# Help me calculate Force to choose an air cylinder

• VanillaFace
In summary, the door would require a force of 153lb to open, and the attachment points need to be sturdy in order to handle the force.
VanillaFace
Hello, this isn't actually homework but I have no physics/engineering background and can't solve this question for a DIY project:

1. Homework Statement

I have a 2' tall, 16' wide door that is hinged/hung from the top (like an awning window scenario) so all of its weight is supported. The weight of this door is ~230lbs. The door will be hanging vertically (hinges at top) in its resting/closed position. I want to use (2) pneumatic air cylinders to push the bottom of this door, to swing it 90º up into an "open" position, similar to an awning window.

I can calculate the air cylinder size/stroke/etc on my own, but how much Force would be required by the (2) air cylinders? I also don't know if the angle and pivoting motion plays a part in this (cylinders will have rotating clevis mounts).

## The Attempt at a Solution

My assumption is the air cylinders would need to exert the same >230lbs of force to pivot/open this door. External force would be gravity... so 230/2 = 115lbs force per cylinder?

Hello VF,
VanillaFace said:
I can calculate the air cylinder size/stroke/etc on my own
Means you can come up with a sketch of the side view ? Your max force depends on where the cylinders are attached to the door and to the building. And a bit on how fast you want it to open, too.

I am guessing at the mounting points, it's possible those would slightly change in the field... but I was trying to replicate those large aviation/agricultural fixed doors that open with hydraulic rams.

Image host site isn't working... https://ibb.co/e8Uhj6

VanillaFace said:
The design does not look good to me. The attachment at the stationary end is too high up. You want it much lower, but you may be limited by the max extension of the piston (which is?).
Also, note that you have shown that attachment point quite differently in the two diagrams. Where would it be horizontally?

Ok, clear enough. Here's what I make of the calculation:

The weight of the door is 230 Lb and it acts at the center of mass, 12" from hinge H. Torque wrt hinge H is 230 Lbf ##\times ## 12".
The door is at equilibrium (does not rotate) if that torque is offset by the torque from the upward force at 18" , ##F_y \times ## 18".
So that ## F_y = {\displaystyle {12\over 18 } } ## 230 Lbf ##\approx## 153 Lbf.

This 153 Lbf is the vertical componenet of ##F_{\rm tot}##. Ratio of vertical component to total is as 5" to 19" , so ##F_{\rm tot}\approx ## 580 Lbf.

A lot more than the 230 Lbf you guessed.
You'll also need a sturdy attachment of the hinge: the door is pulling at it with a lot of force (18/5*153 ##\approx## 550 Lbf)

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Let
• the joint of piston and door be H from the hinge,
• the min piston length be A, max B
• other piston joint be X horizontal from the hinge and Y below it
• depth of door be 2L, weight W
The max force is ##F=\frac{LWB}{HY}##, so we wish to maximise HY.
At max extension, ##B^2=(H+X)^2+Y^2##.
At min extension, ##A^2=(H-Y)^2+X^2##.
From the above two equations we can obtain an equation relating Y and H. In principle, this allows us to find the minimum F.

This makes a lot of sense, thank you guys very much. The design has no rhyme or reason, I was trying to follow rough ratios from similar doors I’ve seen. Example

I’ll look into how long the cylinders get when the rod stroke is increased, but I am also limited on mounting points. I realize I moved the pivot point on the horizontal plane in the drawing, but really all I have to work with is the vertical plane. Will use these formulas to try to come up with the most efficient plan. I am just limited on space and the physical size of the air cylinders

Thank you again so far!

## 1. How do I calculate the force of an air cylinder?

To calculate the force of an air cylinder, you will need to know the air pressure and the area of the cylinder. The formula for force is Force = Pressure x Area. So, you can multiply the pressure by the area to get the force in units of Newtons (N).

## 2. What is the importance of knowing the force of an air cylinder?

The force of an air cylinder is important because it determines the amount of weight or load that the cylinder can lift or move. Knowing the force can help you select the right size and type of air cylinder for your specific application.

## 3. How do I choose the right air cylinder for my application?

To choose the right air cylinder, you will need to consider the force required for your application, the air pressure available, and the size and weight of the load. You should also consider the type of motion needed, such as linear or rotary, and the speed and precision required.

## 4. Can I use the same air cylinder for different applications?

It is possible to use the same air cylinder for different applications, but it is important to carefully consider the requirements of each application. If the force, pressure, or other factors differ significantly, it may be necessary to use a different size or type of air cylinder.

## 5. Are there any safety considerations when using an air cylinder?

Yes, there are several safety considerations when using an air cylinder. It is important to properly secure the cylinder to prevent it from moving or falling during operation. You should also follow recommended maintenance and inspection procedures to ensure the cylinder is functioning correctly. It is also important to use proper safety equipment and procedures when working with air cylinders to prevent injury.

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