Shouldn’t You Already Know?
When selecting a linear actuator for any project, you should always determine an estimate of the amount of force required from your linear actuator as it is a key aspect in choosing the right one for your project. But the calculations to determine these estimates can be complex and subjected to measurement and rounding errors. While some applications can be straightforward, like pushing an object up and down, it becomes much more complex when you need to factor in other forces, like friction which is difficult to identify as the exact coefficient of friction is challenging to determine and prone to errors. Then there are applications that require changing force angles, like with opening a hatch, which means the force required from your actuator will change through its operation. Even with our Linear Actuator Calculator aiding you in your calculations, if you change the mounting position slightly when you physically build your project, it will change the force required to be delivered by your linear actuator.
Why Would You Want to Know?
There are a few practical reasons you would want to know the exact force being delivered by your linear actuator outside of basic curiosity. Firstly, you may need to know the exact force being delivered to problem solve an issue with your design. This could range from the linear actuator being unable to move your desired load to your linear actuator moving slower than desired. For the latter issue, you can use Speed VS Load performance graphs, like the one below, to see how you would expect the speed of the actuator will change for a given load. As you can see in the graph below, how much the speed of your linear actuator is impacted by the load will vary based on your selected linear actuator.
Secondly, you may want to know the exact force delivered by your linear actuator, if you are concerned with the life of your linear actuator. While a linear actuator is rated for a maximum force to be delivered, the closer you are to the limit will result in a shorter life expectancy for that actuator. This is simply because the higher force required will result in more stress in the components of the actuator. If you measure the force being delivered by your actuator and it is close to the load rating of the actuator, you may consider upgrading to a higher force rated actuator for improved life expectancy.
Finally, you may want to know the exact force delivered by your linear actuator, if your system runs off battery power. This is because the higher the force being delivered by a linear actuator, the more power it will draw, and which will drain the battery faster. As seen in the Current VS Load performance graph in the section below, using a higher force actuator will result in a reduction in current draw for a given load. You may also consider changing from a 12V actuator to a 24V actuator as the current draw will be lower for a given load in 24V actuator compared to a 12V actuator.
How Do You Measure the Exact Force Delivered?
To measure the force being delivered by a linear actuator, we can measure the current draw of the linear actuator while it is moving. As the power consumed by the actuator is related to the force being delivered by the actuator and that the voltage will remain consistent, either 12 or 24V, the current draw will increase linearly with an increase in force. This can be seen in the Current VS Load performance graph below. Once the current draw is measured, you can use the Current VS Load performance graph to estimate the force being delivered by your linear actuator. This isn’t a perfect solution and can still be subjected to errors, but it is a good solution to estimate the force being delivered that you can compare to your design calculations. It is also a simple enough solution where you will not be required to drastically change your design to be able to estimate the force being delivered.
In applications where you are moving an object in one axis, i.e. no changing angles, the current value should be somewhat stable, once moving, as the force should be constant in those applications. In hatch-like applications, i.e. with changing angles, the current values will change as the force is not constant. In these applications, you will need to track the current value throughout the operation of the linear actuator to determine where the highest force value occurs. There will also be a spike of current when the actuator starts moving, this is because the static coefficient of friction is larger than the dynamic coefficient of friction for the same materials.
How Do You Measure Current Draw?
To measure the current draw of your linear actuator, there are a few methods you can choose from. The most basic solution is to use a multimeter, setup to read Ampere, in series with one of the leads of the linear actuator, then track the current draw as the actuator moves. As the actuator moves the current draw will be displayed on the multimeter for you to track. Another option is to use a current sensor which, like with the multimeter, will be connected in series with one of the leads of the linear actuator. Unlike the multimeter, the current sensor will not have a display that you can simply read, you will need to measure the analog voltage output of the sensor, which increases with higher current values, to measure the current. You will most likely need to make use of a microcontroller to read this analog value and convert it into an actual current reading using the sensor’s sensitivity value. While there is additional setup with using a current sensor, it does have the advantage that the microcontroller can constantly measure and save the current draw reading much faster than a human can.
