Sunday, December 27, 2009

65> The Efficiency of Absence and Angled Wheels

Before everyone’s eyes glaze over from too much shoptalk, I would like to ask for nominations for the best videos to explain PRT to a complete newbie. It is time for me to update my “About This Blog” sidebar, and I want people who stumble on this site to go away believers without me having to waste a lot of space trying to explain it.

Speaking of the sidebar, I see my “Recent Comments” list is still blank - at least on my computer. If anyone is getting the list, or knows how to fix this widget, let me know. It would really help keep threads alive.

As most of you know, I am trying to finalize the design of the most cost effective, versatile PRT track design for suspended systems. Unfortunately, this entails exploring every conceivable use, limitation and bogie design. Higher speed. Tighter turns. Steeper slopes. Industrial. Freight. Heavier loads. Cheaper Stations. Manufacturability. Longer Spans… “Pod” designs may evolve, but the track stays, so we need to get this right. I have taken the approach that the running and guidance surface dimensions are a somewhat separate issue from the structural truss, and that these surfaces can basically be surrounded by a support structure. Inside, for example, most structure is no longer needed, because the running surfaces can be supported (hung) at frequent intervals. Anyway, it mostly comes down to the bogie design.

I have, lately, been working on a problem inherent to rail based PRT designs - the shear number of wheels required per bogie. Here I show an older bogie design with 18 wheels.

True, half of them need to fully disengage to switch tracks, but still 9 per side seems like a lot. In post 54 I show a much simpler configuration, with railroad style flanged wheels and little guide wheels that fit between the two halves, but this design is unworkable for high speeds. Post 56 shows a high speed-bogie, but with no steering wheels, so do not be confused. As you can see from the picture below, PRT’s acrobatic unpowered cousin, the roller coaster, requires many wheels as well, and would require still more if designed to switch tracks via steering guide wheels. 

In railroads, they cut the number of wheels from 16 to eight by adding a flange to each wheel. The problem is that the flange creates friction with the track which would tend to overheat and wear it out at high speeds, smaller wheel diameters, or if it were made of some material other than conductive, strong (but loud) steel. To minimize wear, the designer must keep the wheels perpendicular to the rail surface, hence the 24 wheels per roller coaster car.

Some years ago, while arguing over a design detail of a piece of factory equipment I was designing with a machinist friend, I came up with this axiom. “There is nothing more efficient than absence!” I have returned to that thought many times since. So how can I get some of these darn wheels to be absent? Without flanging the wheels or track?  While steering guide wheels can be disengaged for straight runs, guide wheels for centering the bogie cannot. One thought is to wedge the bogie in the track with angled wheels. Here is what I drew to help me think.

Could this line of thinking mean I need to take my track design completely back to the square one, after all of these months of exploration? The verdict is still out, and I have some more mature designs to share at a later date, which require some fairly lengthy explanation. But it is Sunday, and I’m in the middle of remodeling my bathroom, so I will bid you all a Happy New Year.  

Sunday, December 20, 2009

64> The ULTra Architecture - Continued

In the last post I touched on the idea that vehicles such as ULTra could be driven by “joystick”. This idea of driving by electronic controls (as opposed to the current practice of having actual mechanical connections between the pedals, steering wheel and the engine and brakes,) is not new. The use of electrical motors and regenerative brakes starts us down that road, which leads to the “skateboard concept.” (scroll down to post 50 for a picture)

Let’s take this line of thinking a step further. If the Ultra vehicles are guided by some kind of laser system that centers them on the track (with accuracy of less than a centimeter, I understand) such a system could presumably be fitted on private, steerable cars as well. An example of a steerable car which could presumably be easily modified for the ULTra control system is this Michelin concept car. The idea is that you drive your car to a ramp (or car “elevator”) and driver control is switched off and automatic control is switched on. Voila! You are now in a fully automatic PRT system until you are dropped off.

That Michelin video raises an important point however. People are really in love with their cars. The very best selling point of this electric car seems to be its muscle. Then there is the addition of luxurious creature comforts, such as adjustable seats, high-end music, etc. It seems to me that private vehicles will always become more and more loaded with features and power until something or someone steps in to halt it. Electric vehicles, in themselves, are not without environmental costs. The electricity they use must be generated, and this, itself, generally involves combustion. The prospect of hundreds of millions of Chinese cars being recharged by way of coal (their principle source of energy) power plants is truly frightening. Coal is, of course, 100% carbon, so there is no fuel on earth that is worse for global warming. Anyway, the point is that there would need to be some kind of societal decision as to how much to limit the power and weight (and therefore luxury) of these vehicles. We can’t afford a guideway network for Hummers. Because any vehicle on the system would need to be meticulously maintained, (combined with the necessary luxury limitations noted above) perhaps some type of leasing model would be the way to go.

