Can a Pulley System Replace Hydraulic Rams for Mechanical Lifting Without Power?

[Yashi234]

TL;DR Summary

Hi all,

My name is Yashi. I am assigned to design a mechanical lifting device to lift a overhead extension cover weighing nearly a tonne. There is no power allowed as its deployable 20 ft. container. Extension is 5.6m wide by 1.5 m. Is there any pulley n winch mechanism to aid ? Any ideas ? See photo attached from supplier drawing. On right elevation, the sheet has to be cut n flap to be lifted at 117 to horizontal. When it is down, it shud be inside the width 2438mm.Feel free to ask queries.

I thought of using hydraulic Ram n actuators but was informed no power available on some site. I am thinking if we can use pulley mechanism from back that connects to top of overhead. I hv modified the container n attached screenshot of how it has to be. Please help if you know of a way to lift this. When this go down, it shud be flush with vertical or inside it, in case we use folding doors in front.

Thanks and Regards,
Yashi

 

[berkeman]

Welcome to the PF.

Is this for schoolwork? If not, why the requirement of no power available? How many people will be able to help with the lifting, and how long do they have to accomplish the lift? What will you attach any lifting devices to? How high do you have to lift it? Who will be in charge of safety while this lifting is being done?

 

[jrmichler]

Try search criteria engine hoist. Most engine hoist are rated for less than half a ton and will not lift high enough, but you should be able to take the concept and design for your actual load and lifting height. Keep in mind that bolted joints allow you to take it apart and fit in a smaller space.

 

[Baluncore]

I am confused by the poorly specified problem. Can you provide a 3D sketch of the deployed extension cover.

Can the cover be detached completely from the container? Is the cover stored inside or outside the container when not deployed. What else is then also inside the container.

A cover that weighs close to one tonne is not there to keep the sun or rain off the area next to the container. Why is it so heavy? What forces must it oppose as a cover, and how is it held in position when subjected to those forces and it's mass.

 

[Yashi234]

Welcome to the PF.

Is this for schoolwork? If not, why the requirement of no power available? How many people will be able to help with the lifting, and how long do they have to accomplish the lift? What will you attach any lifting devices to? How high do you have to lift it? Who will be in charge of safety while this lifting is being done?

Hi Thank you for reply and queriy. Its not school work but real life project. No power is allowed as its movable unit and there is no provision to put them in place. It will be used at remote sites where there may not be any power outlet. There will be atleast 2 people to operate. Overhead extension will be hinged on indoors so when overhead is relaxed, it sits parellel to front vertical surface. So we need to lift it from vertical position to shown angle which comes to 143 deg movement and stay there. It has to sit 4m above ground approx.

Regards,
Yashi

 

[Yashi234]

Hi All,

Thank you for response. I have drawn sketch to give you an idea of what i think should be good. Let me know your thoughts.

To answer some of queries. Its heavy because its made of 6mm bisalloy and padded with 25mm ballistic rubber. Force won't be applied directly on surface but to protect the bounce after hitting at object.

See the sketch and let me know if it will work or any other option. If it does, i will need to determine loading and material. Content inside the box or container is steel plates and bullet catcher but low level ammunition. Max. Force applied is just 70N. Overhead is only for catching anything out of bounce after hitting plate.

Thanks in advance.

Yashi

 

[Yashi234]

I am confused by the poorly specified problem. Can you provide a 3D sketch of the deployed extension cover.

Can the cover be detached completely from the container? Is the cover stored inside or outside the container when not deployed. What else is then also inside the container.

A cover that weighs close to one tonne is not there to keep the sun or rain off the area next to the container. Why is it so heavy? What forces must it oppose as a cover, and how is it held in position when subjected to those forces and it's mass.

Hi Baluncore,

No the overhead can't be detached as it acts as door when it is lowered down or in relaxed position as it rests against front surface as drawn.

Regards,
Yashi

 

[jrmichler]

Here's another idea for lifting the door. Fasten a winch to the top rear of the container. Run the winch cable to a pivoting arm with the pivot near the door hinge. Then another cable from the pivot arm to the door.

The winch must be rated for lifting. Here is a US source for winches: https://www.mcmaster.com/winches/winches-for-lifting/. If you are in a country not served by McMaster-Carr, their catalog gives you some ideas on what is available.

