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I want to know what's the mechanism to maintain this shelf stable even when they tilt the wall-bed:

https://player.vimeo.com/video/400690985

I would like to build something similar myself (not for a bed though).

I researched about gimbal + shelves but I didn't have luck.

Can someone point me in the right direction? Does this mechanism have a name? What are the physics laws that make it possible?

Note: GIF is from the video of the Oslo Bed from resourcefurniture.com

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  • there is probably a set of toothed pulleys and a toothed belt between the bed pivot and the shelf pivot
    – jsotola
    Apr 18, 2020 at 0:39
  • @jsotola - Or a bar that moves inside the frame. Far simpler than pulleys.
    – Hot Licks
    Apr 18, 2020 at 1:11
  • @HotLicks, a bar also possible ... pretty close to the same complexity as two pulleys and a belt though
    – jsotola
    Apr 18, 2020 at 1:15
  • @jsotola - Someone in his garage with a drill press and a hacksaw could do the lever version, while the pulley thing would be much more complicated.
    – Hot Licks
    Apr 18, 2020 at 1:20

3 Answers 3

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The general term for a hinge that allows something to move but keep the same orientation is a "pantograph hinge". The general term for that type of bed would be a "Murphy bed".

The pantograph mechanism takes many forms, but the trick it uses is to have parallel connecting rods that pivot together so that the door or shelf that it is connected to can swing out, but maintain it's orientation because the pivot points remain parallel.

I know that is a bit abstract, but that will give you a starting point to research the topic more. This is not a "standard" piece of hardware that you can pick up at the hardware store, so there't not a specific product I can link to. I'm sure the design for that bed is custom.

Pantograph

Here you can see the basic concept with two parallel arms that allow the black leg to swivel downward while maintaining its vertical orientation. If this was the "leg" on the bed that held a shelf, you could imagine another red bar connected to the head of the bed to actuate the leg movement as the bed is swiveled down.

The bars of the system can also be replaced by cables and a pulley system which is what could make it so compact and hidden in that Oslo bed. I suppose they could even use a gear driven system with cables and pulleys. Either way, it's custom designed and built just for that purpose.

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    If you look closely at the hinge in the clip, you can see there is only one connecting rod on each side of the shelf, not two. In this particular case, they're just using the gravity method shown in DMoore's answer.
    – PhilippNagel
    Apr 17, 2020 at 16:55
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    @PhilippNagel, just because there is only one visible pivot on the outside doesn't mean there isn't something more involved going on inside. I updated the answer to talk about cables and pulleys which could be more easily hidden inside the thin bedframe. I assure you there is a huge design difference between cheap kids furniture and a bed like that Oslo.
    – JPhi1618
    Apr 17, 2020 at 16:58
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    It isn't exactly like this, the mechanism is hidden inside the bed. But it isn't gravity. 1) Zero wobble. 2) The center of gravity is not below the pivot point!
    – Mattman944
    Apr 17, 2020 at 17:11
  • @Mattman944, right, this was meant as a DIY friendly stepping off point into the concept. I've seen murphy beds that do use this for leg deployment, but they were more basic than the one in the question.
    – JPhi1618
    Apr 17, 2020 at 17:13
  • That doesn't seem to match what the bed does. If you image your diagram om the left rotated clockwise 90 degree (bed down position), then shelf would be vertical not horizontal, so everything would fall off.
    – Tom Carpenter
    Apr 18, 2020 at 12:01
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The mechanism -

GRAVITY

What keeps it stable -

High quality materials and balanced weighting in the design.

What is it?

It is a high quality metal shelf with an extended arm on each side of the back.

Why does it look cool?

Because the arm rotation is solid yet flowing and they hid the joint inside of the side of the bed. If it stuck out it would still be cool yet clunky.

What's the secret sauce?

Other than creating a joint that doesn't just drop the shelf - some resistance - the secret sauce is actually the shelf sitting flush on the bed in standing position. So the arm of the shelf has to be offset back to counter the distance between the joint and the bottom of the bed. (I am sure there is an easier way to say that)

Below is a more simple example that shows that this is really about creating the arms as part of the shelf than any hinge magic.

enter image description here

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    This is the "cheap and simple" way to do it, but if you watch the video promo for that Oslo bed, the shelf is mechanically connected to the rotation of the bed. The woman has to pull a release handle built into the shelf and the bed begins to move rather than the shelf flopping around.
    – JPhi1618
    Apr 17, 2020 at 16:53
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    @JPhi1618 - I disagree. He is being careful while lowering. They probably have a nice high quality screw/nut with a rather spongy gasket that limits the rotational speed. You could play with screw/nut and gasket to get many different speeds and limits.
    – DMoore
    Apr 17, 2020 at 16:55
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    Even the most basic fold out sofa bed uses a mechanism to fold out the bottom leg. This high design, expensive bed certainly uses something to positively lower the shelf/leg. This is a good answer and points out an easy way to do it - I'm just saying there are multiple ways to make it happen.
    – JPhi1618
    Apr 17, 2020 at 17:08
  • The simple bed in your answer shows an example of a shelf that would not stay horizontal if the hinge pins were basically free turning and depending upon gravity. The only way that a gravity hung shelf would stay horizontal would be of the hinge point was directly above the long center line of the shelf.
    – Michael Karas ♦
    Oct 11, 2022 at 0:09
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The shelf has a gearing system within the bed frame. You can see this very distinctly in this part of one of the pictures at the bed web site linked in the question.

enter image description here

(Picture Source)

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