Selecting the right linear actuator for your application is a critical engineering decision that directly impacts performance, reliability, and cost-effectiveness. Whether you're designing an automated standing desk, building a custom TV lift, or engineering an industrial positioning system, understanding how to properly size an actuator ensures your project succeeds from the start.
Many engineers and DIY enthusiasts make the mistake of selecting actuators based on a single specification—usually force or stroke length—without considering how these parameters interact with speed, power requirements, and environmental factors. This incomplete approach often leads to inadequate performance, premature failure, or the need for costly redesigns. The reality is that actuator selection is a multidimensional problem that requires balancing several competing requirements within the constraints of your specific application.
This comprehensive guide walks you through the systematic process of sizing a linear actuator, covering force calculations, stroke length determination, speed requirements, power considerations, and application-specific factors. By the end, you'll have the knowledge to confidently specify the right actuator for your needs, whether you're working on a hobby project or an industrial application requiring industrial actuators.
Understanding Force Requirements: Dynamic vs. Static Load
Force is typically the most critical specification when sizing a linear actuator. However, understanding force requirements goes beyond simply knowing how much weight you need to move. Linear actuator manufacturers specify two distinct force ratings that serve different purposes in your application.
Dynamic Force: Moving Loads in Motion
Dynamic force (or dynamic load) represents the maximum force an actuator can apply while actively moving an object. This specification is measured in pounds (lbs) or Newtons (N), with 1 lb equaling approximately 4.45 N. Dynamic force is what you'll reference when determining whether an actuator can physically move your intended load.
Some actuators exhibit different dynamic force capabilities for pushing versus pulling operations. This asymmetry typically occurs because of internal mechanical design—the same actuator might be able to push 500 lbs but only pull 400 lbs. Always verify both push and pull specifications if your application involves bidirectional movement.
Static Force: Holding Capacity at Rest
Static force (or static load) defines the maximum weight an actuator can hold when stationary. This specification becomes critical in applications where the actuator must maintain position under load for extended periods. For example, in standing desk applications, the actuators must hold the desktop and everything on it in a fixed position throughout the workday without drifting or requiring continuous power.
Static load capacity is generally higher than dynamic load capacity because the actuator doesn't need to overcome inertia or friction during movement. However, some electric actuators use self-locking mechanisms like worm gears that provide excellent static holding force even when unpowered.
Calculating Actual Force Requirements
Determining your actual force requirement involves more than knowing the weight of the object you're moving. You must account for the number of actuators, mounting geometry, friction, and whether you're working against gravity or across a horizontal plane.
For simple linear vertical lifting applications, the calculation is straightforward: divide the total weight by the number of actuators. If you're lifting a 400 lb load with two actuators, each actuator must provide at least 200 lbs of force. However, always add a safety factor of 20-50% to account for friction, binding, and manufacturing tolerances.
For angular applications—such as opening a hatch, tilting a panel, or lifting a lid—the force calculation becomes more complex because forces are applied at different points and angles. You'll need to apply the principles of torque (moment force) and trigonometry. The actuator force required depends on:
- The weight of the moving object
- The center of gravity location
- The mounting point locations for both the actuator and pivot point
- The angle of operation throughout the full range of motion
Rather than working through complex trigonometric calculations manually, you can use FIRGELLI's Linear Actuator Calculator, which handles these geometric considerations automatically. Simply input your dimensions, weight, and mounting positions, and the calculator determines the required force at various points in the actuator's stroke.
Building in Safety Margins
Once you've calculated your theoretical force requirement, best engineering practice dictates selecting an actuator with force specifications exceeding your calculated needs. A safety margin of 25-50% is recommended for several reasons:
- Manufacturing tolerances in both the actuator and your application
- Friction and binding that may occur as components wear
- Temperature effects on actuator performance
- Load variations in real-world use
- Extending actuator service life by reducing stress
The specified force ratings should be treated as absolute operational limits, not normal working loads. Consistently operating an actuator at its maximum rated force will significantly reduce its service life.
Determining Stroke Length Requirements
Stroke length is the total distance a linear actuator can extend and retract, measured from its fully retracted to fully extended position. Unlike force requirements, which can sometimes be addressed by using multiple actuators or accepting lower speeds, stroke length is typically a hard constraint—your actuator must physically reach the positions required by your application.
Measuring Stroke for Linear Applications
In straightforward linear applications, determining stroke length is simple: measure the distance between your starting and ending positions. For example, if you're automating a sliding door that needs to move 24 inches, you'll need an actuator with at least a 24-inch stroke. However, it's wise to select an actuator with slightly more stroke than your absolute minimum to allow for adjustment during installation and to avoid operating at the extreme limits of travel.
