooked to a control circuit to tell the arm what position it should be at or travel to. This requires more circuitry compared to a continuous DC motor. Will you use a microcontroller or a special purpose robotics board like Crickit to use the servo?
  4. What are the voltage and current ratings for the servo? Are they compatible with the controller?

Buying Guide

Here are some hobby servos in the Adafruit Shop which have been hand-picked for various applications you may be looking for:

Standard servo - TowerPro SG-5010

PRODUCT ID: 155
This high-torque standard servo can rotate approximately 180 degrees (90 in each direction). You can use any servo code, hardware or library to control these servos. Good for beginners...
$12.00
IN STOCK

Micro servo

PRODUCT ID: 169
Tiny little servo can rotate approximately 180 degrees (90 in each direction), and works just like the standard kinds you're used to but smaller. You can use any servo...
$5.95
IN STOCK

Sub-micro Servo - SG51R

PRODUCT ID: 2201
This is just about the cutest, tiniest little micro servo we could find, even smaller than the 9 gram micro servos we love so much.  It can rotate approximately 180 degrees (90 in...
$5.95
IN STOCK

For high torque applications:

Standard Size - High Torque - Metal Gear Servo

PRODUCT ID: 1142
This high-torque standard servo now comes in a metal-gear flavor, for extra-high torque (10 kg*cm!) and reliability! It can rotate at least 120 degrees (60 in each direction) with a...
$19.95
IN STOCK

Micro Servo - High Powered, High Torque Metal Gear

PRODUCT ID: 2307
Add even more power to your robot with this metal-geared servo. The tiny little servo can rotate approximately 180 degrees (~90 in each direction), and works just like the...
$11.95
IN STOCK

Micro Servo - MG90D High Torque Metal Gear

PRODUCT ID: 1143
Add more power to your robot with this metal-geared MG90D servo. The tiny little servo can rotate approximately 90 degrees (45 in each direction), and works just like the standard...
$9.95
IN STOCK

Two servos in a pan & tilt configuration:

Mini Pan-Tilt Kit - Assembled with Micro Servos

PRODUCT ID: 1967
This fully-assembled pan-tilt kit is the perfect way to give your project full range motion with two micro servos. The pan-tilt can rotate roughly 180° from side-to-side and...
OUT OF STOCK
This guide was first published on Jul 04, 2018. It was last updated on Jul 04, 2018.
This page (About Standard Servo Motors) was last updated on Sep 23, 2020.