125> What's in a Name?

 

I know, acronyms are often useless, contrived and perhaps a bit tacky.  And I suppose I could, in the past, be accused of trying to shoe-horn meaning into the word “SMART” or “SMARTS”, as seen in (posts 53 & 54 … Small-scale Modularized Automated Rail Transport System)  Now, of course, there is even the “Smart Car” to get confused with.  Well, here I am again, same word, new meaning.  I guess it’s a character flaw.  Anyway, here is one that embodies a point worth considering.

Standardized Multi-axis Automated Rail Transport.  There.  I said it. 

“Standardized” because it involves permanent (or at least semi-permanent) infrastructure.   Let’s face it.  Some VERY big companies have filed for bankruptcy in recent years and no city wants to be left holding the bag if their PRT company goes under.  If an untried infrastructure is contemplated, then “open-source” style standardization gives at least a bit of assurance that the track will be useful even if a given PRT provider goes belly-up.  Standards are everywhere in modern life and essential in almost every field of endeavor.  At the very least a system’s viability should not be dependent on a lot of proprietary technology.  Who would buy into that?  Standardization serves to extend the usefulness of any system by promoting development of parts or accessories by third parties, and gives them continuing incentive to innovate.  Standardized track would enable all vehicle manufacturers to compete and exercise their know-how, so it is a natural division between what is standardized and what is proprietary. 

“Multi-Axis” because the main obstacle to speedy ground mobility is the need for long ramps to switch from one level to another.  As I have pointed out in previous posts, objects moving around on a (2D) plane must either wait for each other to pass or leave that plane to go over or under each other. The larger the objects and the greater the velocity, the larger the ramp structures needed to accommodate this action.  Since the vast majority of traffic is in the movement of puny humans, building giant structures that rival the pyramids of Egypt all over the place is not a very rational way forward, especially in these days of fiscal austerity.  Although some PRT designs are essentially two dimensional, being raised to an essentially fixed elevation, I personally feel that this approach is shortsighted.  I fear that once PRT is found valuable and useful, a new generation of more versatile multi-axis designs will appear overnight that will leave these systems seeming quaint and old-fashioned and their track obsolete.  Of course that is just this author’s opinion. There are many reasons to “design in” the ability to ascend and descend within a small footprint. Some neighborhoods might wish to raise the track quite high to minimize the system visually.  In such cases the vehicles would descend to the stations, even if those stations were elevated.  There are cases where elevated stations are impractical or too costly.  Having sufficient stations is paramount, so being able, for example, to descend to ground- level bus stops or parking lots would be very useful.  Such situations would be impractical with long ramps, since they would tend to block private driveways and be visually intrusive.  If industrial or warehousing applications are considered, true 3D travel would be extremely useful. 

 Rail – Because it is smaller, lighter, easier to produce, transport and recycle, and can be designed to lock a vehicle on track in all situations, such as bad weather.  It is the best solution (short of flying) for true 3D mobility.  I know that rail is a contentious issue, and that many would say that a system like ULTra, whose vehicles could be easily be modified to freely roam any pavement is better.  Whereas I can understand this logic, I feel that the long ramps and the canopy effect inherent with such systems trump this argument.  Remember, even though the guideways may be only a bit wider than the vehicles, every time there is a fork for a station this dimension is doubled.  If there ever needs to be a two-way application, this implies up to four overhead “lanes.”   

Transport – not transit, because we are potentially talking about light freight as well as people, particularly at night.  In fact I see a lot of potential use in industry, such as automated warehousing and shipping.  I would point out that the whole way warehousing is currently done is to aggregate goods together to minimize many separate deliveries.  The ability to pick up and move small loads without a driver could change that,  allowing goods to be staged much closer to their destinations.  Taking some trucks as well as cars off of the existing road system can only be a good thing. 

This is a fundamental shift from simply calling for PRT.  Back “in the day,” PRT was revolutionary because it was automated and electric, but those features seem increasingly minor in today’s world.  Is the full automation of PRT really the point?  I could imagine a PRT vehicle that would be capable of processing passenger input on the fly… for instance a last minute decision to go around the block because you had mistakenly passed your destination.  Or perhaps a scenic tour… (“Take the next right.”)

So if it is not really about centralized automation, nor strictly about transit (for humans) what exactly is it about PRT that is so important?  Is it about “Personal?”  That is a bit troubling if by “personal” you mean transporting one person from a unique point of origin to a unique destination, at least in the short-term.  No early network will be that extensive, and skeptics need to see a shorter term payoff.  Is it the small payload we are after?  Partially; I would say that we are after payload-appropriate scaling, both in the vehicles and the infrastructure they run on.  This, of course, encourages the more extensive routing that meaningful networks require, thus leading to that promise of non-stop, point-to-point travel.  Naturally a smaller scale system can be much more economically raised so as to avoid traffic on the ground. These aspects, I think, should be the emphasis, more than “PRT” per se. 

When I try to explain PRT to people, their eyes glaze over.  PRT is the solution to a whole set of problems that must be considered in unison for it to fully make sense.  PRT is a “hard sell” for precisely that reason.  How can you get someone to sit down and try to imagine the limitations of all various future combinations of robocars, smart lanes, and electric cars if they are not so inclined?  Yet that is what they must do if they are to realize that these technologies aren’t the full answer.  If we want to sell PRT, we first need to be able to reduce it to its essence – to start with the aspects that no other system can match. 

Breathe deep and say it with me now… “We need a supplemental transportation infrastructure.”

There.  Feels good to put it into black and white, doesn’t it?  You’ve just cut through all of the explanation of PRT, Dual mode, etc. and put one of the world’s next great challenges into a simple phrase that most people can wrap their heads around.  We need a transportation infrastructure that is designed to do more for less.  One that can relieve us of the huge costs of continually building and maintaining more and more gigantic highway projects.  Stoplights are a ridiculous waste of time and cloverleaf interchanges are a ridiculous waste of real estate.  We desperately need a third option for economically crossing paths without waiting or colliding. 

We need a supplemental transportation infrastructure that is scaled to be appropriate for the task.  We have many, many small objects, (including humans) that are coming from many points of origin and need to be moved to many separate destinations.  These days it is no longer necessary to aggregate cargo and people into great groups and move them in mass.  (At least for land travel)  Modern manufacturing techniques can spit out hundreds of small vehicles with the same ease as a couple of big ones.  Electric vehicles don’t need to be big to achieve mechanical efficiency.  The land is already cleared and ready and we have plenty of infrastructure in place for heavy cargo in the form of existing roads.  There is no reason to build more enormous concrete interchanges when the traffic is coming primarily in the form of small payloads that could very easily slip by each other in a more appropriately sized system. 

I said it in my very first post.  We have to make people aware that the current roadway paradigm is insanely wasteful.  The future will be bleak indeed unless we make the kind of efficiency leaps in ground transportation that have been made in other fields.  It is totally crazy for 160 lb. person to need a 4000 lb. vehicle and eleven million pounds of roadway to get to a grocery store a mile away!  And yet not even be able to travel non-stop! 

