Linear Actuator Sizing Calculations only makes sense when you define the motion, load, environment, and control problem first. The useful answer is not a brand name or a buzzword. It is the set of parts, numbers, and safety decisions that make the mechanism work every day.
Make it a repeatable process: measure, calculate, choose mounting points, wire, test, and maintain. The page should help someone turn the idea into a design, not just admire the idea.
Engineering principle: Measure the hard part of travel, not the easy middle. The actuator must survive the worst position in the stroke — usually near closed on a hinged load, or at full extension where leverage is poor.
"Actuator sizing is not one calculation — it is five. Load, stroke, speed, voltage, and duty cycle each have to survive the worst point in the travel, not the average. The catalog number that looks right at the middle of stroke is the number that fails at the hinge." — Robbie Dickson, FIRGELLI Automations founder and former Rolls-Royce, BMW, and Ford engineer
What problem are you actually solving?
The first job is to describe the physical movement. Is the part lifting, sliding, tilting, rotating through a linkage, pushing a door, pulling a latch, or moving a guided platform? That answer decides the actuator style, bracket layout, controller, and safety method.
Do not start with force alone. A 100 lb actuator can fail in a weak bracket. A small actuator can work beautifully if the load runs on good guides. Motion design starts with geometry.
Where would this be used?
Good applications include hatches, lifts, slides, vents, doors, adjustable furniture, mobile equipment, robotics, test fixtures, and custom automation projects. The common thread is controlled motion through a known path. Known paths are easier to automate, easier to guard, and easier to test.
Bad applications usually ask the actuator to do too many jobs. The actuator should move the load. The frame, hinge, rail, or linkage should guide the load and carry side forces.
What components actually matter?
How would you use this in a real build?
Build the mechanism without power first. Move it by hand. If it binds by hand, power will only hide the problem for a few cycles. Once the motion feels smooth, measure the real load and the real friction.
Then choose the actuator around 5 numbers: load, stroke, speed, voltage, and duty cycle. Add the environment next. Water, dust, vibration, heat, salt, and public access change the design. A clean indoor cabinet lift and an outdoor vehicle mechanism do not deserve the same assumptions.
What is a realistic example?
Assume the moving part weighs 35 lbs and needs 8 inches of travel. If the mechanism uses good guides and the actuator pushes in line, you might start with the load plus a 1.5× safety factor.
Design load = 35 × 1.5 = 53 lbs
That number is only a first pass. If the actuator pushes through a poor angle, or if the hinge creates a bad leverage point near closed, the required force can double. Measure the hard part of travel, not the easy middle.
Worked example — extending the 35 lb / 8 in lift to speed and duty cycle: If the chosen actuator moves at 0.5 in/sec, full stroke takes 8 / 0.5 = 16 seconds. If the actuator is rated at a 25% duty cycle, that means it can run roughly 16 seconds out of every 64 seconds (16 on, 48 off) before thermal cutoff becomes a real risk. If the application requires one full cycle every 30 seconds, the chosen actuator is already on the edge — either a higher duty-cycle actuator or a slower speed is required. Always check duty cycle against worst-case usage, not average usage.
What should you measure before ordering?
Measure the total moving weight, required stroke, available closed length, mounting distance, travel speed, power supply voltage, and current capacity. Then measure the annoying things: friction, cable path, access to fasteners, and where the user puts their hands.
If the project needs position control, define the feedback requirement. Potentiometer feedback gives an analog position signal. Hall and optical feedback count pulses and usually need calibration. If the project only needs full open and full closed, a simple 2-wire actuator and rated switch may be enough.
How should you test it before trusting it?
Run at least 20 cycles with the real load. Check bracket movement, wire rub, heat, noise, and whether the mechanism slows at the same point every time. Then test the failure cases: blocked motion, power loss, limit switch fault, and user reset.
A prototype that works once proves the idea. A prototype that works after repeated cycles with the real load proves the design direction.
What usually goes wrong?
What details help this rank better?
Checklist, mounting diagrams, common mistakes, product-selection table. A strong article should show the design choices clearly. Readers do not need vague inspiration. They need the numbers and checks that stop the project failing in the shop.
What is the practical takeaway?
Start with the movement. Guide the load. Measure the hard position. Protect the wiring. Leave service access. Then pick the actuator, controller, and switches around the real job.
Simple. Practical. Much easier to fix before the holes are drilled.
