Autonomous excavator constructs a six-metre-high dry-stone wall • Hacker News Board

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#141

Post by SiempreViernes » Sat, Nov 25, 2023, 2:37 PM UTC

diroussel wrote: post #138

crotchfire wrote: post #116

Earlier quoted context omitted.

The point is that the concrete manufacturers pulverize and homogenize the aggregate. This makes random sampling acceptable. If you haven't pulverized and mixed the inputs, a random sample is merely a random sample. It isn't meaningful unless it comes from a high-entropy source.

So are you saying we couldn’t estimate the structural properties of autonomous built dry walls from local stone? Or that the error bars would be unacceptably large? Or just that this approach would only work with certain stone in certain locations?

I think the problem is more that you cannot at all guarantee a specific performance of the structure ahead of time, because you can't know what the properties of the local rocks will be before you are on site and have measured them all.

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#142

Post by lapsed_pacifist » Sat, Nov 25, 2023, 3:29 PM UTC

mauvehaus wrote: post #21

beachy wrote: post #8

This seems like game changing technology. There are a heap of such walls around here, some built long ago by Dalmation immigrants (and some allegedly by German POWs). It's quite labour intensive and highly skilled to create them. We have some on our property, used to retain the hillside after land slips. They were built with an excavator by a gnarly old guy who was unbelievably skilled. One thing I wonder is whether…

Visiting Scotland, I was told that the apparent lack of stability is what keeps the sheep from pushing against the dry stone walls there. Apocryphal or true? No idea. It's intriguing to think that sheep have a sense for stable construction, and that people have learned to deceive it.

Not true. A well built fieldstone wall is massive, we estimate around .5T per linear yard when we build one to 4ft. with cope stones. Sheep will not knock it over, but cattle can. For that reason, through-stones are allowed to protrude a few inches on normal pasture wall for sheep, but you should make them flush on walls for cattle because the cows will try to use the protrusions to scratch themselves and could knock the wall over.

A well built wall doesn't appear unstable. One of the tests is whether or not you can see any daylight through the wall, and the wall should easily support the weight of several people leaning against it.

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#143

Post by HPsquared » Sat, Nov 25, 2023, 3:29 PM UTC

fullspectrumdev wrote: post #134

adhesive_wombat wrote: post #122

Earlier quoted context omitted.

Dry stone walling is also very common in the UK. It's a complex and now expensive skill, but a properly-built (this bit is key) wall will stay put for well over a hundred years because the rocks can shift a little rather then cracking the structure as temperatures change and water drains right out of them. It's also very locally distinctive because the shape of the stones and therefore the wall layout and texture dep…

Very common in rural Ireland, and having such a wall repaired or made is either going to cost you nothing or a LOT of money.

As with many of the best things in life, they are either free or very expensive.

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#144

Post by tsimionescu » Sat, Nov 25, 2023, 3:33 PM UTC

nopinsight wrote: post #132

tsimionescu wrote: post #106

Earlier quoted context omitted.

You should take both of those announcements with a huge dollop of salt. Even the article you shared is extremely skeptical of the actual progress of Tesla's robot. And Chinese press releases should really not be read into too much - they are often much more for internal signalling then information. Either way, there are companies which are much farther along than those - Boston Dynamics has a series of extremely impr…

> Imagine a several hundred kilo machine stepping on your toes with its full weight just because it mis-estimated your movements. "Specifications. Tesla Bot is planned to measure 5 ft 8 in (173 cm) tall and weigh 125 lb (57 kg)." https://en.wikipedia.org/wiki/Optimus_(robot) I'm aware that Tesla tends to be over-optimistic in its timeline regarding AI and robotics. I do not endorse the estimates without question and…

Oops, I significantly exaggerated the weight, thanks for finding that.

Still, 60kg is no laughing matter.

Also, isn't the fact that companies which are way further along in developing robot capabilities are not thinking about wide-scale commercialization decent evidence for it not being viable yet?

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#145

Post by lapsed_pacifist » Sat, Nov 25, 2023, 3:34 PM UTC

Daub wrote: post #55

Having made a few dry stone walls I can attest to the merit of this achievement. Judging where rocks are to be placed, and in what orientation is a zen art. Anecdotally... I once tried to get wild flowers to grow on a stone wall. Every year we would seed the wall, only for the seeds to fall out or be eaten by birds. On inspiration, my boss filled a few shotgun cartridges up with seeds and fired them at the wall. Perf…

This isn't really a proper wall though, it's a single thickness stack. I don't think it could handle any lateral force at all without toppling. If this machine could build a double skin wall with batter, wall heads, and hearting throughout the center, I'd be really impressed!

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#146

Post by lapsed_pacifist » Sat, Nov 25, 2023, 3:37 PM UTC

toomuchtodo wrote: post #14

myegorov wrote: post #12

Earlier quoted context omitted.

