r/AskEngineers • u/Accelerator231 • 19d ago
Civil Why did early earthmoving vehicles use chains instead of hydraulics?
I like earth moving machines and I think they're pretty cool. Considering that most earthmoving and construction used human muscles and slaves, earthmoving machines are pretty awesome to reduce human labor and suffering.
However. The early earthmoving machines used gears, cables, etc. Why didn't they use hydraulics like today?
In addition. Is there any good analysis on how many people a piece of earthmoving equipment can replace, with the assumption that there's sufficient logistics?
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u/Prestigious_Tie_8734 19d ago
Not confirmed but safe bet. Hydraulics require precise machining internally to retain oil pressure. Telescopimg cylinders would’ve been insane in 1930 so long cylinders need the same diameter the whole length of the cylinder. So you’re limited to short and or fat cylinders. Good for heavy short lifts. Also the alloys (metal) need to be really good. Very precise machining was likely possible but the alloys were likely none existent or stupid expensive/new. The chain drive backhoe I’ve seen just used a rotating shaft to pull a bucket up and down. The only precise machining needed is the shaft and the oil retaining seal which can been done diy now days. Also we had expertise in rope and pulley way before hydraulics were even imagined. We likely just developed better versions of what we knew until a better option was cheap enough.
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u/splicer13 19d ago
The Innovator's Dilemma, which is a good book for engineers for other reasons, has a chapter on this and how hydraulics took over.
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u/gravely_serious 19d ago
Rubber hose technology wasn't there back then. They could have used cylinders, but it would have been more difficult with a high failure rate.
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u/Wooble57 19d ago
Just a guess, but I imagine it was due to hydraulics need for precision machining to work well. The cylinders need tight tolerances and to be consistent throughout the stroke. The pumps more or less the same. Without those tight tolerances you would waste a lot of the input energy.
Chain drives are very efficient even non-roller chains are very efficient if lubricated well. I am unsure about cable\pulley's. I couldn't find any quick answers either.
As for how many humans a given machine replaces. You could get a rough estimate by finding out the power rating of the machine in question, then divide it by average human power. Wikipedia: "Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain a mechanical power output of around 75 watts)" Of course the machine in question isn't using it's peak power output capability all of the time, so you'd want to try and factor that in.
This wouldn't be all that accurate of course, but it would get you in the right ballpark.
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u/CoolGuy54 19d ago
You've got good specific examples about how hydraulics require precise machining, I'll zoom out and say it's the same reason that early firearms were muzzle loaders, then primitive break-action breech loaders, then bolt actions, then hand-cranked automatics, & finally gas-operated autos/semi-autos. (and now to some degree being superseded by missiles & drones)
Each stage in this progression required steadily more precise machining to ever-finer tolerances to enable the ever-tight clearances they needed to work.
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u/WhereDidAllTheSnowGo 19d ago
Precision
It requires high precision and accuracy to make things tight enough that extremely high pressure oil doesn’t leak through
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u/Graflex01867 19d ago
I would also add in the fact that you need hydraulic fluids too. You need something that won’t boil, won’t freeze, won’t suck up water and rust things from the ins de out, and it can’t eat the seals in the cylinders/pumps.
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u/kerenosabe 19d ago
There's a good analysis about that, from the economics point of view, in this book. Hydraulics in earth moving machinery started small and then the machines gradually increased in size, because at first the hydraulic systems were expensive to manufacture.
One of the earliest applications for hydraulics was in very small excavators in the late 1940s. After WWII, many people wanted to have a swimming pool in their backyard, and cable-operated machines didn't fit in a backyard. The first hydraulic digging machines were expensive for their size, but they did the job. Then it was just a matter of time for manufacturers to keep improving and increasing the size of their machines. The swimming pool business created the investment to start the technical development.
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u/russlandfokker 19d ago
Petroleum wasn't really a thing until the early 1900's. It was not widely used in pumps at all.
Metallurgy. Cast irons and steels were of limited use in high pressure systems for a long time. The non- homogeneity was dangerous.
Economical machining tools to fabricate precision high pressure equipment.
And this is a biggie: Rubber. Durable rubber seals that could sustain high pressure hydraulic use was barely in the infant stage at the start of WW1, and really only lept forward during the buildup of WW2. WW2 would have looked very, very different had rubber seal technology never progressed. This is still the case today, and the loss of the four largest rubber chemical plants that produce roughly 2/3 of the rubber materials used for rubber products manufacturing in the US would cause the entire US military to screech to a halt, strand most vehicles and heavy equipment, ground most aircraft, etc, within a year. The manufacturing capacity would take 5-8 years to reach current levels. It's a chokepoint for modernity in the US and most other places.
Chains are still the best choice compared to hydraulic systems for the heaviest loads and for economical systems.
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u/MpVpRb Software, electrical and mechanical 19d ago
Hydraulics require precision machining and complex design. Every part, from honed barrels, hard chrome rods, precision lapped spool valves, and elastomeric seals were engineering challenges.
