38> The 16th Rule

I was considering my response to alert reader cmfseattle’s comment on my June 7th post when I got to thinking about this addition to his comment. “Rules of engineering” (NIH) and what I was about to write seemed to warrant a post of it’s own and so here it is:

J Edward Anderson, for those who don’t know, is sort of the “grand elder statesman” of PRT. He holds patents, has written books, countless papers, and currently heads up PRT International. One of his papers is “15 Rules of Engineering”, and rule number 9 is “Recognize and Avoid NIH (Not Invented Here)”

So am I just re-inventing the wheel? A quick look at PRT patents would tend to support that case. Here is just one sample illustration. Look familiar?

Well here is my defense. Dr. Anderson left out one rule, one that I will call, “Think Super,” and it goes something like this.

All designs come up against natural constraints such as the laws of physics, social preferences, budgets, time, etc. All designs also carry the limitations implicit in the definition of project itself. Dan’s sixteenth rule of engineering would caution against accepting such restraints without being absolutely sure that there is no simple way to work around them. For example, how big should a PRT vehicle be? Answer. Somewhere between microscopic and celestial, until some factor forces constraint. I know what you’re thinking… (OK, not really…) “If it’s called “Personal Rapid Transit” It should be sized for its purpose, say big enough for 4 adults.” By that logic, it should be sized for one and one only. After all it says “personal”. But are we not designing an automated parcel delivery system where the parcels are people? If all else is equal why exclude the possibility of delivering anything? Now before someone starts writing about the downside of cargo delivery, understand that this is just an example. The downsides that that writer would list would be the constraints I have spoken about.
It is an unfortunate side effect of the profession that engineers are tasked with creating a design from decision-makers with time and budget constraints of their own. I know few engineers with the guts to really think “outside-the-box” in the critical initial stages of a project. Limiting the objectives of a task limits the work involved and speeds completion. That’s sound business practice in most cases but it leaves improvement for later models, making for slow, evolutionary change.
So why re-invent PRT? Because all of the designs I have seen are constrained, not by what is possible, but by what is expected. For example, 95% of PRT is track. It’s the permanent part. Yet it seems to me that precious little time has been spent considering the final form and function of this potentially enormous investment. To my knowledge, I am the only one (or at least one of precious few) suggesting designing-in the capability for carrying modernized street lighting and utilities or having a configuration that could be adopted for use in a warehouse. If functionality can be designed in with no additional cost, why not?

Near my camp in New Hampshire there is bike trail utilizing the remnants of a railroad track that went all of the way to Boston. It was built, however, for smaller trains than are standard today, with narrower track and bridges. Its present use speaks for itself. How did this standard get on the wrong side of history? How do we avoid making the same mistake? In a discussion about an existing PRT design I was reminded that vehicles need not corner quickly because it would buffet the passengers too much. What about a trip to the hospital or freight delivery at 3 am? Or repositioning empty vehicles? I was reminded that all of the vehicles travel at the same speed. Why? I will remind the reader that for most of the history of PRT, control without crashing was the issue. I think we’re moving to a place where the cars can have the intelligence to follow a much wider menu of directives.

So this is my philosophy on designing a PRT system. How fast? Lightning fast. How steep? Vertical. How tight the turns? On a dime. I say, let’s design SUPER PRT first and then back off from there, as required by current constraints, rather than putting time, thought and money into designs that perpetuate limitations simply to expedite a business model. Don't get me wrong. I have nothing but respect for the people trying to bring this technology to market. I just want to prevent track coming down in 20 years because better, newer systems and new uses require a slightly different design.


Lastly I would like to point out that I am endeavoring to create a set of standards first, not a set of blueprints. As I envision it, these standards would be useful for future designers, inventors, contractors and their customers as a means of simplifying navigation in a sea of complex functional concepts. Prioritizing the above-mentioned constraints inevitably leads to differing opinions on design options, and so a natural branching occurs. Such a branching has already occurred regarding PRT vehicles which hang and those that don’t. Have we ever really defined the trunk from which these branches emanate? Or are we just going to let it be defined by Wikipedia or Webster and design from that?