  

Oh yeah, about that picture… If everyone in every vehicle just pulled over and lined up on an overpass (and they were all wearing white) this is what it would look like.  (What looks like a white stripe is actually about 120 little marks sized to represent people.)   Clearly this maze of concrete is insanely huge for the function of allowing those tiny white marks to move past each other unimpeded.  Since it must be designed to accommodate bumper-to-bumper fully-loaded eighteen-wheelers, form does not match function when it comes to moving these commuters.  Only one in ten vehicles in this picture is a truck, and it is questionable how many are traveling with heavy loads that could not be broken up. By the way, did you know that, in terms of smokestack-style industrial processes, cement production is second only to power plants in the emissions of CO2 produced? 

 

Let’s hone the message… We need a supplemental transportation infrastructure that is designed to inexpensively and efficiently provide fast, non-stop travel without blocking any other traffic. That can only be done with a system specifically designed for economical multilevel routing. Here, economical multilevel routing means small, and that is just as well, because it coincides with the idea of individualized point-to-point travel.   

A multi-axis rail system for transporting people-sized loads without getting in the way… Call it PRT or something else. Either way, it’s a “SMART” idea!  OK, that WAS a tacky ending…

124> While We're Still on the Subject...

Since we were discussing switching in the last post, and I have had a few ideas percolating about the subject for quite some time, I thought I might flesh them out in a drawing. The bogie shown above is nowhere near complete, but shows, at least conceptually, the hardware for aligning with the track and switching. The motors are direct drive, hub type. (in the wheels)

What I have attempted to do here is to illustrate a couple of possible solutions to what might be called the “too many guide wheels” problem. (Note: As I am getting this ready for posting, a review of past posts reveals that I have written MUCH more about this subject than I had remembered, with a great many similar designs as well. So to see some variations from the past, I would refer there reader to posts 67, 69, 79, 83, and 90.) OK: First let me remark about the problem itself. 

In the illustration from the last post, I show how a single pulley shaped wheel can be replaced by 3 wheels, a trade that seems of dubious value on its face. (Last frame, click to enlarge) Given the durability of some of the new plastics, in many cases it might not be worth it. I have been, however, primarily designing systems to more fully explore the requirements of the track. There is desperate need for standardization in PRT, and all designs have limitations. If a certain aspect of a track/bogie design inherently creates a speed or weight limit, this should be defined, quantified, and, if possible, overcome. I have therefore endeavored to design for very fast and heavy loads, with the thought that the track can always have lighter iterations if it is known that this will forever be sufficient. Designing for propelling such loads fast, silently, smoothly and safely no matter what (epic weather comes to mind) is a whole different sport than for more stripped-down systems, but it seems foolish to build the latter if the former can be built for nearly the same cost. Unlikely as that may be, only an exploration of the issues can reveal the truth. A good design must assume that the highly stacked luggage will fall, just as the passenger lunges to stop it, just as an extreme gust of wind happens, while the vehicle is just curving into an intersection. My efforts are not unlike the logic that brings car makers to the race track, where lessons are learned from pushing designs far beyond what will ever be expected in the field.

One point about flanged wheels; any material hard enough to roll on reduced points of contact will tend to transmit vibration, if not simply generate noise. Rubber wheels, on the other hand, wear faster but absorb vibration and noise. One possible compromise is to mount harder plastic running or guide surfaces on a intermediary rubber part, such as a large diameter ring or bushing.

While the pulley shape holds the wheel securely on the track, it does so by either allowing the friction of angular contact or by concentrating those points of contact onto a minuscule footprint. This is why roller coasters don’t use them. Yet the flanged wheel concept, or some version of it, is in wide and successful use in lots of applications and is often the best choice. Ordinary railroad track, for instance, is a variation that recognizes that the double flanges of the pulley design are redundant and that opposed singly flanged (steel) wheels will do. So what is really the minimum of flanges or wheels that is necessary for PRT? Surely the 24 opposing wheels suggested by my last post are not all needed. For one thing, it seems unlikely that 4 wheels should be needed to hold PRT down; Gravity should do that perfectly well. And we have seen with the railroad example that the wheel flanges themselves may not all be needed. A few down. What else can be done?

 

Note that track has spread for switching, although it is mostly cut away.

Also note that the widened "ceiling" is missing the guide. 

These illustrations explore a couple of options worth considering. First of all, the disadvantages of flanged wheels come from the effects of continuous hard use. In PRT, many of the flanges (or,alternatively, the corresponding opposing wheels) are only used in switching. Why then, would they wear excessively? The fact is they wouldn’t. Plastic flanges or wheels should work just fine for switching, even in high speed systems.    

Another situation is that guide wheels for switching must either turn continuously or engage and disengage. If they are to remain engaged, good practice would have them be large enough to not rotate at hyper speeds. At 100 mph, for example, a four inch wheel must turn over 5000 rpm, yet four inches is still way too big to start instantly rotating upon engagement. I have posted about this problem previously. By the way, one idea is not to motorize them but rather to use wind forces to keep them turning. Such wheels could be configured with turbine-like blades and since there is substantial captive air in the track that must be channeled around the bogie, keeping them turning should be easy. In this example, however, the main strategy is to minimize use of the steering guide wheels and to keep the centering guide wheels (the purple ones) spinning continuously.

Here I have brought back a very old idea… magnetic switching. In these illustrations, the eight steering guide wheels are small and intended as backup only. The main steering is from the electromagnets (red) attracted to the steel switching strip. (blue) In these illustrations it can be seen that when there is no switching, neither the drive wheel flanges nor the steering guide wheels need get any wear since lateral control is maintained by guide wheels (purple) which are always engaged, save for the moment where one side or the other ceases contact for a few seconds due to the track widening as it branches into two directions. I have included a fifth “hold-down” drive wheel, which provides the geometry to inhibit forces that would otherwise twist the bogie inside the track. (extreme sideways wind gusts for example) It has a plastic groove down its center to receive a rounded, bogie-centering guide, which, like the drive wheel flanges, will get minimal use.  Because I contemplate the potential for very steep or vertical  (elevator-like) travel capabilities, this “hold-down” wheel could help facilitate that purpose as well, were such a scheme ever considered worthwhile. (There would be an addition traction means for this beyond those five wheels, however, such as ordinary "cog railroad" methods) Note that that upper rounded track guide (that fits into the hold-down wheel recess) is missing from the last picture, where the track has been widened as it would for an "off-ramp". That piece would resume further down the track for the each divergent branch. 

I am becoming more and more inclined to give up the idea of pneumatic tires in favor of semi-solid rubber. I really don’t think the bumps created by well-engineered expansion joints warrant that kind of cushioning, and I don't believe custom rubber castings are all that expensive. The flanges would be of a long wearing plastic, such as is used for casters and roller coasters. They can be replaced separately from the rubber. One of the keys to this system is the recognition that the flanges and the rest of the wheel need not be a unified piece or of the same material.

Finally, this track gives a nod to the typical roller coaster track architecture in that the design, as shown, involves bending round pipe only, so there is no compound bending, as would be the case with angle steel or square tubing that must curve sideways and up or down at once while keeping its profile plumb and level. The various steel profiles are shown as unwelded, separate pieces. This arrangement makes banking the track so easy that it begs the question whether it is worthwhile having the self-banking characteristics exhibited by my (and some other) suspended vehicle designs. That, to me, is more about budget,business plan, timing and politics etc. A general purpose bank would do no harm unless it was at the wrong angle for what ended up being the running speed at a future date, if the vehicles could not self-bank. But that is a debate for some other time. Also there is no trussing or triangulation shown as would generally be the case for any larger spans. Nor is there covering over the track in these examples. I kept it minimal for clarity.

