Sunday, December 25, 2011

134> Good Tidings!

Well, as 2011 draws to a close, we PRT believers have been given a Christmas present!  Finally, for the first time in history, a large city with a real traffic problem is actually going to install a meaningful PRT system.  ULTra, having proved its technology in its Heathrow Airport system, has partnered with an Indian company to build a 200 vehicle, 100k passenger per day system in Amritsar, India.

I know.  I’ve been critical of ULTra in past posts.  I have questioned if the system really can be called PRT at all – if coordinated robocars really fit the definition, especially since they do not enjoy the weatherproof speed and efficiency advantages of running on steel rails.  I have worried aloud if the inherent performance shortcomings of steerable soft rubber tires on “pavement” would give PRT a bad name.  But I have to say, all in all, that I’m pretty damned pleased, and I’ll tell you why.

There is one basic concept, best taught through demonstration that can promote PRT globally.  It is the fact that, in an urban setting, ONLY multi-level transportation can be non-stop, and only non-stop travel makes sense in an increasingly resource-strapped world.  Since multi-level roadways are too expensive and massive to deploy en masse, the most straight-forward approach is to create a new, lighter infrastructure that can be more affordably elevated above interfering traffic.  This lighter infrastructure requires lighter vehicles and payloads as well.  The logical way to speed throughput on this smaller infrastructure is intelligent automation - the combination we call Personal Rapid Transit.  I had previously worried that a system like ULTra would end up, for cost reasons, having a great deal of track on the ground, which essentially misses the point.  It appears that this is not the case.

It also appears that this venture is designed to make a profit for shareholders, with affordable fares, no less.  This is obviously a huge deal, especially since every other option ends up being supported with tax dollars.  I wish I knew more of the financing details…It sounds almost too good to be true.

We humans are far better at perfecting things than inventing them from scratch, so even if the world comes to believe that the ULTra design is the very definition of PRT, it won’t be long before more capable versions begin to appear.  Undoubtedly such work is being done by ULTra itself.

What we will see in Amritsar is not at all what the early PRT pioneers had in mind.  There are no grids of one-way track with small, evenly spaced stations.  There is no attempt at blanket coverage.  There are no loops; these guideways will be bi-directional.  The route appears to have a combination of straight runs and a few fairly sharp turns, a combination that will slow fixed speed systems to the speed of the sharpest turn.  Unlike the utopian notion of a car free city, many passengers will park their cars and take the system from there.  There were the predictable protests over the track, although given the climate; I would wager that those shopkeepers will learn to appreciate every bit of shade afforded by the canopy.

The plan calls for connecting seven destinations:  The bus station, the train station, two parking lots, a school (chosen because it was non-private land next to a large commercial complex?) a Bazaar, and a major tourist attraction, the “Golden Temple.”  These people need more roads where there is no space for roads, more parking where there is no space for that either.  There was little choice as to the routing.  What you are handed is you get to work with. Sound like anywhere you know?

The fact remains that we really don’t know how the Amritsar system would compare to the same elevated track populated by ordinary motorized rickshaws, a similarly sized, common form of transportation in that part of the world.  This case, however, bears little resemblance to the 1.2 vehicle occupants we are used to.  They are reportedly going to pack in up to 6 per vehicle, so any driver would represent reduced capacity.  What we do know is that, even though most people’s eyes glaze over when you start talking about a whole new infrastructure, some developers and some people in the Punjab government “got it,” and took a leap of faith.  This is a very, very good thing.  The more successful it is, the more it will attract competition and innovation.

There are a number of lessons here for PRT designers and would-be PRT vendors.  One is to get big local partners.  Who can dispute, for example, the (often greedy) symbiosis between real-estate development, politics and infrastructure?  ULTra’s Indian partner, Fairwood Consultants, boasts 25 billion in projects under management.  That opens a lot of doors.

A related issue is core competency.  Ultra has never really tried to break much new ground, mechanically speaking.  They use pretty conventional electric vehicles on a track that is nothing special either.  They didn’t even opt for advanced batteries, but use simple lead acid ones (like a golf cart) instead.  But this is not really a liability.  Instead of expending energy working the bugs out of a bunch of new, experimental subsystems, they get to concentrate on creating traffic solutions with what they have.  Eventually some company, with deep pockets and great mechanical engineering expertise, will see building a more advanced system as a venture with little downside risk, so long as they themselves are partnered with a company with a proven track record of implementing such systems.  ULTra, by this point, will presumably have further cemented its leadership position in that role.