The ability of a dry stack retaining wall to shift and breathe is a feature, not a bug. For stone walls that require added reinforcement against lateral loads, look into tiebacks or geogrid reinforcement.

Appreciate this. Where can we read more on this engineering? All citations are welcome, I am fascinated by this engineering domain.

Look at the Dry Stone Wall Association of Great Britain, or The Stone Trust in the United States. These organizations still teach traditional methods of dry stone walling which cover a lot of these techniques.

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#147

Post by alistairSH » Sat, Nov 25, 2023, 3:41 PM UTC

galaxyLogic wrote: post #93

samtho wrote: post #86

Earlier quoted context omitted.

The problem with dry stone construction is that you cannot determine the performance characteristics required for, say, a building foundation. Not all boulders are created equal, but a professional concrete pour, mixed and installed to the manufacturer’s specification is going to have a guaranteed maximum strength- something random boulders will not have. What we can do is create our own concrete mix using Portland c…

Why not do a stones-wall like in the article, but add cement as glue between the rocks?

Several reasons… Primarily, because the ground underneath shifts overtime, particularly in area, subject to a freeze and fall cycle. But you also have to solve for water flow - if you build a solid stone wall with concrete, you also need to add drainage on the backside of the wall. With dry, stacked stone, you can often get away without a complex drainage solution

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#148

Post by lapsed_pacifist » Sat, Nov 25, 2023, 3:41 PM UTC

saalweachter wrote: post #56

gerdesj wrote: post #42

Earlier quoted context omitted.

There are Civil Engineers here (I only studied it at Uni - I ended up in IT!) When you deploy a structure like a retaining wall you want to try and ensure that the materials you use will retain their properties as long as possible and if part of it fails, it should not case the whole structure to fail. Add additional design requirements as you like eg colour and texture but always think about function first or you wi…

Another quick tip: resist the urge to stack your stones long-ways parallel to the course of wall. Instead, put the longest dimension perpendicular to the wall. This makes it much harder for the wall to fall outward as it shifts.

The 5 rules of dry stone:

https://thestonetrust.org/5rules/

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#149

Post by dboreham » Sat, Nov 25, 2023, 3:57 PM UTC

s1artibartfast wrote: post #52

zyxin wrote: post #39

Earlier quoted context omitted.

Do operators currently need to manually control every movement of the arm? I always assumed that such heavy equipment uses inverse kinematics to help the operator.

It is usually one lever per hydraulic cylinder. The human brain already automates the kinematics. There isn't much upside to automation and a lot of downside because of the diverse instructions required.

> It is usually one lever per hydraulic cylinder.

Not so much these days, but the general idea is correct.

Usually there are joysticks (one per hand) that provide control over one movement per axis. So for example the right hand joystick on a mini-excavator usually controls bucket curl (left/right) and boom movement (forward/back). Left hand does boom up/down and rotate left/right. There's an ISO standard for this UI. Old school tractor-loader-backhoe machines (what people in the US call "a backhoe") had one lever per cylinder, so more complicated to control and more levers. An old-style motor grader is the extreme example of lever confusion[1].

Operation of heavy machines relies (still) on the brain's capability to virtualize the movement of the machine in terms of the body's limbs. That's why you need some time training to become proficient. After a few hours you just think "I want the bucket over there" and your hands make the necessary movements without thinking.

There's already lots of automation available on high-end machines such as use of GPS to control cut/fill operations with bulldozers, and laser-transit-based automated dig depth control for excavators.

[1] https://www.cat.com/en_US/articles/for-owners/the-basics-of-...

Re: Autonomous excavator constructs a six-metre-high dry-stone wall

#150

Post by hedora » Sat, Nov 25, 2023, 4:23 PM UTC

samtho wrote: post #86

schiffern wrote: post #74

Earlier quoted context omitted.

Not only is this a technical marvel, but it has potential construction physics implications. In simple terms, currently we expend energy to fragment rock, and then we expend additional energy (as concrete) to glue it back together. We do all this to re-arrange rocks into a shape (and strength) we want, and most importantly to do it cheap . Suddenly, an alternative just got a lot cheaper. Clearly this isn't fully bake…

The problem with dry stone construction is that you cannot determine the performance characteristics required for, say, a building foundation. Not all boulders are created equal, but a professional concrete pour, mixed and installed to the manufacturer’s specification is going to have a guaranteed maximum strength- something random boulders will not have. What we can do is create our own concrete mix using Portland c…

Modern concrete only lasts a hundred years or so. Stone walls last much longer when correctly constructed.

Presumably the placement algorithm understands compression strength of the local rocks, soil heaving, etc.

So, software addresses the initial problems you describe at construction, and geology/materials solve the problem of needing to inspect it every decade or so, and replace it in 50-100 years.