Hacker News Reader

Comment by meche123 | Hacker News Reader

Because you have to replicate the same complicated mechanism for all the cars. Moreover, if a gyro in one of cars malfunctions the whole train is at risk.

Another problem is that the system is reactive, meaning that there is a lot of shaking and balancing that is quite unacceptable - think about drinking a cup of tea in such a wobbly train even on straight lines, while on curves it's not staying horizontal by design.

Yet another problem is that it can't share the current infrastructure without major switch changes while sharing the infrastructure the other way around is impossible.

And in the end all of this effort for trying to fix a problem that doesn't really exist, at least not in Europe where most of the rail infrastructure was already built 100 years ago.

View on HN

> ”while on curves it's not staying horizontal by design”

Worth noting that modern tilting trains do this quite successfully (on two rails!), in order to run faster on tracks with tight curves. By “leaning in” to curves, you make the ride more comfortable, not less.

Tilting trains are used extensively on the UK’s West Coast Main Line, for example.

> By “leaning in” to curves, you make the ride more comfortable, not less.

That is the intention, but many people report discomfort due to the non-ideal adjustments, at least for the tilting trains in germany.

I'm one of those people.

I commute 50 mins each way on a Pendolino in the UK (into and out of London) and find that if I'm doing work on my laptop, or responding to emails on my phone as the train tilts I feel uncomfortable and dizzy.

The "slow" Desiro trains that don't tilt take 2 minutes longer to get into London, because whilst their top speed is 15Mph lower they accelerate faster.

Do you still feel uncomfortable if you cannot see outside the train at all (i.e. not even in peripheral vision)? My understanding was that the effect was caused by the scenery outside the window moving in a way that's incommensurate with what your sense of balance is telling you.

It's connected to how our attention works. Attention is very much tied to vision and, for instance, if you are rotating around your central axis (like a Sufi) and can manage not to focus visually on anything around you and do some "proprioceptive attention adjustments", you can keep spinning for quite a long time w/o getting dizzy. Of course you'll have to slow down slowly rather than just abruptly stop the rotation.

It tends to be better if I look out the window, it's the looking at a screen and my inner ear sensing the movement that mucks me up I think.

Interestingly, I don't get motion sickness in VR, which is the opposite problem (movement visually, none in reality).

Ideal adjustments (full compensation) are more uncomfortable.

Thought to be so, because there's a mismatch been visual and inner ear inputs. That is: you can see you're going around a corner, but you don't feel it. Resulting in motion sickness. Since all people have different tolerances of motion sickness, it's impossible to have a "correct" amount.

Almost all systems compromise between zero and full compensation, but passenger comfort is just one of many factors, and not the most significant. The discomfort on German tilting trains is probably because they are too close to "ideal".

Ideal (in the sense of fully compensated) is worse, but ideal in the sense of at the right time, with smooth interior motion, is much better. A "perfect" tilting train shouldn't feel much different than superelevation to the same level, but it does.

One of the issues with the German tilting trains is that they try to compensate up to 8° without track knowledge (BR 612) thus the first carriage (the one after that less so) swinging abruptly to compensate when entering or exiting a curve. Not sure how the class 390s solve that problem.

So you're saying the rate of change of compensation (or "jerk rate" when entering and exiting a curve, as people enjoy calling it) is worse on tilting trains?

I would love to see some data - I assumed this was a solved problem, but I wouldn't be too surprised if the tolerances were revised to fit the problem.

I forgot to mention the 'interesting' part of this problem: that the effects are measured cumulatively. That is, against passenger journey length. Drivers and other staff are not considered as far as I know!

And there's zero redundancy. If 1 of those piston seals or valves fail, the whole train is at risk for catastrophic failure.

Clever engineering without a necessary, defensible, competitive business advantage usually becomes either a hobby or an art project.

And if one rail has a gap or defect.

Yes, the part of the video that said this would work on existing infrastructure is entirely wrong.

It could be interesting with it's own infrastructure, though my first thought is that it might be better suited to tunnels, being able to maximize use of the tunnel profile.

Reply on news.ycombinator.com