In summary, this general design provides full, secure containment of the bogie on either side of a track that is widening to form a "Y" even without bottom support from both sides. (It is fully “half-track” capable) It has no more than seven wheels in active contact at any one time, and those seven are optimized for constant duty. All flanges and steering guide wheels are for (more or less) extraordinary events. Switching guidance, centering within the track, and securing the bogie during extreme events are different issues and the wheel style, profile and materials can reflect this. My general recommendation is use detachable flanges to ensure safety from extraordinary twisting or inertial forces, but to minimize their use by making them redundant in general use. This is done with the centering guide wheels shown in purple in the illustrations. In switching, temporarily engageable, self-turning wheels are used but may only be a secondary safety system if magnetic means are used as the primary way to get the bogie to hug one side-wall or the other. Discontinuous top guides can also be employed.

123> Thoughts on Track Size and Switching

Well, I’m up in New England again, away from the modern world, and probably posting this from the town library.  I have gotten to see both the Atlantic and Pacific oceans in this past month, and had a fair amount of time to think along the way.  And there is something bugging me.  It’s the track.  It’s too big.  I mean, take a look at this.

This is a now defunct “Santa’s Village” out in California.  True, it is supported every 20 ft. or so, and true, it went VERY slow…  But still, does PRT track need to be THAT much beefier? 

The answer is no, if you ask Asko Kauppi. (known to many of you as the frequent contributor to this site “akauppi”.)  His vision of PRT, shown below, runs on nothing more than a pair of pipes.

 True, it may not go very fast, handle steep slopes in ice storms, or draw power from the track.  But still, it can be argued, it would provide very decent mobility in most situations – and at a fraction of the track cost.  Could such a minimal track ever work in America?  Certainly, in certain circumstances.  But we Americans like to get places fast, and there’s a lot of ground to cover in our sprawling cities.  So my designs speak more to the needs of the longer distance commuter market.  Yet I think there are several important lessons to be learned from the design. 

First, it runs on a “half-track”.  That eliminates half of the cost right there.  What is a “half-track” you ask?  Funny that it should come up now, because I recently was mentioned in a “Transport Innovators” posting regarding switching for suspended PRT.  The fact that the viability of switching suspended vehicles was not all-together settled, in the minds of some, led me to re-examine the issue, if for no other reason, than just to explain the concepts in a more understandable way for my readers.  I decided to use primarily illustrations rather than words, and opted to put it all into a single picture.  (Suitable for framing! lol)  Be sure to click on it to enlarge.

 I would emphasize that the last picture is probably the most important, because it holds the key to understanding most of the mechanical drawings on the subject.  (found through patent searches, etc)  I would also point out that most systems do not anticipate the inertial forces that would require so many wheels as the last picture would imply.  I know from experience that some end up being included solely for the possibility of a freak, powerful blast of wind just as the vehicle is switching tracks.  Steep slopes also contribute to the need for the wheels to completely capture the track at all times.  So when I refer to a “half-track” I am speaking about an arrangement such as in the first illustration. 

Asko’s design is not the only one that runs on a “half-track.”  Ollie Mikosza’s “MISTER” system is a suspended system that pioneered the concept for PRT.  There are some new visualizations  for his system, and it appears that he has abandoned the structurally superior but complex triangular truss design in favor of the sleeker, much easier to build three-tube design that is universally favored by rollercoaster makers. 

 

So why not just go with the MISTER/rollercoaster style track?  I have several concerns.  First is the fact that it is open to the weather.  Ollie seems sure that snow and ice are not a problem but I’m a natural skeptic. There is also the matter of limited surface area for traction and braking, and the matter of noise.  I will say right now that these are largely higher speed or higher load issues, and not necessarily a problem with the MISTER system as it is designed.  I am curious, though, about how to safely carry the electricity to run the vehicles in an open track system.  In the case of Asko’s BM One design, the vehicles are battery powered. This obviously cuts track costs and there is no shock hazard.

Anyway, I have, so far, opted for a covered design.  I am not sure, though, that it ALL must be covered. For example, the track as I have specified it seems over-designed for many “last mile” applications.  Consider, for example, a large residential subdivision where there would be little or no through- traffic and speeds would be very low.  Perhaps a central loop would put all within walking distance.  It occurs to me that perhaps a vehicle could get around such an area on battery power alone, and that a cheaper, lighter, open “half-track design might be appropriate.  So far I have designed to include highway speeds and even faster.  Could such a vehicle also operate on a stripped-down, ultra-cheap half-track?  I will be devoting considerable time to this question…from my Yucatan hammock.

 Oh! And speaking of hanging around in the woods… Take a look at what was hanging over that little structure I am building when I arrived! One tiny little oak tree saved the project. It took a lot of cable to lay that sucker down in the driveway. And yes, that’s me, in all of my country scruffiness.

122> Still Toying with Trikes

Well folks, they say a picture is worth a thousand words, so here are a couple thousand worth. Shown above is how a three-wheeled PRT vehicle could be tipped forward to create a ramp, and how the swing-arm can be detached to allow the vehicle to travel away from the track.  The second picture illustrates how the swing-arm can be used to tilt the vehicle back to give it a more even aerodynamic profile.  In this embodiment I assume that the vehicle will not be roadworthy, and that it would have very limited range and speed on battery power.  The steering would be accomplished by having a pivoting back wheel and independently controlled front wheels. The rear wheel would extend downward for boarding, and retract for high-speed use, as shown. 

In this design windows were minimized to avoid the high air conditioning requirements of a vehicle with lots of glass.  Anything short of completely automated driving, however, requires high visibility for the driver, even if the vehicle only goes 10 mph and is controlled by a joystick, so some configurations might need more glass than what I have shown.  I envision the ground-driving capability to be primarily for parking lot use, for either ferrying people to their cars or from the PRT station to the front door of a store or other destination. In this capacity it would go one way empty, on autopilot.  Allowing passenger control risks taking a vehicle to where it could get stuck or get into traffic, so perhaps the manual-drive option should be limited to privately owned vehicles. Such personal vehicles, in addition to the extra glass and AC requirements, could also have extended range, greater speed, more ground clearance and better suspension.  The bogie would only accept a limited amount of weight, however, so such modifications would be at the expense of payload capacity. After all, if we want to have cheap, extendable track we need to draw the line on weight somewhere. In the example above the extra hardware (two motorized drive wheels with rudimentary suspension, rear pivoting wheel with a screwjack for tilting the vehicle forward and a small battery pack) adds an estimated max weight of (perhaps) 100 lbs.

121> Solving Traffic with 3D PRT

The other day I read a paper promoting “robocars” and related technologies and I ran into the following quote:

“There are two weaknesses in the PRT idea.

1.       1. The need to construct new infrastructure. PRT proponents argue that the guideways would be light, requiring little space.

2.      2. There is no good reason why the vehicles must be held captive to the guideway.  Vehicles captive to the guideway are called Single Mode (SM) and those capable of operating off the guideway are called Dual Mode. (DM)  There has been considerable discussion of the merits of each approach.”