Calculating Stroke for Angular Applications
For rotational or angular applications—such as opening a hatch from 0° to 90°—determining the required actuator stroke requires geometric calculation. The stroke length depends on where you mount the actuator relative to the pivot point. Generally, mounting the actuator farther from the pivot reduces the required force but increases the required stroke length, and vice versa.
Key considerations for angular applications include:
- Measuring from the pivot point to both mounting locations
- Accounting for the changing angle throughout the movement
- Ensuring the actuator doesn't reach a "dead center" position where mechanical advantage is lost
- Verifying clearances throughout the full range of motion
Stroke Length Impact on Overall Actuator Length
An important consideration when selecting stroke length is that it directly affects the actuator's retracted length. Most standard rod-style linear actuators have a retracted length approximately equal to the stroke length plus 8-12 inches, depending on the model. An actuator with a 20-inch stroke might have a retracted length of 28-30 inches.
This relationship matters when space is limited. If you need significant travel but have limited installation space, consider alternative actuator types:
- Track actuators offer longer strokes in more compact form factors
- Bullet actuators provide a more compact design for shorter strokes
- Slide rails can achieve very long travel distances with minimal retracted length
Speed Requirements and Performance Tradeoffs
Speed specifications indicate how fast an actuator can extend or retract, typically measured in inches per second (in/s) or millimeters per second (mm/s). While speed might seem like a straightforward specification, it's actually the most flexible parameter in actuator selection and involves important tradeoffs with force.
The Speed-Force Inverse Relationship
In electric linear actuators, there's a fundamental inverse relationship between force and speed: higher force actuators move more slowly, while lower force actuators move more quickly. This relationship exists because most electric actuators use gear reduction to convert the high-speed, low-torque output of an electric motor into the low-speed, high-force output needed for linear actuation.
A higher gear reduction ratio increases force capability but reduces speed proportionally. For example:
- A 200 lb actuator might move at 2 inches per second
- A 500 lb actuator might move at 0.8 inches per second
- A 1000 lb actuator might move at 0.4 inches per second
If your application requires both high force and high speed, you may need to consider alternative actuation technologies, such as pneumatic or hydraulic systems, or use multiple lower-force actuators in parallel rather than a single high-force unit.
How Load Affects Actual Operating Speed
The speed specification provided by manufacturers represents the actuator's no-load or light-load speed. In real-world applications, the actual speed decreases as load increases. Some manufacturers provide speed-versus-load performance curves that show this relationship, allowing you to estimate actual operating speed based on your specific load.
For critical applications where speed consistency matters under varying loads, consider feedback actuators paired with closed-loop control systems. These systems can monitor position and adjust motor voltage to maintain more consistent speed regardless of load variations.
Speed Control and Precise Positioning
Standard actuators typically operate at full speed whenever power is applied. However, many applications require variable speed control or precise positioning. To achieve this, you'll need to integrate your actuator with additional control electronics:
- PWM motor drivers allow variable speed control by modulating voltage
- Arduino microcontrollers or similar platforms provide programmable control logic
- Feedback actuators with built-in potentiometers or hall-effect sensors enable precise position monitoring
- Control boxes offer pre-configured solutions for synchronized multi-actuator systems
When selecting an actuator for precision control applications, verify that it's compatible with your control method and provides the necessary feedback signals.
Power Requirements and Electrical Specifications
Understanding power requirements is essential for integrating actuators into your electrical system, selecting appropriate power supplies, and ensuring safe operation. Two primary electrical specifications define actuator power requirements: input voltage and maximum current draw.
Input Voltage: AC vs. DC
Input voltage (also called rated voltage) is the voltage for which the actuator is designed and represents the maximum voltage that should be applied. Electric linear actuators are available in both AC and DC voltage configurations, with common voltages including:
- DC voltages: 12V, 24V, 36V, and 48V
- AC voltages: 110V, 120V, 220V, and 240V
DC actuators are most common in automotive, marine, mobile, and battery-powered applications, while AC actuators are typically used in fixed installations with access to mains power. The voltage you select should match your available power source. Operating an actuator significantly above its rated voltage will damage the motor and void the warranty, while operating below rated voltage will result in reduced force and speed.
Maximum Current Draw and Power Consumption
Maximum current draw specifies the highest current the actuator will safely draw under full load conditions. Unlike voltage, where you should match the rating exactly, the actual current draw of your actuator will vary based on the load it's moving. An actuator might draw 2-3 amps while moving a light load but reach its maximum rated current of 8 amps when moving a heavy load at the limits of its force capacity.
