by Grummy » Sat Oct 12, 2019 11:25 am
I think many of what I have seen are a little complicated, often with ugly mechanical things where you really do not want them (guide rails, pressurized shocks, etc.)
I did one in an old bus/coach many years ago where I just used a shaft with bearings across the back.. just behind the back edge of the bed frame when the bed was up.
Just think of a roll up door shaft on any ramp door trailer.. It is what I actually did use... parts from a garage door, the hollow shaft and end bearings.
I attached THREE lengths of nylon webbing to it via metal strap and rivets, one on each end, and one in the middle. For that one I did use "Seat Belt" webbing because it was thinner yet dense, and being thin, kept the diameter as small as possible when rolled up.
The outside two pieces of webbing were directed forward, went through to two, one on each side simple pulley blocks I made (just wide enough flat roller units attached to a beam in the ceiling), then down, close to the walls to the front corners of the bed. The center webbing went more or less straight down to the center of the rear of the bed frame. The shaft itself was located behind the bed when fully raised, and far enough back for the rolled up webbing to clear the bed frame when rolled up.
When one wound the shaft (I used a gearmotor), the webbing wound itself onto the shaft, pulling the bed up evenly to the ceiling. When lowered, the front straps would not cause any access to bed issues as they were near the wall, and in this case, the one rear strap down the back did not matter.
The things to keep in mind with this concept:
1. The shaft must be located behind the bed when raised,
2. The wound diameter of the webbing on the shaft must be no larger in diameter than the thickness of the bed unless you do not mind if it is there.
3. I used wider webbing so when it wound up on the shaft, it stays 100% on top of itself. Otherwise some discs or large washers might be required.
4. The webbing/strap used only needs to meet weight specs that are enough to lift an empty bed.
5. The bed will need to REST on rigid rails or cabinet edges when lowered, NOT rely on the webbing to hold occupants weight.
6. You may need to incorporate adjustment facilities on the BED END of the straps to adjust for the bed pulling up tight and parallel to the ceiling.
7. Once up, a mechanical latch method is probably a good idea. When down, gravity should suffice as long as that is still turned on :-)
This concept is smooth, quiet, can be manually or electrically powered, concealed with upholstered cabinetry, minimal in weight and hardware, and not requiring any rails or mechanical garbage on the side walls. It also doesn't leave you with dirty/gnarly steel exposed cables whereas webbing is available in almost any color decor you need to match. I did this many, many years ago, and I have seen the same quiet lovely concept used in modern multi-million dollar coaches in more recent years.