Let me quickly address the author’s second assertion.  I would point out that the obvious reason for holding a vehicle captive on a guideway is speed, which clearly relates to issues like safety and weather.  The author indicates, through this assertion, that he envisions improvements that are, at best, incremental.  OK; on to the main topic.

The article got me thinking about something that many PRT advocates seem to get, but many otherwise rational and educated people completely miss.  I will state it as bluntly as possible, because it occurs to me that only very distilled concepts seem to get traction (and funding) in our society.  You know, “war on terror,” “no child left behind,” etc.  Effective leaders understand the power of a sound bite.  I know that I am “singing to the choir,” and I know my readers are much more astute than most, but I have heard too many discussions  where even the most well-read PRT people stumbled around on this issue.  So here it is, boiled down to two pithy sentences, ready to pull out at the next opportunity.

Efficient urban transportation at ground level is a physical impossibility.  Therefore the best transit solution will necessarily require a whole new infrastructure.       Period.   End of story.  

It is simple physics.  Objects moving in different directions on a single plane will either bump into each other or have to wait for each other.  This is the universal truth behind traffic.  By moving in groups this effect can be minimized somewhat but never eliminated.  The best solution to urban congestion, by far, is to move in three-dimensions.  This, and only this, gives many-fold, rather than fractional improvement. 

Consider that once-modern, transformative invention, the superhighway.  Can you imagine eliminating all of the overpasses and putting stop lights in their place?  Each and every overpass can, in a sense, be thought of as a wormhole, a portal, that effectively eliminates a standstill condition in two directions.  A highway can even be thought of as a string of traffic solving overpasses, with the higher speeds just being a byproduct of this linear arrangement.  

It is the ability to leave ground level – to go from 2D to 3D - that makes efficient high-speed urban transportation possible.  You can have a 200 mph bullet train, but without getting off of the ground, there will be people waiting for it to pass all along the way.  And all of that wasted time adds up, even if it is distributed.  By the way, this example illustrates two important points, which I will call “Herd behavior” and “Saturation”. 

In herd behavior, which is the 2D version of flocking or schooling, many move as one.  This is the animal kingdom’s mimicry of fluid dynamics.  In the case of the bullet train many passengers are moving as one, like a herd, and very fast.  This is a great dynamic but it becomes decreasingly effective as cross traffic becomes denser.  At a certain point the traffic slowdown created by cars that must wait for the train to arrive and then pass creates compounding gridlock that would otherwise not exist.  A related problem, found along freeways, is the fact that underpasses are often few and far between.  There is just no free lunch with fast ground-level travel in the city. The slowdown is just distributed in a way that obscures the cause and effect.

   

Or take the example of a four-way crossing.  If there are only a few cars in town, obviously there is little chance of delay.  An intersection might only need a yield sign.  With moderate traffic, timed lights and other means can help greatly by moving groups in unison. (Like a herd).  To illustrate, consider how fowled-up things get when a traffic light is broken, so it is treated as a four-way stop.  Yes, moving groups in unison really works, and all kinds of clever routing and timing schemes are in common use.   With high-density traffic, however, a point is reached, which I will call saturation, when nobody, in either direction, “makes” the light.  In this case each stoplight necessarily cuts traffic flow by over 50%.  The avoidance of this degree of saturation should be the first object of any remedy.  Indeed, all of the potential benefits of robocars, intelligent lights, contraflow lanes, etc. fall into this category.  They don’t even attempt bidirectional non-stop movement.   

It is the difficulty and cost of building a 3D road infrastructure that is responsible for our traffic.  Roads and the vehicles that travel on them can only go up and down gradually, high-speed or sharp turns lead to skidding, and roads must carry extremely high weight loads.  It is impossible to use overpasses and cloverleaf interchanges on every block.  So nothing that runs on roads, as we know them, will ever be more than a “Band-Aid” solution...  The cost and space constraints of roadwork will keep cars largely earthbound and in each other’s way, and this will limit speed and efficiency.   

So the logic is very simple.  We need to move under and over each other to get around a city efficiently.  It may be cost prohibitive to do this with cars and trucks, but people are light and easy to lift, and account for almost all traffic.  Therefore it stands to reason that a very good solution to our problem is to start with the creation a 3D infrastructure for moving people. (and not, say, cement trucks)  If that is the starting point, logic ends up dictating the rest of PRT design.  I would even go so far as to say that a measure of the effectiveness of an urban transit infrastructure is the ease with which it can utilize multi-level routing. 

The PRT message has become muddled.  Now, when people think of PRT, they increasingly envision publicly rentable robocars.  Having a designated guideway that is really a roadway in disguise misses the point.  Any efficiency gains that such a system produces will almost certainly be at the expense of other forms of transportation.  I do not believe a network of golf cart lanes is the answer for in most cities, and having the self-driving vehicles for them doesn’t change that.  In any case, if it is non-stop, it is either elevated or it makes someone wait.  PRT, in my opinion, should no longer be all about automation or being electric.  The real key is that PRT is the only model which can cost-effectively initiate the transition toward a fully 3D urban transportation network.  Personally, I think the question of private vs. public vehicles, PRT vs. dual mode, is secondary as well. 

No, constructing a new infrastructure is not a liability.  It is an opportunity to take a quantum leap in efficiency by specifically designing for 3D space.  And making the vehicle captive would mean much higher speeds in any weather, and allow electricity to be fed to vehicles directly, eliminating the efficiency losses associated with batteries.  This infrastructure would, at last, be appropriately sized for the job, and so would move many more people per dollar spent, and do so with almost no physical  footprint.  It would be blazing fast to construct and could also provide invisible housing for unsightly and weather-vulnerable utility wires, as well as house next generation street lighting.  It could be engineered to allow silent vehicle movement, even with highly efficient hard wheels.

But this new infrastructure, unlike improvements such as fiber optics or gas pipelines, will not be decided in boardrooms, and so requires a degree of generalized public understanding to get traction.  We need sound-bites so simple even that the “experts” will get it.  We need to win the war of the pundits.  It is they who echo ideas until they become commonly accepted by the masses.   

A NON-STOP URBAN TRANSPORTATION NETWORK… Not a too bad a phrase.  If only we could get industry and academia busily pursuing this as a goal, they would return again and again to what we already know to be the answer.  Then maybe some of the funding that is going to improving legacy technologies worldwide could be shifted to where it would do more good.  We already can’t afford to maintain the pavement we have. How long are we going to continue to throw good money after bad?  

120> Back to the Drawing Board

Well, it is “back to the drawing board.” In the course of the continuing debate about dual mode I have started to lean more and more toward the idea that the shape and functionality of the vehicle is secondary to bogie function and design. If the control system is shifted to the bogies, then the vehicles can almost be viewed as simple containers. As such, the main concern is how much they weigh and little else.  

Of course there must be some degree of control from the passenger compartment. An emergency “abort trip” command comes to mind. It wasn’t previously so clear to me, though, where the computers and communications equipment would primarily reside and why. In post 56 I raised the possibility of autonomous “engines” that could live within the track and be called upon to boost the speeds of otherwise slower PRT vehicles. Clearly this would require command and control that is sometimes free from the vehicle below. Now I am contemplating taking this idea to its logical conclusion, which is to have a mobile, standardized “skyhook” that can latch onto a passenger compartment. Primary communications and driving functions would be from the bogie, which is only networked to the cab. (Please bear with the simplistic nature of the “hook,” as shown in the illustration. There is a lot to consider design-wise, and I haven’t gotten very far.)  

