Understanding Stroke in Linear Actuators
When selecting a linear actuator for your project, you'll encounter numerous technical specifications: force capacity, speed, voltage requirements, and perhaps most fundamentally, stroke length. For first-time buyers and even experienced engineers transitioning from hydraulic to electric actuation systems, understanding stroke is essential to ensuring your actuator will physically accomplish what your application demands.
Stroke length is more than just a number in a specification sheet—it directly determines whether your actuator can create the range of motion your project requires, influences the physical footprint of your installation, and affects which actuator type will work best for your application. Whether you're building a TV lift mechanism, automating drawer slides, or designing a custom standing desk, choosing the correct stroke length is critical to project success.
This comprehensive guide will explain what stroke means across different actuator types, how to measure it correctly, and what factors you should consider when selecting a stroke length for your specific application.
What is Stroke Length?
For most linear actuators, stroke or stroke length refers to the total distance the actuator can travel between its fully retracted and fully extended positions. In mathematical terms:
Stroke Length = Fully Extended Length - Fully Retracted Length
This measurement represents the actual working distance your actuator provides—the amount of linear motion it can create in your application. If you need to lift a cabinet door 8 inches, you need an actuator with at least an 8-inch stroke. If you need to extend a platform 300mm, your actuator requires a minimum 300mm stroke.
Understanding stroke starts with knowing how to measure it correctly. The image above shows an actuator in its fully retracted position. This is your starting point for measurement.
The second image shows the same actuator fully extended. The difference between these two lengths is the stroke—the actual usable motion the actuator provides.
Stroke in Rod-Style Actuators
For traditional rod-style linear actuators—the most common type in automation and home automation applications—stroke has a straightforward meaning. These actuators feature a telescoping rod that extends outward from a cylindrical body containing the motor, gearbox, lead screw, and electronics.
The stroke length equals how far this rod extends beyond the actuator body. For example, a micro linear actuator with a 2-inch stroke will have a rod that extends exactly 2 inches from its retracted position. A 12-inch stroke actuator extends 12 inches.
Rod actuators are available in stroke lengths ranging from as little as 1 inch (25mm) in compact bullet actuators to 36 inches (914mm) or more in heavy-duty industrial actuators. The stroke you select directly impacts the actuator's retracted length, which we'll discuss in detail later.
Common Rod Actuator Stroke Lengths
Standard stroke lengths typically follow incremental patterns to accommodate common application requirements:
- Short Strokes (1-4 inches / 25-100mm): Ideal for compact applications like small enclosure lids, ventilation flaps, or adjustable feet
- Medium Strokes (4-12 inches / 100-300mm): Suitable for cabinet doors, hatch covers, adjustable furniture, and general automation tasks
- Long Strokes (12-24 inches / 300-600mm): Used in TV lifts, larger furniture automation, and industrial positioning
- Extra-Long Strokes (24-36+ inches / 600-914mm+): Required for large-scale applications like height-adjustable workbenches or specialized industrial equipment
Stroke in Track Actuators
Track actuators represent a different design philosophy. Instead of using an extending telescoping rod, these actuators employ a sliding carriage that travels along a fixed-length track or rail. This design offers advantages in applications requiring higher precision, better lateral load handling, or integration with existing rail systems.
For track actuators, stroke length has a slightly different meaning. Rather than being calculated as the difference between extended and retracted positions, the stroke simply equals the length of the travel path along the track. If you have a 500mm track actuator, the carriage can travel 500mm along that track—that's your stroke.
The key distinction: track actuators don't change their overall length during operation. The actuator body remains a constant size while the carriage moves along it. This makes them excellent choices when space constraints prevent the use of extending rod actuators, or when you need to mount components directly to a moving carriage.
Advantages of Track Actuators for Specific Strokes
Track actuators excel in several scenarios:
- Applications requiring guided motion with minimal side-to-side play
- Installations where the actuator length must remain constant
- Systems needing to carry loads perpendicular to the direction of motion
- Projects requiring integration with slide rails or linear bearings
Stroke in Multi-Stage Column Lifts
Multi-stage column lifts represent an innovative solution to a common problem: how to achieve long stroke lengths while maintaining compact retracted dimensions. These actuators use telescoping stages—typically two, three, or even four sections that nest inside one another when retracted.
