Electronic components: Servo Motors

Mar 18, 2021

Learn how a servo motor like the SG90 rotates to any angle within 180 degrees, controlled by the pulse width on its signal wire, then driven from Arduino.

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A servo motor is a motor that can programmed to rotate to a position spanning over 180 degrees.

Diagram showing servo motor rotation range from 0 to 180 degrees with curved arrows indicating the sweep motion

It can be used for many useful applications that involve movement. They come in many different sizes.

Common ones for what we do (Arduino, battery powered applications) are called micro servo or RC servo, like the SG90:

Blue SG90 micro servo motor with white horn attached and colored wires on a wooden surface

and the MG90S:

Close-up of black MG90S TowerPro micro servo showing the pink and black product label

Those 2 I mentioned work in the same way.

You can see a bunch of MG90S mounted on a mechanical arm here:

Black robotic arm assembly with multiple MG90S servos mounted on base with Arduino board and colorful wires

Close-up view of robotic arm showing multiple MG90S servos, Arduino board, and detailed wiring connections

A servo will likely come with several different horns you can attach to it, like these 3 ones I got:

Blue SG90 servo with three white plastic horn attachments and mounting screws laid out on wooden surface

You can choose the one to use depending on the thing you need to do with it:

Blue SG90 servo with white cross-shaped horn attached and screwdriver nearby for assembly demonstration

We have 3 wires coming out of their box: the brown cable is negative (0V), red is positive (5V), and the orange wire is the signal.

A servo motor is controlled by sending an electrical pulse on the signal wire.

The pulse width will determine the rotation of the motor.

In particular:

1ms pulse will make the servo rotate to 0°
1.5ms pulse will make the servo rotate to 90°
2ms pulse will make the servo rotate to 180°

Diagram showing relationship between pulse width and servo position: 1ms for 0°, 1.5ms for 90°, 2ms for 180°

All values in between 1ms and 2ms will cause a rotation relative to that value.

As we’ll see in the projects, using Arduino we will us a library that abstracts this low level signal pulse for us, so we can simply say which angle from 0° to 180° we want it to rotate to.

Tagged: Arduino · All topics

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