  

The approach enables multiple, concurrent business models. For example, privately owned vehicles could “hitch a ride” right along with public PRT vehicles. Freight vehicles could be little more than containers with an RFID tag. It also enables some promising schemes that can only be accomplished via privately owned, dual mode vehicles. Since one or two seat vehicles could be robust enough for some general road use without being overly heavy, they could play an important role in a transportation mix. Such small vehicles would not pass ADA compliance rules for public transportation, yet clearly should be encouraged for environmental and energy efficiency reasons. With this scheme they could be developed and sold by vehicle makers directly to individuals.

In another model there could be multiple taxi or limousine fleets. I particularly like the idea of separate business entities competing for the most comfortable fleet of vehicles. “Fit and finish” issues have always been a weakness in public transportation, since there is little competition in the field. By putting the brains into the bogies we simplify the challenge of creating a great, aesthetically pleasing and ergonomic passenger vehicle. This is no simple matter. Modern cars employ assembly lines many miles long to assemble tens of thousands of parts. Since there is so much to it, why not ensure that this part of the project is completely within the core competency of a wide and competitive field of companies?

I do not mean to totally confuse the PRT world with endless choices. But the “last mile” problem is real and not going away, and I doubt the notions of dual mode or private ownership will either. From a design point of view it is a question of “Why not?” 

Ultimately, the obvious business model is one of collecting a fee for using the track and the auto-navigating bogies within it. The “chicken and egg” problem would seem to mean that the service would start out as purely public transit, meaning the cabs are “rented” as well.  The company responsible for this service would have to keep vehicles clean and in good working order. I would think the cab interior, save the seat cushions, would be bare-bones, of hard, scrubbable materials. A taxi or limousine company, on the other hand, would pay for bogies only, at a discount, and then charge passengers a premium price for riding in cabs fitted for more comfort. Rigorous passenger screening or even memberships would minimize vandalism of the amenities required for a truly luxurious ride. 

Privately owned vehicles can be introduced even if they are not dual mode. “Pods” could be centrally garaged, for a fee, and made to arrive at any station upon request. (Failure of the owner himself to arrive on time would have to result in a penalty charge.) Eventually privately owned and garaged dual mode vehicles might appear, but I question how they would compare with regular cars, which themselves might be automated at that point. After all, if that is the case they could simply drop you at a station and go back home. An automated taxi could be waiting for you at your destination. (No, robocars alone CANNOT replace PRT, which is specifically designed for 3D, non-stop travel. Robocars will never be able to get across a city as fast unless they sprout wings!)

But back to the sky hook. A quick look at the illustration above makes another point about the design we have been developing. That is that the swing-arm itself is a fairly complex gizmo, which is a bit troublesome. Seeing it without the vehicle, though, gives a clue about who might want to make it. Below is a gantry robot. I am very glad these things are getting much cheaper, although they are not exactly following Moore’s Law.  

In fact, here is a clip of the machine in action. Doesn’t it seem like this system would be a lot more useful if it were untethered? Such an arm connected to a bogie would clearly need to clamp the track for precision positioning, but other than that..

Finally, when I say back to the drawing board, I mean it. Below is an example of how the three-wheel design from the last post might play out. Such a design can “land” on a flat surface like an airplane. The back wheel can be jacked up to pivot the front down creating a front-loading boarding ramp. The wheel size would be dependent on the anticipated use. Were it to remain permanently attached to the bogey, they would be very small. For dual mode they would be replaced with larger, motorized ones, and the maximum passenger weight would have to be restricted accordingly. I figure I might as well share it, because I plan to shift my focus back to the bogey for a while. Chances are it will end up buried deep in the dustbin that is my hard drive, at least in its current form.

119> Further Thoughts on Dual Mode

I want to express a few more thoughts on the subject that I raised in the last post, that being using something along the lines of the EN-V as a dual mode PRT vehicle. The first conclusion that I have come to is that the ability to balance on two wheels is not really that advantageous for PRT. This is especially true in countries that have the equivalent of the US’s “Americans with Disabilities Act.” ADA requirements for wheelchair accessibility mean vehicles need to be longer than the very short configuration that the self-balancing hardware was meant to enable.

I realize now that what enthused me most about the EN-V was not the self-balancing capability but rather the maneuverability afforded by the side mounted, independently engageable drive-wheels. Actually, steering in this way is not at all new. Inspired by aviation design, geodesic dome pioneer R Buckminster Fuller developed and prototyped what he called the “Dymaxion Car” back in the early 1930’s to address some of the same weight and efficiency issues that we are concerned with today. This mammoth eleven passenger vehicle got 22 mpg!

 

I remember reading anecdotes about amazed onlookers staring wide-eyed as the vehicle made a U-turn and parallel parked into an impossibly small spot in a single motion by using the full 90 degree pivoting ability of its single rear wheel. The same geometry is widely used today in the form of “piggyback” forklifts, primarily for the maneuverability it affords. This rear-wheel steering concept should not be confused with the many other “reverse trike” designs out there that have front wheel steering. Front wheel steering is undoubtedly better for roadworthiness at higher speeds but the space and position requirements tend to highjack a vehicle’s design more than Bucky’s layout. 

Those following the comments section of the last post have already heard my opinions on the dangers of adding anything more than the most modest weight gains to a vehicle. I still believe that the concept of cheap light track should be the primary design consideration because the main advantages of PRT only really manifest themselves within a network. Configurations of simple loops or figure eights would be better served by GRT, shuttles, etc. If dual mode capabilities compromise this priority… Well, in Texas we call that “Lettin’ the tail wag the dog.” There needs to be some limit to how much weight that ground travel capability imposes on the system design, and that limit is a painfully small amount. 

I think it is time to consider the matter though, because certain aspects of the whole system design may be contingent on the results. For example, having wheels on the sides strongly suggests having a front-loading door, and that influences station architecture. Any ground clearance creates an elevation that must be navigable by wheelchair. Seating changes could influence weight limits and distribution, possibly changing bogey design. So here are a few thoughts.   

The case for 3 or 4 wheels is not completely clear. With a four legged table, if you remove a leg it may or may not balance on the remaining three. In any case it won’t immediately crash over. A four wheeled vehicle behaves similarly when going over a pothole. The momentary removal of support has little effect. This is not so with fewer wheels. At least with the two in-line wheels of a motorcycle you can steer around bumps. Not so true with trikes or Segways. This leads to the design choice (for 2-3 wheeled vehicles) of larger diameter wheels that can better span dips. This can also be accomplished by wider or double wheels but this adds weight quickly. For four wheelers, the wheels can be smaller, but only with all four wheels being highly steerable can you match the maneuverability of those two side mounted wheels. 

