Trying to determine linear actuator force needed

In summary: FYI, you can quote a part of a post that you want to respond to here at PF by click-dragging your mouse over the text that you want to quote, and then click "Reply" in the pop-up menu. That results in much cleaner quotes and replies....In summary, the geometry of your design will not achieve a horizontal position for the orange frame, it will sag on its own weight. You may not need to resort to expensive machined parts, a bolt into its nut makes a good pivot point for this application.
  • #1
bphillips921
8
1
I'm designing a pivot lift system to lift my movie projector up when not in use. I've designed the parts and begun 3D printing, but am concerned that the 3D print won't be strong enough, so I may bite the bullet and have the parts CNC machined. If I do that I want to be certain that I have the correct linear actuator since changing that could change the parts. I can't figure out how to calculate the force the linear actuator needs to lift my 11.5KG projector from a dropped position rotated 90 degrees up to the ceiling. My CAD design is below with the dimensions and the weight of the projector. I bought a 750N (160lbs) 100mm stroke linear actuator, will this be enough? Any guidance would be appreciated!

Bottom View (retracted)
top.jpg


Side View (retracted)
side.jpg


Side view (Extended)
extended.jpg
 
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  • #2
Welcome, @bphillips921 !

That geometry will not achieve a horizontal position for the orange frame, it will sag on its own weight.

As you can see in this animation, the actuator is not subjected to excessive force along its stroke.
Yours is fighting a huge force at the end when the screen is up.

You may not need to resort to expensive machined parts, a bolt into its nut makes a good pivot point for this application.

Undercarriage_anim.gif
 
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  • #3
Lnewqban said:
Welcome, @bphillips921 !

That geometry will not achieve a horizontal position for the orange frame, it will sag on its own weight.

As you can see in this animation, the actuator is not subjected to excessive force along its stroke.
Yours is fighting a huge force at the end when the screen is up.

You may not need to resort to expensive machined parts, a bolt into its nut makes a good pivot point for this application.

View attachment 319266
Thanks for the help! I figured the forces to get the orange piece near vertical would be huge. I like the design of what you posted much better, my issue is clearances. If I just mounted the projector fixed to the ceiling it would be about 12 inches below the ceiling. In order for it to make sense to have a lift on it I need the projector to be tight to the ceiling when lifted. On your example, I'd need to mount my projector on a pivot at the end of the arm and 180 degrees of where the oval is on the example. By the time I made room for the actuator and lever above it I wouldn't be gaining much. I'll have to think this through better.
 
  • #4
Would I be able to get the orange piece near vertical and limit sag by redesigning it like this?
side view2.jpg
 
  • #5
The vertical position does not present a problem, the horizontal (Side View (retracted)) does.
Sorry, I can’t understand the layout that you describe in post #3.
Could you post a simple hand drawing showing the whole planned movement of the projector and the surrounding space available?
 
  • #6
Here is a picture of the space with a mock up of the two projector positions. The movie screen will drop down from the ceiling in front of that black fireplace. The projector will mount just behind that 2nd beam (closest beam in the picture)

20221223_113221.jpg


Here is a simplified mock-up in both the retracted and extended positions.
20221223_113229.jpg
 
  • #7
So, the projector will not be concealed, only elevated to a position underneath the ceiling.
Will it remain horizontal for all positions of the arm?
Is there accessible room above that hard ceiling?
 
  • #8
So, the projector will not be concealed, only elevated to a position underneath the ceiling. - Correct.
Will it remain horizontal for all positions of the arm? - Correct. The projector will pivot at the end of the arm and will stay horizontal
Is there accessible room above that hard ceiling? - No, this is a basement with a finished floor above. The rafters above the ceiling drywall have been spray foamed. 2X6 boards are also behind the drywall where the projector will mount in order to provide a secure mounting surface.
 
  • #9
Excellent!
Now, approximate dimensions of projector and actuator?
 
  • #11
bphillips921 said:
Would I be able to get the orange piece near vertical and limit sag by redesigning it like this?
View attachment 319285
You don't want the actuator pushing (or pulling horizontally), I think it would probably tend to bind. What you've done here is an improvement, but maybe you haven't gone far enough.
 
