How to choose and use DC motors, servos, steppers and solenoids

Adding motion to your project can be an exciting yet overwhelming task, given the vast range of actuators available. Whether you are working on a robotics project, an automated mechanism, or a simple DIY experiment, selecting the right actuator is crucial for efficiency and performance. But how do you determine which type of actuator—DC motors, servos, steppers, or solenoids—is the best fit for your needs?

This guide dives deep into different types of actuators, their working principles, strengths, limitations, and real-world applications. By the end, you’ll be equipped with the knowledge to make informed choices for your projects.

What is an Actuator?

Simply put, an actuator is a device that converts energy into motion. Electrical actuators, which we’ll focus on in this guide, take electrical energy and transform it into either rotational or linear movement. While actuators can also be powered pneumatically (using air) or hydraulically (using fluid), electrical actuators remain the most commonly used in hobbyist and industrial applications.

Actuators fall into two primary categories based on their motion type:

• Rotational Actuators: Produce rotational movement (e.g., DC motors, stepper motors, and servos).
• Linear Actuators: Move objects in a straight line (e.g., linear actuators and solenoids).

Now, let’s explore each type of actuator in detail.

Linear Actuators: When You Need Straight-Line Motion

A linear actuator is designed to convert rotational motion into linear motion using a mechanism like a gearbox. These actuators are commonly used in applications that require objects to be moved along a straight path, such as adjustable desks and lifting mechanisms.

Key Considerations:

• Force Output: Measured in Newtons (N) or kilogram-force (kgf). For instance, an actuator with a maximum output of 128N (~13kgf) can lift or push an equivalent weight.
• Holding Force: Also called static load capacity, this determines how well an actuator maintains its position when power is off.
• Speed vs. Power Trade-Off: Longer stroke actuators generally trade speed for power.

Applications:

• Sit-Stand Desks: Uses linear actuators to adjust height.
• Automated Gates: Pushes or pulls gates open.
• Medical Equipment: Used in hospital beds and adjustable chairs.

Advantages & Disadvantages:

• Precise linear motion with high force output
• Holds position even when unpowered
• Typically slower compared to other actuators
• More expensive for high-power applications

Servos: The Precision Rotational Actuator

Servo motors are specialized actuators designed for precise control of angular movement. They are commonly used in robotics and remote-controlled systems where exact positioning is required.

Understanding Torque:

Torque is a force applied at a certain distance from the axis of rotation. It is commonly measured in kilogram-centimeters (kg-cm) or Newton-meters (N-m). A servo with 10 kg-cm of torque can apply 10 kg of force at a 1 cm distance from the axis.

Applications:

• RC Planes and Cars: Controls ailerons, rudders, and steering mechanisms.
• Robotic Arms: Positions the arm at precise angles.
• Automation Systems: Used in factory conveyor systems for precise product placement.

Advantages & Disadvantages:

• Precise angle control
• Internal feedback mechanism maintains position
• Easy to interface with microcontrollers
• Limited rotation range (typically 180°)
• Lower torque compared to stepper motors

DC Motors: The Workhorse of Continuous Rotation

DC motors are among the simplest and most widely used actuators. These motors rotate continuously when powered, making them ideal for applications requiring sustained rotation rather than precise positioning.

Speed vs. Torque:

Most DC motors spin at high speeds but have low torque. To increase torque, a gearbox is often attached, reducing the speed but increasing rotational force.

Applications:

• RC Car Propulsion: Drives wheels efficiently.
• Fans and Blowers: Spins blades to move air.
• Electric Drills: Converts rotational motion into a high-power tool.

Advantages & Disadvantages:

• Simple and cost-effective
• High-speed capabilities
• Can be controlled via motor drivers
• Not suited for precision applications
• Requires additional gearing for torque boost

Stepper Motors: Precise and Repeatable Motion

Unlike DC motors, stepper motors do not spin freely. Instead, they rotate in discrete steps, making them ideal for applications requiring precise and repeatable movements.

Key Characteristics:

• Steps per Revolution: Defines how fine the motor’s movements are (e.g., 200 steps per revolution = 1.8° per step).
• Microstepping: Allows finer control by subdividing steps.

Applications:

• 3D Printers: Moves the print head in controlled increments.
• CNC Machines: Provides precise control in machining operations.
• Vending Machines: Rotates product spirals to dispense items.

Advantages & Disadvantages:

• High precision and repeatability
• Can hold position without external sensors
• More torque than servos in some cases
• Requires a dedicated driver circuit
• Not ideal for high-speed applications

Solenoids: Simple On-Off Linear Motion

A solenoid is a type of actuator that provides quick, short-range linear motion. It consists of an electromagnet and a spring-loaded plunger that extends or retracts when energized.

Applications:

• Pinball Machines: Flipper movement.
• Door Locks: Electromagnetic locking mechanisms.
• Automated Switches: Controls mechanical levers.

Advantages & Disadvantages:

• Simple on/off control
• Very fast actuation
• Cost-effective
• Limited range of motion
• Not suitable for high-force applications

Conclusion

Selecting the right actuator depends on your specific project needs. Here’s a quick summary to help guide your choice:

By understanding the strengths and limitations of each actuator, you can confidently choose the best one for your next engineering or hobby project. Whether it’s robotics, automation, or DIY tinkering, using the right motor will ensure optimal performance and efficiency. Happy building!