None of these limitations bode well for the goal of speedy, comfortable, or long range dual mode. The question becomes one of how much hardware one is willing to haul around everywhere. Way back in Post 50, I brought up the idea of a drive-by-wire skateboard approach to address the problem of carrying this deadweight. Obviously this is a complicated solution, but one that completely addresses issues like larger batteries, robust suspension, etc. There is a tipping point where carrying around integrated dual-mode hardware becomes impractical weight-wise and the skateboard becomes the better choice. In my opinion this threshold is reached well before the vehicle is roadworthy. This is not to say that seldom-trafficked residential streets wouldn’t be drivable, just that busy streets are not safe for such vehicles just as they aren’t safe for golf carts. 

If you preclude busy streets, with their crazy drivers and potholes, and assume that trips will be fairly short, then the PRT vehicle could carry around the needed hardware without too much extra weight. The emergency battery could be split between the bogie and the cab, and that cab portion could be sufficient for short trips. If travel is mostly on paths specially paved for the purpose, suspension requirements are minimal. If the trips are short, minimal tires will last an adequately long time. If trips are short, speed is not a concern, so motors can be small and light. If speed is not a concern, wheel and load balance geometries can be used that would be less than satisfactory for ordinary driving, such as the Dymaxion car design.   

In conclusion, I think the best balance may be in the old Dymaxian car design, with a clamshell front door. Two large diameter (but thin) wheels (think dirt bike) with “in wheel” motors would fit into a pair of skinny wheel wells. In the rear would be an external (but shrouded) steering wheel. Some means would be needed to rock the vehicle forward to facilitate entry for wheelchairs. The wheels could be designed as modular, removable components and vehicles without wheels might coexist within the system. I would shoot for under 50 kg of total added weight. I was hoping to include some preliminary illustrations, but these things take a lot of time.

118> GM and Segway’s Unintentional Dual Mode Platform

As many of you know, I have never been a big fan of dual mode.  The problem is simple.  If a vehicle is light enough to be part of an effective elevated PRT system, it is too light to be a robust road vehicle.  Conversely, if it is sturdy and comfortable enough to not seem ridiculous as a car, it would require a track that would be unacceptably massive and costly.  You tend to either have a bad car or bad PRT or both. Yet if you thread the needle just right, they are off by tantalizingly little . Lithium based batteries, ever-shrinking computing power, carbon fiber technologies and miracle plastics are nudging things forward, but what is needed is something really dramatic.  Something to knock off half of the weight form the start. 

The other day I was thinking about all of this, or at least how to transport people that last mile.  I was considering bicycles, scooters, and Segways, and wishing for something that would have a roof to keep the rain out.   I was even considering what technology would be involved in matching PRT to a Segway, instead of the other way around.  I even have a picture to prove it.  

It was around then that I decided to do an image search for a rain-proof Segway, and I stumbled onto something that had passed beneath my radar when I first heard about it.  It is the EN-V concept car, which, as it turns out, which may well be the “best-yet” dual mode platform.  It is a joint venture between GM and Segway, and it does two things that really reduce the weight problem.  First of all, it runs on two wheels instead of four.  Roadworthy tires and wheels are heavy, after all, especially if you include durable shocks and springs.  This vehicle also lacks a mechanical steering wheel and all associated linkages.  Like the ULTra, it is self-navigating, or at least, “drive by wire.”  That brings up the intriguing notion of having the vehicle drive itself back to the station after dropping off a passenger.  The side-by-side, two-wheel arrangement enables steering without any pivot assembly, and also allows 360 degree rotation in place, something that might add considerable flexibility in station design.  

The relationship between the EN-V and PRT seems symbiotic: PRT can’t go the “last mile”, and the EN-V can’t go all that far.  The EN-V’s shortcomings in speed and battery life could be rectified by an electrified track.  Equally promising is that the EN-V weighs in at under 500 kg, and that is for a version with a much bigger battery and motor than would be required for dual mode use.  Also, as long-time readers well know, I have my doubts about how good of a PRT vehicle can be designed and constructed by any fledgling company without seriously deep pockets for R&D.  GM and Segway have dumped a lot of money and knowhow into this project.  They have based the vehicle on what they call the “Puma” platform, which is literally just that… a versatile, self-balancing platform slung between two wheels.   

I really think this combination deserves some serious consideration, more than I have time for within the context of a single post.  Look forward, therefore, to more on this subject in days to come.

Here are some related videos: This short clip shows the “Puma” platform without the passenger compartment. 

This second video shows a bare-bones version in action as well as a simulation of a city street designed for using the vehicle as an ULTra-like PRT.

The EN-V comes in three flavors, as shown in action in these vids.

http://www.youtube.com/watch?v=-fyIGp2qrmw

http://www.youtube.com/watch?v=hCGUmsdMifo&NR=1

117> Snow Day Musings

Well, we’re having a snow day in Houston…Well not really a snow day, actually it is an ice day. The buses are not running. Everyone is being advised to stay home. At the moment, all of the freeways are closed. It seems like a good moment to curl up with a warm laptop, and tap out some thoughts about this epic winter.

Being a mere six hours from Mexico, we are not well prepared for these kinds of weather events. We have no salt trucks or snowplows, but yesterday a truck preemptively applying a deicing solution caused a great traffic jamb, of which I was a part. It did no good.

It boggles the mind to think of the calamity that these weather systems are causing across the US (and Europe?) this year. In the last one, there were even fatalities in New York because ambulances couldn’t make it through. Enough, already! Is this really the best we can do?

The ongoing recession should serve as a “teachable moment” that illustrates the effects of a few percentage points of reduced economic activity. Clearly, these weather events must work against our collective well-being, event though we may not make the association.  Such shutdowns further compound the wasted productivity caused by simple traffic, illustrated in the chart below.

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Being paralyzed like this should point out the consequences of having all of our transportation “eggs in one basket.” For example, the rise of radical Islam makes me wonder if anyone has really considered what would be the effect of a sustained campaign of sabotage against road-based travel in a modern society. After all, a single disabled vehicle can nearly freeze a whole highway. Imagine the effect of terrorists simply targeting the tires of moving vehicles on a continuing basis… or even traffic lights for that matter. (I’m glad my readership is a very small and constructive group, or I would not share such notions)

There is also the warm weather counterpart to the “snow day,” which is street flooding. PRT systems can be specifically designed with this in mind. As ridiculous as it sounds, many urban areas around the world are built on floodplains. What would have been, for example, the result of a PRT system in New Orleans? If predictions of climate scientists are correct, we are in for lots of major weather events of all types in years ahead.

Anyway, my point is that society has reached a point of unprecedented interdependency, and is very vulnerable to any disruption in travel. These are not the days when everyone had canned leftovers from their large gardens and a cord of firewood on hand. If our transportation stops, our means of survival (and escape) does too.

Astute reader Lars Endre recently referred to raised PRT as exploiting “the virgin third dimension.” I love the phrase. It occurs to me, however, that it is not really virgin at all, at least around here. Here we have lots of spaghetti-like highway interchanges that are many stories tall. The interesting thing is that these forays into that third dimension are the very reason this city has drawn to a halt. Raised roadways and overpasses freeze first. We have many miles of raised HOV (High Occupancy Vehicle) lanes, connected to “Park and Ride” parking lots. Our embryonic light rail system continues to work, but nobody can get to the stations.

Too bad we can’t exploit the nice dry undersides that such elevated structures enjoy. Oh wait… We can! Yes, it’s the underside of that virgin third dimension that offers the possibility of completely weatherproof transportation. (You knew I would turn this into a shameless plug for suspended PRT sooner or later, right?) 