I think they had better not wait too long before they get such a partner however.  If their system in Amritsar proves successful and they land subsequent deals, there will be imitators and competitors coming out of the woodwork.  My own design explorations have convinced me that there are huge performance improvements to be had across the board, as measured by essentially every important metric.  But their success can only make such a partner easier to find.  I believe that there is huge amount of positive PR to be gained by any company that takes this plunge.  They would be seen as agents of change, as green, and as technological leaders, saviors of the taxpayer, solvers of government debt and on and on…  Again, if ULTra can handle the “behind the scenes” grunt work involved in landing deals, planning routes, working with local partners, and generally handling the logistics,(and/or operations)  they will become the indispensable (although less glamorous) part of what could become a very big and profitable industry.  Wouldn’t it be interesting if a future headline read, “Airbus Industrie Partners with ULTra Global to Create Next Generation Pod-Cars?” Or how about Honda?  Or Embraer? Or Bombardier? Or even GM?  

So, on this special day, I tip my hat to the folks at ULTra.  Well Done.  Yes, my friends, we have good tidings!  And a Merry Christmas to all of you!

Monday, December 12, 2011

133> Maglev Mania

Recently there was a posting in the Transport Innovators site that caught my eye.  It was entitled “SkyTran a Sham?” I know… I really should join that group and post my thoughts on that site, and lend a little support to what I consider to be a valuable public resource.  But I like to scratch my head and measure my words a bit more than most before I open up my mouth, and I am usually too busy to even consider an issue on a timely basis anyway.  So I hoard my musings away, like precious little nuggets, to be used as rainy day subject matter for this blog.

I am not so interested in the charge that was made against SkyTran but rather by whom it was made.  It was leveled by the author of this study, which starts out promoting and then later disparaging nearly the exact same concepts as SkyTran.  In my opinion both have severe problems.  The author threw in the towel.  SkyTran still purports to be a practical system.

What is it about maglev that makes smart people so crazy as to think that it is appropriate for PRT? maglev’s major advantage is being frictionless, except for air.  This is a very minor consideration at city speeds, and yet they want to shoehorn this high speed technology into the sharp cornered, stop and go world of urban transit.  A friction free object wants to glide at a steady speed, in a straight line.  Navigating a city requires something wholly different.  Both systems are designed to travel in excess of 200 km/h (124 mph), far too fast for short trips.  Even though he states that, because of G-force constraints, average system speed can never exceed 100km/h (62 mph) in an urban environment, he never wavers from his 200 km/h maglev design, and the inflated track cost that it entails.   

In the case of Swift PRT, the author, after all kinds of analysis and simulations, concludes that the track is too expensive (Duh! It’s full of copper coils!) and that vehicles that fast must be spaced way apart to allow exiting, entering, or even simple turns.  (Or, alternatively, they need 600 meter ramps to and from the stations.)  He states, “If your intersection or station spacing is meant to be <1km apart, you effectively need two lanes in each direction:  a fast lane, and an acceleration/deceleration lane.  The net result is you have at least doubled your track costs, and the width of your system.” It seems to me that the problem lies with trying to connect 200 km/h fast lanes to every downtown station!  That seems to be what SkyTran is advocating as well.  Like I say, there seems to be something about maglev that makes people lose their senses.

The conclusions are what bother me most:  While I have no problem with his realization that maglev PRT is not cost effective, he then applies his figures to PRT generally.  His assumption is that all PRT track must cost 7m/km, even though his own figures show that one way track without the copper coils and in-track electronics would come in at 2m/km.  He then, through mathematical inference, extends this inflated cost to justify only putting one station per 2.7 km, and then uses this spacing to assert that PRT (in general) cannot compete because of the long walks to get to the station.  His reliance on formulas over common sense has led to the “crap-in, crap-out” phenomena.

