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Comment by jay_kyburz | Hacker News Reader

Yeah, instead of a swarm you could have one gigantic arm that can reach anywhere.

Gigantic arms are not feasible because of how torque and leverage work.

As your arm gets longer, it has to get stronger, thus heavier, thus requiring larger motors, and anchored to the ground better. After a handful of meters, robot arms can’t hold themselves up, let alone carry a useful tool.

There are multiple meter long robot arms for lifting big things in factories but they are enormous, enormously expensive, and consume enormous power.

But here’s a delightful concept that sidesteps this, by making the arm weigh nothing:

https://youtu.be/INTHRNcyW9w

This could simultaneously absolve the need for autonomous vehicles, because whenever you need to go somewhere, you could just make the giant arm put you there.

That's called a train. It's great. You can read a book while you are transported, it uses very little power to get you there, it can be 0 emission, there are no traffic jams. Sadly it's not fashionable cause you can't show off how wealthy you are by using it.

I occasionally take the train because I like the atmosphere.

In Europe, taking the train is often more expensive than flying.

Sadly it's not fashionable because it isn't cheaper and takes a lot longer.

That's because trains get taxed, while flights _still_ get subsidised. It's maddening.

It's faster than flights on short (<3 hour) routes because you don't have the whole security theatre thing. Also train stations are in the city center usually and airports are in the outskirts.

On more actual security concerns side, you will have a hard time hijacking a train and jet into the side of a skyscraper.

The far more common scenario - a bomb in a bag - is very devastating in closed spaces such as trains and buses.

Nobody does it in trains/buses, cause it's much more efficient to do it at the train/bus station. Or any other place where people queue.

It's happened dozens of times in my country - I've lost schoolmates (not personal friends) in bus bombings.

First class wagons are used exactly for that, to show the wealth.

Not really. I often take 1st class because 2nd class is full and I'd have to stand for 2 hours and the difference is 5-10 USD.

> There are no traffic jams

In the US, most tracks prioritize freight traffic over passenger rail. And there is a tremendous amount of freight traffic. There may not often be traffic jams, but when you are diverted to side track to wait and allow a priority freight train through, it's not uncommon to wait a very long time (I've been delayed more than an hour on the 3 hour train ride from Portland to Seattle).

There are also huge bottlenecks in US track infrastructure that absolutely do lead to traffic jams - perhaps most infamously in New York City. Vetoing the addition of 6 additional tracks through NYC is one of the reason Chris Christie was so hated.

Why not both? You could have each train actually be an array of arms that reach out and pick people up and move them along their route. The arms wouldn't have to be as long since the train is moving along the rail, and a select number of arms could be reserved for first class passengers.

Sure you can

https://www.amtrak.com/privately-owned-rail-cars

There was even some hn post on it where someone detailed how much it costs and what you get

Just piggyback off of center-pivot irrigation arms. Attach little arms to it that destroy weeds and apply pesticides

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