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Old 09-27-2021, 10:03 PM
CactusBob CactusBob is offline
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Default Pulley Problem.

Awhile back you guys helped me with a hanging bed I made for my daughter which came out great and she really likes it. This time is for a bed that can raise and lower.
I am looking at getting a cargo trailer to turn into a camper and to maximize the space I want to be able to raise the bed during the daytime. In the picture if it loads correctly, the dark grey frame is unistrut bolted to the frame of the trailer, the light grey is the bed frame that is supposed to go up and down. There will be trolleys bolted to the ends that ride inside the unistrut and the red is the cables to raise and lower.
At the top left is the attach points where the cable will be secured, and the bottom right will be a hand crank that goes the whole length which both cables will spool onto and off of.
There will be pins for this to rest on in both the up and down position so the cables will not be stressed.
I forgot to put them in the drawing but under the bed frame will be pulleys for the cable to ride on.

So, after countless hours trying to find decent info I think I have a slight understanding of MA and change of direction,

Here's my questions...

What is the MA of this? I think this will have an MA of 2 (or would it be 4 since there is 2 separate cables)

Is there an easy way to increase the MA

Will this rise evenly or will the left side rise faster since its closer to the crank

Thanks for any help in advance
Bob
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  #2  
Old 09-27-2021, 10:17 PM
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milomilo milomilo is offline
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It will rise level, provided the tag ends wind around the same drum diameter.
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  #3  
Old 09-27-2021, 10:34 PM
CactusBob CactusBob is offline
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Quote:
Originally Posted by milomilo View Post
It will rise level, provided the tag ends wind around the same drum diameter.
they will both be on the same shaft so that is one issue down. Do you know if this would have any Mechanical Advantage or how I could get that to make the lift easier. the height it needs to raiseis about 4 to 5 feet

Thanks,
Bob
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Old 09-28-2021, 01:20 AM
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Gadgeteer Gadgeteer is offline
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You just need more pulleys, and longer cable to increase MA. Think snatch block.

Last edited by Gadgeteer; 09-28-2021 at 01:42 AM.
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Old 09-28-2021, 06:23 AM
Samcord Samcord is offline
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Reminds me of a 4 post car lift. They use 4 cables. You can get ma from the winder. The ratio of the crank handle to the spool diameter. Or adapt a geared winch winder like on a boat trailer.
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Old 09-28-2021, 06:29 AM
Samcord Samcord is offline
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Here is another idea - Murphy bed, except you might need to hinge on the long side.
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Old 09-28-2021, 09:34 PM
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arizonian arizonian is offline
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Your cables-to-frame have a mechanical advantage of 2. Multiply that by the handle divided by the drum diameter. Example: Both the vertical pull cables need to completely wind up (say, 5 ft each) to raise the bed 5 ft. 5 ft cable times 2 equals 10 ft cable. 10 ft cable to raise bed 5 ft is a MA of 2.

Your going to wind up a whole lot of cable the way it's rigged now. It looks like you will need a long drum to take up all the cable. How will you keep both drums synchronized without going across the walkway? Underneath the trailer?

Good Luck, I'm in Tucson if you need a second set of eyes.

On edit, the MA stays at 2, but the total load that is being lifted is halved by using two cables, one set of cables lifting one end of the load, the other cable lifting the other end. You will wind up 20 ft of cable in the same motion as winding one separate cable.
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Last edited by arizonian; 09-28-2021 at 09:43 PM.
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Old 09-29-2021, 07:13 PM
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Whitetrash Whitetrash is offline
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What if you used a garage door torsion spring with just enough tension to raise the bed if you lifted up on it a little and a set of lock pins to keep it from banging around during travel.
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Old 09-29-2021, 09:55 PM
CactusBob CactusBob is offline
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Quote:
Originally Posted by arizonian View Post
...How will you keep both drums synchronized without going across the walkway? Underneath the trailer? .
Lol, the best idea I have found for this was actually on a dump truck. The roller for the tarp that goes over the load can extend to over 8 feet and has mounting points on each end. The other option was two winches for a flat bed and connecting them with a rod or pipe. right now Im thinking of putting that to one side or underneath directly in the center of the bed

I did think of the torsion spring but I don't want that much spring energy at head level if its under the bed or over my head if I'm sleeping.

The murphy bed idea was nixed from the start, SWMBO doesn't want to have me crawling over her during the night if nature calls or vice versa. So I need a way to exit each side of the bed. If I put a murphy bed lengthwise I would need at a very minimum of 7' clearance and that raises the trailer cost significantly. An elevator bed seemed to be the best option.
If I can get the MA to 4 or better yet 8 the wife should be able to raise and lower it as well

Thanks you guys for the help
Bob
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  #10  
Old 09-30-2021, 03:51 PM
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Quote:
Originally Posted by CactusBob View Post
Lol, the best idea I have found for this was actually on a dump truck. The roller for the tarp that goes over the load can extend to over 8 feet and has mounting points on each end. The other option was two winches for a flat bed and connecting them with a rod or pipe. right now Im thinking of putting that to one side or underneath directly in the center of the bed

I did think of the torsion spring but I don't want that much spring energy at head level if its under the bed or over my head if I'm sleeping.

The murphy bed idea was nixed from the start, SWMBO doesn't want to have me crawling over her during the night if nature calls or vice versa. So I need a way to exit each side of the bed. If I put a murphy bed lengthwise I would need at a very minimum of 7' clearance and that raises the trailer cost significantly. An elevator bed seemed to be the best option.
If I can get the MA to 4 or better yet 8 the wife should be able to raise and lower it as well

Thanks you guys for the help
Bob
The handle that you use in relation to the drum diameter will determine your final MA. Say, a 12" handle length divided by a 3" drum would be an MA of 4, multiply that by the MA of the cables you wind up with 8. A boat winch has gearing to increase the MA and it also has a ratcheting mechanism to hold what you have.

I have an old boat winch laying around. Come over and take it off my hands and take this old shaper with it. I don't have any cutters tho.
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