Friday, January 30, 2009

18> PRT Motor-in-the-Wheel Design

This illustration shows how a motor can be mounted inside of a PRT “Pod-Car” wheel.
I was first inspired by a design from an electric “concept car” where the wheels were actually motors. The idea is simple. If you plug in a motor but hold the shaft, it will spin, (winding up the cord until it unplugs itself). So why not feed the cord through the shaft somehow? That way the motor itself would be a wheel, instead of mounting a wheel on the shaft? (Or more likely, a sprocket, gear or pulley) It turns out this idea is actually widely used. A Google search revealed that the concept is commonly employed to move conveyor belts, (drum motors) and to electrify bicycles in China (hub motors) and in fans, especially computer and ceiling fans.

Despite the obvious simplicity (and efficiency) of the idea, apparently the motors don’t perform well in terms of torque, as compared with a much higher speed motor fitted with a reduction gear. Also they are not exactly cheap or easy to find, so I bit the bullet and researched some more conventional motors.

My switching design calls for hard wheels, so I put in a bunch of them to have the traction to climb steep smooth slopes. I don’t really know how many is really optimum, at this point, but I checked out some “NEMA” standard sized brushless motors, and found that the NEMA 42 standard comes with sufficient torque that if each or the wheels had a motor within they could pull (together) with between 300 and 800 lbs. of forward power, while having a top speed of 60 mph. (Sorry, younger and euro readers, I am not natively metric and feeling lazy) Obviously, reducing the top speed increases torque proportionately, but it also worthy to note just how much of a trade-off is required between the weight, the steepness of the climbs and the top speed. There is no free lunch. For example a combined vehicle/payload weight of 1600 lbs. will probably not make a 45-degree climb.

It is also worth noting that the separate motors solve the fact that my system has no differential gears. For those who do not know what a differential gear is, here is a brief explanation – On car, when turning a corner, the outside wheels have further to travel than the inside wheels. Therefore they have to revolve faster, making more revolutions than the inside wheels. The differential gear accommodates this, preventing one or both wheels from slipping on the pavement, which would create wear and partial loss of control. Even though the right and left wheels in my PRT design are fairly close together, the same phenomena would apply to a lesser extent. With separate right and left motors, however, the RPMs of the wheels can be precisely controlled to actually create the appropriate steering forces.

Wednesday, January 21, 2009

17> The Role of a PRT Standard

A good PRT standard would
1. Give all decision makers (city, state, federal) the security of knowing that the system design was not rushed, coerced, short changed, tailored by self-interest.
2. Give those decision-makers the assurance that the design is suitable for competitive bidding in initial construction, expansion, and maintenance and therefore they are not utterly dependent on the initial contractor.
3. Give PRT contractors a vetted design more likely to be accepted by the public.
4. Reduce PRT contractor’s liability risks.
5. Make a PRT project easier to manage and subcontract.
6. Give customers more faith in the system
7. Allow innovation in system components outside of the standard.
8. Be divisible so that variations can be introduced without scrapping the entire standard. (A proprietary car for a standard track, for example)
9. Be designed with altruistic intent, including benefit to the environment, local contractors and other vendors, as well as commuters and the communities they pass through.
10. Be continuously updated
Did I leave anything out? Anyway, A good set of open-source specifications would greatly enhance the chances of a truly ambitious implementation. Let’s remember, a scaled down test will always go from a place where people congregate to different, similar place. In other words, companies with millions tied up in engineering and marketing and testing and selling have to recoup costs by jacking the cost of track so high that only a loop is affordable. Meanwhile cities have to ensure usage by placing stations only in congested areas. Almost by definition, then, a simple shuttle service will always be more cost-effective. Only confidence and optimism can produce a first implementation that is scaled for success.

So what would a first standard be? I would think that the first stage would be (for example) to standardize a track profile, switching and control protocol and weight limits. If there are deep-seated divisions in these matters, there could branching specifications. For example, I outline, in the last post, a method of using external power to lift cars up very steep (to vertical) slopes. A “podcar” designed for the track, weight, and switching specifications but incapable of this adaptation might be called PRTSO 100.2 compliant, but not PRTSO 100.2.5 compliant. A city could look at a proposal and decide whether this would be an issue or not. At any rate, they would know what kind of track to buy.

It is interesting to consider that, for design Darwinism to occur, one needs a number of competing designs. It is therefore not the function of this site to design a single system, but a number of competing systems to see what common threads emerge. None-the-less, it is equally important that each idea be critiqued, as though it is the one and only alternative.

Sunday, January 18, 2009

16> How to Lift a Podcar

I want to start by noting the obvious difference between the designs I have shown and those of the other two hanging pod designs I am aware of, Beamways and MISTER. Neither has the vertical connecting beam I have illustrated. Besides the obvious advantages of having the track being high and out of reach, the connecting beam has one other advantage.

