Harbour Crane

[Nequmodiva]

I always liked harbour cranes. Especially the level-luffing cranes with their unique shape. But until recently I knew neither the purpose of their structure nor that they're called level-luffing. Only the official B model of 8053 Mobile Crane made me look into harbour cranes.

For all of you who don't instantly remember this model, here is the official product image of 8053 Harbour Crane:

While building and playing with this model, I became aware of how accurate this model is. By way of comparison, here is a photo of a real level-luffing crane:

Dillingen Kran [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0/) or CC-BY-SA-2.5-2.0-1.0 (www.creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], by Lokilech (Own work), from Wikimedia Commons

Cranes like these are called "horse-head" cranes, because of the additional horse-head jib on top of the main jib. To make sure you understand what I'm talking about, I labelled the elements in a picture:

The structure has a purpose: level-luffing. Level-luffing means, that the hook remains at the same height when moving the main jib back and forth. There are two benefits from that:

• it's easier to control the movement of the hook, especially useful where precise positioning of the hook is required.
  
• when a load is moved horizontally there's no energy wasted on lifting the load.
  

Here is an animation of level-luffing from Wikipedia:

Crane double-lever-jib-type sideview animated [CC-BY-SA-2.5 (www.creativecommons.org/licenses/by-sa/2.5)], by Silberwolf (created by Silberwolf), from Wikimedia Commons

And here is an animation I made of the 8053 Harbour Crane luffing:

From the following montage I made it's clearly visible, that the hook of the Harbour Crane does not remain exactly at the same height. I think it's pretty accurate, though.

A bigger version of this and a few other montages can be found in my brickshelf folder.

Another two details I want to highlight for their accuracy:

• when moving the main jib the counterweight also changes position. In reality this is needed to keep the crane in balance.
  
• the rope is guided along the tieback and the horse-head jib and through pulleys in the joints, because if hung straight through the quadrangle the rope would change length while luffing and therefore raise or lower the hook.
  

As I told you, the purpose of the harbour crane geometry is to achieve a linear movement which is in the best case horizontal. Furthermore we've seen, that in the 8053 Harbour Crane the movement isn't exactly horizontal, but it's linear, though. It could be easily modified into a horizontal movement by tilting the structure. The remaining question is, how did they achieve to make it a linear movement?

Actually the movement is only approximately a linear one. When skewing the geometry of a harbour crane the lower end of the horse-head jib describes a coupler curve. Only when cleverly constructed the coupler curve is partially an approximated straight line.

To show this I've constructed this test apparatus:

Then I made an animation and recorded the position of the yellow Technic Bush.

The measurements of this apparatus are orientated by the values form this site.

So now to my last question, and this question is for you: What other LEGO models are there that have a somehow clever mechanism to achieve level-luffing?

I took a look around already, but I found no prove for a working level-luffing mechanism.

Among the official Technic models there have only been very few stationary cranes. The second model of 8074 Universal Building Set is one of them. But as these animations made by Blakbird from Technicopedia show, this crane does not care about level-luffing:

In LEGO's City line there have been some harbour cranes. But I guess no one precisely recorded their movement. As I own none of them I wasn't able to check either. The only thing I was able to do is this montage made of two photos of 7994 LEGO City Harbour photographed by Dandily:

While this crane is obviously a horse-head design, it clearly fails to achieve level-luffing.

It seems harbour cranes aren't a very popular subject for MOC building too. Nevertheless there are some models. The most accurate ones I found were these two build by Marinus:

Figee level luffing shipyard crane

http://www.youtube.com/watch?v=QF1zPjQStTA

However level-luffing is not limited to harbour cranes. There are other solutions than horse-head designs too. For example think about a system where the movement of a boom is coupled with the winch to compensate rope length. If you've seen or built something like this let me know.

[DLuders]

Wow, you should consider entering this in the March 2011 Lego Technic Challenge for its great example of "linear movement"! Your analysis and animations are superb.

[Countdown]

Very nice explanations there, it really cleared things up and "scientisize" something that is somewhat obscure.

//So now to my last question, and this question is for you: What other LEGO models are there that have a

//somehow clever mechanism to achieve level-luffing?

//I took a look around already, but I found no prove for a working level-luffing mechanism.

I don't know if this qualifies but, take a look to the cherry picker 8292, the vertical motion is "level".

[Nequmodiva]

I don't know if this qualifies but, take a look to the cherry picker 8292, the vertical motion is "level".

Thanks, that's a good idea. Wondering about how to adopt this for a horizontal movement I came up with the following concept. The mechanism is known as scissor arm or pantograph. It's an odd design for a crane but it's level-luffing (hook remains at the same height).

[Rook]

Always amazed be stuff like this. Makes me wish I had an engineering degree. :(

[rjk1977]

I'm working on a crane like this http://farm4.static...._b9892cde17.jpg , http://farm4.static.flickr.com/3358/3592251119_c5cb09927a.jpg at the moment, its keeping the hook leveled athough the main boom is moving.

Edited March 10, 2011 by rjk1977

[Nequmodiva]

Now I made a mini Harbour Crane MOC. It's an alternate from parts of 8067 Mini Mobile Crane.

Photographic building instructions are available in my brickshelf folder or for download as PDF (3,48 MB).

[JunkstyleGio]

@Nequmodiva

Thanks for the Pdf instructions!I was a fun little build!

(and you made me save a lot of money; with this model I don't have to get me the big version...)

This is a fantastic piece of MOC-ing.

Keep your MOC's coming!

[Nequmodiva]

@JunkstyleGio

Thanks for the photo. That's the first time I see something I built having been rebuilt by somebody else. Never thought this would make me as happy as it does.

[dunamis]

Wow, that is really cool. Thanks for sharing!

[DarkShadow73]

I personally think the 8053 B Model Harbour Crane is the best B model Lego has ever designed for an alternate in a Technic set. Its not only great to look at, but also very functional. I only made one small modification to mine, I took the wheels off the bottom of the stabilizers so it wouldn't 'roll away'. First time it rolled off the top of a piece of furniture I had it on I looked at redesigning it so it would 'stay put'.

[mpec82]

Mine 8053B has been also modified into a fixed one and will be modified again once I have all the pieces I need for my cargo yard.

Imho it's a fantastic 8053B is a fantastic B-model but with some tweaks can be also better.

[Mr. McDuck]

Wow! this is a great design!

[grohl]

Very nice harbour crane. I love these small alternates.