What is Linear Actuator Stroke Length?
When selecting a linear actuator for any motion control project, one of the most critical specifications to determine is the stroke length. The linear actuator stroke length is the total distance the actuator's rod or shaft can travel from its fully retracted position to its fully extended position. This measurement is typically expressed in inches or millimeters and directly defines the maximum range of motion your actuator can provide.
Understanding stroke length goes beyond simply measuring the distance you need to move an object. The stroke length determines whether your actuator can physically accomplish the task you're designing for, influences the mounting configuration, affects the overall footprint of your installation, and impacts the mechanical advantage in hinged applications. A micro linear actuator might offer stroke lengths from 10mm to 100mm for compact applications, while industrial actuators can provide strokes exceeding 1000mm for heavy-duty automation projects.
The importance of calculating the correct stroke length cannot be overstated. Specify too short a stroke, and your actuator won't complete the required motion. Specify too long a stroke, and you'll unnecessarily increase costs, physical dimensions, and potential mechanical complications. This guide will walk you through the precise calculations needed to determine the exact linear actuator stroke length for both straight-line push applications and more complex hinged installations.
How to Measure the Required Stroke for a Straight Push
For direct linear applications where the actuator pushes or pulls an object in a straight line, calculating the required stroke length is relatively straightforward but requires careful measurement and consideration of several factors.
Basic Straight-Line Measurement
The fundamental calculation for a straight push application is simple: measure the total distance the load needs to travel from its starting position to its final position. This is your minimum required stroke length. For example, if you're designing a TV lift that needs to raise a television 24 inches from a concealed position to viewing height, you need an actuator with at least a 24-inch stroke.
However, this basic measurement represents only the theoretical minimum. In practice, you must account for several additional factors:
- Mounting clearances: The actuator's body length when fully retracted adds to the overall space requirement. Most actuators have a collapsed length approximately equal to the stroke length plus 4 to 8 inches, depending on the design and force rating.
- Mechanical tolerances: Manufacturing variations and installation imperfections mean you should add 5-10% buffer to your calculated stroke to ensure the actuator can complete the full range of motion under all conditions.
- Safety margins: As we'll discuss later, you should never operate an actuator at its absolute limits. Plan for at least 10mm of unused stroke at each end of travel.
Accounting for Mounting Point Offset
In many straight-line applications, the actuator cannot be mounted directly in line with the direction of travel. When the actuator is offset from the load's path, you must use basic trigonometry to calculate the actual stroke required. If the actuator is mounted at an angle θ to the direction of travel, the required actuator stroke is the desired travel distance divided by the cosine of that angle.
For instance, if your load needs to travel 20 inches vertically, but space constraints force you to mount the actuator at a 30-degree angle from vertical, the required stroke would be 20 ÷ cos(30°) = 20 ÷ 0.866 = 23.1 inches. This angular mounting also affects the effective force the actuator can deliver, reducing it by the same cosine factor.
Multiple Actuator Configurations
When using multiple linear actuators in parallel for applications like standing desks or large platform lifts, all actuators must have identical stroke lengths to ensure synchronized movement. Using a control box designed for synchronization helps maintain even extension, but starting with properly matched stroke lengths is essential for balanced load distribution and preventing mechanical binding.
Calculating Stroke for a Hinged Application
Hinged applications represent the most common and most complex scenario for determining linear actuator stroke length. When an actuator opens or closes a lid, hatch, panel, or door that rotates around a hinge point, the relationship between actuator stroke and panel movement becomes a geometry problem requiring careful calculation.
The Triangle Method
The most reliable approach to calculating stroke for hinged applications involves treating the system as a triangle that changes shape as the panel moves. At any given position, three points define this triangle: the hinge point, the actuator's mounting point on the fixed frame, and the actuator's mounting point on the moving panel.
To calculate the required stroke, you need to determine the distance between the two actuator mounting points in both the closed and open positions, then subtract the closed distance from the open distance. This calculation requires knowing:
- The distance from the hinge to the fixed mounting point
- The distance from the hinge to the moving mounting point
- The angle between these two measurements when the panel is closed
- The desired opening angle
Using the law of cosines, the distance between mounting points can be calculated as: Distance² = A² + B² - 2AB × cos(θ), where A is the distance from hinge to fixed mount, B is the distance from hinge to moving mount, and θ is the angle between them.
Practical Measurement Technique
While the mathematical approach provides precision, many builders prefer a direct measurement method that accounts for real-world installation variables. This technique involves temporarily installing the mounting brackets at the planned locations, then physically measuring the distance between mounting pivot points with the panel fully closed and fully open.
Using a tape measure or, more accurately, a length of string or wire held taut between the two mounting points, measure and mark the distance in both positions. The difference between these measurements is your required stroke length. This method inherently accounts for any geometric complexities, offset mounting, or irregular panel geometry that might complicate theoretical calculations.
Optimizing Mounting Positions
The placement of actuator mounting points dramatically affects both the required stroke length and the mechanical advantage throughout the range of motion. Mounting points closer to the hinge require shorter stroke lengths but demand higher forces. Conversely, mounting farther from the hinge increases the required stroke but reduces force requirements due to improved leverage.
