Comment by saulrh | Hacker News Reader

Comment by saulrh | Hacker News Reader

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No need for a reference; now that you mention it it's obvious that the duty cycle will be totally different. In fact, I'd bet that cycle time is the limiting factor - the graphic [1] shows about 100 cylindrers per layer, 18 layers already stacked, and the system looks to be around 60% loaded, so total count could be around 3k cylinders to move for a full load. Six arms, then each is doing 1000 cycles a day. Assume 4 hours down a day, 20 hours up, 50 cycles an hour, a bit less than a cycle a minute. Yikes.

I did notice that the cylinders were around twice the quoted capacities for tower cranes I was finding. It also sounds like they're building a much more expensive crane; that many cylinders, at 35 metric tons per and $90 for a yard of concrete, is upwards of $5m, and the article says that the concrete "could" be the most expensive part. Aaaaand random googling is giving me price tags for tower cranes that can't possibly be right - <$300k?! So the quoted system might be using a crane that's ten times the cost of a "normal" tower crane? I can... sort of seeing that buy a six-armed crane with twice the lift capacity but permanent construction, no need for a counterweight assembly, and better continuous performance. But now I feel like these numbers are lining up too well and I have to have done something wrong.

1. https://cms.qz.com/wp-content/uploads/2018/08/energy-vault-l...

2. http://www.wolframalpha.com/input/?i=3000+*+($90+%2F+cubic+y...)

>I did notice that the cylinders were around twice the quoted capacities for tower cranes I was finding.

A "normal" (very large) tower crane rarely exceeds 12 tons, BUT, more than that, usually these use not "single" cable, i.e. a largish crane is usually 6 tons max, but can lift up to 12 tons doubling the cable/rope (which implies halving the lifting speed).

Moreover, cranes are rated/designed (loosely) on their reach, they are intended - within limits - to cover a whole building site, so arms of 20-30-40-50-60 meters.

An electric tower crane (a "normal" one) is well below US$ 300 K, I seem to remember we paid for a very large one, 80/100 meters tall, 50/60 meters arm, 6/12 tons at arm point around 250,000 Euro a few years ago (but costs have not increased much as it is a stale market AFAIK).

The "key factor" is the "overturning" moment at the base (that implies a much sturdier tower and heavier coounterweights), and the single tower design is aimed to have a "light", "transportable" and "easily assemblable/disassemblable unit" the actual lattice is subject to very heavy tensile cycles as it is extremely flexible.

It would make much more sense (to me at least) to have a specially designed crane with an as short as possible arm, traveling on a track (which is also a setup commonly used in building sites) or a portal crane, like the ones used in quarries or pre-fabrication sites 35 tons are a lot of weight.

Besides (reinforced) concrete is at the most 2.3 tons per cubic meter, so it is not very efficient as a weight/counterweight, though possibly it is among the lower cost per kg material.

On the other hand rebar concrete is an excellent material for the actual tower, so in a fixed place it makes much more sense to build a (say) 100 m tall pier/pylon than using a "light" lattice /truss structure for the tower.

Thanks for sharing. This is helpful info.

If a tower crane did not need to be transported, how much would the design change? I’m guessing not much, but curious.

I was imagining there would be no counterweight but just opposing loads, then I realized that might be a safety hazard. But, I really don’t know about these things.

I just love the elegance of this solution and immediately obsessed. I think it just ruined my productivity for the day.

> that might be a safety hazard.

You can get around that, and they probably have to anyway, by just having a perimeter around the system that must be cleared by humans before the system can go active.

A normal tower crane must:

1) be easily transportable, which among other things means that the lighter it is the better it is AND that in most countries the girdles cannot exceed 2.40 meters in width

2) most would be self-erecting (there are two kinds of self erecting cranes, the one in [1] is a kind limeted to smaller/shorter/less load models and it is properly "self-erecting") but any tower crane is normally assembled on the ground (using a crane truck) up to a given size/height, usually up to 30-40 m height at the most, for taller cranes, the arm and the base is assembled on the ground, but later the crane is assembled using a self-erecting "cage" or "climber" see [2], this again calls for "the lighter, the better", and implies besides the truss design the use of high tensile strength steel (which as said before is very elastic, meaning that the operation of the cranes is not as easy as you may think, particularly when high loads are involved, it is not uncommon that the point of the arm has several cms oscillation when the load is lifted/released)

3)transport/assembly/erection/disassembly is done relatively often it is rare that a tower crane remains in the same place more than a few months, at the most a couple of years, so the points above are very relevant.

A "static" crane would resemble more than anything else a port crane, more or less like this one:

https://commons.wikimedia.org/wiki/File:Port_crane_of_Mammoe...

[1] video of a self erecting crane:

https://www.youtube.com/watch?v=pqSFxZV6OvY

[2] video/animation of a climber crane assembly:

https://www.youtube.com/watch?v=RB91Sm-kGJ8

Eerecting and dismantling are key functions of typical construction cranes.

If you build a permanent crane for 30 year operation for most weather conditions it can be heavier and made of larger and heavier body segments. More like cranes in harbors.

I think the counterweights can be removed if you have symmetric working arms lifting exactly the same weight at the same time.

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