This design breaks the usual rule that retracted length must equal stroke plus internal component space. A three-stage column lift might have a 24-inch stroke but collapse to just 12 inches when fully retracted. This is possible because the extending sections are hollow tubes that can slide inside one another, unlike the solid rod of a standard actuator.
Column lifts are particularly valuable in applications like:
- Height-adjustable standing desks where desktop clearance is limited
- Compact TV lift mechanisms that must fit in shallow cabinets
- Medical equipment requiring substantial height adjustment in confined spaces
- Marine applications with tight storage requirements
The trade-off for this compact design is typically higher cost and slightly more complex installation, but for applications where space is at a premium, column lifts provide stroke capabilities impossible with standard actuator designs.
How Stroke Length Affects Physical Dimensions
Selecting a stroke length isn't just about motion—it has direct implications for the physical space your actuator will occupy in both retracted and extended states. This is where many first-time actuator buyers encounter surprises during installation.
Retracted Length Calculation
For rod-style actuators, the retracted length (also called closed length or minimum length) must accommodate both the collapsed rod and all internal components: motor, gearbox, lead screw assembly, limit switches, and electronics. As a general rule:
Retracted Length ≈ Stroke Length + 6-10 inches (150-250mm)
This means a 12-inch stroke actuator will typically have a retracted length of 18-22 inches. A compact 4-inch stroke actuator might still be 10-14 inches long when retracted. This relationship is crucial for installation planning—you need sufficient space for the entire retracted actuator, not just the stroke distance.
Extended Length Calculation
The extended length is simpler to determine:
Extended Length = Retracted Length + Stroke Length
If your retracted actuator is 20 inches and your stroke is 12 inches, your extended length will be 32 inches. This dimension matters when determining swing paths, clearance requirements, and potential interference with other components.
Installation Clearance Requirements
Beyond the actuator itself, you need to account for:
- Mounting brackets: Add 1-3 inches (25-75mm) to each end depending on bracket style
- Wiring clearance: Allow space for cable routing and connector access
- Service access: Ensure you can reach limit switches, mounting hardware, and connections
- Safety margins: Leave buffer space to prevent over-extension or collision with other components
Selecting the Right Stroke Length for Your Application
Choosing the optimal stroke length requires careful analysis of your application requirements. Here's a systematic approach:
Step 1: Measure Required Motion
Determine the exact distance your application needs to move. For a TV lift, measure from the lowest position (fully hidden) to the highest (optimal viewing position). For a hatch, measure the full opening distance. Add a small safety margin—typically 5-10%—to ensure you have adequate range.
Step 2: Verify Installation Space
Measure the space available for the retracted actuator. Remember to include mounting hardware and clearances. If your available space is less than the calculated retracted length for your required stroke, you may need to:
- Consider a multi-stage column lift instead of a rod actuator
- Redesign the mounting arrangement to accommodate the actuator
- Select a different actuation method (perhaps a rotary actuator with linkages)
Step 3: Account for Mounting Geometry
The effective stroke your actuator provides depends on mounting geometry. If your actuator mounts at an angle or uses lever arms, the actual motion produced may differ from the actuator stroke. For angled mounting, use the formula:
Effective Motion = Stroke × sin(mounting angle)
An actuator mounted at 45° provides only 70% of its stroke length as vertical motion. This is where proper engineering calculations become essential.
Step 4: Consider Future Needs
If there's any possibility your motion requirements might increase, select a slightly longer stroke now. Upgrading an actuator later often requires complete disassembly and reinstallation. The cost difference between a 10-inch and 12-inch stroke is typically modest compared to the labor of replacement.
How Stroke Length Affects Performance
Beyond physical dimensions, stroke length influences several performance characteristics worth considering:
Speed Considerations
Longer stroke actuators typically take more time to complete their full travel, though this depends primarily on motor speed and gearing. If you need a 20-inch stroke actuator to move quickly, look for models with higher RPM ratings or consider whether you truly need the full stroke for every operation.
