If you’ve ever looked at a datasheet and wondered why an actuator can’t be both the fastest and the strongest in the lineup, it comes down to a fundamental trade-off. Think of it like a seesaw: when force goes up, speed almost always goes down.
This isn't a design flaw; it’s just physics. Every motor has a finite amount of power; the rate at which it can do work. Because that power is limited, speed and force are always a trade-off. To get more pushing force out of the system, you have to sacrifice the distance it travels per second.
What Actually Drives the Trade-Off?
Most of our actuators, such as the L12 series, use a small DC motor. On its own, that motor spins at thousands of RPMs but has very little torque. If you hooked it directly to a lead screw, it might move incredibly fast, but it wouldn't have enough strength to push much more than a piece of paper.
To fix this, we use a gearbox. A gearbox acts as a force multiplier. By using a high gear ratio, like the 210:1 option on the L12, we trade high-speed motor rotation for a massive 80N of lifting force. This is why you’ll see the same actuator model offered in several different configurations. It’s the same motor and chassis, just with different internal gears swapped in to shift where that specific model sits on the speed-vs-force scale.
Key Concept: Lead screw pitch also plays a role in this conversion; most standardized actuator lines use a fixed pitch optimized for the frame. That makes the gearbox the primary lever used to tune an actuator for your specific needs.
The Precision Advantage: Stepper Motors
Not every actuator follows the same mechanical blueprint. Our stepper-based designs, like the S20 or P8-ST, offer a different approach to motion.
In many linear actuators, the relationship between the motor and the lead screw is defined by the gearbox. Stepper motors are capable of providing a useful amount of torque without necessarily requiring a gearbox stage, which allows for compact and highly responsive designs. While they don't always need a gearbox to be effective, they can still be paired with one—as seen in the P8-ST—to reach even higher force levels at the expense of speed.
The primary advantage of this technology is precision. Stepper motors move in discrete steps, making them far more accurate for applications requiring fine positioning or repeatable increments. This makes them the go-to choice for high-accuracy tasks where exact control is more critical than raw speed.
Why Your Actuator Slows Down Under Load
It’s a common question: "My actuator is rated for 25mm/s, so why is it only moving at 14mm/s?"
The answer is almost always the weight you're asking it to move.
Manufacturers typically list "Max Speed (no load)" as the speed the rod travels when there is zero resistance. As soon as you add weight, the motor draws more current to overcome that resistance. This extra work naturally slows the motor down.
Looking at the graph, you can see this clearly: the 50:1 gear ratio starts at 25mm/s with no load but drops significantly as force increases.
The "Lab vs. Reality" Gap
A datasheet is a map, but it isn’t the terrain.
When we test actuators in our lab, we do it under "perfect" conditions. But your project probably isn’t living in a climate-controlled room. In the real world, several hidden variables can act like a "brake" on your actuator’s performance:
Ambient Temperature: The L12 is rated for -10°C to +50°C. At the colder end of that range, internal lubricants thicken, forcing the motor to work harder.
Voltage: If your power supply isn't steady or the battery is draining, performance will suffer. Even a minor "sag" in voltage under load will cause an immediate and noticeable drop in speed.
Side Loading: Friction caused by improper mounting or other side loading will cause internal drag. The L12 side-load limit drops from 50N to as low as 15N depending on the stroke length.
Duty Cycle: Exceeding an actuator’s max rated duty cycle leads to heat buildup that can degrade performance over time.
The Golden Rule: The math gets you in the ballpark, but a physical test is the only way to be 100% sure that a particular component is appropriate for your application. Before committing to a final design, build a prototype and test it in the actual environment it will be operating in.
A Practical Checklist for Your Next Design
- When you're spec-ing out an actuator, don't just pick the one with the highest speed and hope for the best.
- Identify your "working load": This is the weight the actuator will be moving 90% of the time.
- Consult the performance graphs: Check the speed at your specific force, rather than relying on the no-load speed.
- Add a safety margin: Aim for an actuator that can handle about 20–25% more force than you actually need.
Frequently Asked Questions
Does increasing voltage make my actuator faster?
Generally, yes. Increasing voltage increases motor RPM, but it also increases heat. You must stay within the max input voltage (e.g., 7.5V for 6V models) to avoid damage.
Can I change the speed of an actuator after I buy it?
For DC actuators, you can use a Pulse Width Modulation (PWM) controller to slow it down, but you cannot make it go faster than its rated speed at a given load. The easiest way to achieve a lower speed would be to use a P-Series actuator with an LAC board. The speed can be dialed down using the speed control pot on the board.
Why is my actuator louder when it's moving a heavy load?
As the load increases, the motor and gears are under higher stress, increasing vibration.
Moving From Theory to Application
At the end of the day, understanding the relationship between speed and force is key to setting your project up for long-term success. While it’s tempting to simply pick the fastest actuator on the list, the most reliable designs are those that respect the mechanical limits of the motor and the realities of the operating environment. By accounting for your actual working load and leaving a healthy margin for variables like voltage drops or temperature changes, you ensure that your actuator won't just work on day one, but will continue to perform for years.
If you need assistance selecting a product that meets your application requirements, please contact our sales team for assistance. Actuonix can create custom designs for all OEMs.
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