Sunday, December 20, 2015

Modularizing PRT

Let’s Hope, for Santa’s sake, that the nations of the world make 2016 a banner year by actually acting on the agreements reached at the recent international climate summit! PRT is too good of a solution to languish for long in a world that is finally getting serious about carbon reduction!

One problem that is holding up the implementation of PRT, ironically, is the speed of technological progress. In eras past, such big projects could be tackled with the assurance that they would remain cutting-edge for years to come, so any government contributions would remain relevant and financial stakeholders would enjoy a fairly long-term leg up on the competition as well. These days, better techniques, materials and methods come along almost faster than whiteboard ink can dry. In particular, the progress toward electric and self-driving cars, better batteries, robotics, communications and so forth creates the impression that any major innovations in transportation field may well be obsolete or unneeded soon anyway. After all, many of us still have our share of VCR players, film cameras, and cassette tapes somewhere in the basement, and what mayor or transit chief wants to create a highly visible, far-flung legacy that ends up looking as modern as an eight foot home satellite dish? Like it or not, cutting-edge means little-explored, unvetted, vulnerable to being leapfrogged. With the speed of technological change being as fast as it is, is it any wonder that neither government (local, state or federal) nor private investors want to stick their necks out on tech ventures that involve so much untested ground?

Making sure that the PRT infrastructure remains useful for decades to come requires a careful analysis of the problems that PRT is supposed to solve and designing the machinery, software and architecture with an eye on that distant future. To do this, we must bet on various assumptions, many of which are, luckily, quite likely. For example, it can be wagered that land for stations in the inner city will not get cheaper or more plentiful. It can be assumed that the expectations for comfort, speed, quietness, will become more demanding over time. It is not good enough to come up with the best option currently available. What is needed is a solution that will evolve to be better and better, and will never be eclipsed by some new technology that unexpectedly becomes polished and cost effective.

Too bad the challenge isn’t confined to the just the vehicles. Daily use always reveals design shortcomings, and new additions to a fleet will surely sport many improvements. Evolution happens more quickly for parts of a system that are frequently replaced. Conversely, (and this is the problem) since the track should last for many decades, we are seemingly stuck with whatever we start with.
The obvious downside of making such wrong choices was a motivation for establishing this blog and a call for consensus and standards. It soon became clear, however, that various PRT developers would always differ on what design approaches would win the day, and that it hardly mattered anyway. Financial backers have little interest in anything beyond getting an initial contract and ownership of proprietary technologies. Yet perhaps there is a way to address this whole problem of obsolescence that makes sense for all stakeholders in both the long and short term; Modularization!

Modularizing PRT (or any other system) ensures that only a barest minimum of components cannot be easily swapped with updated versions. As readers of this blog know all too well, a tremendous amount of work has been done herein on bogie designs that were later scrapped. The bogie, of course, fits within a mating track, so if the bogie is not perfect all of the track for years to come will have the same shortcoming. It is like introducing a bad gene into an organism that will be carried down through generations of offspring. By modularizing the mating components, this risk can be minimized. In particular, PRT track, of the sort we are dealing with here, can be divided into two functions. The first is to provide rigidity across a span, like a bridge, and the second is to provide the interior with rolling surfaces, electrical and data carrying structures, and so forth. This second aspect can, in whole or in part, be replaceable, adjustable, or otherwise be modifiable. This is not an intuitive way to treat track design, the first instinct being to make the track as simple, strong and affordable as possible through tight integration. There are, however, natural boundaries within the track that can be exploited. Issues of thermal expansion, sound and vibration isolation, third rail and cable maintenance, etc. all tend to favor fastened inner structural elements over direct, permanent (welded) attachment to the structure. Note also that, within the SMART framework, there are already specialized track “innards” for climbing or making tight turns. Even the structural shell has some modularization, first, because lengths of track would most likely be manufactured off-site in prescribed lengths and turning radii, but second, because the left and right halves from a length of track would optimally be detachable from each other so as to facilitate the insertion of switch points or just for ease of access.

Modularizing elements of the track also makes the initial design of the bogey much easier because it can be designed for what is most practical and cost-effective today without as much fear of introducing some demon-seed design detail that will be impossible to exorcise at a future date.