What is curious (and unfortunate) is the illogical leap from discovering that his system is too fast and expensive to the conclusion that the future of transportation is in vehicles that run on asphalt.  This argument is made without anything to back it up, save the cost and ubiquity of the road system itself. Was it not the shortcomings of the road system that lead him to explore PRT in the first place?  Sure, I think we all agree that traffic problems can be reduced by using networking and AI technologies.  But asphalt will always be primarily a two dimensional, stop and go system.  Multilevel interchanges simply cost too much and are too big to be ubiquitous.  So when he compares the cost of his 130 mph, non-stop system against asphalt, he is comparing apples and oranges.  If I had to venture a guess, I would say that the author set up an experiment that he was forced to carry it out with scientific rigor, even though the basis for the experiment (his hypothetical system) was clearly flawed.  Having exhausted his time and/or interest, he was in no mood to do it all over with a better system, and so hastily framed his results.  These conclusions certainly do not reflect the thoughtfulness shown in the sections where he first discusses the original problem.

That being said, one other interesting result of the study highlights the parking problem, something that is often glossed over in PRT discussions.  While it has been admitted that PRT vehicles will have to travel around empty sometimes, the extent to which this will occur has been a subject that has remained somewhat opaque.  Obviously, during off-hours, if the system is only operating at half capacity, there are 50% empty vehicles, and they have to be somewhere.  Are they traveling around in circles?  Clearly these vehicles should be staged somewhere, but I have not seen this reality reflected in the various PRT designs.  It occurs to me that this is still one more argument for a fully multi-axis (3D) system.  Warehousing numbers of empty vehicles would be much more space-efficient if they don’t require long ramps.  As with parking cars, a vehicle with a small turning radius is a plus.  In PRT, such a radius might be horizontal or vertical.  Compact parking is especially important if an attempt is going to be made to shelter those vehicles from the elements.  A PRT design that allows a combination of tight turns and compact track switching in full 3D can clearly minimize the real estate (and roofing) required for such storage.  Being able to make multiple track configurations in tight spaces would be particularly advantageous in utilizing whatever real estate might be available, including very small or oddly shaped lots.  Such parking can be envisioned more in terms of a lattice or matrix, as compared to lines of cars on  long parallel tracks typified by the storage of railroad cars.

I might add that tight turning radii in both vertical and horizontal axes is inherently difficult to achieve in systems that use the track as part of the propulsion. This is because of the required tight spacing between track and bogie. Magnetism loses force with distance, so using magnetism between track and bogie for propulsion will always entail a fairly tight fit. This is my major beef with linear motor propulsion, even non-maglev varieties such as simple LIMs, which don’t require coils in the track.   

Anyway, to those of us not under the maglev spell, this study illustrates some of the challenges of PRT design that must be, and, indeed, can be properly addressed.  The challenge of G forces, of storing and staging pods, the track cost issues, the station spacing… All of these must be carefully balanced and tweaked if PRT is to succeed without the blunt instrument of generous government subsidies.  Any good PRT design must address these issues from the onset, not as afterthoughts.  Otherwise it will either fail outright or be relegated to a few niche markets.

Wednesday, November 30, 2011

132> Forward Compatibility

I know I said that my next post would be about standards, but I think this topic should come first since it weighs into that discussion. There has been something in the back of my mind, in every design that I have posted on this blog. It is the recognition that progress often happens in baby steps, yet baby steps often don’t go in a straight line or a logical direction.  

I am talking about forward compatibility. The vexing thing about designing PRT (or anything else) to be forward compatible is that it requires a design that allows evolution toward an end that must first be defined itself. In the case of PRT, that eventual product would ideally be very fast, silent, comfortable, able to be deployed with minimal cost, and be adaptable for every contingency a city could throw at it. These adaptions  would include a variety of station types for different locations and passenger volumes, being practical within buildings, being able to be elevated to a level deemed acceptable by the effected parties, etc. The vehicles themselves can be assumed to be, in this future world, mass produced to point of enjoying economies of scale.

I am sure that many readers have dismissed my designs as being too ambitious. The vehicles, in particular, have very advanced electro-mechanical systems which are designed to remedy situations which could largely be avoided in the first place with little negative impact. Well now you know the reason. By designing the vehicles as though Toyota had been building them for decades, one can better consider the best design for the track and stations that may still be around when that day comes.