For most applications, positioning the moving mounting point approximately one-third to one-half the panel length from the hinge provides a good balance of stroke length and force efficiency. The fixed mounting point should be positioned to create an angle between 30 and 60 degrees relative to the panel when closed. This configuration ensures the actuator operates within its most efficient force delivery range throughout the motion cycle.
Using the Actuator Calculator
For complex hinged configurations, FIRGELLI offers an actuator calculator tool that simplifies the geometric calculations. By inputting your hinge location, mounting points, and desired opening angle, the calculator provides the required stroke length and force specifications, eliminating the need for manual trigonometric calculations and reducing the risk of measurement errors.
Why You Shouldn't Bottom Out Your Actuator
One of the most common mistakes in linear actuator applications is specifying a stroke length that matches exactly—or falls short of—the required travel distance. Operating an actuator at its absolute mechanical limits by allowing it to "bottom out" at full extension or retraction creates multiple problems that compromise performance, reliability, and longevity.
Mechanical Stress and Component Wear
When a linear actuator reaches its physical limit of travel, the internal mechanical components experience impact loading rather than gradual deceleration. The lead screw or ball screw mechanism, which converts the motor's rotary motion into linear motion, contacts its end stop with the full momentum of the moving load. This repeated impact creates shock loads that can damage the precision threads, accelerate wear on the drive nut, and potentially bend or deform the actuator rod.
Feedback actuators with position sensing capabilities face additional risks. The Hall effect sensors or potentiometers used for position feedback can suffer calibration drift or component failure when subjected to the vibration and shock of hard stops. For applications requiring precise positioning, this degradation can compromise the accuracy that made the feedback system valuable in the first place.
Electrical and Control System Implications
From an electrical perspective, bottoming out creates a stall condition where the motor continues attempting to drive the mechanism against an immovable obstacle. This stall current can be two to three times the normal operating current, generating excessive heat in the motor windings and controller electronics. While most quality actuators include thermal protection, repeated thermal cycling reduces component lifespan and increases the risk of premature failure.
The control circuitry also suffers when managing an actuator operating at its limits. Without built-in limit switches or proper control logic, the system must rely solely on current sensing or timing to determine when travel is complete. These methods lack precision and can result in either inadequate travel or excessive force against the mechanical stops.
Recommended Safety Margins
Professional motion control design practice calls for maintaining a safety margin of at least 10-15mm (approximately 0.4-0.6 inches) of unused stroke at each end of the actuator's travel range. This buffer provides several benefits:
- Mechanical protection: The actuator never reaches its hard mechanical limits during normal operation, eliminating impact loading.
- Installation tolerance: The buffer accommodates minor measurement errors or installation variations without compromising functionality.
- Thermal expansion compensation: Materials expand and contract with temperature changes; the safety margin prevents binding under extreme conditions.
- Wear accommodation: As components wear over thousands of cycles, the available stroke may decrease slightly; the initial buffer maintains full functional travel.
For critical applications or high-cycle-count installations, consider specifying an actuator with 20-25% more stroke than the theoretical minimum requirement. While this increases initial cost modestly, the extended service life and improved reliability often justify the investment.
Implementing Soft Limits
Beyond physical margins, implementing soft limits through your control system provides another layer of protection. When using feedback actuators or microcontroller-based control with Arduino or similar platforms, program position limits that stop the actuator 5-10mm before its mechanical extremes. This software-based approach allows you to adjust travel limits without physical modification and provides diagnostic data if the actuator begins approaching its boundaries unexpectedly.
For simpler installations using a rocker switch or basic remote control, proper stroke selection becomes even more critical since you lack fine-grained electronic control over end positions. In these cases, the physical safety margin built into your stroke length specification is the primary protection mechanism.
Browse Actuators by Stroke Length at Firgelli
Once you've calculated the precise linear actuator stroke length required for your application, selecting the right actuator becomes a matter of matching that specification with the appropriate force rating, speed, and form factor. FIRGELLI Automations offers an extensive range of actuators across multiple product lines, each optimized for specific application requirements.
Compact and Micro Stroke Options
For applications requiring precise motion in confined spaces, micro actuators provide stroke lengths ranging from 10mm to 100mm. These compact units excel in applications like camera positioning systems, small hatches, ventilation controls, and instrumentation where space constraints demand minimal footprint. Despite their small size, these actuators deliver forces from 15N to 150N, sufficient for lightweight automation tasks.
The bullet actuator series represents another compact option, featuring a cylindrical body design that minimizes lateral dimensions while providing stroke lengths from 50mm to 300mm. The streamlined form factor makes these ideal for marine applications, automotive projects, and industrial equipment where the actuator must fit within a narrow envelope.
Standard and Heavy-Duty Stroke Ranges
The core linear actuator collection spans the most common stroke requirements, with options from 2 inches to 40 inches. This range covers the vast majority of automation projects, including furniture automation, access control, adjustable workstations, and medium-duty industrial positioning systems. Force ratings in this category extend from 50 lbs to 1500 lbs, providing flexibility to match both stroke length and load capacity to your specific requirements.
