Wednesday, October 28, 2015

There Will Be a Quizz.



In the last post I referred to PRT as a kind of “Urban Wormhole” and spoke of how self-driving taxis could never replace PRT. I would like, in, this post, to follow up on that a bit. I think it is important to make the relevant arguments clear and on the table for all who will listen. An entirely new and untried transportation infrastructure is a tall order, yet I believe there are unassailable arguments why such an augmentation to our current systems is necessary and inevitable. I have included a short quiz in this post, designed to (hopefully) win someone over. Now, if I could just come up with a really catchy slogan….
  
The robotic car push reminds me of that stage of the internet revolution that centered on perfecting the dial-up modem, which of course, can only be as good as the phone wires it is connected to. In the case of mobility, at least in urbanized areas, the main problem is that there is an inherent cap on our surface transportation’s efficiency. It is, at best, 50%. The reason is simple. Simple physics dictates that if 50% of traffic wants to go east/west, and the other half wants to go north/south, each will have to yield right-of-way 50% of the time, once a line for each direction has developed. Nothing but passing over or under that crossing traffic can improve this dismal number. And that is the best case for the intersection itself. Were we to measure efficiency based on the time difference between “making the light” in no traffic and what can typically happen in rush hour for individual cars, that efficiency number would be much, much worse… 15 – 20% perhaps? And that is only one, and they add up! In what other endeavor would we put up with such inefficiency?

This is all unfortunate because, with the possible exception of bike trails or sidewalks, there is no current surface transportation infrastructure that can be elevated or buried economically enough to generally allow multi-level, non-stop traffic flow. If it WERE economical, we would not have such gridlock today!

Vehicles, and the surfaces constructed for them to roll upon, (this includes rail) have evolved to be too big, cumbersome, and expensive to be the only alternatives in space constrained, urban areas.  How ironic that, in a quest for the efficiency of carrying more load per vehicle trip, we have accomplished exactly the opposite! In all fairness, bigger really IS better, once you get out of town a bit – yet gridlock is the elephant in the room when it comes to urban mobility and robotic cars can only be of peripheral help in the current context. Any real solution demands an infrastructure specifically designed for non-stop travel in all directions at once, and logic dictates that this architecture be smaller, not bigger. The fiber optic cable of transportation! Actually, it is within this framework that automatic driving technology can really shine. With a faster, yet smaller “pipeline” the driving decisions would come at a much faster rate as well. No place to be texting!

So here is the quiz. It is more for making people think and to stimulate conversation than anything else. Maybe it will help win a few converts!

1] Non-stop ground transportation can only be achieved by incorporating overpasses/underpasses but this is impractical for widespread use because of the heavy loads that our current roads and rail systems are designed to carry.  True/False
2] The majority of vehicles on the road are carrying payloads, including people, that weigh just a tiny fraction of what roads are built to carry, and this represents a waste of resources if more appropriately scaled infrastructure is possible. True/False
3] The ONLY way for most travel to be non-stop within an urban/suburban environment is to create a new, more affordable infrastructure which is necessarily aerial and sized appropriately for lighter payloads, such as people.  True/False  
4] The technologies for automatic vehicular and traffic control to utilize such an infrastructure have now come of age.   True/False 

There. Saying “False” to any one of these will hopefully start a thoughtful debate at least. “Grass roots” movements have to start with consensus, and consensus must start somewhere!   

When I started this blog, part of the mission was to create some standardization, particularly with regard to the track. Seen in this light, it can be better understood why so many PRT bogie/track designs have been explored on this site. The world needs an infrastructure for urban/suburban mobility that allows non-stop travel. Dual-mode? Fare based? Privately owned? In a way it really doesn’t matter. To me the question is, “What are the mechanical/architectural underpinnings that will best encourage the development and proliferation of such a system?”  We need the combination of present practicality and boundless future possibilities if we want to propose it as a solution worthy being added to skylines across the globe. I believe a PRT track can be designed that includes very little beyond the architectural structure that is required for spanning between support posts. Sort of a standard PRT building block, which (as most of you know) I have dubbed the SMART (Suspended Multi-Axis Automated Rail Transport) platform.


A brief progress report is, perhaps, in order. In the design pictured up top, I have continued with the theme of using off-the-shelf-parts, and experimented with putting the four motors between the drive wheels instead of off of the ends, and this shot highlights a new cam-driven lever-type switching-guide-wheel mechanism.



Right this minute, the holdup is this – I love the idea of being able to remove the side of the track that normally switches off (right if you are American, left if you are British) without diverting PRT traffic. This would allow switches to be added or removed with minimal disruption in instances where no alternative routing exists, such as is likely to happen again and again on the outer edges of any growing network. Unfortunately this entails running on the left wheels alone and doubles the load on them. If the wheels are to be soft enough to cushion vibration and smoothly handle expansion joints, and especially if they use ordinary, safety-rated pneumatic tires, they will compress under the load and maybe even deform side to side, adding substantial complication to what could otherwise be a super simple switching scheme.

