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I agree that it's important to talk about motion sickness. I was pointing out that the way the article deals with it (remarking that the proposed system may inv

by zeteo 13y ago

I agree that it's important to talk about motion sickness. I was pointing out that the way the article deals with it (remarking that the proposed system may involve 12% higher lateral accelerations than HSR, and instantly dismissing it as a "barf ride") is inadequate. Here are a few questions that I don't know the answer to, but seem a lot more interesting: - Do we have studies that estimate the effect of lateral acceleration on motion sickness? What do they indicate (e.g. 0.1% of passengers get it at 4 m/s^2, 2% at 5 m/s^2 etc.)? - To what extent is motion sickness in HSR comparable to the proposed system? Are the differences (no outside visibility, different vibrations model, possibly different seating) significant and if so how? - To what extent do potential passengers care about motion sickness? Has anyone compared cost and convenience trade-offs for systems with different expectations of motion sickness e.g. ferry vs. train? How comfortable are passengers with self-medication in such contingencies? Etc. And motion sickness is only one of hundreds of possible serious weaknesses in this project. But this is inherent in anything that hasn't been tried before; anyone can think of hundreds of ways in which it can go wrong. Does this mean we should never work on anything that isn't fully proven?

akjj 13y ago
> (remarking that the proposed system may involve 12% higher lateral accelerations than HSR, and instantly dismissing it as a "barf ride") You're comparing apples to oranges here. If I understand the OP correctly, the 4.37 m/s^2 (which is a claimed maximum, not actually in practice, but let's ignore that) is in the plane of the ground. Canting will convert that acceleration into a mixture of horizontal and vertical acceleration, as experienced by the passenger. The hyperloop track has 11.1 m/s^2 of acceleration in the plane of the ground based on their path assumptions (= (480km/h = 133 m/s)^2 / 1600 m), which the OP claims can get converted to 5 m/s^2 of vertical acceleration. This 7 times greater than "track specifications" of 0.5-0.67 m/s^2 and 5 times greater than the 0.93 m/s^2 of vertical acceleration coming from the Transrapid's 4.37 m/s^2 in the plane of the ground. To step back for a minute, the issues with curve radius for high-speed transit have existed since the beginnings of high-speed rail 50 years ago and maybe longer. It's one of the major issues preventing Amtrak from going faster in the Northeast corridor, for example. If there was some easy way (blocking windows, lowering vibrations, changing expectations, self-medication) to deal with it, our first assumption should be that someone's already tried it. If Elon Musk had some new, breakthrough ideas in this regard, then our assumption should be that he would somehow mention it, rather than expecting the Internet to figure it out from the numbers he uses. In the absence of evidence that any of the thousands of people who have designed high-speed transit allow for such sharp turns, or that the hyperloop designers have any way to mitigate the effects of high acceleration, I think the most likely possibility is that they (some of whom work for SpaceX, remember) used acceleration limits coming from the space program. Since they seem never bothered to compare to look at actual high-speed rail systems, they never noticed how different their assumptions where.

by zeteo 13y ago

akjj 13y ago

> (remarking that the proposed system may involve 12% higher lateral accelerations than HSR, and instantly dismissing it as a "barf ride") You're comparing apples to oranges here. If I understand the OP correctly, the 4.37 m/s^2 (which is a claimed maximum, not actually in practice, but let's ignore that) is in the plane of the ground. Canting will convert that acceleration into a mixture of horizontal and vertical acceleration, as experienced by the passenger. The hyperloop track has 11.1 m/s^2 of acceleration in the plane of the ground based on their path assumptions (= (480km/h = 133 m/s)^2 / 1600 m), which the OP claims can get converted to 5 m/s^2 of vertical acceleration. This 7 times greater than "track specifications" of 0.5-0.67 m/s^2 and 5 times greater than the 0.93 m/s^2 of vertical acceleration coming from the Transrapid's 4.37 m/s^2 in the plane of the ground. To step back for a minute, the issues with curve radius for high-speed transit have existed since the beginnings of high-speed rail 50 years ago and maybe longer. It's one of the major issues preventing Amtrak from going faster in the Northeast corridor, for example. If there was some easy way (blocking windows, lowering vibrations, changing expectations, self-medication) to deal with it, our first assumption should be that someone's already tried it. If Elon Musk had some new, breakthrough ideas in this regard, then our assumption should be that he would somehow mention it, rather than expecting the Internet to figure it out from the numbers he uses. In the absence of evidence that any of the thousands of people who have designed high-speed transit allow for such sharp turns, or that the hyperloop designers have any way to mitigate the effects of high acceleration, I think the most likely possibility is that they (some of whom work for SpaceX, remember) used acceleration limits coming from the space program. Since they seem never bothered to compare to look at actual high-speed rail systems, they never noticed how different their assumptions where.