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  • #12
bphillips921 said:
So, the projector will not be concealed, only elevated to a position underneath the ceiling. - Correct.
FYI, you can quote a part of a post that you want to respond to here at PF by click-dragging your mouse over the text that you want to quote, and then click "Reply" in the pop-up menu. That results in much cleaner quotes and replies. :smile:
 
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  • #13
bphillips921 said:
Here is a picture of the space with a mock up of the two projector positions.
I haven't read the whole thread, but is there a reason you are using a complicated mechanism instead of just dropping the projector platform straight vertically?
 
  • #14
berkeman said:
I haven't read the whole thread, but is there a reason you are using a complicated mechanism instead of just dropping the projector platform straight vertically?
I don't think I have the space to drop it vertically. I want the projector tight to the ceiling when raised but I don't have any room above the drywall for any mechanics that I'd need to raise it vertically. At least from what I can think of to raise it.
 
  • #15
bphillips921 said:
I don't have any room above the drywall for any mechanics that I'd need to raise it vertically. At least from what I can think of to raise it.
A rope?
 
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  • #16
bphillips921 said:
I don't think I have the space to drop it vertically. I want the projector tight to the ceiling when raised but I don't have any room above the drywall for any mechanics that I'd need to raise it vertically. At least from what I can think of to raise it.
1671852944985.png


Generally, here is the issue you could run into. The vertical component of the retraction force ( dotted purple arrow) has to at least be the weight ##W## of the projector in this position. That implies ##F## must be much larger than the weight ( from the geometry currently shown). ##F## might be in excess of ##5W##!

So, while you think that you have ample load bearing capacity, you are actually going to be cutting it much closer than that. Furthermore, that large force is going to be transmitted to the supporting structure (a.k.a. your upstairs floor joist)
 
  • #17
erobz said:
View attachment 319316

Generally, here is the issue you could run into. The vertical component of the retraction force ( dotted purple arrow) has to at least be the weight ##W## of the projector in this position. That implies ##F## must be much larger than the weight ( from the geometry currently shown). ##F## might be in excess of ##5W##!

So, while you think that you have ample load bearing capacity, you are actually going to be cutting it much closer than that. Furthermore, that large force is going to be transmitted to the supporting structure (a.k.a. your upstairs floor joist)
That's what I was worried about. I'm starting to think this isn't worth it for the small amount of lift I'd get out of the projector. Although it's still fun to tinker!
 
  • #18
bphillips921 said:
That's what I was worried about. I'm starting to think this isn't worth it for the small amount of lift I'd get out of the projector. Although it's still fun to tinker!
It's always fun to play around, but there is probably a reason why they usually sit there statically or ascend\descend vertically.
 
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  • #20
erobz said:
It's always fun to play around, but there is probably a reason why they usually sit there statically or ascend\descend vertically.


 
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  • #21
This actuator can live an easier life:

 

1. What is a linear actuator?

A linear actuator is a device that converts rotational motion into linear motion, allowing for precise control and movement in a straight line. It typically consists of a motor, a screw or rod, and a nut or gear mechanism.

2. How do I determine the force needed for a linear actuator?

The force needed for a linear actuator can be calculated using the formula F = ma, where F is the force, m is the mass being moved, and a is the acceleration required. You will also need to consider factors such as friction and the weight of the actuator itself.

3. What are the units of measurement for linear actuator force?

The most common unit of measurement for linear actuator force is Newtons (N), which is a unit of force in the International System of Units (SI). Other units that may be used include pounds (lbs) or kilogram-force (kgf).

4. How does the speed of a linear actuator affect the force needed?

The speed of a linear actuator can affect the force needed in two ways. First, a faster speed may require a higher force to overcome inertia and accelerate the load. Second, if the actuator is moving at a constant speed, a higher force may be needed to overcome friction and maintain the desired speed.

5. Are there any other factors to consider when determining the force needed for a linear actuator?

Yes, in addition to the mass, speed, and friction, there are other factors that may affect the force needed for a linear actuator. These include the angle of the actuator, the type of load being moved, and any external forces acting on the load. It is important to carefully consider all of these factors when determining the appropriate force for your specific application.

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