Load Capacity and Stroke
Longer strokes can experience greater deflection under load, particularly with side loading. The extended rod acts as a cantilever beam—the longer it extends, the more it can flex. For heavy loads with long strokes, consider:
- Selecting actuators with thicker rod diameters
- Adding external guide rails or linear guides for support
- Using multiple shorter-stroke actuators instead of one long-stroke unit
- Choosing industrial actuators designed for heavy-duty applications
Precision and Positioning
If your application requires precise positioning, longer strokes make this more challenging. A 1mm positioning error represents 1% of a 100mm stroke but only 0.25% of a 400mm stroke. For high-precision applications, consider using feedback actuators with built-in position sensors, regardless of stroke length.
Stroke Considerations in Complete Systems
When actuators are part of larger automated systems, stroke selection interacts with other components:
Control Systems and Stroke
Your control box and remote control setup should account for stroke length. Longer strokes take more time to traverse, which affects:
- Timing sequences in multi-actuator systems
- User experience (how long someone waits for motion to complete)
- Safety considerations (e-stop response time)
- Battery capacity requirements for portable applications
Power Supply Implications
While stroke length doesn't directly affect power consumption, longer strokes mean longer run times, which impacts power supply and battery sizing. A 24-inch stroke takes twice as long to complete as a 12-inch stroke at the same speed, drawing power for twice as long.
Integration with Arduino and Custom Control
For DIY enthusiasts working with Arduino or other microcontrollers, stroke length affects programming considerations. Feedback actuators allow you to track position throughout the stroke, enabling sophisticated control algorithms. Without feedback, you rely on timing, which becomes less accurate with longer strokes due to load variations and mechanical tolerances.
Frequently Asked Questions
What stroke length do I need for my application?
Measure the exact distance your application needs to move and add 5-10% as a safety margin. For example, if you need to lift a TV 16 inches, select an 18-inch stroke actuator. Always verify that your installation space can accommodate the retracted length, which is typically the stroke length plus 6-10 inches for rod-style actuators. For complex mounting geometries or angled installations, account for the trigonometric relationship between actuator stroke and actual motion produced.
How long is an actuator when retracted?
For standard rod actuators, the retracted length is approximately the stroke length plus 6-10 inches (150-250mm) to accommodate internal components like the motor, gearbox, and electronics. A 12-inch stroke actuator typically has an 18-22 inch retracted length. Track actuators maintain a constant length equal to the stroke plus component space. Multi-stage column lifts are the exception—they can collapse to roughly half their stroke length due to telescoping sections that nest inside one another.
Are longer stroke actuators weaker?
Not inherently, but longer strokes can experience greater deflection and bending moments when extended under load, particularly with side loads. The extended rod acts as a cantilever beam—the longer it extends, the more potential for flex. To maintain performance with long strokes, manufacturers use thicker rod diameters and robust internal components. For heavy loads with long strokes, consider adding external guide rails for support or using multiple shorter-stroke actuators instead of one long-stroke unit.
Can I get custom stroke lengths?
Most manufacturers, including FIRGELLI Automations, offer standard stroke lengths in common increments (2", 4", 6", 8", 10", 12", etc.). Custom strokes are sometimes available for specialized applications, particularly for industrial customers ordering in volume, but typically involve higher costs and longer lead times. In most cases, selecting the next larger standard stroke length is more practical and economical than requesting a custom size. The additional stroke can serve as useful buffer room for adjustments during installation.
Does stroke length affect actuator speed?
Stroke length itself doesn't change the actuator's speed rating (typically measured in inches or mm per second), but it does affect how long the actuator takes to complete its full travel. A 12-inch stroke actuator moving at 1 inch/second takes 12 seconds to fully extend, while a 6-inch stroke actuator at the same speed completes its motion in 6 seconds. If you need both long stroke and fast operation, look for actuators with higher speed ratings or consider whether your application truly requires the full stroke for every operation cycle.
How do I measure the stroke on an existing actuator?
To measure stroke on an installed actuator, fully retract it and measure the total length from mounting point to mounting point. Then fully extend the actuator and measure again. The difference between these measurements is the stroke. If the actuator is unmounted, measure from the center of one mounting hole to the center of the other mounting hole in both retracted and extended positions. For track actuators, the stroke equals the distance the carriage can travel along the track from one end to the other.
