The concept of a servo motor dates back to the early 1900s, but the first practical version emerged in the 1930s. Originally used in military applications like anti-aircraft guns, they gradually found their way into various other fields thanks to their unique capabilities. They not only spin, but also precisely stop at specific angles, almost like a well-trained dancer hitting the exact mark.

Are servo motors similar to stepper motors?

Both servo motors and stepper motors are commonly used for precise positioning tasks, but they achieve this goal in very different ways. A servo motor uses a closed-loop control system, meaning it constantly receives feedback from a position sensor (like a potentiometer) to compare its actual position to the desired one. This feedback loop allows the motor to continuously adjust its movement until it reaches the target position with high accuracy. A stepper motor operates on an open-loop control system. It receives instructions in the form of electrical pulses that dictate the number of steps to rotate. However, this motor doesn't have any feedback mechanism to confirm if it truly completed the steps, making it susceptible to losing steps under heavy load or other disturbances.

How does it work?

A servo motor starts with a regular DC motor, like the one in a toy car. This motor spins when it gets electricity, but it can't control how much or in which direction it turns. A special sensor, called a potentiometer, is attached to the motor shaft and constantly checking the shaft's position. As the shaft turns, the sensor sends a signal that tells the motor exactly where it is. The control circuit receives information about the target and the current position. The target tells the motor where it needs to turn the shaft to base on the current position. The target position is often sent as an electrical pulse with a specific width. The width of the pulse corresponds to the desired angle of rotation. Therefore, the control circuit constantly compares the target position with the actual position. If they don't match, it sends a signal to the motor:

  • Turn right: If the shaft needs to move right, the circuit tells the motor to spin in that direction.
  • Turn left: If the shaft needs to move left, the circuit tells the motor to spin the other way.

The motor's rotation is then amplified and slowed down by gears. This helps the servo move more precisely and hold its position even if something pushes it. The control circuit keeps checking the sensor, making tiny adjustments to the motor until the shaft reaches the exact target position and stays there.

The servo motor offers diverse options like standard servos with limited rotation (typically 180°) to continuous rotation servos that spin endlessly. They are available in various sizes, torque (rotational force), and speed, catering to different application needs.

Applications of servo motors

From the tiny servos that power the movements of remote-controlled toys to the industrial giants controlling robotic arms in factories, servo motors are everywhere. They play a crucial role in applications such as:

  • Robotics: Guiding and positioning robotic arms with high precision.
  • Radio-controlled models: Steering cars, airplanes and even drones. For example, in modern cars with electric power steering, a servo motor is responsible for assisting the driver's steering input. The motor receives signals from the steering wheel sensor and interprets the driver's intended direction. It then applies additional torque to the steering column, making it easier to turn the wheels, especially at low speeds or while parking.
  • Camera control: Precisely panning and tilting security cameras. For instance, for cameras that require both panning and tilting, two servo motors are used. One controls the horizontal rotation (panning) of the camera housing around the base, while the other controls the vertical rotation (tilting) up and down.
  • Animation: Animating characters in robots or puppets. These motors function as the artificial muscles for animatronic characters in robots and puppets. They are strategically attached to different parts of the character, such as the limbs, head and facial features.

While powerful, servo motors are not without their limitations. They can be expensive compared to regular DC motors, and their torque and speed are often limited. Additionally, programming and controlling them requires some technical expertise.

Conclusion

Servo motors have revolutionized precise control in various fields. They not only spin, but also precisely stop at specific angles. Their unique blend of power and precision makes them an asset for robotics, automation and countless other applications. As technology evolves, we can expect even more exciting possibilities to emerge from these versatile motors.

To contact the author of this article, email GlobalSpeceditors@globalspec.com