Pick the wrong actuator and you’ll either stall under load or waste time creeping along at low speed—neither is good. This Linear Actuator Speed vs. Force Tradeoff Calculator helps you work out the speed under load, mechanical power output, and load ratio if you know the no-load speed, max force rating, and real-world load. These calculations come in handy across industries like automation, medical devices, or adjustable furniture where load and speed rarely stay constant. Below, you’ll find the formula, a worked example, technical notes, and common questions.
What is the speed vs. force tradeoff in a linear actuator?
The heavier the load a linear actuator moves, the slower it goes. As you get closer to the actuator’s max force rating, speed drops off. This isn’t an optional feature—it’s just how electric actuators work.
Simple Explanation
If you’ve pedaled a bike, you’ve felt this: flat ground lets you spin quickly, but a hill slows you down even though you’re putting in just as much effort. An actuator’s motor works the same way—there’s only so much power to split between speed and force, so loading it up means everything slows down. If you know this, you can predict the actual speed you’ll get at any load and avoid surprises.
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Linear Actuator Speed-Force Relationship Diagram
Linear Actuator Speed Force Calculator
This calculator is intended for education, concept evaluation, and preliminary design. Results are based on the equations and assumptions described on this page, but cannot account for every real-world load case, tolerance, material property, environmental condition, installation detail, safety factor, code, or regulatory requirement. Verify all inputs, assumptions, units, and results independently before selecting components or using the result in a real application. Safety-critical, structural, medical, lifting, transportation, or regulated applications must be reviewed by a qualified engineer.
📹 Video Walkthrough — How to Use This Calculator
Linear Actuator Speed vs Force Tradeoff Interactive Calculator
See how actuator speed drops as load increases. The plot and numbers update in real time as you adjust the input sliders for loaded speed, power output, and load ratio. This helps make the actuator’s limits clear before you spec or buy hardware.
LOADED SPEED
30.0 mm/s
POWER OUTPUT
12.0 W
LOAD RATIO
40%
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How to Use This Calculator
- Choose metric or imperial units.
- Enter the actuator’s no-load speed and max force from its datasheet.
- Type in your application’s required load value.
- Hit Calculate to see results.
Mathematical Formulas
Speed-Force Relationship
Use the formula below to calculate loaded actuator speed.
vloaded = v0 × (1 - Fapplied / Fmax)
Mechanical Power Output
Use the formula below to calculate mechanical power output.
Pmechanical = Fapplied × vloaded
Load Ratio
Use the formula below to calculate load ratio.
Load Ratio = (Fapplied / Fmax) × 100%
Where:
- vloaded = Actuator speed under load
- v0 = No-load speed (maximum speed)
- Fapplied = Applied force/load
- Fmax = Maximum force rating of actuator
- Pmechanical = Mechanical power output
Simple Example
No-load speed: 40 mm/s
Max force rating: 500 N
Applied load: 250 N
Load ratio: 250 / 500 = 50%
Loaded speed: 40 × (1 − 0.50) = 20 mm/s
Understanding Linear Actuator Speed-Force Tradeoff
If you’re sizing actuators, the speed-force link is unavoidable. You won’t get maximum speed at maximum load, and vice versa. The calculator above is mainly for seeing how much speed you’ll lose as your load gets heavier, and for checking if an actuator is a good match before you spec hardware.
The Physics Behind Speed-Force Relationship
In most linear actuators—electric, pneumatic, or hydraulic—there’s always a compromise between speed and force. For electric actuators, it traces back to how electric motors work: as you draw more torque (and thus, more linear force), the motor slows down because there’s just so much available power from the drive and internal losses. The lead screw or nut simply converts what happens on the shaft to linear output.
The equation v = v₀(1 − F/F_max) works well for estimating electric actuator performance over most of their useful range. It assumes the actuator operates with more or less constant output power—not always true at the extremes, but it gets you close enough for specification and first-cut selection.
Practical Applications and Real-World Examples
This speed drop-off with load shows up everywhere—from pick-and-place machines to hospital beds. In a packaging machine, heavier products slow down the actuator unless you have headroom in the rating. You can set up the machine so you never fall below your minimum required speed on the heaviest cycle.