Key points about current requirements:
- Your power supply must be rated for at least the maximum current draw, preferably with 20-30% overhead
- Wiring and switches must also be rated for the maximum current
- Higher current draw generates more heat, which can be a concern in enclosed installations
- In battery-powered applications, current draw directly affects runtime
Optimizing Voltage Selection for Efficiency
When you have flexibility in voltage selection, choosing a higher voltage actuator (for example, 24V instead of 12V) offers several advantages. For the same power output, a higher voltage actuator draws proportionally less current. This reduced current provides multiple benefits:
- Smaller wire gauge requirements, reducing weight and cost
- Reduced resistive losses in wiring and connections
- Longer battery runtime in mobile applications
- Better performance over longer cable runs with less voltage drop
However, higher voltage systems require more expensive power supplies and present greater shock hazards, so the choice involves balancing efficiency against safety and cost considerations.
Environmental and Durability Considerations
Beyond the core specifications of force, stroke, and speed, the environment in which your actuator operates significantly impacts which model is appropriate for your application. Environmental factors affect both actuator longevity and safe operation.
IP Rating: Ingress Protection Against Dust and Water
The IP (Ingress Protection) rating indicates an actuator's resistance to solid particles (dust) and liquids (water). This two-digit code is critical for applications exposed to harsh environments. The first digit represents solid particle protection (0-6), while the second digit represents liquid protection (0-8).
Common IP ratings for linear actuators include:
- IP54: Protected against dust and water splashes from any direction—suitable for indoor applications with minimal exposure
- IP65: Dust-tight and protected against water jets—appropriate for outdoor equipment and washdown environments
- IP66: Dust-tight and protected against powerful water jets—needed for exposed outdoor installations
- IP67: Dust-tight and protected against temporary immersion—required for marine applications or areas with potential flooding
- IP69K: Dust-tight and protected against high-pressure, high-temperature washdown—essential for food processing and harsh industrial environments
For industrial actuators used in manufacturing or outdoor applications, selecting an appropriate IP rating prevents premature failure due to contamination. Standard indoor actuators with low IP ratings will fail quickly if exposed to moisture or dust ingress.
Operating Temperature Range
Temperature specifications define the ambient temperature range within which the actuator can safely operate. Exceeding these limits can cause:
- Motor overheating and damage at high temperatures
- Lubricant stiffening and binding at low temperatures
- Seal degradation affecting IP rating performance
- Electronic component failure in extreme conditions
Standard actuators typically operate in the range of -20°C to +65°C (-4°F to +149°F). Specialized industrial actuators are available for extreme temperature applications, including cold storage facilities, outdoor installations in harsh climates, and high-temperature industrial processes.
Material Construction and Corrosion Resistance
The materials used in actuator construction affect durability, especially in corrosive environments. Common materials include:
- Aluminum housings: Lightweight and adequate for most indoor applications
- Stainless steel components: Essential for marine applications and corrosive chemical environments
- Plastic/polymer housings: Used in micro linear actuators for light-duty, low-cost applications
- Protective coatings: Anodizing, powder coating, or galvanizing for enhanced corrosion resistance
Marine applications, outdoor installations, and industrial environments with chemical exposure require careful material selection to prevent corrosion that can cause binding, reduced force output, and eventual failure.
Physical Constraints and Mounting Considerations
Overall Dimensions and Space Constraints
Beyond stroke length, the physical dimensions of the actuator itself must fit within your design constraints. Key dimensional considerations include:
- Retracted length: Total length when fully closed, which determines minimum installation space
- Extended length: Total length when fully extended, affecting maximum space requirements and potential collision risks
- Body diameter or width: Critical in applications with limited lateral clearance
- Rod diameter: Affects both strength and the available mounting bracket options
For applications with severe space constraints, specialized designs like micro linear actuators, bullet actuators, or track actuators may provide better solutions than standard rod-style actuators.
Mounting Options and Bracket Compatibility
The mounting method affects both installation ease and operational reliability. Linear actuators typically offer several mounting configurations:
- Clevis mounts: Provide rotational freedom in one plane, ideal for angular applications
- Double clevis: Allows rotation at both ends, accommodating minor misalignment
- Trunnion mounts: Offer rotation around the actuator body, useful for complex angular applications
- Flange mounts: Provide rigid, fixed mounting when no angular movement is needed
Ensure your selected actuator offers mounting options compatible with your design, or verify that appropriate mounting brackets are available. Improper mounting can cause side-loading, which reduces actuator life and may lead to premature failure.
Duty Cycle and Operational Requirements
Understanding Duty Cycle Ratings
Duty cycle refers to the ratio of operating time to rest time, typically expressed as a percentage. For example, a 20% duty cycle means the actuator can operate for 2 minutes out of every 10 minutes, requiring 8 minutes of rest. Exceeding the rated duty cycle causes excessive heat buildup in the motor, leading to reduced performance and premature failure.