This scenario does not eliminate “ordinary” PRT operations. Fully automatic “taxis” could still populate the track. PRT vehicles could come down to ground level and use a special lane to get to stops which cannot be served by raised stations. This would, of course, create the same interferences with vehicular and pedestrian traffic that plague other forms of surface transportation.

The main problem with the whole idea is the same problem that plagues all supported PRT systems. All supported systems inherently discourage true point-to-point travel compared to hanging systems. If they come to the ground they interfere with other traffic and pedestrians. Ramps must be fenced off for safety and are ugly. Stations must be positioned so that ramps won’t block driveways. If elevators are used to raise the passengers or lower the vehicle, the station is considerably more expensive. This is a big deal if you consider the economics of the network. I believe that in many cities the ridership figures are such that a great percentage, maybe even most, of the city would go unserved by the PRT network unless simple “bus-stop” type boarding areas are employed. I think this is a point worth repeating. It is a very big problem if the cost of stations precludes their use in large areas of a city. PRT needs the “network effect” to fulfill its promise as a transformational technology. Of course this is just money problem. If the government wanted to switch some road funds into PRT that would be a different matter. From a business perspective though, there will always be a number of riders under which it becomes unprofitable to create local service.
For the time being I remain very wary of any system that can only take the “low hanging fruit” to market.
Merry Christmas!

Sunday, December 13, 2009

63> ULTra – Architecture and Iteration

There has previously been, in my mind at least, some question about whether ULTra is really PRT. After all, the 40 km (25mph) speed is hardly “rapid”. And the distances that passengers will be willing to travel at those speeds are somewhat limited as well, although I suppose they are far enough to be legitimately called “transit”.

I started writing this post with a number of negative suppositions. I have previously criticized the ULTra design for being little more than a golf cart, and wondered aloud what the advantage of automating such a vehicle really was. Actually I was about to call for ATS (The company that makes ULTra) to consider a purchase of company like Taxi 2000, or PRT International, as a way forward out of the constraints of it’s present design limitations. I am forced, however, to reconsider.

I have been selling the ULTra designers short, I now believe, and this is why.  Many of the aspects I don’t like about ULTra are truly intermediary. They will not stop ULTra from becoming much better (and more versatile) in future iterations. It seems that the designers over at ITS have a motto of extreme simplicity and conservatism. Anything else is kept “close to the vest”.   Here is one example. The traditional steering, (as opposed to track constrained steering) at first glance, would seem to have all of the negatives of cars. It would skid on ice, for example. Safety issues would seem to prohibit any kind of speed with an automated guidance system. The idea of a track would seem SO much better than trying to center the vehicle with lasers and sensors. So why didn’t they do it? Well for one thing, tracks are less versatile, because they prohibit the vehicle from being able to move freely on any paved surface. But it is mostly, I believe, because they didn’t need to. Tracks would offer the potential of much higher speed but they don’t need speed. It’s only an airport “people-mover”. But the fact is that a track or guide rail is still perfectly compatible with ULTra. They just chose not to use one, for now. Lasers can be turned off, but you can’t easily pull up the tracks. Therefore lasers win. If and when speed becomes an issue a simple rail that sticks up under the center of the vehicle could be added, with minimal modifications to the vehicle.

One interesting aspect of ULTra is that it could presumably be driven away by a human operator, using a plug-in video game style controller. This would seem like a natural way for mechanics to move vehicles around a maintenance facility, for example. That raises intriguing questions about dual-mode, doesn’t it?

Don’t be too put off by the weight. They are using the old, heavy, lead-acid batteries. But once again, the only trade-off has been to design-in some extra space. They can upgrade to Lithium-Ion or even third rail at any time. It was explained to me that track electrification was deemed too costly, but I can’t help but wonder about partial electrification, so that the batteries could get some on-route charging. The possibility of easily swappable batteries also comes to mind.

