Start with numbers, not a catalog

Choosing a linear actuator starts with quantifying five things — force, stroke, speed, duty cycle, and positioning accuracy — plus the environment it lives in and the voltage available. Arrive at a supplier with those five numbers and an inexpensive off-the-shelf unit usually exists. Arrive with "it needs to move," and you will discover much later that the whole product architecture was built around the wrong component.

That matters because the actuator choice is not a detail. It determines package size, noise, current draw, battery sizing, control electronics, and whether the product is safe when power is removed.

The five numbers that define the requirement

  • Force. Not just the steady-state running force. You need the breakaway force to start motion, the holding force when stopped, and the worst-case force with cold grease, misaligned load, high friction, and any off-center loading. Real designs fail on the worst case, not the nominal one.
  • Stroke. The required travel plus margin for calibration and tolerance stack, weighed against the actuator's retracted length. This is the constraint that eliminates the most candidates — a screw actuator's retracted length is usually longer than its stroke, and that total length has to fit inside your housing.
  • Speed and cycle time. How many seconds the motion is allowed to take, and how much acceleration and deceleration ramp you need so the structure is not shocked at each end.
  • Duty cycle. The ratio of run time to rest time. An actuator rated at 25% duty cycle will overheat and shorten its life dramatically if you run it continuously. This spec is ignored more often than any other.
  • Accuracy and positioning. Is end-to-end travel enough, or do you need intermediate stops and repeatable positions? The answer changes the entire control architecture — two limit switches versus closed-loop feedback.

Add to that the environment: temperature range, ingress protection, washdown or chemical exposure, and shock and vibration during transport. All of them affect life more than the datasheet suggests.

The main actuator types

  • Motor with a lead screw. The most common choice in products. Inexpensive, reasonably quiet, and self-locking — it holds its load with no power applied. Efficiency is low, often well under half, so it suits high force at low speed.
  • Motor with a ball screw. High efficiency, higher speed, better accuracy, and long life — but expensive, and not self-locking, so it needs a brake or a holding mechanism if the load must stay put.
  • Belt drive. Long strokes at high speed with low inertia, at the cost of compliance and no self-locking. Common in machines rather than handheld products.
  • Solenoid. Very short stroke, fast all-or-nothing action, cheap and compact. Right for latches, valves, and detents; wrong for moving a load along a stroke.
  • Pneumatic cylinder. Powerful, fast, and simple on a production line that already has compressed air. Impractical in almost any consumer product.
  • Rotary-to-linear conversion. A crank, rack and pinion, scotch yoke, or cam driven by an ordinary rotary motor. Frequently cheaper than a packaged linear actuator, and it lets you tailor the force-versus-position curve — a crank naturally gives high force near the ends of travel. Design considerations for these are in how to calculate motor torque.

The motor inside, and the math behind it

Even when buying a complete actuator, know what is in it. A plain DC motor gives cheap motion with no position information. A stepper gives open-loop positioning. A servo gives closed-loop control with feedback and can report a fault when it stalls. The full comparison is in stepper vs servo vs DC motor.

Translating required linear force into motor torque is where lead screw efficiency bites. Because that efficiency can fall below one third with a fine pitch and no lubrication maintenance, the actual force delivered is far below what a frictionless calculation promises. Always size from measured or specified efficiency, and confirm on hardware.

Self-locking, back-driving, and safety

The question that comes up in nearly every project: what happens when power is removed? A self-locking actuator stays where it is — excellent for a lift or a positioning stage, and potentially dangerous in a chair, a door, or a lid that someone must release in an emergency, because it cannot be moved by hand.

If a person can be in the path of motion, the design needs a safety layer: force limiting in hardware or firmware, obstruction detection via motor current monitoring, a compliant element, and a manual release. Define startup behavior too — does the system home to a reference position on power-up, and what happens if it was powered off mid-stroke with an unknown position? Getting that wrong produces a product that crushes something the first time it is plugged back in.

Integration details that are almost always forgotten

  • Who carries the load. An actuator is meant to push, not to guide. Side load will destroy the screw and nut. Provide separate linear guidance and let the actuator see axial force only — this single mistake accounts for a large share of premature failures.
  • End-of-travel stops. Limit switches, sensors, or current monitoring keep the mechanism from driving into a hard stop every cycle. Repeated hard stalling is a fatigue and heat problem; the mechanism behind that kind of slow failure is explained in material fatigue in product design.
  • Holding without power. If state must persist through a power loss, you need self-locking, a brake, or a mechanical latch.
  • Inrush current and noise. The peak current at startup dictates power supply and battery management sizing — see battery pack design for a product. Mechanical noise, meanwhile, is one of the most-noticed qualities in a household product and is very hard to fix late.
  • Margin and structure. Size the surrounding structure for the actuator's stall force, not its rated force, because a jammed mechanism will deliver the former. How much margin to carry is the subject of factor of safety in mechanical design.

Buy first, then design

Catalog numbers are measured under ideal conditions. In practice, off-center loading, low temperature, a sagging battery voltage, and aged lubricant all move the numbers meaningfully. The reliable approach in most projects is to start with an off-the-shelf unit, measure real performance on a prototype under worst-case conditions, and only move to a custom mechanism if nothing fits. Designing the surrounding parts for manufacture at the same time avoids a second redesign — see design for manufacturing, and more subsystem guidance in our mechanical engineering hub.

If you have a motion requirement and want help turning it into a specified, sourced, and validated actuator solution, get in touch through our contact form and the Projects House team will work through it with you.