Sunday, March 29, 2009

25> Just Some Thoughts...

Here’s a bunch of loose ends.

It worries me that my blog is not that friendly to newcomers. It makes more sense to start from the beginning, which gets more buried with time. I am considering starting a general PRT advocacy blog to feed potential contributors,
I really don’t know what I will do if and when I get some volunteer engineers working on this. I don’t have Autocad, nor any web based design collaboration software. I’ve been told I should start a Wiki.

I’d like to thank Mr. Grant for another “to the point” link. This MISTER FAQ sheet also sights a design issue that I had raised earlier, that being the question of climbing steep slopes with a minimum of available onboard power. It seems they have opted for an external motor, the concept I took to the extreme in my post about raising a vehicle vertically.

I really have to say that there seems to be precious little difference between what I envision and the MISTER or Beamways systems. When I started this blog I was unaware of either. Simply getting a serious discussion about putting the track on top was reason enough to start the blog. I have since become more aware of the degree of consensus on most issues. In reviewing the rejection of the OKI project (Taxi 2000) I am struck by how just a few decisions did them in, particularly too big a turning radius, too big a track too low, too expensive, too proprietary, too unproven. I would like to change that type of outcome. A lot of the problem was the “single source” part. The transit people wanted independently verifiable proof. They wanted a 25 million dollar study. Why not? After all, a big corporation, (Raytheon) was trying to sell them a 45 million dollar, unproven product. Now what if, for example, there were five companies bidding on the track, three on the cars, four on the control system…(you get the idea) If all these people thought that they could provide THEIR parts for a given price and they would perform as advertised, wouldn’t the customer feel a bit more secure? This is not to discount the idea of a primary contactor, but rather the contractor that wants to provide ALL of the solutions “in house.” If the contractor proves inept, the transit authority is left with mud on its face. No, this hurdle, in the U.S., anyway, needs to be approached with a good deal more tact than that. I submit that this is more about pschycology than technology. It’s about public awareness, enthusiasm. It’s framing the issue. It’s politics. Anybody checked out the X prize site lately?

Lastly, about LIMs (linear induction motors) Does anyone have any links to manufacturers besides this (Baldor) site? After comparing torque, weight and frame style specs for various (rotary) motors, I have become a bit disillusioned, especially with the torque/weight ratio. It turns out that the Baldor LIMS compare a bit more favorably than I would have expected. Anyway, I’m toying with designs.

Sunday, March 22, 2009

24> One Little problem.....

There is a problem that I have yet to solve with the gondola-like design I have proposed for PRT vehicle design. It is the problem of balancing the load. When two heavy people sit together, if the “pod” simply hangs by gravity alone, it will be very far out of level.

Let me back up and state the advantages of the design. The first is turning speed. If an ordinary vehicle makes a sharp turn at high speed, it creates sideways G-forces. The answer to this has always been to avoid such turns by designing the road with only gradual curves. (Consider the real estate consumed by a “cloverleaf”) Sometimes the roads are banked somewhat. The problem with gradual curves is that they are very unwieldy (design-wise) in an urban environment. With city streets generally designed with sharp corners, gradual curves have to use the airspace above valuable corner real estate. Right-of-way issues will be untenable. Highly banked track has drawbacks too, such as being banked only for a certain optimum speed, and adding expense to every curve and corner network-wide.

The second advantage is a quicker acceleration and deceleration rate. Any driver who has owned a compact car or a car with bad brakes or has tried to save gas by hardly pushing the petals knows that limiting acceleration and deceleration too much is a recipe for late arrival. If the name of the game is passenger throughput both acceleration and deceleration should be robust enough that having the vehicle be able to rock forward and back to minimize G forces would be desirable.

The third is steep slopes. In order to descend to street level without blocking driveways, or even just for versatility in a hilly town, handling steep slopes is a must.

Then there is the issue of passenger comfort and safety. The gondola design creates a means by which all G-force is diverted downward, toward the floor of the vehicle. This greatly enhances passenger comfort, safety and saves a lot of otherwise spilled coffee.

So the unsolved question is this; How do we keep the advantages of a free-hanging vehicle while not having it tilt from an uneven load? Note that making the vehicle wheelchair friendly tends to mean other seating is further from the center of gravity, making the problem worse.

So that’s the problem. If you have an idea, please post it, if it involves a picture, email it to me and I will post it for you.

Sunday, March 15, 2009

23> Podcar Control part 2

I would like, first of all, to thank alert reader Mr. Grant for sharing this paper by J. Edward Anderson, who is truly an authority on the subject of PRT. Unfortunately the material seems somewhat dated. Although there is a date on the PDF, (2003) I suspect the paper was actually written a few years earlier.