In a hospital bed, the actuator must provide controlled motion even as patient weight varies. The calculator helps designers check if their chosen actuator keeps up the minimum speed for the heaviest anticipated load—something you want to know before cutting metal or ordering parts.
Worked Example: Selecting an Actuator for a Lifting Application
Here’s a quick real-world scenario for an adjustable desk:
- Desktop: 150 N (about 15 kg)
- Extra equipment: 300 N (another 30 kg)
- Total: 450 N
- Target speed: at least 10 mm/s even at full load
Try two actuators in the calculator:
Option 1: 25 mm/s no-load speed, 600 N max force
Load: 450 N –> Speed = 25 × (1 − 450/600) = 6.25 mm/s (too slow for the spec).
Option 2: 40 mm/s no-load speed, 800 N max force
Load: 450 N –> Speed = 40 × (1 − 450/800) = 17.5 mm/s (passes target and gives some cushion).
The second actuator keeps the desk moving faster than required, and tolerates some extra friction, wear, or unexpected weight.
Power Considerations and Efficiency
Mechanical output power (P = F × v) doesn’t peak at max force like you might expect—it maxes out at 50% of maximum force, because speed is halved at that point. You get a curved output (“parabolic”) with max output in the middle. If you’re chasing power efficiency, aim for around half the actuator’s force rating, but in practice, other design constraints usually matter more.
If you run much lower force ratios (say, 20%-40%), your speed and responsiveness go up—handy for positioning jobs. If you need brute force, you’ll get less out of the actuator in terms of speed, and the power output drops as you push toward max load.
Design Considerations and Best Practices
This calculator gives a good first look, but don’t forget a few key factors:
Safety Factors and Load Margins
Don’t design so the actuator runs flat out—give yourself a margin. Stick with a 1.5–2.0 safety factor to cover tolerance stack-ups, changing conditions, surprises, etc.
Dynamic vs. Static Loads
The calculation here is static or slow-moving. If you’re accelerating loads (for example, fast starts/stops or impacts), you’ll need to account for that extra force—just use F = ma and add it to the usual load.
Environmental Factors
Performance shifts with temperature, humidity, and contaminants. Motors lose torque when hot. What you calculate here is for average, normal conditions—expect to need adjustment or derating outside those.
Duty Cycle Considerations
Running at high loads for long periods heats up motors and electronics, causing early failure. Short, intermittent cycles let the system cool off and sometimes enable higher peak loads than continuous ratings.
Advanced Considerations for Precision Applications
For high-precision work, even minor things matter. System friction, backlash, and elasticity can throw off the ideal speed-force curve, especially if you have a low-efficiency lead screw (like acme or trapezoidal). Efficiency can be as low as 25% in those cases, but ball screws run 75–90%, so the calculator will be more accurate there. Less efficient screws will lose speed (and power) sooner under load.
Ball screw actuators hold performance closer to the math model, so you can trust the estimate more, unless other system parts are the weak link.
Integration with Control Systems
If your actuator has feedback (like encoders), you need to account for this speed-vs-load drop within your control scheme. The system’s speed won’t stay constant as loads change—controllers must adapt and may need tuning for stability and smooth operation.
For motion profiles needing fixed speed when the load isn’t fixed, it takes careful controller programming, and you may still hit limits. The calculator shows where the uncontrollable drop-off starts so you don’t exceed what’s realistic on your bench or production line.
Use tools like this calculator early, so you catch mismatch between actuator, controller, and application—from selection all the way to tweaking. Just remember that real-life builds in extra loss, friction, and drift from spec, so treat calculator output as a good guide, not a final answer.
Frequently Asked Questions
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About the Author
Robbie Dickson
Chief Engineer & Founder, FIRGELLI Automations
Robbie Dickson brings over two decades of engineering expertise to FIRGELLI Automations. With a distinguished career at Rolls-Royce, BMW, and Ford, he has deep expertise in mechanical systems, actuator technology, and precision engineering.
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