Selecting the right gas spring 2

[concepts206]

I'm building a fold-down bed off a wall using door hinges attached to the bed frame and the wall, using gas springs to decrease the weight of the bed when lowering. The base of the gas bring is attached to the wall 6" below the hinge axis and the top of the gas spring is attached to the bed frame 20" above the hinge axis. The stroke of the gas spring will compress about 10" when the bed frame is lowered to the bottom position. The weight of the bed frame with the mattress is 160lbs. I've tried two gas springs with 100 lb pressure and it help very much. My question is would two gas springs with 200 lb pressure be adequate?Or should I go much higher?

 

[desertfox]

Hi concepts206

Its a question of moments about the bed frame, you need the centre of gravity of the bed mass relative to the hinge point and as the bed lowers the moment of the bed increases,
this needs to be offset by the gas springs whose line of action will change during bed lowering and hence a change in the supporting moment provided by the gas springs.
I would draw free body diagrams of the bed and gas springs at various angles of the bed lowering and workout how much counter balancing the gas springs gave.
I cannot answer your question directly as I don't have all the information which is why I have outlined the above procedure.
If you have already tried to springs which worked okay why not stick with those.

regards

desertfox

 

[mechengdude]

desertfox is correct, the first thing you need is a free body diagram. Knowing the CG of the bed, its diminsions and the open and closed lengths of teh gas springs you are almost ready to calculate the forces. The remaining item is the angles which will be based on where you choose to mount the springs. In the past I have set up an excel spread sheet which is handy. It makes it easy to see how changing the mounting position impacts the springs behavior. Note pressure in the gas spring is not important. Force required to close the gas spring is.