Pulley system for folding bed

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claire-scarlet

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Hi,

I have designed and built a folding double bed for my small bedroom. I currently push it up manually each morning. I would love to design a pulley system to take most of the weight and would appreciate your assistance in seeing if its possible and if so designing it right. Here is some information and sketches.

i have estimated the bed to be about 20 - 30 kg. I can lift it fairly comfortably from a squat position. At present it has foam mattress but i would like to replace with sprung mattress if possible - that will add an extra 15 - 20kg!

my thoughts are:

*the bed needs to be lifted from two pulleys at either end to ensure it is lifted straight.
A design difficulties with this is there is a flat suspended roof (no joists) above bed upright position
- so either fix pulleys to wall (if this could work and be strong enough?)
- set out from wall enough (if there is a joist at the end positions)

* ideally the place where the rope at the point where it attaches to the bed frame could be detached. The weight would need to be supported..

* these pulleys will need to be able to angle as bed comes up but also somehow the rope needs to do a right hand turn.... do I need a seperate device for that?

I then assume I need a third pulley with a double wheel above the weight. The pull up ropes will come in from left and right, and so perhaps this third pulley needs wheels that can operate in different directions?

* the weight then needs to drop down in to a cupboard – I plan to cut an access hole. There is not a lot of space as also hinge for bed in that position. Thus I think the weight needs to be somehow attached to a guide rope so it goes down smoothly through the hole. I am thinking this guide rope would join with the pulley above to make one continuous loop? (meaning I might need a three wheel pulley.

* I am going to look in scrapyards for something to use as the weight , needs to be quite rectangular shape with a hook on it..

many thanks
claire
 
One hell of a problem Claire, I would imagine.....to get a mechanical advantage with a pulley system, each pull would need to be vertical initially and only one pulley wouldn't give any advantage at all. Have you googled 'pulley mechanical advantage' to see what you are up against? Space is quite a concern.
I believe most systems either use springs or hydraulic struts - the latter may be worth investigating.
John :)
 
wont work with heavy weights very well unless they are about 1/3 the weight off the bed once you get to around 45 degrees you will have to hold the bed back as it will now be about half the weight
a way to reduce the effective weight is move the pivot point to around 25% off the bed length this will in effect half the weight as the 25% overhanging will counteract a further 25%
this will off course move the pivot point around 19" from the wall and up from the floor by a simillar amount [think off tower bridge ]
 
Bear in mind that while it it down, the ropes at the ends will simply "get in the way", feet will get caught in them.

May be better to allow more rope out so that while connected at the end away from the hing, they can be clipped back horizontal along the bed for use then unclipped to allow the bed to be pulled up.

For a weight, how about sash window weights?
And consider the height the weight needs to be so that it does not touch the floor until the bed is fully up.

IMO it's not going to do it on its own, but only aid you in lifting it.
 
I doubt if we are going to hear any more about this one, but you know those trailers with the ramp that goes vertical on the back? Impossible to lift by yourself, but a hydraulic strut its dead easy.....that would be my route, I think but I wouldn't know how to calculate the power of the strut needed.
John :)
 
Hello all,

Thanks all for your thoughts and ideas.

On the pulley/weight idea, I was imagining the pulley working as part of a counterweight system and that i would still provide some of the lifting force. There is no worry about the bed falling - its sits safely on a platform once vertical.

From some folks comments, I get impression that if the angle of the rope from pulley to bed means the weight would need to be proportionally greater than if the rope was vertical. ie i lose some of the contribution of the weight.

I can see why many of you have suggested hinges and springs. Seems a less fun but much more practical solution. I will look in to them and see if there is a way to make them work with my bed design. Think i will need to extend the base that the bed sits on when horizonal, in order to attach them.


Claire
 
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