Modularizing key track elements also facilitates adjustability. Rather than setting internal dimensions in stone, why not build-in a range instead? Especially if it only involves punching a few alternative bolt holes – sort of like adjustable shelves? 
This illustration shows just how simple modular PRT running surfaces can be. Two pieces of angle steel, (red) and two inner guide rails are the only continuous components in this (evolving) “Mama Bear” configuration, other than the “third rail” electrical contacts and “leaky cable” Ethernet communications. (Not shown.) In other words, if a city were to, for some reason, change to some other system, there need not be a whole lot to swap out.

Today, PRT’s advantage shouldn’t be seen so much in terms of robotic vehicles, but rather as the most practical way to enter, exit or bypass the stop-and-go ground-level congestion that is an unavoidable part of urbanized life. It is the exploitation of unused “air-corridors,” and it can only be accomplished in such an affordable and compact fashion (and with such high vehicle density) using automation, or it would have been done long ago. We may well even be entering an era of “If you build it, they will come,” when it comes to PRT track, since exploiting these corridors represents a quantum efficiency advance in the same vein as the ongoing efforts of companies like Amazon, Google, Apple, Tesla, etc.       

In a future where ground-based automated vehicles are commonplace, PRT will still add an important, complimentary contribution, but besides being affordable and long lasting, it must be versatile. Making track components modular and adjustable seems like a vital first step in making sure that first iteration systems do not become obsolete in the face subsequent designs and this, of course, is prerequisite to being seen as a good long term investment for a city. In other words, any PRT system isn’t seen as future-proof is toast because nobody will take a chance on it in the first place! Well, back to the drawing board...

Happy Holidays from Dan the Blogger!


dygituljunky said...

I think I would be careful with modularity. The bogie design looks pretty solid, as is. Since the bogie and the track have to work together, I think they should be designed as a married pair.

About the only modularity that I would suggest within the bogie is the option of linear induction motors or larger mid-bogie motors with the power transmitted to the wheels via a transfer case. The rest of the bogie design looks pretty solid, already.

I think that a better way of considering modularity at this point is to consider bogies, themselves, to be modules in a larger carriage system. In particular, I mean that bogies can be connected by bridges to distribute the mass of heavier carriages along the guideway.

The end-game iteration of bridged bogies is carrying everything from personal-sized vehicles to train-sized vehicles or individual maximum-dimension ISO containers in the same guideway as PRT. Carrying freight is important because freight pays the bills (for railroads, anyway) and freight deliveries can use extra available headway. Containerized freight is also a prime candidate for automation.

It's pretty hard to scale an under-sized system up but pretty easy to design lightweight bogies to use a system built for heavy loads.

dygituljunky said...

Hmm, it seems I missed at least one post where you consider these very things (the post about the Three Bears).

Dan said...

DTBR (Dan the Blogger Responds)...

Welcome, dygituljunky! Your comment points out a real problem with my SMART initiative and this blog in general. There is no central place where the whole system is described. Some aspects are brand new and some date back years, and I doubt that even 10% of readers have a full grasp of the design as it now stands. For example, without going all of the way back to 2011, (post 131) and extrapolating from that earlier bogie design, there is little logic to having a motor for every wheel. (131 explains how they need to run at different speeds when initiating a climb, and using the google widget you can find a discussion of the left and right wheels rotating at different speeds to act as a differential – but you need to type “differencial” or you’ll never find it!) And that is just one example. What new reader will ever discover my 2009 idea of integrating continuous (angled away) LED street lighting?

For what it is worth, I have a draft of new “About this blog” text and have otherwise given a fair amount of thought about how to update this beast. This Blogger format is not really structured for lots of static content, but I already know it and that frees me up to concentrate on what I do best. My current thinking is that I will re-introduce the key elements of the SMART design one-by-one as new posts, then link to them in some updated cover page material. There are a couple of old posts that I can also overwrite in this effort.

Bottom line – a person should be able to visit this site and come away with an understanding of the system as it stands, which, at this point, is really pretty mature. It is certainly not the blank slate we started with in ’08 and that the cover material still represents! There are still lots of “i”s to dot and “t”s to cross, I still value reader input, and I do not doubt that that a few major breakthroughs might still be in store, but it clearly is time to package “SMART” and “run it up the flag pole,” as they say.

What happened to you, dygituljuncky, has happened to others, and no-doubt the jumbled state of this blog is an inhibiting factor in having people post comments in the first place. Thanks for taking the plunge!