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How Servo Motors Work
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How Servo Motors Work

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“See here? Someone has tampered with the servo. They switched the ground to the negative, so when he put the key in the lock…”

“He completed the circuit.”

Ghost in the Machine (1993)

First of all, what exactly is a servo? A servomechanism is technically any automatic device that can correct its own position based on negative feedback. Negative feedback is the process by which electrical signals are fed back in a manner that ultimately reduces further fluctuations. Servo motors can rotate or push components with amazing accuracy using this method.

Servos are very widely used in a vast array of electronics. Volume knobs, gas pedals, even the auto focus on your smart phone camera is a servo. They’re everywhere and most of us don’t even realize it. They’re so important, in fact, that without them pilots wouldn’t be able to safely land airplanes. Thanks, servos!

There are three main components that make up a servo motor- a motor (obviously), a control circuit, and a potentiometer. The motor can be either AC or DC, but generally speaking, anything less than industrial grade will be DC. A potentiometer is a resistor that performs the turning or pushing action depending on the size of the signal wave sent through it. The control circuit is exactly what it sounds like- it sends the control signals out to the other parts.

The signal sent to the motor actually causes it to spin much faster than the potentiometer will eventually turn. This is achieved through the use of various gears on the outside. The reason for this is basic physics- Work = Force x Distance. A tiny motor spinning quickly covers a lot of distance but doesn’t generate much force. Once the gears are added, however, the tiny motor’s distance decreases considerably. Since this doesn’t change the work (the motor is still spinning at the same speed), it instead increases the force. That’s how such a tiny little motor can achieve such feats of strength.

Most servos that rotate can only do so 90 degrees in either direction, giving them a total of 180 degrees of movement. You can also buy specialty servos that can spin infinitely in either direction, but these are generally more expensive and require more power.

Now that you know how servos work, you may even be able to implement them into a project you otherwise may not have thought to try them in. Servos are incredibly useful and chances are if your electronics project is more than just a breadboard, you can find a great use for one.