While we're talking about snow, although this is a bit off-topic, I would like to take this opportunity to mention the troublesome act of repeatedly salting roads. It reminds me of the age-old notion of dumping waste into the ocean or atmosphere because “It’s just so darn big that it can’t be hurt.” We know better now, but we continue to salt the earth on a mega-industrial scale. (10 million tons per year in the US, which works out to 66 lbs. annually per person) It works its way downward, eventually, to the water table, where it migrates “away.” Some readers may have seen these structures along roadways and not known what they are. They are structures for storing all of that road salt. I only wish PRT could solve this dilemma too.  

Finally I just thought I would share these pics that I happened upon. As you can see, the need to remove snow from our 2D transportation systems is not confined to just roadways.

Well it’s a day later and the sun is shining and the roads are clear once again. Time for me to wrap this up…

PRT cannot mean an end to roads or the costs of maintaining them. There still will be the need to move heavy loads, that last mile problem, and the whole countryside beyond. But an extensive, all-weather PRT network could, in times of crisis, be a very important backup system to have. We sure could have used it yesterday.   

 

116> Parkin' On the Hill...

This post is in response to comments made regarding the last one. In order to illustrate my points, I have used a modified version of the following picture, which I had originally intended to use in a different manner, so even though it is a bit off-topic, let me start with an explanation this illustration first.

This picture is the result of a design exercise, the object of which was to create the highest capacity station possible with the smallest footprint. In order to do this, I used elevators with curved doors, so that they can retract without needing much space in the walls. There are two of them, one for entering and one for exiting the station. This station is not “off-line,” but would rather be bypassed by a track that is not shown. Four cars can be loading while four are unloading, and (guessing a time of thirty seconds to get seated and on your way) the capacity of the station would be one car per 7.5 seconds, which works out to 480 vehicles per hour. It was designed to be ADA compliant, yet has a footprint of only about 50 square ft. One thing to think about is that if 8 of these stations where operating at capacity, the track they would be feeding would need sub-second headways to handle the passenger load. A station like this would be factory-built and delivered to the site in several pieces. Obviously the design is a bit misplaced in this setting, which isn’t exactly downtown, (so a footprint small enough for a crowded sidewalk isn’t really needed) but I had no other jpeg to “shop” the model into.

This leads me to the next picture, which shows a two-way variation of the same station. In this one, each elevator handles both arriving and departing passengers, with one elevator being for each direction. I drew this in response to alert reader Lars Endre, who suggested the possibility of using sloping track to capture the energy lost in deceleration. While this would be impractical for most PRT designs, it’s a concept that is well suited to self-leveling, hanging systems. The idea rests on the recognition that it takes a great deal of energy to get a vehicle up to speed and that it wastes a lot of kinetic energy to get it to stop. Parking atop a hill, so to speak, addresses both issues. This picture shows such an arrangement.

An alternative (frequently mentioned) approach to the problem is regenerative braking. As the vehicle slows, the momentum of the vehicle turns the wheels, which rotates the motor faster than it wants to go. This turns the motor into a generator and a brake at the same time, and the power is fed back into the track to be reused elsewhere. Sounds good when you say fast. I am not, personally, completely sure that this is an efficient process that is practical to exploit, what with electrical transmission losses, etc., especially with minor voltage supplementation in a DC system. 

Regenerative braking raises another fundamental question. How much braking do you want to do? After all, if the system is smart enough, it ought to have vehicles coasting more and braking less, right? The problem boils down to the need for speed. To some, it is assumed that assumed that PRT has a natural speed limit. Studies have shown that as speed increases, the safe spacing between vehicles must increase as well. Thus a system with a densely populated track going slower could move more people than one with faster, more widely spaced vehicles. The problem with those studies is a glaring fault in logic. It assumes that nothing can improve braking ability or crashworthiness of the vehicles. Fix that and you can both pack them tighter and go faster. But then we need brakes, and must deal with those mechanical inefficiencies. Consider the off ramp leading to a station. Making the split-off ultra gradual and giving a very long lead-up track is not very practical. 

 

Here is a different angle to show more track. While my first instinct was to think that raising the boarding area was a waste of materials, I soon realized that this cost could be offset by allowing shorter on/off ramps. Obviously this is more of an attractive option for fast, densely populated systems than for slower ones with few vehicles.

Another consideration is the “Umbrella Effect,” where overhead structures block the sky, a concern for landowners along the route. While this is less of a concern for minimalist track systems like I advocate, in a bi-directional station like the one shown there is still a lot of track up there, as can be seen. (Imagine the ULTra track four lanes wide!)  Long acceleration lanes represent additional visual obstruction. If raising the station can shorten these ramps, that would seem to be a plus for public acceptance as well as cost.  Even the station itself would appear somewhat less imposing by being higher, as more light would get in beneath it, and individual areas would remain shaded for less time. 

Astute reader Andrew F further pointed out that in tight turns, a sloping track could also be used to “bleed off” speed. (and give it back again after the turn) There are plenty of tight turns in a city environment, so this is something to consider. The negatives here are about ride quality, the way the system looks, the extra engineering, etc. Clearly, going very fast downtown would require a system that would be designed like a roller coaster, and I doubt we really want to go that far. On the other hand, in a system fast enough for commuting from the suburbs, there will always be the interface into the slower urban environment, just like freeway exits feeding downtown streets. Such an approach should certainly be in the toolbox. The case for using slopes to slow or speed a vehicle naturally arises, I believe, from the fact that it is so easy to do, considering that the track is raised anyway and the vehicles are designed to handle slopes and turns with minimal discomfort to the rider.

115> Swing Low, Sweet PRT...

Sometimes a technology pops up out of the blue that unexpectedly solves stumbling blocks that have been around for years. In this case I will refer the reader to the 3-axis accelerometer, a nifty little device that you probably own a few of. Own a car? There’s probably one in the airbag controller. Own a digital camera? Probably one there too, to help you take a clear shot with shaky hands. Got a smart phone? That’s how that nifty feature that keeps the screen upright works. Game controllers. The Segway. The list goes on.

What I am exited about is how the device can operate as a level, a feature that was exploited to create the iPhone app above. You see, because gravity and acceleration are essentially interchangeable, an accelerometer senses gravity as constant acceleration. Zero this force out with software, and your accelerometer senses “acceleration” every time you tip it in any direction… a thousand times a second.  Voila! A level! Or actually, to be more precise, an inclinometer!

Meanwhile, in the world of motion control, engineers are redesigning the electric motor. In the old days, it was realized that rather than putting bunches of electromagnets in a large circular array to make a motor, just a few would do, if the rotation were faster. That way, the same magnets could come around and around again, faster. More power, less materials. Magic! Only problem was that many people didn’t want fast rotation, and a century’s worth of bulky and inefficient reduction gearboxes ensued. Recently, a revolution has been taking place in the world of motors, the conversion from mechanically switching the electromagnets off and on (brushed motor) to using an external controller. Now, rather than simply rotating at a given speed, motors can be made to stop, change speed, reverse, hold a position, etc. The modern servomotor has been born.

