Robert Comsol wrote:
I don't think [pneumatics is] a credible idea either.
As I was showering for work this morning, the problems just kept piling up in my head. First, the object driven by air pressure has to travel along its long axis, bullet-style; you can't push a cab from the side, because once it tips just slightly, it jams against the tube interior. So you'd still need some means of registering the cab precisely against the tube, and once you have that then it might as well be your locomotion method as well.
Artificial gravity could theoretically let all the tubes fire bullet-style, but then we would never see the "deck lights" moving horizontally, the gravitational micro-management would be a nightmare, and I hate to think of the effect on everyone's inner ear.
Then, you have to think about acceleration, deceleration, emergency stops, sharp turns, horizontal/vertical switchovers ... we're going to control all that by shooting air down a shaft that 12 other cabs are sharing right now?
The audio cues are a problem, too. They indicate mechanical processes, not pneumatic, and they track with the cab
, not the shaft. Surely each cab doesn't have its own blowers and vacuums spread across all surfaces? Might as well make them all little shuttlepods instead (which I guess is another possibility).
showed us the inside of a Picard-era tube (yeah, it's not TOS, but I do think it's relevant), and it certainly wasn't an airtight seal. The ladder, lights, control panels, and other in-shaft textures make that impossible. Also, how would you use pneumatics to precisely stop the cab at either of the decks shown in this shot?
And even if you could, the need to close valves at both ends of every section a cab is in means only one cab per section; you could never serve multiple termini per section in the same time frame. That's a lot of doors all waiting their turn, and where are the valves anyway?
Finally, pneumatics completely forbids any possibility of multi-lane tubes or cabs passing each other, unless we build expensive and wasteful parallel tubes, each of which is fully formed with its own valves and blowers in every segment. Essentially, every individual "shaft segment" (by which I mean the smallest stretch that could be isolated by closing valves) becomes the equivalent of a rickety old one-lane country bridge, where cabs have to stop and wait their turn to use it, one at a time regardless of direction. And there would need to be an "airlock" at every juncture between segments, too.
What a mess! Pneumatics really seems like just about the worst possible explanation for turbolift locomotion. Site-to-site beaming and micro-warp tunnels, as ridiculous as those would be, probably offer more feasible options. But I still think it can all be done with wheels or gears on the cabs.
As I thought about that more, I began to think that the main shafts in each section perhaps need to be double-wide, like two-lane highways, with a convention that cabs "travel on the right" or whatever. Like subway tubes. This would eliminate the need to stop and wait for somebody else going the opposite way through the same shaft, and also minimize the need for "passing."
Back to the wheels issue, if (for simplicity) we imagine the cab as an elongated cube with six faces, then it needs swiveling wheels on all six faces (at least two per face, possibly more). For motion, it would engage and align all wheels on the four faces that are parallel to the travel axis. Then, as junctions come along, it doesn't matter where they are; the wheels just continue to grab whatever tube walls are available as other walls temporarily drop out and return.
Under this scheme, cabs could traverse complex intersections and could always move as long as there were at least two opposing faces to get traction against. You could have a four-way or even six-way horizontal intersection, as long as it has a floor and a ceiling. You could have a vertical tube intersect a horizontal one, as long as the third axis has no junctions so there are still two opposing "sides" to grab hold of (as Albertese pointed out).
In my animation, since the side walls have so much variability, most of the time it is primarily the top/bottom wheels that are providing the traction on the cabs you see moving. To intersect a vertical tube into my hypothetical setup, you have to do it at a point where the horizontal situation is less 'busy' (i.e., out in the travel shaft; you can't do it above or below the terminus itself or its standby area). Basically, you can't have a cab in a "corner" — just like Santa climbing a chimney, you need at least two opposing faces at all times to push against. Fortunately, this should be easily doable with prudent deck design.
Now, those TNG images have no visible means of locomotion on the top of the cab, leaving us to wonder exactly how it would travel horizontally in complex tube junctions. Perhaps we chalk it up to TV production, or maybe in that era they use force fields to shove the things around. But I still think wheels are the most practical and cost-effective means. If we have the technology and the energy
to use force fields or transporter beams or warp conduits or wormholes or mini impulse engines to move the cabs around, then why not dispense with the cabs altogether and just move people
that way, a la Futurama
's pedestrian tubes or just simple site-to-site beaming?
The fact that turbolifts need to continue to function when other ship's systems are down (and indeed we do see this in many episodes) suggests that they should use the simplest technology available, not the most complex.
The thing about force fields and antigravity is that they are slow. Dog slow. Think about all the times we've seen an antigrav sled or M-4 or Nomad slogging around at a top speed of 0.7 miles per hour. We can blame TV production again here; but also, when people's lives are at stake and collision avoidance is paramount, you can't really afford high speed or acceleration when there's no friction-based means of slowing things back down. Ever see a hovercraft stop on a dime? Me neither. Turbolifts need to be fast. Cheetah fast. Wheels can do that for us, safely and cost-effectively.
Fanciful, exotic explanations that sound all GR-whiz-bang (like the unseen 'sonic showers' Mr. Roddenberry was so proud of at the convention I attended when I was 12, or the oft-repeated nonsense about there being no money in the future) are fun to think about, but usually fall apart under a bit of real scrutiny. In the end, for believability, relatability, and (don't forget this one) good storytelling, we still see the ship's crew drinking good old-fashioned coffee from cups, washing their faces with water
, bribing people, purchasing souvenirs, eating turkey on Thanksgiving, and having conversations about all kinds of mundane things that will still be part of the human condition even if we make it to the year 3,000. Like wheels.
When it comes to engineering a real solution, we'd be foolish not to at least consider the simple one.