How to choose damper for soft opening of the lid?

[Azzazil]

Hello folks, I need sanity check. I am designing lid and I need to choose damper for soft opening since I have torsional spring which opens the lid when latch for the lid is released.

So from internet one source is referring that is necessary to get toque of lid and torque of spring. So torque of spring for my case is 150 N*mm, while torque to the lid is needed to calculate.
Weight of my lid 0.25kg, and length from pivot point of rotation to center of the gravity of the lid 50 mm.

T(Lid) = 0.25kg * 9.81 m/2^2 * 50 mm = 122 N*mm;

And torque for damper is T(Damper) = T(Torsional spring) - T(Lid) = 28 N*mm convert to N*cm is 2.8 N*cm for easier search of catalogues for dampers.

I am interested is this correct way of defining damper, or I am missing something? Below is sketch, green circle on the left represent torsional spring and dashed rectangle is lid in open position.

Regards,
Azzazil

My CATIA v5 Macro channel:

https://www.youtube.com/@joenitnelav/featured

 

[kjoiner]

I recommend checking with Guden and Ace Controls. The manufacture dampers and have calculators and design assistance for use with various orientations of opening lids. Another option would be Sugatsune. They make various opening mechanisms with dampers for kitchen cabinets etc.

Kyle

 

[LittleInch]

Why just not use a gas strut like they use a lot on cars for hatchs, bonnets (hoods) etc? Does both in one unit.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Azzazil]

Why just not use a gas strut like they use a lot on cars for hatchs, bonnets (hoods) etc? Does both in one unit.

Due packaging reasons, any gas strut is too big for my packaging constraints.

I recommend checking with Guden and Ace Controls. The manufacture dampers and have calculators and design assistance for use with various orientations of opening lids. Another option would be Sugatsune. They make various opening mechanisms with dampers for kitchen cabinets etc.

Kyle

This is not helping me since I need to calculation for rotary damper with gear, and on their web page is only gas strut calulcation not rotary dampers as far as I can see.

Regards,
Azzazil

My CATIA v5 Macro channel:

https://www.youtube.com/@joenitnelav/featured

 

[BrianE22]

So the damper is meant to slow down the lid when the the lid is nearly vertical? You are assuming the torque due to the weight of the lid is constant. It isn't. When the c.g. of the lid is straight up then the torque from the lid equals zero.

 

[Azzazil]

Hello @BrianE22, yes you are correct I want to slow down motion of lid when it moves toward vertical position. In my case torque to open the lid is 122 N*mm, so to move that torque I need spring with torque bigger than torqe to raise the lid in my case that would be 150 N*mm. The ammount of the torque that was left is 28 N*mm, so I assume that I need damper which which will work against this torqe that is left. Using damper with torqe below 28 N*mm will not damp lid in the correct way, while damper with torque bigger than 28 N*mm will make lid hard to open. I don't know is my logic correct since on internet I am hardly finding answer for my question?

Regards,
Azzazil

My CATIA v5 Macro channel:

https://www.youtube.com/@joenitnelav/featured

 

[BrianE22]

So with more torque from the spring than torque from the weight (at closed horizontal position) the lid will accelerate upwards (counter clockwise) when unlatched, correct?

I don't think the damper will make the lid hard to open since it offers zero torque at zero RPM.

 

[Azzazil]

That is true, but I think damper has constant torque isn't it?

Here I found guidelines for damper for soft opening. Link

Regards,
Azzazil

My CATIA v5 Macro channel:

https://www.youtube.com/@joenitnelav/featured

 

[BrianE22]

No, the torque is related to speed. On your link it says:

The torque of the rotary damper varies according to rpm.
In general, if the rpm goes up, the torque increases;
If the rpm goes down, the torque decreases.
In addition, please note that the starting torque slightly differs from the rated torque

 

[LittleInch]

"The amount of the torque that was left is 28 N*mm, so I assume that I need damper which which will work against this torque that is left."

This is why you can't find anything as your statement is only correct when the lid is closed like other people have been telling you and you've been ignoring it.

What it should say is
"The amount of the torque left at 0 degrees (lid closed) is 28 Nmm. The amount of the torque left at 90 degrees (lid open) is 150 Nmm, So I need a damper which changes (increases) torque by a factor of 5 to work against this "excess" torque.

Even with rotary dampers which change with speed, the lid opening angular velocity will increase as the lid lifts up. So the lid will continue to accelerate as the lid opens.

What happens at 90 degrees? Does the lid hit something?

This is what gas struts were invented for.
Or counterweights which reduce torque in the same way as the lid needs less and less torque.
Have you ever looked at how the Tower of London bridge works?


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Brian Malone]

Azzazil have you clicked on the "Get In Contact" link on the Peir rotary damper web page?

https://peirdamper.com/contact-us/

They are indicating six worldwide locations. To get your business they will probably help you size your damper and with their application experience can give you guidance on the possible subtleties related to human interaction and perception of lid motion and start/stop acceleration preferences.

The rotary dampers are quite nice for providing soft/cushioned lid stopping in concealed packaging provided you have space near the pivot of the lid. They do have some risk of being somewhat fragile to overly agressive actuation depending on the size you have space to install. Certainly gas struts and counterweight can do the job but they can be obtrusive, and less than elegant cosmetically. Good luck with your project. Leverage the tech assistance offered by Peir.

 

[MintJulep]

As BrianE22 has already pointed out, the torque caused by gravity acting on the lid is not constant. It's a function of the opening angle. You need to write that equation.

As also pointed out by Brian, the damper torque will be a function of speed. You need that equation.

The torque from your spring is probably also a function of opening angle.

You'll need to work out the angular moment of inertia of the cover relative to the pivot, write the equation for angular acceleration, then integrate that to get velocity.

Solve those four equations simultaneously for velocity and decide if the velocity vs. opening angle profile is ok for your application. Repeat with different combinations of damper and spring until it is.

Going over vertical complicates things, because the damper force will change from slowing things down to speeding them up.

 

[kjoiner]

Talk to the application engineers at the two companies I mentioned. That is why I mentioned them. Good luck.

 

[LittleInch]

The link is very clear, but is not clear how the damper torque varies by a factor of 5....

Acceptable speed range is critical here as well.

If kept very low then even a doubling or tripling of speed would probably be ok and result in enough increase in damper torque to be acceptable.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Azzazil]

This is why you can't find anything as your statement is only correct when the lid is closed like other people have been telling you and you've been ignoring it.

I am not ignoring it I just want to understand how this work so I can find solution.

What happens at 90 degrees? Does the lid hit something?

Yes it hits stopper which prevents lid to go more than 90 degrees.

This is what gas struts were invented for.
Or counterweights which reduce torque in the same way as the lid needs less and less torque.

I know but as I already said I can't use gas struts due packaging constraint.

Azzazil have you clicked on the "Get In Contact" link on the Peir rotary damper web page?

Yes but I think I will find somebody from Europe since I am not stated in Asia, North and South America.

Talk to the application engineers at the two companies I mentioned. That is why I mentioned them. Good luck.

Will try to contact them to check if they will be helpful with their comments.

Solve those four equations simultaneously for velocity and decide if the velocity vs. opening angle profile is ok for your application. Repeat with different combinations of damper and spring until it is.

Going over vertical complicates things, because the damper force will change from slowing things down to speeding them up.

Thanks for pointing out those equation I will try to pull set them and to solve them.
I think going over in vertical position won't be a case since I can probably restrain lid to be stopped at 82°-89°

Regards,
Azzazil

My CATIA v5 Macro channel:

https://www.youtube.com/@joenitnelav/featured