Now a new generation of brushless, direct-drive motors is emerging which return to large diameter magnet arrays for torque, rather than gearboxes. These offer powerful and accurate rotational control without requiring that a machine be designed around standard gearboxes and motor mounts. I am referring, specifically, to frameless torque motors, which have reduced this architecture down to a simple pair of concentric rings. They are simply inserted between the machine and the shaft to be turned, like a bushing or ball bearing unit.

So here’s how it all comes together. Pictured above is the swing-arm for the PRT vehicle that I have detailed in previous posts. Two pair of frameless torque motors (shown in red) are controlled by an accelerometer. These keep the vehicle in line with the normal gravitational forces. The accelerometer-torque motor combination can, in theory, eliminate any errant, sideways G forces. The idea is to emulate a free hanging system, without really being one. Why not just let it hang? Unbalanced or shifting loads, sudden gusts of side winds, or continual rocking back and fourth are all effects that need to be canceled. Other than that, a free hanging design has the wonderful effect of self-canceling motion-related forces from acceleration, deceleration, or turning. It’s like a bucket on a rope. No matter how you swing it around, water in the bucket won’t spill, because all gravity gets shifted toward the bottom of the bucket. With a vehicle-mounted accelerometer, any forces that it senses other than “downward” (in a relative sense) would cause the motors to lock up to arrest that movement, with the exception of a slight dampening, to control of the tendency to swing repeatedly like a pendulum.

I have mentioned in previous posts how the swing-arm design is extraordinarily safe, because rather than throwing occupants through the windshield in a head-on collision, the cab would swing forward, absorbing shock and transferring the direction of momentum so that it would essentially push the occupant into the seat instead of out of it. In this system, extreme forces will initially simply break the magnetic bond, allowing this forward swing. As the swing continues toward its apogee, however, the relative strength of the torque motors increases geometrically, applying ever greater braking force. Meanwhile the cab has gone from traveling forward to traveling upward, so it is additionally fighting gravity. All of this absorbs the force of impact without any mechanical damage to the vehicle. Combine this with bogey-to-bogey bumpers, and you have an extremely effective crash protection system. There are theoretical and mathematical ways demonstrate that split-second headways are not dangerous for PRT vehicles, but it’s pretty hard to beat coming out of a crash test damage-free to drive the point home.

Bottom line:

 You could set down a full cup of coffee and be whisked away at high speeds without spilling a drop. There is no reason why PRT can’t put any luxury car to shame in ride quality. An added bonus is unprecedented safety.  

114> In Search of a Cheap Lunch

One of the dirty little secrets of “green” electric cars is that the batteries have consumed a lot of energy and created considerable greenhouse gases before they are even installed in the vehicle. The real environmental cost of batteries goes all of the way back to the mines, where diesel fuel is used in large quantities to extract ore. Fossil fuel is an ingredient in the plastic battery cases. Refining the ore into metals and useful compounds often is extremely energy intensive. It takes fossil fuel to ship the materials to the battery maker and still more energy to assemble them. Of course then they need to be shipped to distributors or to the vehicle manufacturers.  More energy lost. The real energy costs should probably even include the energy budgets of all of the employees of all the companies involved insofar as those expenses are directly tied to the manufacturing process. (A miner’s gasoline costs getting to the mine, for example) Then there is the energy to move the electric vehicle’s extra battery weight, and eventually everything involved in the steps of removal and recycling. Then there is the fact that fossil fuel is burned by utilities to generate electricity to recharge the batteries, but let’s leave that one aside for the moment.

It is a reasonable to ask, “How much energy is actually saved over simply fueling vehicles with gasoline directly?” After all, gasoline has one thing going for it. The pipeline between the well and your car is very efficient. This is something to consider with other supposedly “green” products as well. Solar cells, for example, are notoriously energy intensive to make and, likewise, do not last forever. It’s like the oil used to make the fertilizer for the corn to make cleaner burning ethanol fuel. There is no such a thing as a “free lunch…”

I am certainly not saying that this stuff is a waste of time to pursue, but that it should be considered in the design considerations of nascent technologies like PRT. This applies to all design choices, not just whether to use batteries. In particular, I would point out that my call for a minimalist track profile is not purely for aesthetic reasons. We ought to be asking ourselves, “What is the greenest possible medium for moving from point A to point B within the urban/suburban environment?” This, as luck would have it, will also probably be the cheapest, and least objectionable to look at.

I submit that a power-carrying micro-monorail system is the greenest alternative, all things considered, unless we can invent a way to make ski lifts have branching routes and off-line stations. It should be as close to invisible as possible and use minimal materials. It should allow very flexible routing options including tight turns, steep slopes, etc. If it can’t be run somewhere, then people can’t use it. I further submit that it should be thick enough to be a “workhorse” that can take fast vehicles and span wide streets without shaking or sagging. Being too thin mandates closely spaced supports, which can also be a disadvantage. On balance, this trade-off puts me squarely in the Ed Anderson camp, size wise, of about a meter high and about two thirds of that in width. Long-time readers of this blog know how much I have agonized over these dimensions. One advantage to a self-leveling suspended vehicle, I would note, is that it can transition in elevation easily, so that the main routing need not be on the same level as the stations, enabling track that can be higher and more out-of-the-way, if that is what the community demands. We don’t want to cut trees to put PRT in.

PRT has been caught up in kind of a “Gee-wiz, I’m so futuristic!” mindset, even though there is nothing, in this age, futuristic about it. But it is still about being green. My last post was about how free-roaming robocars had co-opted the PRT moniker, and we’ve been having a lively debate on better names. I would just like to add this thought to that debate. If PRT is the physical equivalent of the internet, then the track is the equivalent of telephone wires or fiber optic lines. I say, “Let’s go broadband from the start!” Furthermore, let’s make that infrastructure as green as it can be. That means not being designed to be scrapped, but rather being modular, so it can be moved and reused rather than melted down; It should contain zero fodder for the landfill.  PRT, of the powered rail variety, isn’t just another green transportation alternative. It is the ultimate green alternative, bar none. (I’m not counting open-air or human powered vehicles) So maybe it should be presented that way, by the infrastructure, and not the vehicles or the difficult-to-explain operational characteristics.

After all, if you are promoting “elevated microrail transit,” then the whole rest of the PRT paradigm becomes implied. 

“Automated or involving lots and lots of drivers?”  - Automated.

“Make everyone wait behind a stopped vehicle or have off-line stations?” - Off-line. You get the idea.

In the end, being green, being efficient, and being prosperous are all one-in-the-same. Battery powered electric vehicles, though not a complete red herring, do start with substantial energy deficits that should not be ignored, so environmentalists should be made aware of the fact that powered rails are a much more efficient option.

Elevated, line-powered, mini-monorail transit: To me, it’s a no-brainer. There should be non-profits promoting it, universities developing vehicles for it, the works. It’s where we need to go. Delay in doing so is simply squandering resources, including our land, our raw materials, our fuel, our time, (spent in traffic) our time (spent building and unbuilding stuff) our (still not totally carbonated) atmosphere, and of course, our money. 

PS - If there’s anyone who can find a link to actual studies on the energy used in the life cycle of batteries I would be grateful if you would share… I have only found this paper, which is so outdated that it doesn’t even have figures for Lithium-based types. Finally, I would like to share this video, listed as “300 years of fossil fuels in 300 seconds”.