 

[Lnewqban]

... Its heavy because its made of 6mm bisalloy and padded with 25mm ballistic rubber. Force won't be applied directly on surface but to protect the bounce after hitting at object.
...

Yashi,
Being so heavy, I would start by verifying that the extended overhead can keep its shape, as well as the rolling stability of the container, when fully lifted.
The of the overhead edge may tend to bend and deform by areas not supported by the lifting mechanism.
The hinges may need reinforcing as well, in order to resist high forces that may develop at certain angles and induced by the lifting mechanism.

Consider that any external mechanism will be exposed to heat and rain and corrosion.
You could also estimate the time required to complete the work of lifting that heavy door and overcome friction of the mechanism by the muscular power of one man.
Then decide how many persons you will need actioning that mechanism.

 

[Yashi234]

Hi Thank you for insight both of you. I have done bit of search online. I found following winch and pulleys. I learned about Mechanical advantage of pulleys so more the pulleys weight bearing capacity on winch is that much less. So for using 2 pulleys, 800 kg will result in just 200 kg. Is that correct ? Is it possible to show the force and load on the pulley and winch using my design and the one jrmichler suggested ?

I mean how can i prove mathematically that winch will hold it. I m planning to use 2 set of winches, 1 at each end to uniformly distribute load...although winch is rated for 700 kg. In short, i want to understand physics behind this mechanism so i can prove it will work. We hv to build prototype first.

Thanks n Regards,
Yashi

 

[Lnewqban]

You can reduce the weight to be lifted and the muscle effort by using counterbalance weights (like in elevators) or pre-loaded spring coils (like in electric powered garage doors).

Pulleys will reduce the effort at the winch, but will increase the length of wire rope to wind, which works against the maximum capability of the drum.
The smaller the diameter of the mobile and fixed pulleys, the greater the effort to bend the wire rope and the shorter its life time.

Being a mechanism, you will need to calculate the actual efforts at several angles of opening.
Normally, either the beginning or end of the stoke are the hardest.
If movement of both winches are not coordinated (and they will not be occasionally), one winch and cable will be overloaded (while the other slacks).
Then, you want to introduce some safety factor and redundancy if possible, existing the potential for human harm or death in case of failure.

Some alternate ideas:

 

[Baluncore]

No the overhead can't be detached as it acts as door when it is lowered down or in relaxed position as it rests against front surface as drawn.

The thing that confuses me is the term "front" being used to refer to what I and the Royal Wolf document call the "side".

 

[Yashi234]

The thing that confuses me is the term "front" being used to refer to what I and the Royal Wolf document call the "side".

Hi Baluncore, the reason the terminology is different because Royal wolf is off the shelf product but we are modifying it to use the side as front. We are working on their side hence operationally, its our front.

Regards,
Yashi

 

[Yashi234]

You can reduce the weight to be lifted and the muscle effort by using counterbalance weights (like in elevators) or pre-loaded spring coils (like in electric powered garage doors).

Pulleys will reduce the effort at the winch, but will increase the length of wire rope to wind, which works against the maximum capability of the drum.
The smaller the diameter of the mobile and fixed pulleys, the greater the effort to bend the wire rope and the shorter its life time.

Being a mechanism, you will need to calculate the actual efforts at several angles of opening.
Normally, either the beginning or end of the stoke are the hardest.
If movement of both winches are not coordinated (and they will not be occasionally), one winch and cable will be overloaded (while the other slacks).
Then, you want to introduce some safety factor and redundancy if possible, existing the potential for human harm or death in case of failure.

Some alternate ideas:

Hi Lnewqban,

Thank you for valuable advise and youtube links. Let's call top plate as overhead extension. How about i split the plate into 2 halves, that way weight of plates will be just 350 kg each n i can use 500 kg rating winch x 2. There won't be any issues with bending or coordination of 2 winches an issue ?

As per information attached earlier, rope dia is 5mm max. N its 22m cable length while i hv to play with max. 5.5m.

I have visited boat, camping n fishing shops and hardware shops locally and all directed me to marine shop (closed today) which can stock more variety. Also, someone advised winch may not hold it upright for longer time. If i divide the load by splitting overhead plate, i believe it shud be fine.

Regards,
Yashi

You can reduce the weight to be lifted and the muscle effort by using counterbalance weights (like in elevators) or pre-loaded spring coils (like in electric powered garage doors).