In these last two pics first note that the steering wheel guides have been turned upside down (compared to the one on top) and there are no longer two sets per side, like in previous posts. It looks like this would be sufficient, even in this "half-track" mode, if we wanted to use custom solid tires designed not to rock or compress too much. Unfortunately I would like to make this cheap and straight forward enough for an individual, company or university to build for experimental purposes…, hence the “off-the-shelf” trailer tires. (Smaller, higher pressures and stiffer sidewalls than automotive)

Finally note how the track’s spine is missing the opposing C channel, since that side has been removed. That otherwise sandwiched plate is a splicing means, a potential hanger for cable stays and placing an upside down “U” channel over it can create a waterproof seal, like in a standing-seam metal roof, when used with the sheet metal sheathing, which is curved to stiffen it between structural ribs.  Work continues! 

7 comments:

Lee said...

Dan,
You express concern about having the wheels compress or requiring foam filled tires. I feel that the reason autos today have air filled tires is due to the fact that the roads are not smooth and have holes in them. With the steal rimed wooden wheels on wagons of old the wheels were so large that the ruts and holes were not of great concern. The seat had springs to cushion the rough ride. The smaller auto wheels required some shock absorbing material to allow the wheel to go over the ruts and holes without the jarring that would occur with solid wheels.
When railroads came along the rails were smooth so the wheels are steel. The cushioning comes from springs between the wheels and the cars. Why not do the same thing on the bogie? Have steel wheels and put shock absorbing units in the POD support column?
Lee

Lee said...

Dan
In your June Blog you were thinking about redistributing the weight of the POD so the rear wheels would not tend to lift as wind resistance increased. I have wondered for some time how you deal with speed changes. I feel that on a system there would be different ‘speed limits’ for different sections. In addition the slowing and stopping at stations and the acceleration would seem to have the POD swinging front to back like the ringer in a bell. Passengers would get ‘sea-sick’ with this motion.
My solution is to have the POD suspended on two columns and from two Bogies. If the Bogies were connected with a platform mounted on top of the bogies with a bearing unit so each bogie could turn independent of the other one the unit could still navigate tight turns. If the plate were to dip in the space between bogies there would be a place for the electronic controller, backup batteries etc. I have wondered on your bogie drawing I never see provision for the control unit etc.
Another advantage of having two bogies is that there are twice the wheels and motors. The motors could be smaller (lighter?) and if one bogie develops a problem the other one should be able to drive the unit to a station.
Lee

Lee said...

Dan,
When I first saw your ‘papa bear, moma bear and baby bear’ proposal I did not think much of it. However looking at the bottom drawing in your January post, where there were two together, I think I saw what you are proposing. The top picture seemed to show three totally different track designs but the bottom one seemed to show the same basic design for all three only different heights (and support abilities) for each one.
In the area where I would like to see a demonstration system built I can see applications for all three tracks. In residential areas the track should be as lightweight as possible so it will be as invisible as possible, so here you have ‘baby bear’ track. In commercial areas this would not be as much of a problem so ‘mama bear’ works. However for longer sections where the use of GRT would be more efficient the large ‘papa bear’ track would be used and as it would follow main highways the larger size would not be a problem.
In my desired area there are of course residential neighborhoods so when the system expands into these areas the small 'mama bear' track and PODs that carry 2 – 4 passengers only will be allowed. In the commercial areas the 'baby bear' PODs can travel but some larger 'mama bear' PODs that carry 6-10 passengers will be allowed to move people between commercial and employment centers. The ‘papa bear’ track would only carry larger GRT PODs that carry 10 – 20 passengers. These would service centers where larger groups of people will want to go together. I envision the last track connecting 'transfer' stations around the town and taking people to the airport or larger work centers. People could park by these stations or catch a local POD that brings them to the transfer station and go to work or the airport.
It seems that the ‘mama bear’ and ‘papa bear’ PODs could be modified to carry freight which would reduce truck traffic and I think be cheaper than trucks. Restricted tracks could go behind commercial units for deliveries. Only authorized units would be allowed. Well I suppose the ‘baby bear’ PODs could deliver pizzas to residential neighborhoods too.
Having the same ‘basic’ track would reduce costs and allow interaction between tracks. The ‘baby bear’ PODs could travel on any track. The mama bear’ PODs could travel on ‘mama bear’ and ‘papa bear’ track and the ‘papa bear’ PODs could only travel on the ‘papa bear’ track. Am I seeing your proposal correctly?
Lee

Dan said...

Dan The Blogger Responds.
Lee, you put a lot on my plate, but I will try to take these on, one-by-one.