Duty cycle ratings vary significantly among actuator types:
- Light-duty actuators: 10-20% duty cycle, suitable for intermittent use like opening hatches or occasional positioning
- Medium-duty actuators: 25-50% duty cycle, appropriate for applications with moderate frequency like adjustable furniture
- Heavy-duty/industrial actuators: 75-100% duty cycle, designed for continuous or near-continuous operation in industrial automation
If your application requires continuous operation or frequent cycling, invest in industrial actuators rated for high duty cycles. Using standard actuators beyond their rated duty cycle will void warranties and result in rapid failure.
Noise Level Considerations
Actuator noise level matters in applications where quiet operation is important, such as home automation, office furniture, or medical equipment. Electric actuators generate noise from several sources:
- Motor operation and gear meshing
- Mechanical vibration transmitted through mounting points
- Resonance in attached structures
Noise levels typically range from 45 dB (quiet, suitable for bedroom applications) to 70+ dB (noticeable, but acceptable for industrial environments). If noise is a concern, look for actuators specifically designed for quiet operation, which typically feature precision gears, sound dampening, and higher-quality motors.
Feedback and Control Requirements
For applications requiring precise positioning or synchronized multi-actuator systems, feedback actuators with built-in position sensing are essential. Common feedback technologies include:
- Potentiometer feedback: Provides analog voltage proportional to position, simple and cost-effective
- Hall-effect sensors: Offer digital feedback with high accuracy and no wearing components
- Optical encoders: Deliver very high resolution for precision positioning applications
Feedback signals enable closed-loop control, allowing you to command specific positions, synchronize multiple actuators, and detect obstacles or binding conditions. When integrated with Arduino or other controllers, feedback actuators enable sophisticated automation capabilities.
Application-Specific Selection Guidance
Automation and Furniture Applications
For applications like standing desks, TV lifts, and adjustable furniture, consider:
- Medium-duty actuators with appropriate duty cycles for daily use
- Quiet operation (45-55 dB) for residential environments
- Sufficient static force to hold loads indefinitely without power
- Control boxes for synchronized multi-actuator operation
- Safety features like anti-collision detection in furniture applications
Industrial Automation Applications
Industrial environments demand industrial actuators designed for harsh conditions:
- High IP ratings (IP65 or better) for dust and water protection
- Extended duty cycles (75-100%) for continuous operation
- Robust construction with metal housings and corrosion-resistant materials
- Wide operating temperature ranges
- Feedback capabilities for integration with PLCs and control systems
Mobile and Marine Applications
Vehicles, boats, and RVs present unique challenges requiring specialized consideration:
- DC voltage matching vehicle electrical systems (typically 12V or 24V)
- High IP ratings (IP66 minimum, IP67 preferred) for weather exposure
- Stainless steel construction for marine corrosion resistance
- Compact form factors like bullet actuators for space-constrained installations
- Low current draw to minimize battery drain
- Vibration and shock resistance for mobile environments
Making Your Final Selection
Properly sizing a linear actuator requires balancing multiple specifications and constraints specific to your application. Begin by identifying your non-negotiable requirements—typically stroke length and minimum force—then optimize for speed, power consumption, and environmental factors within those constraints.
Remember to build appropriate safety margins into your specifications, particularly for force requirements where a 25-50% overhead is recommended. Consider not just the actuator itself, but the complete system including power supplies, mounting brackets, and control electronics.
When in doubt between two models, choosing the higher-rated actuator provides greater reliability and longer service life, even if it costs slightly more initially. The engineering principle of not operating equipment at its design limits applies directly to actuator selection—what's adequate on paper often proves marginal in real-world conditions.
Frequently Asked Questions
How much force do I need for my linear actuator?
The force required depends on the weight you're moving, the number of actuators, and your mounting geometry. For vertical lifting, divide the total weight by the number of actuators and add a 25-50% safety margin. For angular applications like opening lids or hatches, you'll need to account for leverage and changing angles throughout the movement. Use a linear actuator calculator or apply torque calculations to determine exact requirements. Remember that the force specification should be treated as a maximum limit, not a normal operating load.
What's the relationship between stroke length and retracted length?
The retracted length of a standard rod-style linear actuator is typically the stroke length plus 8-12 inches, depending on the model design. For example, a 20-inch stroke actuator will have a retracted length around 28-30 inches. This relationship is important for installation planning in space-constrained applications. If you need significant stroke but limited space, consider alternative designs like track actuators or slide rails that offer better stroke-to-retracted-length ratios.
Can I control the speed of a linear actuator?
Yes, actuator speed can be controlled using PWM (Pulse Width Modulation) motor drivers that vary the voltage supplied to the actuator. Lower voltage results in slower movement, while full voltage provides maximum speed. For precise speed control, you'll need to integrate the actuator with a motor driver and controller like an Arduino. Feedback actuators with built-in position sensors enable more sophisticated control including programmable speed