Pulleys will reduce the effort at the winch, but will increase the length of wire rope to wind, which works against the maximum capability of the drum.
The smaller the diameter of the mobile and fixed pulleys, the greater the effort to bend the wire rope and the shorter its life time.

Being a mechanism, you will need to calculate the actual efforts at several angles of opening.
Normally, either the beginning or end of the stoke are the hardest.
If movement of both winches are not coordinated (and they will not be occasionally), one winch and cable will be overloaded (while the other slacks).
Then, you want to introduce some safety factor and redundancy if possible, existing the potential for human harm or death in case of failure.

Some alternate ideas:

Hi Lnewqban,

The first video of using 3 pulleys from 2 ends sounds good. Rest of them are motorised or automatic or power driven i think.

Regards,
Yashi

 

[jrmichler]

There are two types of hand powered winches - those rated for lifting, and those not rated for lifting. The difference is that the winches rated for lifting have an automatic brake that locks the winch drum in position when the operator let's go of the handle. Winches not rated for lifting do not have this brake. If the operator let's go of the handle, the load drops while the handle spins around and breaks the operators arm.

A winch not rated for lifting is extremely dangerous for lifting a one tonne lid.

 

[Lnewqban]

You are welcome, Yashi
I recommend you postponing the selection of any hand operated winch until you have calculated the forces and displacements of the mechanism you prefer.

Don't assume that the load on your winch will be equal to the weight of the door(s); as stated above, mechanisms often develop higher loads as they adopt different angles.

With some modifications, the motor of each mechanism shown in the videos could be converted to manual operation; I posted those only to give you an idea about other possibilities.

As jrmichler has explained above, a suitable winch for this application should have a ratchet mechanism that automatically locks the load at any point and in any direction (winding and unwinding).

Please, run a wind load calculation and determine the tipping resistance of the box when door/overhang is fully extended, terrain is not flat (has some negative slope) and the highest wind and gust speed rated for your area is blowing perpendicularly to the side of the box that is opposed to the opened door/overhang.
If danger of tip-over exists, you will need to use counterweights or cables anchored to the ground on the opposite side.

I believe that your idea of splitting the door/overhang is excellent.

 

[anorlunda]

Please, run a wind load calculation and determine the tipping resistance of the box when door/overhang is fully extended

Wow. Excellent point. I didn't think about that.

There are several safety hazards in this project if not done carefully. Pulling one ton with a hand cranked winch is common. Every boat trailer does that. But using it to lift a heavy object over people's heads is very different.

 

[Yashi234]

Hi All,

Thank you for valuable advise and tips. So far over 2 days we have come to conclusion, split the overhead extension, use hand brake winch which is self locking so it can hold on its own when released and calculate the wind load. so that makes each overhead to 350 kg and if i use double rated (700kg capacity) hand winch that should sustain load ?

Few more consideration or option as i am told today, Winch is only for lifting and once extension is lifted to desired height or angle, it should stay there and winch has to be removable so to avoid any weather effect and then packed in the container.

If it was flat horizontal, it wouldn't be that issue,but here I need to lift from vertical to horizontal and then raise 53 deg. Now lifting mech has to be removable. Which one is better wire rope or webbing (strap) ?

Regards,
Yashi

 

[Lnewqban]

What fabrication capabilities do you have available (on-site welding, oxy-cut, lathe and mill machining, etc.)?
Steel wire-rope can handle more load but it rusts and needs big bending radii.
Nylon straps can bend much more, but deteriorate with Sun light.

How did we come down from "overhead extension cover weighing nearly a tonne" to 350 Kg x 2?
Same about the angle: from "flap to be lifted at 117 to horizontal" to 143 (vertical plus 53)?

 

[Yashi234]

What fabrication capabilities do you have available (on-site welding, oxy-cut, lathe and mill machining, etc.)?
Steel wire-rope can handle more load but it rusts and needs big bending radii.
Nylon straps can bend much more, but deteriorate with Sun light.

How did we come down from "overhead extension cover weighing nearly a tonne" to 350 Kg x 2?
Same about the angle: from "flap to be lifted at 117 to horizontal" to 143 (vertical plus 53)?

Hi Lnewqban,

117 to horizontal was for dimensioning but 143 is the angle the overhead needs to move or raised from its vertical position. Add them n u get 270 deg which is angle between horizontal n vertical faces.

As far as fab goes, none on site once the container requires transportation, all attachments need to come off. Once it reaches site, you bolt on items so it needs to be detachable. Width and height for transportation is just lil more than size of container. So cannot keep permanent.