I agree with your general assessment of tires. With the possible exception of expansion joints, the track should be very smooth, so ordinary road tires would not be my first choice either. As far as cushioning, I am mostly concerned about resonant frequency vibrations in the track itself, which could even act as a sound box, amplifying wheel noise the way pipes in a pipe organ make a great bellowing sound from a small amount of air. I think it would be highly dangerous to design a system than anyone might ever consider even slightly noisy, so I aim for silence, although I know that is unachievable. I have always planned on vibration dampening means between cab and bogie as you suggest.

The wheel material should be softer than the track material for reasons of track wear, particularly because it is so hard to get to. Softer wheels also enable the kind of traction for acceleration and deceleration that we are accustomed to when we drive, and with G-force compensating servos, (instead of the “gondola” swinging freely) maneuvers that would make you tensely grip your car seat will feel quite tame, not even tipping your drink, so I don’t want to “design in” potential performance (traction) limitations at this stage.

The main reason for the trailer tires, however, is cost. I think we should be wary of assuming economies of scale in the design stage, since prototypes will need to be constructed and tested, and small scale demonstration systems will come before any widespread adoption. It would be particularly useful if individuals or universities could actually afford to experiment with full-size systems. Such budgets will undoubtedly be extremely tight and using commoditized components, where possible, keeps the experimentation affordable. Someday, I’ll design a solid wheel that uses a rubberized formulation of Dupont’s Hylene, which will last forever while cutting wind resistance by a third, but one step at a time!

Dan said...

Lee, in regard to your second comment I would refer you to post 115 to understand why swinging or uneven loads are not a problem. (actually 24, 28 first raise the issue and propose solutions) As far as the rear wheel lifting, that is a problem that would only occur at very high speeds into very strong headwinds if at all. Also, while I used to think that extremely close wheel spacing was necessary for very tight turns, I have identified track modifications to enable this, so I can expand my wheelbase somewhat. In any case, as long as there is forward compatibility with speeds over, say 90 mph, I don’t see any need to get too excited about it in a first-generation design whose vehicles might not go much more than half that fast. I just want to make sure any track installed now would not limit performance of vehicles years down the road.

A double bogie is an idea I have worked on myself, and has its advantages. Actually, that was my working assumption in the early days of this blog and was all I would show prior to mid-2009. The thorny issue, though, lies with the connecting platform you speak of … it needs a universal joint at each end or you can’t do tight turns up and down as well as side-to-side. Then the vehicle may need to hang from it, because if you had hangers coming down from the two bogies, they will be closer together when turning down and farther apart when turning up. Anything so attached would need to be of variable length and have its own universal joints, as the bogies may have different inclinations.

The ability to turn upward or downward in a tight radius enables many small-footprint station designs, and I eventually came to regard the double bogie design as too mechanically cumbersome for 3D track layouts to continue to pursue. As far as space for batteries and controllers is concerned, there are lots of options, so I have just left that detail off.

Dan said...

Lee, it would be helpful to readers if you would place your comments at the post to which it refers. Now about your third comment...

Your division between weight classes is a bit off from what I propose. Mama Bear is for PRT, and I do not advocate 6 person PRT. PRT is essentially a taxi service, and as any taxi driver will tell you, even four passengers is an extreme rarity. The emphasis of PRT, I think, should be about building the most expansive network possible. Making everything able to handle six passenger vehicles runs counter to this goal.

I do advocate 6 passenger GRT, such shuttle services, but that is a different (but complimentary) goal. Here the emphasis is to connect more important destinations. The stations and track are bigger, as everything is expected to handle more traffic. This would use Papa Bear, as would even larger vehicles. Papa Bear is the way to create major arteries, such as along freeways. There is no weight or size limit on Papa Bear track. It is beefed up externally and supported as much as necessary. All PRT vehicles can use Papa Bear track, but large shuttles will not “see” Mama Bear track as part of their network.

The division between Mama Bear and Papa Bear is at the 4 passenger level for more than weight and aesthetic reasons. Being able to be travel freely in 3D is more and more difficult as vehicles get bigger because self-leveling is less practical and, frankly, less important. Lee, you may be gratified to know that I agree with a double-bogie solution for 6 passenger vehicles.

Baby Bear track is sort of the bike lane of the whole scheme, and would have a weight limit of, perhaps, 350 lbs. It is in response to the simple fact that most travel is done solo, and it would be many times cheaper than the larger track styles. This is a cheap, bare-bones transportation solution – the scooter of elevated transit solutions. It would be not be terribly fast and would keep a passenger dry, but not much more. Baby bear vehicles might even be privately owned. There could even be rental bogies that one could summon and hook on to. There are obvious light freight uses as well. Baby Bear vehicles could use Mama or Papa Bear track, but would automatically yield right of way, with no guarantee of non-stop travel on the larger tracks.

You are about correct having private “spurs” or even small networks that can access the public portion for some kind of fee.

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