37> Coming …Soon?

At the very beginning of this blog, I envisioned the possibility and intention of collaboratively designing a PRT system, and I have taken a step in that direction. The first problem was the fact that not everybody who could make a valuable contribution to a design has access to, or knows how to use, AutoCAD, or even a vector based drawing program. (Or a decent paint program for that matter)
Alert reader and frequent commenter akauppi, when asked about this matter, suggested Inkscape for a Drawing program and Acorn for a paint program, both free to download. Apparently Acorn is only for Macs, but I have found what I consider to be a great, free paint program in Paint.Net, which, by supporting layers of variable transparency, allows on-screen positioning of separately created parts. The most exciting to me, however, are the tools provided by Google. Besides hosting this blog and my email account and analytics, they give away a very competent 3D design program called SketchUp, which I used to draw the second illustration of the last post. But there’s still more. Google also hosts space and tools for project collaboration. Although they are intended for code development, there is no reason why they can’t be used for the design software listed above. They even include tools for revision control and a wiki. So coming soon, you’ll be able to modify my designs and post those revisions. But I have to warn you, I know very, very little about SVN (look it up in Wikipedia. I had to) and Sketchup takes time to learn as well.. Meanwhile, a simple question was asked about my last post. What’s so special about the layout of those wheels? (Refer to the illustrations from the last post) well, if akauppi, doesn’t get it, I guess I better explain for all.
A good design begins, foremost, with a good understanding of what you’re trying to do and what you have to work with. In the case of all of those wheels, vs. the expected forces exerted on them, it is geometry. Move the wheels up or down, forward or backward, and the performance changes. (I would like to note, however, that these illustrations are consistent with PML’s wheel-motors and my scheme for climbing steep slopes) And then there is the track (which, because track is reproduced into infinity, is really, really important to get right)
I could write a few paragraphs on every dimension and every angle, but have not, because I recognize that I have attracted many readers who are not engineering oriented, and this is a good thing, because we’re not designing transportation for engineers. This blog has attracted a group of very thoughtful contributors, and I feel confident that the core design issues are being dealt with in a forum that will eventually yield superior results to the “top-down” approach that commercial enterprises have to use. I want to urge patience, however, because good designs take a long time, even for teams of full-timers.

36> BACK TO DESIGNING

Remember how I said I was all fired up and ready to design a PRT drive unit around the PML “motor wheels?” Well despite being in the deep woods without any meaningful communications or electricity (and a garage to build up by the road), I have nonetheless managed a bit of progress.
Here’s a drawing that shows the basic structure I have been working on. There are 5 drive wheels which are self-turning “wheel-motors.” The figure on the left shows how many wheels it takes to do the job (although 3-wheel sets may be substituted for 4-wheel sets on turning and guide wheels, with minor loss of stability, just as a three-legged table or a 3-wheeled car is possible but not as stable). Note that half of them become inactive in the process of switching tracks (3rd figure). In the second and third figures the red “right turn” wheels are in the upward, engaged position, allowing all of the wheels on the green “left turn” side to disengage. The ability for cars to do the switching themselves, instead of having to build many switches in the tracks (like a railroad) is pretty much a standard feature of all modern PRT designs. Keeping all of the wheels aiming parallel to the track even as the track turns sharply is the challenge, although such tight cornering would only be for very low speeds anyway. Nonetheless, any good designer would want to reduce such frictional losses and associated wear and I am no exception. If the wheels seem very bunched together it is because I originally drew this as part of a 2 assembly set, much the way train cars have two separately pivotable wheel assemblies per car. These assemblies, connected by a universal joint, would enable extreme flexibility in track layout including those very tight turns I referred to earlier.

Addendum – I wrote and drew that post while still up in the woods of New England, and have since spent some time at RIT (Rochester Institute of Technology) hooked up to broadband, so I have had a chance to further my education (via online video tutorials) on what I consider to be a pretty exciting development, a free 3D modeling program from Google. So here is the extent of my abilities so far. Here I have experimented by using the “3-wheel sets” that I referred to above. In this one the green wheels are in the engaged position and the red ones are down.

35> Troubled

I am a troubled by the business model that would-be PRT providers are taking, either by choice or necessity. The first thing that troubles me is the lack of emphasis on the transformative potential of the technology. I understand that they want to be professional, to focus on immediate doable objectives. But the immediate doable objectives are such that they really are not “the only game in town,” but rather an arguably risky way to achieve a limited set of goals which may not be that well suited to PRT in the first place. It is no wonder light rail is so vocal in its derision or PRT, since the PRT companies have chosen light rail as the sweet spot in the market. Somewhere in the mix, the whole promise of PRT goes missing.
I would like to see a long-term vision for PRT adoption added to the mix. Without that, the future of PRT could just be the sporadic limited construction of incompatible systems, assuming that they all work as advertised, are within budget, and don’t end up being a technology principally beneficial to the makers of the deal.
Is it not possible to go head-to-head with roads, instead? To be a commuter alternative instead of a downtown crowd shuffler? I’m afraid the limits of design and business imagination have led away from the true value proposition; a better alternative to the network of urban/suburban highways and roads. It is the power of that network that makes the automobile (and therefore eventually traffic) ubiquitous.
I will say it again. The true value of PRT is that of a substitute for cars and roads, not a substitute for light rail or trolleys. PRT companies need to figure out a way to leverage the full value of proposition of their product. I would submit that that would entail a fully articulated long term plan that reaches well outside the realm of what one company can do. It requires all PRT companies, environmental groups, standards organizations, as well as partners in government and education. Until they have a plan for a system that you don’t need to commute in your car to get to, I’ll keep reminding them.

34> Access for the Disabled

Bengt Gustafsson (www.beamways.com ) in his comments on my most recent post reminded me of a subject that has been long troubling me; Access for the disabled. I think I read somewhere that in one of Ed Anderson’s many attempts to get a project going, he was rebuffed when he tried to offer a special vehicle for the disabled and had to do a complete redesign after his idea of requiring wheelchair bound travelers to sit sideways was ruled out. Apparently every serious design is now bigger, heavier and more expensive than would ordinarily be the case. The track must also be heavier, meaning more support posts, and heavier vehicles take longer to stop, as well as consuming more power to operate. In other words, ADA (Americans with Disabilities Act) compliancy for a uniform fleet will hugely and negatively affect the cost of the whole network. Getting appropriations for infrastructure is already a challenge that restricts the scope of such projects. ADA compliancy, if they are unwilling to budge on these issues, can only mean leaving more areas unserved. Don’t these people see what they’re doing? A fully implemented PRT network would open new worlds for anyone who cannot drive, especially the elderly and disabled. Waiting a minute longer for a special vehicle would be a very small price to pay.
Unfortunately the language of the ADA is in fundamental opposition to efficient PRT. PRT should take advantage of the fact that the average occupancy of a vehicle is only 1.2 persons, by optimizing for the common case and hence saving an enormous amount of energy and infrastructure costs. The ADA seeks to absolutely equalize the perceived experience for the disabled to the standard experience- but since the disabled require additional resources, this in turn forces us to expend additional, unnecessary resources on each and every rider. While an identical experience for the disabled is a nice ideal, the conservation of diminishing world resources and global warming are far more pressing.
So how about this; the vehicles come in two or more sizes. I know that seems like a lot of gratuitous headache and overhead, but I can think of no other option. Rather than have a special vehicle for the disabled (which has been deemed unacceptable) I would suggest segregating the fleet into two weight classes, with the lighter being only for a couple of passengers with luggage, for example, and passengers with any more than that would call for the heavier model. This would include anyone with need for such a vehicle, not just the disabled, such as families. The control software would dial the headway way up for the heavier vehicles to minimize the weight factor, which would not adversely affect system performance much because of the proportionally low ridership of the vehicles.
These heavier vehicles should naturally cost more, but the handicapped can always be given a discount, I bet that kind of discrimination gets little challenge.

33> In Defense of the “Track-on-the-Bottom” Design

After my last post I received and email from an industry insider in defense of the track-on-the-bottom design who gave me some facts and figures to chew on. One of those, the proposed height for the stations gave me cause to pause. It was much lower than I had envisioned. This got me thinking. What is the lower limit on raised station height?

One of the problems I have pointed out about bottom track design is that track descending to ground level would block driveways and invite climbers and graffiti. But what if the track only descended to, say, 9 ft.? It would still block some driveways from tall trucks, but the impact would be much less than going to ground level. A “not so raised” station would presumably be much cheaper to build. It’s a thought worth considering.

I still believe in the hanging vehicle approach, personally, but I don’t pretend to have a business model for it at this time. Companies don’t need to solve the whole “transportation/traffic/climate change/wasted productivity/polluted world” thing to have a viable product. A PRT system for (fairly) flat, high volume urban areas is a viable and needed product. It’s not all things to all people, but it is a foot in the door. I think we could call that “PRT I,” and what I am thinking about “PRT II.” I will be glad to see any kind of PRT take root, but those companies should be preparing for PRT II, (not necessarily my design, but the expanded role and capabilities) even as they endeavor to sell PRT I. That is simply keeping ahead of the curve.

As for my design work, I am still hard at it, although I have little internet access and even limited electricity for the time being, as I am at my cabin. I have been designing the old fashion way, with pencil and paper. I will say, though, it looks very promising. Very tight turning radii both vertically and horizontally, very fast speeds, climbs of any angle, (right to vertical) great acceleration and braking. Beside the gondola design, one thing that sets my designs apart from the status quo is the articulated drive unit, which is for better traction and tighter turns. A two part unit will have twice the wheels. Add to that that my switching scheme requires redundant wheels and now you have a drive unit that is bristling with wheels, all needing sizing and placement. This could take a while. So, from the town library in beautiful Canaan, NH, this is Dan, signing out!

32> I Just Can’t Let This Stand Unchallenged

I have just finally gotten a few days to devote to PRT and have spent some of it studying PRT International. I am glad to see that a lot has changed since the days of Taxi 2000. One of my major peeves, the huge track, has been replaced with a stronger slimmer skinned truss. The control system apparently will allow for more and variable speed. The one problem I have with it is the top riding design. In the site www.prtnz.com there is a point-by-point comparison by Ed Anderson. The arguments are pretty thin, I’d say. I would invite my inquisitive readers to open it up in a separate window so as to get both sides.

It starts with the fact that it is harder to do switch. I’ll certainly admit that. That’s point (1) Then in (2) it says that vehicles on top look better, and that they have so much experience we should believe them. The gondola design hangs 8 feet lower; the theory goes, so it is closer and more visually apparent. (Of course the part that is always there is 8 ft closer but anyway, to that I say, “OK, if it’s really a problem, let’s raise the rail 10 or twenty feet.” Oops! There’s a problem. If all your stations need elevators, I guess you don’t want to do that, do you? Especially if your system isn’t designed for slopes. The next point (3) deals with the costs and size of foundations and supports. Please. What about the costs and foundations for elevator-equipped stations? He says the weight is off balanced, doubling the stress at the ground. First that isn’t much of a problem, Second, it doesn’t take an aerospace engineer to see that you could make a “?” shaped top to the supports and balance the load if it was a big deal. As for (4) and (5) he makes some good points that took some pretty fancy math to figure out. I’ve studied the equations as best I could and will not quibble about the conclusion of the study which says that, in effect, if all else is equal, then hanging vehicles have essentially no structural advantage. Fine. But all else isn’t equal. I have seen studies where municipalities have voiced concern over corner “clipping,” (that being where right-of-way is needed over valuable corner property) to put in a proposed turn of PRT track. Now I don’t pretend to know exactly how sharp a turn his vehicles can make but I would bet they would lose a cornering speed contest.. In point (5) he talks about “natural frequency.” I really don’t think that will be a problem if the turn is essentially a right angle, because that will always involve two closely spaced supports anyway. It will also require slowing for the turn and quick acceleration out of it. By the way, about banking the track- What speed to you bank it for in his system? Gondolas self-bank to the proper amount for any speed, a fact left out in his comparison. Anyway, by his own figures hanging wins point 4 and I say nothing in point 5 really tilts that balance. As for (6) I really think he is just looking for another point to make. He implies that hanging vehicles need more beef. Note the qualifier, “all else being equal” and the actual wording “the sidewalls will be heavier.” I suppose that implies that if one looped a couple of steel bands around one of his vehicles and lifted it, the sidewalls would collapse. He should have claimed overall weight advantage, and I think there probably is one, because of the added functionality of the hanging design, so I’ll stop and just give him that one. I would maintain, however that it is a minor point. Number (7) ..Huh? If it runs underground ? Geeze. O.K, How ‘bout this. When it floods his track will have to be pumped out. I would be really interested to know just how long a run it is to get his system back up to altitude..
Number (8).Cabintaxi? CABINTAXI? “Somewhat more people preferred riding above the guideway than below” in giant square boxes on giant concrete roadways in the 70s? Sheesh. Number (9) He gives that one (not having the track in the way) to the hanging vehicle, but only as an advantage in buildings. He never mentions that the same applies everywhere else as well. Finally number (10) mentions that he has a successful plow and a ditch to push stuff (that falls into his track) into. I think he could at least say that he gives this one to the hanging camp.

Let me add a number (11) to the list. If you are in a hilly city, like San Francisco, and you are going down a hill and there is a turn at the bottom, the non-hanging vehicle will throw the passengers right out of their seats, unless it goes very, very slowly. In fact it has not been demonstrated, (to me at least) that bottom-mounted vehicles are capable of serving hilly cities at all. Not once is the self-leveling quality of hanging vehicles mentioned. Although I touched on it before, I think it deserves a number (12) to note that track banking is speed specific, and therefore inexact. Not so self-banking, hanging vehicles. Also previously mentioned but worthy of it’s own number (13) is the need for expensive raised stations with elevators, Too few stations take away a huge advantage of PRT, that is the “point-to-point” aspect. They cannot come down to earth because if they did they would either tip people out of their seats or block a huge swath of real estate on a gradual descent. That would open up the possibility of vandals climbing, painting, or putting stuff in the slot. Heck, if he would add a number just to make a point about what would happen to PRT underground, we should be able to call this number(14). Stuff in the crack. If the track isn’t above the trees, then leaves, seeds, etc will fall in the crack. Add a little rain and time and it will be a planter full of soil and rust. If it ever is at ground level, there’s a lot more than leaves to worry about. There’s garbage, and that a five inch crack is big enough to fall into up to the thigh. That’s point (15),

I guess my main gripe is that he never mentions the major drawbacks to his system (no slopes, major problems at ground level, and consequently expensive (and therefore less numerous) raised, elevator equipped stations. He keeps using the term “all else being equal.” All else is not equal. Raised stations may not be a big deal downtown, but they render the whole system impossible to scale outward into the suburbs, where station traffic would be less but the benefit of car miles eliminated would be more. There is already a system out there that can move people around downtown but is too expensive to scale. It’s called light rail. In all fairness, however, he’s locked in. Once money is raised, it’s pretty hard to tell your investors that it would be better to start from scratch. It is also a fact that, from a business point of view, you don’t want to shellshock your customers with too many new ideas. I just hope he makes his track easily upgradeable.

31> Fired Up!

I am all fired up about the wheel-motors from PML. They are back-up battery ready, very powerful, light, efficient, recapture energy upon braking. They are easily capable of high speeds or very steep slopes.

Here is a system I designed to do just that. The smaller diameter of the gear reduces the travel of the wheel while increasing pulling torque. The PLM wheel motors are, in this way, easily capable of a thousand lbs (453 kg) of lift each, while still being able to achieve horizontal speeds in excess of 50 mph (80 k/h)

This system works because the wheels can be independently disengaged (powered down) during the transition to gear/tire drive or held to an RPM, which is consistent with the vehicle speed, rather than the speed of the other wheels. Therefore one wheel (which is gear engaged) can be rotating at a different RPM than a wheel whose tire is still engaged. The final effect is the same as motor, transmission and clutch, all with no moving parts except the wheels.

30> Active Wheels

Back in my January 30 post, I brought up the concept of the “motor in the wheel” design. I like the idea a lot because it has no more moving parts than a LIM (linear Induction Motor) but is all contained in a neat little package, as opposed to having to provide miles of “reactor plate” in the track. Also, the tolerance between the rotor and stator parts of the motor can be very small. With a LIM these spaces would be a challenge to maintain, effecting efficiency. Check out this excellent simulation by Paul Nylander (http://bugman 123.com)



Oops. Bloggers' videos don't loop so it doesn't go 'round- Check out the web site...There's lots of neat stuff..

I found motor in wheel suppliers for bicycle conversions, and conveyor belts (drum motors) but I missed the obvious search words “wheel motor” until I ran into this interesting innovation from Michelin.



Anyway, I found a UK company, PML that produces a range of “wheel motors” sized for vehicle use. I have not had a chance to consider the various choices or to work them into a design, but they appear to be sufficiently small as to enable the many wheel, split carriage design I favor. (lots of traction, very tight turning radii, both up and down and side to side)

Designs will be forthcoming.

29> Thinking Outside the Box on Earth Day

Happy Earth Day, readers. Actually it is more like “Earth Evening”, right now.
I would like to punctuate my PRT posts with a personal note. As of the May 1st I will be leaving Texas and blogging from my land in New Hampshire, where, bit by bit, I am taming the land. There I live the greenest of lives. It brings out the Thoreau in me. (If “Walden”was required reading in every high school, we wouldn’t be in this environmental mess) Anyway, bear with me if I’m slow to post or respond, as there is no internet, phone, not even cell phone, on the land.. I must go to the town library for internet. I will spend about half of my time there until mid fall.

Pictured is my sole source of electricity, other than my car. These (3) 15W solar cells can be pivoted from the ground to aim directly into the sun. I started with a deformed tetrahedron made from six lengths of conduit strung together like beads with galvanized wire. Pipe brackets, some 1x4s, some steel cable, and an afternoon, and Voila! Total cost to put these collectors 30 ft. in the air? Less than $75. Now That’s Green. What's this got to do with PRT? Not much, but, hey, this is a mid-week post...about green..ah heck, I was looking for an Earth Day photo and just felt like sharing thus one.

So, my friends, on this Earth Day, let’s resolve to think “outside the box” to imagine a cheaper, faster, more reliable, more comfortable, more acceptable PRT design. (cheezy tie-in)

And one more thing, do not assume I know the latest PRT news. I was so busy with my land last summer I missed the Ithaca conference because I didn’t even know about it. I was only an afternoon’s drive away. So post those links folks! And don’t be afraid to comment on something that is a bit off-topic if you believe it would be of interest to the readers of this blog. Give me your suggestions! Mother Earth and I thank you.

28> An “Ah-Hah!” Moment

In the post dated 3/22, I posed the question about what to do with an unbalanced load. I got the answer that I didn’t want, that the cabin couldn’t hang freely, but rather needed an active mechanical positioning system to correct the problem. Unfortunately, the beauty of the gondola design is that it minimizes errant G forces within the cabin by free hanging, so having an active system to correct for “level” would seem to be counter-productive. I think I have solved the problem. First let’s look at a little picture (above) I did to explain how to stop a passenger compartment from swinging too freely. If a vehicle swings too freely a turn or a gust of wind could get it swinging back and forth like a swing set. Pictured are two hydraulic/pneumatic cylinders tapped to work in both directions. (Sorry they look like car shocks, personal clip-art)
The cylinders are connected by hydraulic fluid lines with valves. When the valves are fully open, the “gondola” swings freely. When fully closed it doesn’t swing at all. The valves can then be adjusted for best performance. My guess is that a small bubble of air in the system will enhance performance. Note that two pair of such cylinders are needed, one for front to back swing control and one for side-to-side control. These would be integrated with any other suspension system.

Here is the “Ah-Hah!” part. The unbalanced load creates a difference between the (loaded) cabin position and the position that the cabin should take from (unoccupied) gravity. But this gravity is not necessarily down. It is whatever the forces of momentum make it. Therefore a simple “out of level” detector will work continuously during a journey, because it won’t just detect down, it will detect gravitational force and an active system meant to detect a severely unbalanced load can be added to a free-swinging system. It can straighten out a weight-tipped cabin while still allowing the cabin to swing.

Here’s how it works. A simple tilt detector like this
mercury switch (similar to those found in a pinball machine) determines that the cabin is tilted and the motor (pictured in blue) activates a screw jack to adjust the level. This process is purposely a bit slow, say 3 seconds. During a trip, the cabin will swing somewhat freely. (dampened by the hydraulic system) Any variation from the cabin floor being perpendicular to gravity or G forces will activate the motor, which will contribute to G force mitigation in a minor way during velocity changes and banking, but will principally keep the “gondola” level during constant velocity straight-aways and during “docking.” I have to say that this is a very immature, out of proportion design, posted as a conceptual drawing only.

27> Designing For The U.S. Market

One thing I need to express is that, as an American, I cannot help but design for the U.S. market. Back in the 50s, then President Eisenhower spearheaded the construction of the U.S. interstate “super” highway system, and state and local governments quickly followed suit. By the late sixties suburban communities were popping up like weeds far from city centers, because without traffic lights and driveways greater distances were now commutable.

Fast-forward a generation and we have the great American suburban sprawl. Instead of a single “downtown” there might be ten. There are few pedestrians, because nothing is within walking distance. Traffic is not just confined to one direction. It is everywhere and may be worse thirty minutes from downtown than downtown itself.

Such a situation demands something much more ambitious than the little projects that the world has seen so far. It requires thousands of kilometers/miles of rail per city and speeds that are consistent with long commutes.

Obviously, no project can start on such a grand scale, but I believe any system that has a chance of adoption in the U.S. must be scalable to meet these needs. That means the cheapest possible track, the cheapest possible stations, and the fastest possible vehicles, designed for rides up to thirty minutes. That means a smooth ride is a must. The system, including stations, must have a minimal footprint. The station design, for example, promoted by the MISTER system is great, but only for about 10% of the stations, because, as I have said, there are no pedestrians. The sidewalks are empty but the streets are full.

Going fast means banking on corners or slowing for them, or clipping them (buying right-of –way) for larger radius turns. Banking track means more expense, complex engineering, and more specialization is required of the track builder. Perhaps there is a simple track design to do this but I have (so far)opted for the self-banking gondola design to address this issue. I am also inclined toward adaptable vehicle speed architecture rather than a set cruising speed. Empty vehicles should be very fast, traffic permitting, since there is nobody on board to get motion sick.

The U.S. transportation system is broken and needs to be fixed, and no little downtown “people mover” project is going to change that fact, just like light rail won’t nor will more buses, but that’s for a different post.

Finally, a question for my readers – In those systems with linear motors, what are the provisions for a power interruption? I was surprised to find that In the Taxi 2000 design they envisioned special “tow truck” type vehicles. Any thoughts on stranded passenger protocol?

26> Linear Induction Motor Tractor Unit

Here is a simple conceptual drawing of how Linear Inductions Motors (LIM) could be employed in a tractor unit for a gondola style Personal Rapid Transit (PRT) vehicle. Shown is a simplified track encasement, without outside structural support. The 3.2mm (1/8”) gap between is maintained by making internal rails (shown in orange) and the reactor plate (blue/green) both setscrew adjustable. With tight radius turns, the gap will be uneven and perhaps somewhat larger, but this diminished power and efficiency will not materially affect performance. By having two units in tandem closer gaps can be maintained. This design is compatible with the switching protocol illustrated earlier. The LIMS on one side must be turned off during switching, so the pod cannot accelerate strongly through the switching process. There are four LIMs. The proportions shown are consistent with the (Baldor) # LMAC16123D99. (12”x16”) (30.4 x 40.6 cm)

The performance of each are as follows. Each weighs 105 lbs. (48kg) and can produce up to 190 lbs. (845N) of pull (15% duty) and 38lbs. (169N) continuous. That’s a total of 760lbs. (3380N) max total, and 152 lbs. (676N) of continuous pull. The motors (total) weigh 420lbs. (190.5 kg)

The downside is this. These figures are for 60 Hz, 460 volt, 3 phase current. The maximum velocity for these LIMS at 60 Hz. is only about 15 mph. It is unclear how much pull would be sacrificed for additional speed, which is achieved by increasing the frequency of the AC current beyond 60 Hz.