Regards,
Yashi

 

[Lnewqban]

Thank you, that is good info.
What about the weight and the off-site fabrication capabilities?

 

[Yashi234]

Thank you, that is good info.
What about the weight and the off-site fabrication capabilities?

Hi there,

Nearly a tonne was an approximation it was around 800 kgs cutting into half n then had to trim some distance to clear ends.

Got to around 720 kg. N that angle was 90 + 63 = 153 was typo in writing 143.

When u use 2 pulleys, does rope cable go alternatively up n down or can go up to up on sheave? How does tension in rope get affected in either case ?

Regards,
Yashi

 

[Lnewqban]

... When u use 2 pulleys, does rope cable go alternatively up n down or can go up to up on sheave? How does tension in rope get affected in either case ?
...

Please, see how it works and how you can calculate tensions and rope displacements for different positions of the door, using the idea in post #8 above:
https://www.engineeringtoolbox.com/pulleys-d_1297.html

 

[Yashi234]

Hi All,

Thank you every1 who has helped me so far with their advice. I am down to last few queries to every1 who is following this thread.

1. Since the weight to be lifted is 350 kg eachover angle of 153 deg is it safe to use 700 kg capacity / rated hand brake winch in centre or use 2 x 500 kg rated at the ends of plate to avoid bending ? So technically there will be 4 winches.

2. Other thing to consider is load will not be fully on winch as the overhang extension is hinged so the lifting will be aided with pivot. I have used rud lugs of 6.7t (from online lib) but what tonnage or swl rating rud lugs shud be used ?

3. Attaching the drawing for ref i hv added both options of winch, on the side and on top. I hv added an option of holding the plate using 2 plates n string to hold in upright position. Let me know if this pulley arrangemnt will be enough. Most of examples of pulleys i hv seen is vertical load but this more of horizontal load.

Please answer them as best as you can.

Thanks again and regards,
Yashi

 

[Tom.G]

Just some ideas to think about.

The drawing shows possible winch mounting on top at the rear edge. Definitely NOT a good idea, you will lose a lot of winch operators falling off the container (or ladder). People just do not have much control or balance when doing heavy labor in motion. Mount the winches for Ground level operation.

I am a little concerned that from a closed position, the cable is pulling almost vertically on the overhead. Hopefully you have calculated the torque applied to the panel over its lifting path, and the cable tension.

A possible solution is replace the vertical post on top of the container with a tripod that projects past the front of the container.

Another idea is have a bar sticking out from the overhead to serve as cable attachment point. The bar could be either bolted on as needed or hinged at its top so it will fold down for shipping. If hinged of course it will need a stop when at 90° from the overhead. You seem to have the start of that idea in your drawing.

I noticed the pole on the top that the cable runs over. A simple post without bracing is likely to bend, especially if the pulley seizes and stops turning. Be sure to brace that post. Perhaps the dotted lines in the drawing are for that purpose, but it is not clear.

You state the winches will be removed after use. What will you do with the cable? If you plan to remove the cable with the winches, how will you access the end that is attached to the overhead?

For weather protection, wire rope (cable) is available Galvanized, and at least in the smaller sizes,with a Nylon jacket (or other jacket).

Yet another possibility is to use winches and cables rated for Marine use, they withstand outdoor use and salt water spray.

If you use two winches on each overhead, size them, and the cable, and the vertical pulley supports, so just one winch can hold the overhead. If or when one winch fails the remaining one can stop an accident. Account for the extra force when one corner of the overhead falls and is stopped by the remaining winch and cable.

The manual brake release on the winches will require a hand to operate. That leaves only one hand on the handle. Account for one-handed winch operation when sizing. (But probably size the handles for 2-handed operation; much easier to operate that way unless there is a large gearing ratio!)

Cheers,
Tom

 

[Yashi234]

Just some ideas to think about.

The drawing shows possible winch mounting on top at the rear edge. Definitely NOT a good idea, you will lose a lot of winch operators falling off the container (or ladder). People just do not have much control or balance when doing heavy labor in motion. Mount the winches for Ground level operation.

I am a little concerned that from a closed position, the cable is pulling almost vertically on the overhead. Hopefully you have calculated the torque applied to the panel over its lifting path, and the cable tension.

A possible solution is replace the vertical post on top of the container with a tripod that projects past the front of the container.

