Trying to determine linear actuator force needed

[bphillips921]

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)

Side View (retracted)

Side view (Extended)

 

[Lnewqban]

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.

 

[bphillips921]

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.

 

[bphillips921]

Would I be able to get the orange piece near vertical and limit sag by redesigning it like this?

 

[Lnewqban]

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?

 

[bphillips921]

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)

Here is a simplified mock-up in both the retracted and extended positions.

 

[Lnewqban]

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?

 

[bphillips921]

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.

 

[Lnewqban]

Excellent!
Now, approximate dimensions of projector and actuator?

 

[bphillips921]

Projector
17.7"W x 20.5"L x 6.7"H
24.5 pounds
https://www.amazon.com/gp/product/B07GYP68HW/?tag=pfamazon01-20

Here are the actuator specs.
https://www.amazon.com/dp/B07W8N8X22/?tag=pfamazon01-20

 

[erobz]

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.

 

[berkeman]

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.

 

[berkeman]

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?

 

[bphillips921]

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.

 

[Tom.G]

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?

 

[erobz]

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.

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)

 

[bphillips921]

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!

 

[erobz]

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.

 

[Tom.G]

Maybe a Scissor Lift approach with the projector nested between the scissor mechanism.

https://cdn-jlg.scdn5.secure.raxcdn...x547.png?rev=cc56511f258a4fb1889d41bd09de945b

 

[Lnewqban]

It's always fun to play around, but there is probably a reason why they usually sit there statically or ascend\descend vertically.

 

[Lnewqban]

This actuator can live an easier life: