Threading string for large cranes

[nerdsforprez]

Anyone who has built a large crane understands that treading the string to additional pulleys (like below) increases lifting capacity, but it is a pain in the rear end to do. Playing around with my crane this weekend resulted in the string coming off the pulleys.....so I am re-threading. Pain. Big pain. However, I found a video that is helping me out. Using some putty and rubber bands helps.

Fast forward to the end of the video to speed things up. approx. to the 7 minute mark

[DrJB]

Few points that need clarification:

1 - Need to be 'precise' about what is exactly meant by lifting capacity. Using multiple pulleys simply enables you to use a smaller motor to lift heavy loads. The lifting capacity of the actual crane is determined not only by the motor's horsepower, but also by the strength of the structure and what's the max it can carry.

2. The pulleys you're using are not suitable for such application. In real life, all pulleys rotate at different speeds and as such, they need to be free-rolling on the same/common axle. Those you're using have an axle hole, and thus are not suitable.

3. Because (I'm assuming) you're using stock pulleys (non-modified), whatever you gain in lifting capacity, you'll be losing in friction as the thread will be sliding on the pulleys. Yes, it looks neat/realistic, but it works nothing like the real thing.

I believe efferman has special pulleys he designed precisely for this application ... though not for the 'purists'.

Edited March 22, 2015 by DrJB

[Saberwing40k]

I see another problem with this: I've had issues with raising and lowering the hook when I have more than 2 pulleys on my crane, and I honestly cannot make the load big enough, yet small enough to not break the crane. Even 42009 has issues with the hook not lowering well, with one pulley, because of the fact that the hook is so light. Sure, it looks more realistic, but having a large number of ropes going to the hook on a Lego crane is a functional impairment.

Edited March 23, 2015 by Saberwing40k

[dr_spock]

I think painter's masking tape can help with reeving the crane hoist cables too. I also find you need to have a heavy hook when you do more than one pulley unless you have a load attached. The more pulleys the longer it takes to winch up and down it seems.

[nerdsforprez]

Few points that need clarification:

1 - Need to be 'precise' about what is exactly meant by lifting capacity. Using multiple pulleys simply enables you to use a smaller motor to lift heavy loads. The lifting capacity of the actual crane is determined not only by the motor's horsepower, but also by the strength of the structure and what's the max it can carry.

2. The pulleys you're using are not suitable for such application. In real life, all pulleys rotate at different speeds and as such, they need to be free-rolling on the same/common axle. Those you're using have an axle hole, and thus are not suitable.

3. Because (I'm assuming) you're using stock pulleys (non-modified), whatever you gain in lifting capacity, you'll be losing in friction as the thread will be sliding on the pulleys. Yes, it looks neat/realistic, but it works nothing like the real thing.

I believe efferman has special pulleys he designed precisely for this application ... though not for the 'purists'.

Woah woah hold on there pro. If you actually take the time to consider the whole post, and that I actually use a video using a MODEL to demonstrate what I am discussing, you will see that what I am discussing IS all about looks.

I am not discussing the authenticity of the build. MANY, many have used this exact method long before I, and no one argues the proper nature of it. Large cranes are one of the earliest large MOCs. Each of us already know of what you pretentously said in your post but we continue to use the methods because it LOOKS cool. Your response actually doesn't even have anything to do with the actual post. I was posting something that I find a real pain. I found a video to show how to make it easier. I did not create the post to argue what I was doing had any functional value. Seperate the signal from the noise my friend, the wheat from the chaff; see the forest among the trees.

Perhaps before you try to impress us all with your physics/engineering acumen, show us that you can actually read

[Saberwing40k]

Woah woah hold on there pro. If you actually take the time to consider the whole post, and that I actually use a video using a MODEL to demonstrate what I am discussing, you will see that what I am discussing IS all about looks.

I am not discussing the authenticity of the build. MANY, many have used this exact method long before I, and no one argues the proper nature of it. Large cranes are one of the earliest large MOCs. Each of us already know of what you pretentously said in your post but we continue to use the methods because it LOOKS cool. Your response actually doesn't even have anything to do with the actual post. I was posting something that I find a real pain. I found a video to show how to make it easier. I did not create the post to argue what I was doing had any functional value. Seperate the signal from the noise my friend, the wheat from the chaff; see the forest among the trees.

Perhaps before you try to impress us all with your physics/engineering acumen, show us that you can actually read

While you may not be discussing the authenticity of the build with this post, DrJB still has many valid points. Plus, the whole point of Lego Technic is realism and functionality, and there often has to be a compromise between them. I don't think it was that pretentious of him to say that there might be some functional issues. but, it's still a good tip, as I have seen some (extremely) large models that could benefit.

[TheRacker]

Woah woah hold on there pro. If you actually take the time to consider the whole post, and that I actually use a video using a MODEL to demonstrate what I am discussing, you will see that what I am discussing IS all about looks.

I am not discussing the authenticity of the build. MANY, many have used this exact method long before I, and no one argues the proper nature of it. Large cranes are one of the earliest large MOCs. Each of us already know of what you pretentously said in your post but we continue to use the methods because it LOOKS cool. Your response actually doesn't even have anything to do with the actual post. I was posting something that I find a real pain. I found a video to show how to make it easier. I did not create the post to argue what I was doing had any functional value. Seperate the signal from the noise my friend, the wheat from the chaff; see the forest among the trees.

Perhaps before you try to impress us all with your physics/engineering acumen, show us that you can actually read

He might have come off as pretentious, but he probably thought you didn't realize the practical error you made when building it, because you made no mention of it. It's like if you saw someone post about a car that they were making but it was missing a wheel, and you said that putting the 4th wheel on would stop it from tipping, only to find out later that the OP took a wheel off as a stylistic choice.

[nerdsforprez]

Good points, but I think that its pretty well known that Technic wheel pulleys do not serve the purpose DrJB discusses. This technique has literally been around for over a decade for large cranes and we all know that it does not serve the purpose that a real crane does, but... the reason why we add it is because it personifies the real thing. In illustration. In illustration only.

Much, much better and well known builders than myself have used this technique. A quick search on brickshelf will reveal its frequency. Top builders such as Erik Leppen. No one would call Erik out on using this....... some things go with out saying

[DrJB]

Good points, but I think that its pretty well known that Technic wheel pulleys do not serve the purpose DrJB discusses. This technique has literally been around for over a decade for large cranes and we all know that it does not serve the purpose that a real crane does, but... the reason why we add it is because it personifies the real thing. In illustration. In illustration only.

Not to dwell too much on the topic, as the limitations of some lego parts are obvious to the long timers (not necessarily everyone though), but your opening statement was/is mis-leading:

Anyone who has built a large crane understands that treading the string to additional pulleys (like below) increases lifting capacity ...

... This is very true for real cranes. It is NOT a correct statement for Lego cranes, especially with the stock pulleys. As many have said on here, Lego is about functionality and realism, at least to many amongst us, and when I see something fundamentally 'wrong', isn't it the point in this forum to discuss? Lastly, I'm not after impressing anyone with my credentials, but only share what I know, as I've learned a lot too from people on here.

So, what's the point behind your post: That threads come off easily? The answer is very simple: 1. They do come off easily because they're not rolling with the pulleys, they're sliding... and 2. For the threads to remain on the pulleys, the latter need to be heavy. But of course you knew this already ...

*peace*

Edited March 23, 2015 by DrJB

[dr_spock]

A way to cheat is to put an axle across the top or bottom of the pulleys. I did this 5 years ago. Bad thing is it is a pain feeding in the string. Good thing is it keeps the string from coming off the pulley during transport to events or kids at events touching it.

[bonox]

So, what's the point behind your post: That threads come off easily? The answer is very simple: 1. They do come off easily because they're not rolling with the pulleys, they're sliding...

The point as I see it is threading - ie putting the giant loop of string around all the pulleys in the first place. Nothing at all to do with operation once it's threaded.

I found the link helpful.

[rocklego]

2. The pulleys you're using are not suitable for such application. In real life, all pulleys rotate at different speeds and as such, they need to be free-rolling on the same/common axle. Those you're using have an axle hole, and thus are not suitable.

I think there is a existing lego part which might replace pulley wheels with cross axle hole .

This one http://www.bricklink...p?P=56902&tab=I definitely will be free-rolling on the common axle.

Edited March 23, 2015 by rocklego

[Bricktrain]

A way to cheat is to put an axle across the top or bottom of the pulleys. I did this 5 years ago. Bad thing is it is a pain feeding in the string. Good thing is it keeps the string from coming off the pulley during transport to events or kids at events touching it.

It is not cheating, it is a neccessity on real cranes also, it is called a keeper, as it keeps the ropes on the correct sheave.

Many large cranes have a reeving winch which pulls a small line through the sheaves to connect the winch rope to for helping in reeving the hook. Tomorrow I will be assembling a 7150 Kobelco but since it is just in the yard to test with its new luffer it wont be having many parts of line, probably only three or four.

I think there is a existing lego part which might replace pulley wheels with cross axle hole .

This one http://www.bricklink...p?P=56902&tab=I definitely will be free-rolling on the common axle.

The only problem with that one is that it is a little wide for a large multi sheave hook, if you wanted 5 or more sheaves.

I have increased hook weight for my large mobile by building a boat weight into the hook.

[bonox]

just came across this little picture of a pair of keepers - might be of use to someone if building a large hook assembly. Interestingly, this one is strung with synthetic rope rather than wire.