Electric, Hydraulic and Pneumatic Actuators

6.2. Electric, Hydraulic and Pneumatic Actuators#

The three most common actuation systems you’ll encounter are electric, hydraulic, and pneumatic. Each system has its own way of transmitting power, its own strengths and limitations, and its own best-fit applications. Understanding how these systems differ is crucial to choosing the right one for a project.

To summarise:

  • Electric systems deliver work using current through wires e.g. motors, solenoids.

  • Hydraulic systems use pressurised liquid (usually oil) to create high forces.

  • Pneumatic systems use compressed air for fast and lightweight motion.

Hint

Since we’ve already learnt about motors, the main component of electric actuators, the video below focuses on hydraulic and pneumatic actuators.

6.2.1. Electric Actuators#

Electric actuactors are by far the most common in small-scale robotics and mechatronics. Electrical energy is carried through wires to power actuators such as DC motors, stepper motors, servos, heaters, pumps, LEDs, and speakers. All components in the system, from the power source to the controller to the actuator, operate using electrical signals.

Because they are relatively clean, compact, and easy to control precisely, electric actuactors are the dominant kind in mechatronics. They are especially suited to tasks that demand accuracy, fast response, and fine-grained control.

Advantages

  • High precision and responsiveness

  • Relatively clean, compact and low maintenance

  • Easy to control from microcontrollers by connecting to driver circuits and feedback sensors

Examples

  • 3D printers and CNC machines using stepper motors and leadscrews

  • Small robot vehicles driven by DC motors with encoders

6.2.2. Hydraulic Actuators#

Hydraulic actuators use pressurised liquid, usually oil, to transmit power. They are designed to produce very high forces, which makes them ideal for heavy-duty machinery. Because liquids are incompressible, hydraulics can deliver smooth and steady motion even at low speeds.

A typical hydraulic system consists of a fluid reservoir, a pump driven by an electric motor, and a network of hoses, valves, and actuators. The pump pressurises the fluid, and valves direct it into cylinders (for linear motion) or hydraulic motors (for rotary motion).

Hydraulic systems are more complex and heavier than electric ones. They require careful maintenance to prevent leaks and to keep the fluid clean.

Advantages

  • Extremely high force and torque

  • Smooth, stiff, and controllable motion

  • Can hold a load without power if valves are closed

Examples

  • Excavators and backhoes lifting tonnes of material

  • Hydraulic presses used for forming and stamping metal

  • Aircraft control surfaces operated via hydraulic servos

6.2.3. Pneumatic Actuators#

Pneumatic actuators use compressed gas, typically air, to transmit power. They operate on the same principle as hydraulics, but because gases are compressible, the behaviour of pneumatics is quite different. The compressibility makes them fast and lightweight, but also less precise and less stiff than hydraulics.

In a pneumatic system, an air compressor fills a storage tank. The pressurised air is then fed through filters, regulators, and lubricators before reaching the actuators. Solenoid valves open to let the air flow into cylinders or rotary actuators, creating motion. When the valve closes, the air exhausts into the atmosphere.

Pneumatics are excellent for fast, repetitive actions, especially where absolute positioning accuracy is not required. They are simpler, cleaner, and lighter than hydraulics, and they are widely used in factory automation.

Advantages

  • Fast response and simple hardware

  • Lightweight and safe to use

  • Clean operation without fluids

Examples

  • Pick-and-place robots that quickly move parts

  • Pneumatic grippers that open and close on command

  • Sorting or ejecting mechanisms in packaging machines

6.2.4. Electrification of Hydraulic and Pneumatic Systems#

While hydraulic and pneumatic systems traditionally relied on manual levers and purely mechanical valves, modern designs are increasingly electrified. This means that the pumps, compressors, valves, and sensors are now controlled using electrical signals, allowing them to be integrated with microcontrollers and computers just like electric actuators.

In these systems, electric motors power the pumps and compressors, replacing constantly running or engine-driven versions with more efficient, on-demand designs. Solenoid valves are switched electronically to route fluid flow, while sensors measure position, pressure, and flow. These measurements are fed back to the controller, which can adjust the system in real time.

Advantages of Electrified Fluid Systems

  • Much greater precision using electronic feedback control

  • More energy efficient through on-demand operation

  • Easy integration with other digital systems

  • Fully programmable behaviour and motion profiles

Examples of Electrified Fluid Systems

  • Electro-hydraulic excavators controlled with electronic joysticks and position sensors

  • Electro-pneumatic pick-and-place systems driven by solenoid valves under microcontroller control