Another idea is have a bar sticking out from the overhead to serve as cable attachment point. The bar could be either bolted on as needed or hinged at its top so it will fold down for shipping. If hinged of course it will need a stop when at 90° from the overhead. You seem to have the start of that idea in your drawing.

I noticed the pole on the top that the cable runs over. A simple post without bracing is likely to bend, especially if the pulley seizes and stops turning. Be sure to brace that post. Perhaps the dotted lines in the drawing are for that purpose, but it is not clear.

You state the winches will be removed after use. What will you do with the cable? If you plan to remove the cable with the winches, how will you access the end that is attached to the overhead?

For weather protection, wire rope (cable) is available Galvanized, and at least in the smaller sizes,with a Nylon jacket (or other jacket).

Yet another possibility is to use winches and cables rated for Marine use, they withstand outdoor use and salt water spray.

If you use two winches on each overhead, size them, and the cable, and the vertical pulley supports, so just one winch can hold the overhead. If or when one winch fails the remaining one can stop an accident. Account for the extra force when one corner of the overhead falls and is stopped by the remaining winch and cable.

The manual brake release on the winches will require a hand to operate. That leaves only one hand on the handle. Account for one-handed winch operation when sizing. (But probably size the handles for 2-handed operation; much easier to operate that way unless there is a large gearing ratio!)

Cheers,
Tom

Hi Tom, Thats great set of options. We had review meeting with managemnt n every1 agreed ground operated winch is better. If possible could you do hand sketch of other options i got the idea but will be gud to see them.

All things on top has to be detachable so bolt down plate has to be under each post or mech. No i have not yet done calculation it was just concept. But i hv time frame for all calculation n drawing.

Regards,
Yashi

 

[Tom.G]

If possible could you do hand sketch of other options i got the idea but will be gud to see them.

And one more comment: The pulleys should capture the cable so when the cable is slack it does not completely fall off!

Cheers,
Tom

 

[Yashi234]

And one more comment: The pulleys should capture the cable so when the cable is slack it does not completely fall off!

View attachment 266418

Cheers,
Tom

Hi Tom,

Thank u for sketch.

You mentioned calculating torque of lifting plate. Wat are info required to work torque in this case ? Is there a formulae for an angle ? I hve hinged the overhang plate on a 20mm dia solid bar/rod and plate is welded to 32nb pipe. I would have thought with the winch guiding plate over a hinge, it would come up easily when hook attaches to lug on plate. Solid bar is held by lug plates (n secured by r clip) which is welded.

I hv attached sketch. Lug is close to door n plate stops wen it contacts the front edge of container.

One more thing i wanted to ask is I beam vs RHS for post to mount pulley. I beam has more strength compared to RHS ?
Regards,
Yashi

 

[Yashi234]

Hi All,

Thank you for the guidance. I will need to start making production drawings for this task. With all your inputs, i m pretty condident of getting it right. Do you reckon 20mm dia n 32nb pipe for hinge mechanism is sufficient or need to increase to 32mm rod n 40 nb or 50 nb pipe ? I really got benefitted by this thread.

Regards,
Yashi

 

[Tom.G]

Hi Tom,

Thank u for sketch.

You mentioned calculating torque of lifting plate. Wat are info required to work torque in this case ? Is there a formulae for an angle ? I hve hinged the overhang plate on a 20mm dia solid bar/rod and plate is welded to 32nb pipe. I would have thought with the winch guiding plate over a hinge, it would come up easily when hook attaches to lug on plate. Solid bar is held by lug plates (n secured by r clip) which is welded.

I hv attached sketch. Lug is close to door n plate stops wen it contacts the front edge of container.

One more thing i wanted to ask is I beam vs RHS for post to mount pulley. I beam has more strength compared to RHS ?
Regards,
Yashi

That is getting down to the engineering details, in which @jrmichler or maybe @Lnewqban are much better informed than I. Let's see if either of them can supply information on the material requirements and calculating methods. I'm sure they can do a much better job!

Have Fun!

Cheers,
Tom

 

[jrmichler]

Before sizing parts, you need to calculate the loads on those parts. The next step is a free body diagram (FBD)(search the term). This will take some time because there is a lot to learn. Expect that you will need at least three FBD's, one each with the door closed, one with the door fully open, and one with the door half open.