I also hate the track, especially as seen from below. That would seem to be a hard sell for city streets.  This, also, is not really an issue that can’t be much improved. There is nothing that says that the track must be massive concrete, for example, although noise could become an issue of the track was pure steel. There is a gradation between rails and roads. If redundant road area (anything not in line with being directly under the wheels) is removed you are left with a pair of very narrow beams – seems pretty much like a pair of rails to me. ULTra can theoretically drive on such “rails”.

I guess the lesson here is to beware of false choices. This does not just apply to Ultra. I was bemoaning the huge turning radius of the Anderson designs and a similar thought occurred to me. There is nothing inherent in the concept that prohibits tight turns. It I just that it necessitates a more complex bogie than is called for in the current business plan. 

It is easy to look at a system from afar and the hard choices that have been made and to rap them up as defining that system, rather than see them as a collection of business decisions. ULTra is not a clunky, slow, heavy vehicle on an ugly, massive roadway. ULTra, like other systems, is an architecture first, and the rest of it is a means to salable iteration of that vision. This architecture, I am finding, is surprisingly tweekable.

Sunday, December 6, 2009

62 > Mission and Miscellanea

First on the agenda, readers may note that our “Recent Comments” feature has disappeared. It was rather peculiar. I was on the phone with someone asking if it was just my machine, which it was, and then he refreshed his screen and it was gone for him too. It turns out that it’s a third party “widget” and I have left a cry for help on their site. We’ll see what happens.

I have recently included an index under the search box. It is very incomplete at this point. It is actually a link to post number 0, so if you find I have a glaring omission you can say so in the “comments.” I will try to periodically delete these comments as I address the issues to which they refer.

I want to clarify something. I have shown a lot of different designs since this site started and one might be tempted to think I am just throwing them out there, to see what sticks, or that every design cancels the one before it. One might think that I am inventing and improving “my system.” This is not exactly true. Actually what I have been doing is trying to verify a “best” suspended track design and finalize its dimensions. My reasoning is that while a PRT provider could go out of business and vehicles may come and go, wear out or be improved piece-by-piece, the track will stay until someone tears it down. We cannot know what technologies or configurations will be desirable or employable in, say, 30 years. (Or how the city’s transportation needs might change) We can, however, create a design that is as flexible as possible. This flexibility can include the ability to accommodate different neighborhood types, vehicle weight classes, speeds, special purpose vehicles, propulsion types, and station types, turning radii and slopes, while being easy to construct, deconstruct, and connect to.

I do not think it is altogether coincidental that the two active PRT platforms run on a road-like surface, which can be used for other vehicles if the projects or companies fail. It is simply insurance for the buyer.

Therefore one of my aims is to provide a track profile that is not entirely incompatible with the various PRT technologies available. I would like to see a track that could be readily adapted by one or more PRT venders, so that the track expense does not represent a total financial and political risk. In this respect I diverge from most would-be providers, who require absolute faith in both their proprietary products and their companies. (Most of which are not scaled for any actual contract) I hate to say it, but this seems extremely naive. Is it any wonder that their proposals don’t carry much currency with those entrusted with the public’s money? We, in America at least, have seen many of our pillars of industry and finance file for bankruptcy in the last couple of years. Do these “companies” actually think that they can scale up to manufacture vehicles, lay track, and manage an untried network all at once? More importantly, do they think they can sell that scenario? There’s a clock named after this kind of optimism.

My approach, again, (43% of this site’s readers sample as new, so I repeat myself with purpose) is this. Standardize the basics. Document consensus. Establish common ground.

Where do the companies promoting bottom-supported PRT fit in with all of this? It is my intention to eventually examine these systems as well, with an eye toward addressing any major shortfalls constructively. (Readers will note that in Post 48 I suggested a way to double the throughput of a small-footprint elevated station for almost no additional expense, for example).

A common pitfall in design stems from starting with a set of assumptions and continuing from there. The more you invest in those initial design assumptions, the less likely you are to consider that, perhaps, you were wrong in the first place. I have invested a good deal of time exploring suspended systems, and almost none with the supported designs. Perhaps my original objections can be easily addressed. How can one tell without actually going back to square one?

Finally, there are a couple of obvious flaws in the classification system I suggested last week. One is the use of the letter “x” for both spacers and to mean “Does not apply.” A minus sign would be seem to be a good alternative. Also, (as pointed out by an alert reader) the term “articulation” is not self-explanatory. It does indeed refer to tilting the cabin with respect to the track to adjust for slopes and curves. Pitch and Roll are aviation terms. In the system I did not allow space for both Pitch AND Roll articulation. This, as you can see, is a work in progress.