I have long wondered if PRT vehicles, (OK, Podcars), would need a transmission of some sort. Clearly the advantages that have led to their universal adoption in automobiles would seem to apply here as well, although I am led to understand that electric motors are a bit more forgiving in this regard. Anyway, my concern was about the on-board power needed for steep ascent, and my thoughts went to roller coaster design, where the cars are pulled up the track by a means outside of the vehicle, so there is no need to carry around a heavy motor.

I have taken a design philosophy that is consistent with open-source by seeking to not foreclose options that someone else might find useful, and the roller coaster method seems to have enough merit to at least keep as a possibility, Then the question becomes, “how steep?” Obviously straight up is as steep as possible, so my attitude is “why not?”
One problem that our societies must someday face is our land usage footprint. The future is UP!

Since vertical ascension, however, is not part of any immediate plan, I will not explore the matter further, other to say it’s not challenging, engineering-wise. Now you know another reason for the “beam”. This design also has some comfort (g-force) advantages, and possible collision safety advantages. One challenge, however, is with how to deal with loads that are highly unbalanced, front to back. Inventors, engineers,.. we need you!

By the way, that brings up one obvious problem with this site and format. You can’t post pictures. For the time being, if you have a pic that you think would help out the cause, send it to me at and if it’s worthy, I’ll make a post out of it. Meanwhile, I would be interested in suggestions on how to get a past this problem for good. Wiki? Forum? Tell me what you think!

Thursday, January 8, 2009

15> The "Podcar" and the PRT Dream

First, I HATE the term “Podcar” or “pod”. Unfortunately, Since the PRT thing in Ithaca last summer, it seems that a lot of “PRT” Googling results in this awful term. Are people who ride “pods” considered “Pod-People”? (Anyone remember that movie?) Anyway, I use it here in the title solely for the cynical reason that it might bring in some (Googled “POD”) readers, and some of them might become contributors to the cause. I would like to reiterate that cause now, as many people might tend to scan the site, without realizing it’s purpose, which is buried in the end of the “About this Blog” section
The ultimate dream would be to realize the world’s first large-scale open-source mechanical, software, legal, environmental and social engineering project, with a full set of blueprints, contracts, position papers, environmental studies, etc. provided by the masses, for the benefit of humanity and the planet. A “Wikipedia” of how to build a truly 21st century transportation system with local talent and resources, with a hefty “how –to” section on every possible situation. A framework by which primitive “model T” iterations of PRT are skipped, leading to successful and ever more efficient and beneficial implementations worldwide.
But on a much more humble scale, a bunch of us are “second-guessing” each other, on the topic of the day, or week, and our thoughts are being archived in the “cloud.” Anything we say may provoke a design breakthrough, or cut off some bone-headed approach that would only be a setback. In other words, it’s all good, as long as we get enough contributors to be a real resource that can, at least, be found.
I am not free to work toward this full time, but it is my passion. I wish I could post daily, but I can’t. I have many more ideas than I have posted so far, but I have to meter them out. I don’t want the best ideas buried too deep. So to any readers out there- Please post your thoughts about anything I write or any comments you read. Please spread the word! At some point I will start an email campaign to known advocacy groups and academia, but I need a blog gushing with comments, arguments, and ideas. If we, the people, reach a definable consensus, that is powerful stuff. It is the stuff of dreams.
Last but not least . Enjoy the illustration. I would like to note, however, the motor units shown don’t represent any particular design based on inner parts, size of the inner workings or anything else, for that matter. It’s hard enough just making them look shiny. But sometimes a picture says a thousand words, (and one blog address). I wanted to get this out sooner rather than later.

Saturday, January 3, 2009

14> Personal Rapid Transit and Streetlights

I heard, the other day, about a proposal whereby streetlights would be turned off to save energy but could be switched on by cell phone. Odd idea, but it gets the old mind working. I was mostly working in Tucson, AZ for the last few years, and they have a number of observatories near town, so they are keenly aware of what is called “light pollution.” I fly a lot, and have for many years, and I must say the brightness below is really getting out of hand. Remember a barrel of oil saved domestically is as good as a barrel of oil produced domestically. Energy is wealth, and the celestial glow of the city is the glow of would-be prosperity diffusing into space.

So how does this apply to PRT? Well let’s imagine the ideal street lighting. First, it wouldn’t blind you, so your eyes could see more with less of it. It would be more uniform, softer. It would shine away from you, not at you. It would be directed mostly toward important things like signs and curves in the road and blind driveways, If there was no one to see it, it would go out, or at least cut back. Intelligent street lighting is an idea whose time has come. PRT could be the platform and catalyst for that change. . This is just one more selling point to PRT that shouldn’t be ignored.