Although I completely agree with most points in this article, (in fact most of it is a MUST READ) I have to say that there are a few points I disagree with as well. Since a monologue on my take on this article may be a bit more than many readers would want to wade through, I will include those as a comment on this post.

Anyway, I would suggest, as a guideline, to make traffic control decentralized, and make the individual “podcars” behave much like good drivers, I.E. following road signs, not tailgating, but seeking shortcuts and less trafficked routes. This begs the question, however, of how to achieve a redundancy of control to safeguard against malfunctions

Another missing piece of the control puzzle is exactly how communications reach a “podcar” (I still hate that term, but if it gets us noticed…) Anyway, I guess the problem is as follows: There is a constantly updating traffic map wherein stations and track segments are self-reporting their status. Their reports would probably be little more than a segment/station number, and a condition number, (like a scale of one to ten) This simple communcation needs to have a success rate that is near absolute. This communication could be optically/electrically/mechanically/wirelessly redundantly reproduced at intervals along the track so a passing “podcar” gets an update every so many feet/meters. Redundancy creates a multiplier effect in terms of reliability, and enables faulty components to be replaceable on a maintenance schedule

There is one other VERY important communication, which can take place from the track to the podcar. That is a report of having been just traveled upon by another podcar. If a PRT vehicle is to react much like a human driver, it needs to see ahead and slow down when necessary. If there is any aspect of this system that needs 99.999% reliability it’s the system that prevents “rear ending “ the vehicle ahead. This means redundant, separate reporting means so that anything less than complete agreement between sensing systems results in an immediate cautionary response. As part of such a system the track could inform a trailing vehicle that there is another “podcar” just ahead. Here is an example of how it could work. Imagine a little line of lights in the track illuminate when they sense the passing of a “podcar”, only to dim and go out over the next couple of seconds. (Imagine the tail of a comet) A light sensing, following podcar would know, by measuring the light intensity, how far ahead the first vehicle is. Why not just use taillights on each vehicle? Because of the problem of seeing around curves. What about Bluetooth, GPS or other wireless technologies? I, frankly, don’t know. This is where a small army of alert readers would help. Don’t feel like posting a comment? As always, I can be contacted at

Monday, March 9, 2009

22> This Just In...

Yeah, I'll get back to PRT control soon. Sorry for my little vacation from the blog.
I'm working on a bunch of design work. Anyway, I had earlier written this piece on Houston's light rail, only to get a further insight on PBS tonight. It seems that more than 60 Transit authorities (nationwide) are broke, as reported on the News Hour. The PBS (NewsHour) site allows browsing by subject, recent stories, etc. I just tried to upload the MP3 audio of the program but Blogger wouldn't let me. It's

another link to transit situations is

Sorry to make you type it in, seems that even in Explorer my links are saved as Firefox documents.

21> 1.4 Billion?

I heard on the news a few days ago that the Metropolitan Transit Authority in Houston, TX voted to spend 1.4 Billion expanding it’s light rail system. I really haven’t figured out what to think other than it sure sounds like a lucrative business to be in. That is reportedly $73 million per mile. And apparently it doesn’t even cover all of the road “improvements”, but does include $118 million for new light rail cars.

I have always advocated for a place for other forms of public transport beside PRT. As I have written, most forms of transportation rely on fully or partially aggregated groups of people. A light rail system requires a fairly large group of people at each station to be efficient. This begs the question, “How did the people get to the station in the first place?” or rather “How COULD or SHOULD they get together to board this train?” I think PRT competes with buses more than light rail, because buses, rather inefficiently, stop for individual riders as well as groups.
But this kind of price tag gives me second thoughts. I wonder, for example, why don’t they just create a special road or lane and just run a fleet of buses instead of having them on a rail? (I confess I don’t know if Houston’s light rail is electric or what) How much does a bus cost? How many does $118 million buy?
It’s not that PRT CAN’T compete in the densely populated areas. (I would refer the reader to the “MISTER” system for what I consider the most efficient larger station design) It’s just that light rail really can’t compete in the one-passenger-at-a-time world.

Using a previously posted rail design I recently figured out the cost of steel per mile. (This was a VERY rough estimate) I came up with a between 1 and 3 million dollars per mile (depending on station frequency and support design) Of course this doesn’t include labor, and I’ll do all of this in some future post, but I just thought I’d mention it, being on the theme of money and all…And speaking of money…

I Googled (news) the term “cost of burying electrical lines” and came up with repeated estimates of $1 million per mile. This has been a much talked about issue after the recent massive power outages due to Hurricane Ike and the recent ice storms in the Midwest. Anyway, I’ll get back to the concepts of PRT control soon, but I just thought I’d post this stuff so I’m not the only one left scratching my head…