For demanding industrial environments and high-force applications, industrial actuators deliver stroke lengths up to 40 inches with force capacities exceeding 2000 lbs. These heavy-duty units feature reinforced construction, sealed housings for environmental protection, and enhanced duty cycles suitable for continuous operation. Applications include automated machinery, material handling equipment, and process automation where reliability under sustained loads is paramount.
Specialized Stroke Configurations
Track actuators provide an alternative approach to long-stroke applications, offering parallel guidance that prevents rod rotation and increases side-load capacity. Available in stroke lengths from 4 inches to 36 inches, these actuators suit applications where the load must remain precisely aligned throughout travel, such as sliding doors, panels, or platforms requiring both extension and lateral stability.
For applications requiring rotational motion rather than linear travel, rotary actuators convert linear stroke into controlled angular movement. While not strictly linear stroke applications, understanding the relationship between linear actuator stroke length and rotational angle helps when designing hinged systems where a rotary actuator might offer advantages in terms of mounting simplicity or mechanical efficiency.
Complete System Integration
Beyond the actuator itself, achieving precise stroke control requires appropriate supporting components. Power supplies must deliver adequate current throughout the actuator's entire stroke to maintain consistent speed and force. A speed controller allows adjustment of extension and retraction rates, which can be particularly important in applications where the load characteristics change throughout the stroke range.
Proper mounting brackets ensure that the calculated stroke translates into the intended motion. Standard clevis mounts provide pivot capability at both ends, accommodating the slight angular changes that occur in many applications as the actuator extends. For installations requiring precise alignment, fixed mounting brackets combined with careful measurement during installation ensure the actuator's stroke aligns perfectly with the required motion path.
Conclusion
Accurately determining linear actuator stroke length is fundamental to successful motion control design. Whether you're working on a simple straight-line application or a complex hinged mechanism, the calculations and measurement techniques outlined in this guide provide the foundation for selecting actuators that will perform reliably throughout their service life. Remember to always include appropriate safety margins, avoid operating actuators at their mechanical limits, and consider the complete system integration including mounting hardware, control systems, and power delivery.
By investing time in precise stroke calculation during the design phase, you'll avoid the costly mistakes of undersized actuators that can't complete the required motion or oversized units that unnecessarily increase project costs and complexity. The wide range of stroke lengths available across FIRGELLI's product lines ensures that once you've determined your exact requirements, you'll find an actuator perfectly matched to your application.
Frequently Asked Questions
What happens if I choose a linear actuator stroke length that's too short?
Selecting an actuator with insufficient stroke length means your mechanism simply won't complete its intended motion. In straight-line applications, the load will stop short of its target position. For hinged applications, the panel or door won't open to the desired angle. Beyond the obvious functional failure, attempting to force an undersized actuator to complete the motion by bottoming it out repeatedly will cause premature mechanical failure, damage to internal components, and potential motor burnout from continuous stall conditions. Always add a 10-15mm safety margin beyond your calculated minimum stroke requirement.
How do I calculate stroke length for a hatch that opens at an angle?
For hinged applications like hatches, lids, or angled panels, you need to measure or calculate the distance between the actuator's mounting points in both closed and fully open positions. The easiest method is to temporarily install mounting brackets at your planned locations, then directly measure the distance between pivot points with the hatch closed and at maximum opening angle. The difference between these measurements is your required stroke. Alternatively, use the law of cosines with the distances from the hinge to each mounting point and the angles involved. Adding 20-25% to this calculated minimum accounts for mounting tolerances and prevents bottoming out.
Can I use different stroke lengths when running multiple actuators together?
No, when operating multiple actuators in parallel for applications like platform lifts or large panels, all actuators must have identical stroke lengths. Using mismatched strokes causes one actuator to bottom out while others continue extending, creating uneven loading, mechanical binding, and potential structural damage. The actuators should also have matching force ratings and speeds. For synchronized operation, use actuators from the same product line and consider a dedicated synchronization control box that manages multiple units, ensuring they extend and retract together even if minor variations exist in their electrical characteristics.
Does mounting angle affect the stroke length I need?
Yes, significantly. When an actuator is mounted at an angle rather than directly in line with the direction of motion, you need additional stroke to achieve the same displacement. The required stroke equals the desired travel distance divided by the cosine of the mounting angle from the direction of motion. For example, a 30-degree offset requires approximately 15% more stroke, while a 45-degree angle requires about 41% more stroke. This angular mounting also reduces the effective force the actuator delivers by the same cosine factor, so both stroke and force specifications must be adjusted when working with angled installations.
What's the difference between stroke length and collapsed length?
Stroke length is the distance the actuator rod travels from fully retracted to fully extended, representing the working motion range. Collapsed length (also called retracted length or mounting length) is the total physical dimension of the actuator when fully retracted, typically equal to the stroke length plus 4 to 8 inches depending on the actuator's design and force rating. When planning your installation, you must accommodate the collapsed length in your space constraints, not just the stroke. Extended length equals collapsed length plus stroke length, and this total dimension determines the maximum space the actuator occupies during operation.