Most past models for PRT have assumed speeds of about 30 mph. (48 kph) That may be fine for short haul downtown environments, but that’s where trolleys, shuttles and even light rail are most competitive. The urban/suburban sprawl typical of many cities (especially American) requires considerably more speed because of the distances involved.

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.

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.

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 danverhoeve@gmail.com.

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 http://www-tc.pbs.org/newshour/rss/media/2009/03/09/20090309_transit.

another link to transit situations is

http://www.pbs.org/wnet/blueprintamerica/reports/transit-in-trouble/overview/481/

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…

20> Podcar Control and Encoders

I’ve been wanting to start a conversation about PRT control for some time, so I thought I would start with this primer on motor control.

I don’t know a whole lot about brushless motors, other than that brushes are the means regular motors use to time the advance the magnetic fields ahead of the advancing rotor. With modern electronics, however, motors do not require mechanical means to achieve this timing. Triggering the magnets electronically offers great precision. Instead of “full-on, full-off”, magnetic forces can be ramped up or down; the motor’s rotation can be advanced or reversed, even held frozen.

Whereas in theory one could always know just where the shaft is, rotation-wise, under load the actual rotations or speed could differ from what is expected. One answer is the optical encoder.

My thanks to ikalogic.com for the logic diagram and shaft encoder pic. I just glanced at the site, but it looks educational. Sorry about the resolution. Click on the image to enlarge it.

The key is the C shaped “electric-eye”. (optocoupler) As holes in the disk align with the beam, a logic pulse is created. In the third picture, I depict how the same principle could be used to inform a PRT system on a pod-car’s position (and speed) along the track.

Some thoughts:
1. The track can be fitted with the PRT equivalent to traffic signs. Unlike drivers, PRT vehicles will follow their instructions to the letter. “Signs” in the track can trigger precise deceleration rates for upcoming turns, acceleration rates for merging, etc.
2. These “traffic signs” can be dynamic, reflecting real-time data.
3. The track itself should also receive data from the PRT vehicles. Track segments can “know” their traffic counts, for example, to upgrade or downgrade their availability factor, for routing decisions. It would seem that the process of merging would be the result of direct cross talk between cars and track.

There’s a lot more to be said about the division of control responsibilities, so I’ll save that for a separate post.

19> A More "Mature" PRT Track Design

Here is a section of a more mature PRT track design. I envision this with a skin to keep out the elements. Not shown in the picture is the soundproofing, except for the vibration absorbing material shown in purple, which isolates track vibration from the truss structure. The circular holes are for utility conduits. I have not figured out the cost or even the weight yet, but I must say it is dirt-cheap. Greater height and steel gauge enables longer spans. Note that the design does not show a great strength against sideways forces such as very high winds. A horizontally triangulated truss can cap the structure to address this, but it probably should be in removable sections, so as to provide access to the conduits.

In the traditional business model, a big company would keep the details of the track secret or proprietary, even though it could provide lots of local jobs and that could be a selling point. The integration of utility lines and street lighting could also be of interest to local companies, but again, if the PRT company wants to keep complete control, this is less likely to be in the cards.

The design obviously has to be made approvable by structural engineers for anticipated weight and span, but after that any structural steel fab shop can whip the stuff out. Any city has a dozen such firms. Let’s remember that city managers like to “bring home the bacon”. Also, once the track (at least the structural aspect) is free to be outsourced to locals, and city officials can get bids that they believe in, those in charge will be forced to justify the much greater expense of every subsequent road expansion project against the backdrop of this simple, outsourcable alternative. That would seem to be a battle that PRT can win.

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.

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.

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 danverhoeve@gmail.com 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!

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.

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.