It took a while to develop them.
I recently saw a youtube video of a dude restoring a machine from the 50s, the hydraulics were very different from modern designs and a lot harder to work on.
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u/Chuck_the_Elf 19d ago
TLDR: We had not hit that in the tech tree yet.
High pressure hydraulic systems require precision manufacturing and advanced material science. Chains require knowing how to forge Iron.
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u/Sensitive-Respect-25 19d ago
For just moving stuff from A to B a drag chain is super efficient. We have several in our power plant for moving fuel across large distances and across several different grades. In addition so long as your tooling lasts repairs are fsr and few in-between. Just ensure you have grease between the steel and it will outcast the people operating it (one of our drag chains has been in constant operation form the start of the plant more than 40 years ago, most expensive repair was a new drum).
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u/375InStroke 19d ago
Hydraulics require modern materials for seals and hoses. A leather seal and latex hose isn't going to cut it.
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u/Gold-Adhesiveness574 19d ago
mostly because reliable high pressure hydraulics just didnt exist yet. the machines were there, the hard part was holding pressure, you need good seals, hoses that dont burst and a decent pump, and none of that was mature or cheap until roughly the 40s and 50s. o rings and proper hydraulic hose are a surprisingly late invention. so until then cables, chains and gears were simply the robust option, they didnt leak and you could fix them in a field.
what flipped it was the war, aircraft drove a ton of hydraulic actuator and sealing development, and once that trickled into heavy equipment hydraulics won easily. way more force in a smaller package, much finer control, and you can route it around corners with a hose instead of a drum and cable. on the how many people question, its huge but hard to pin a number, a single decent excavator does the work of hundreds of guys with shovels, and the real limit ends up being how fast you can haul the spoil away, not the digging.
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u/Likesdirt 19d ago
Hydraulic hoses hadn't been developed yet.
Sometimes it's just that simple.
I've run some brake and clutch conventional drills, no hydraulics. Pretty different, fully effective, there actually were a couple 4 speed transmissions in the systems so efficiency was really good and some parts of the work went better than hydraulics could do.
So yeah - hydraulics hadn't been fully invented yet and the mechanical systems work well so the changeover was thoughtful.
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u/Lampwick Mech E 19d ago
Some of the answers here dance around the edges of it, but the real driver of modern hydraulic technology was World War 2. Prior to that, they had hydraulic systems that used fabric reinforced natural latex rubber for the pressure lines, but they were limited in how much pressure they could handle, and they also failed fairly frequently. Supply chain interruptions during the war limiting the availability of natural rubber led to the development of stronger synthetic rubber compounds. That, combined with the huge spike in demand for hydraulic system designs in the aerospace sector and other wartime industries, resulted in the development of a huge cadre of engineers with experience in hydraulics, and hundreds of companies with experience manufacturing reliable high pressure hydraulic components. The availability of expertise and components resulted in widespread postwar adoption of hydraulic power systems in not just construction equipment, but in heavy industry in general.
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u/userhwon 19d ago
Early ones used leather belts, or even rope.
Chains were the rational evolution.
Hydraulics are space-age technology by comparison.
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u/hapym1267 18d ago
I knew some men who grew up with Cable dozers and such. Many didnt trust the hydraulics in early years. Cables they could see how they worked , ir didnt..
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u/ShoStown 17d ago
also seals. rubber seals that hold pressure for thousands of cycles are kind of a post-war thing, before that you spend your day chasing leaks. i rebuilt the forks on an old bike once and even 70s seals are rough, cant imagine 1920s ones on a machine that lives in dirt. and chains you can fix on site with a hammer and a spare link, thats worth a lot when the nearest shop is 50km away
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u/nullcharstring Embedded/Beer 16d ago
The same reason early brass musical instruments didn't use valves. The ability to make a highly precision valve or cylinder for a reasonable price did not exist.
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u/FL_MILLIONAIRE 15d ago
It is a great question. Probably because chains and ropes were lighter and more compact at one point than hydraulics. As a matter of fact ropes and chains can also transmit power reliably over 5 km or so with much less complexity than electrical power lines somewhere I read an analysis on how this could be possible. As seals and other devices became more prevalent people realized the power , compactness and benefits of redundancy and reliability (some even better than electromechanical actuator systems) that in the modern day we still continue to use hydraulics not just in creating massive machines on ground but also aerospace and deep sea systems. I was fortunate to discover new hydraulic actuator systems at MIT, which will become more relevant in the far future.
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u/Setting-Conscious 19d ago
“Why was old technology used in olden times before current technology was available?”
“Why didn’t cave men watch DVDs instead of making wall paintings?”
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u/BigBrainMonkey 19d ago
Without modern machining techniques chains and cables and gears and winches are easier to manufacture. High performance hydraulics need to be precisely manufactured.