 

[Lnewqban]

I see that the location of the door and of the hinge have changed some respect to the original idea.
I am not sure that such set up will allow the angle of opening previously discussed.
Working on scale drawings will help us to help you.

You will need to calculate the resistance to bending of the structural member running sideways, as well as the rigidity of the area supporting the tripods guiding the cables.
Therefore, you will need the vertical component of force exerted by the cables on the tripods when the doors are in horizontal position.

Besides taking the steps properly advised by @jrmichler above, I would again suggest a wind load calculation prior proceeding to final phase of the project.
It seems that you have many details to solve before stepping into it, making changes latter can be expensive.

Since in your other thread you have mentioned weight of piece of sheetmetal to be handled by two persons, I would like to know what that part is and why the need for on-site manipulation.
You will need to calculate the weight of the tripods as well, reducing it as much as possible.

Regarding your question about the pipe-round bar hinge: that greatly depends on the kind of welding you can achieve against the sheet metal of the original box, as well as on the best possible alignment of the several hinges.
That was one of the reasons for which I have asked you previously about the fabrication capabilities that are available to you, on-site and in shop.

 

[Tom.G]

Oh, I just realized that wind loading on the open overhead should also be checked with the wind coming from the front, open part, of the device. If the wind blows the overhead to vertical and then stops, the vertical will fall down towards the closed position, putting a peak load on the cables, etc.

Cheers,
Tom

 

[Yashi234]

Oh, I just realized that wind loading on the open overhead should also be checked with the wind coming from the front, open part, of the device. If the wind blows the overhead to vertical and then stops, the vertical will fall down towards the closed position, putting a peak load on the cables, etc.

Cheers,
Tom

Hi Tom, Michler and Lnewqban,

Thank you very much. Here is the link of video i found to determine torque which fits my situation.
As far as wind loading is concerned, its 80kmph which comes to 62N. Another piece of info is, when its in upright position, it will be held by 2 pivot points on end of each extension so its 3 way hold. So there is 25mm thick lug on either side of winch path n same on the overhang plate. Once in upright position, they will be tied by cables n chain to secure it.

To all 3 legends, i hv final few queries.
1. Can you tell me what is SWL lifting lugs will be required to lift it ? 2 T rud lug shud be gud enough to weld on overhang plate to lift it ?
2. Can you tell me what info does Torque calculation reveal ? I mean if i use above video n calculate torque how do i use it ?
3. Can any of you show me rough calculation of pulleys based on 140 deg of lift and 350 kg using 2 pulleys. Weight of tripod to mount pulley is just 50 kg. Most pulleys calculation is vertical loaded. This is different n i cudnt find any equation to show if this system will work.
4. What is difference between rated lifting capacity n pulling capacity ?

Thank you in advance.

Regards,
Yashi

 

[Lnewqban]

Hi Tom, Michler and Lnewqban,

Thank you very much.
...
2. Can you tell me what info does Torque calculation reveal ? I mean if i use above video n calculate torque how do i use it ?
3. Can any of you show me rough calculation of pulleys based on 140 deg of lift and 350 kg using 2 pulleys. Weight of tripod to mount pulley is just 50 kg.
...

You are welcome, Yashi

Answer to question #2:
Your metal box has no anchoring to ground or concrete base. High velocity wings could overturn the box, especially while the door is open and weight is not balanced, hurting people standing close to it.
Please, take a look at this article:
http://edge.rit.edu/content/P14414/public/Reference Documents/windtestofharborcontainers.pdf

Answer to question #3: Based on dimensions of box and positions of door, knowing weight of each, you should produce a free body diagram.
That will give you an idea of the forces that the wire-rope, winch, hinges, support of pulley, roof of box and bolts will “feel” for different positions of the heavy door, while opening and closing it.
Please, see:
https://courses.lumenlearning.com/s.../chapter/12-2-examples-of-static-equilibrium/

Until you complete those steps, you are can’t know how to dimension hinges, anchors, structural re-inforcement, etc.
You need to have some values of forces for many critical points, even if they are not too exact.

Even the amount of wire-rope that should be admited in the drum of the winch depends on its capability (how many turns before becomes full) and the location of anchors to the door and the geometry of the mechanism.

For all those reasons, nobody could properly answer your questions without seeing scaled drawing and calculated forces.

It seems that you have already designed and dimensioned the tripod.
The weight of the tripod (50 Kg) is excessive for two workers to carry it from ground to roof using only ladders.