In the meantime, however, PRT will be subject to the restrictions that our current economic, political and technological realities place on it. The problem is that designs for today and designs for tomorrow are strikingly different. The main culprit is the tire wear and noise/vibration associated with speed. It is true that smooth running surfaces and track clamping emergency braking capability enable harder rubber, solid tires which don’t need to flatten out on pavement to achieve the high traction requirements associated with gripping slippery roads. Still, highly wear resistant plastics, such as are seen in rollercoaster wheels, are a recipe for a very noisy system at high speeds, especially on pipe, which is notoriously good at amplifying sound. (This is the basis for many musical instruments)

I should point out that the design I show in the Oct. 30 post enables both steering guide wheels to be raised for high speeds, eliminating contact (and therefore noise and wear) by the plastic flanges. Also, these flanges are to rotate independently of the drive wheels, so that they may make contact with the track (pipe) anywhere on their surface and create their own rotational speed based on the diameter established by that point, rather than the smaller diameter of the tire. This reduces wear on what is a tiny contact point.

The main point remains, however, that high speed systems should have larger wheels (OK, not Maglev) or risk lots of wear and/or lots of noise. A system that requires wheels or tires to be changed every few thousand miles would be a disaster. But longer wearing, larger tires means bigger track, something that is nearly as bad, in that it raises the cost and visual impact of a system which will, in the beginning, be under intense scrutiny from critics. Also initial systems will probably be slower anyway, because such trial systems will have to first prove themselves for short-distance downtown use. 

Could there be a two tier system? Would it be crazy to start with a system for downtown that would preclude high speed vehicles? I know it sounds like a terrible idea, but it would probably shave 20% off of the track costs, and vehicles would be discounted considerably more. And let’s face it. The other PRT systems out there aren’t exactly fast or flexible either.

In the illustration above, the system on the left, which is obviously simplistic and incomplete, would only need to raise and lower the small pairs of wheels to steer. I do not believe that the middle “hold-down” wheels (illustrated in previous posts) would be required, so that’s really all there is. There are inexpensive “off the shelf” hub motors available that would fit in the drive wheels, and the flange and hubs could be cast as one, (in urethane) so that solid rubber tires would slip on. Such a bogie would be extremely cheap to produce. The complex (expensive) articulation capabilities of the swing-arm and gondola could also be dialed back in such a “starter” system.  

The obvious problem comes from the fact that the fast vehicles wouldn’t fit in the smaller track, although the slow vehicles could run in the high speed track. So what is a city to do? Well, there are a couple of things to note here. First, the high speed track would be equally usable for GRT. (Group Rapid Transit.)  A track going out to an airport, for example, might well be a good stand-alone investment used in this way. Passengers coming from the airport to downtown would need to change vehicles to use the downtown PRT, but the upside is that they didn’t have to make the long trip at 30 mph.  Faster, express PRT could share the track at some point, and slow vehicles could use the track at certain times of day. Because PRT is a smart technology, if high-speed track is running through a grid of low speed track, the slow vehicles could still, in theory, get on and off without disrupting the high speed service. (Assuming sparse high speed traffic) If the track is modular, standardized and interchangeable, the slow track could be removed (during an upgrade) and be reused elsewhere. In the airport example, for instance, slow track taken from downtown could be used to build a network around that airport. In such a case changing vehicles would be a minor inconvenience for relatively few passengers. It is also noteworthy that, in a downtown environment with mixed track, fast vehicles can’t get up to speed anyway, because of sharp turns. Therefore slow vehicles sharing the (fast) track would be no problem. In such a case the system could simply send a slow vehicle if a trip would involve a stretch of slow track.

I have come to the conclusion, reluctantly, that there are theoretically reasonable migration paths from slower, inexpensive PRT to faster systems capable of tackling longer distance commuter traffic. The examples above are just a sample of the possibilities.  They also show that it takes some creativity to undo what many of us would say is a very shortsighted decision. (To put down track that can’t take fast vehicles)  But at least it’s better than having no forward compatibility at all!  It is unfortunate that such a complicated situation should ever exist in the first place, but I have my doubts that we can ever get to PRT 2.0 without first dabbling in PRT 1.0.

Sunday, November 13, 2011

131> Climbing a Chain

Suspended PRT has the advantage (over bottom supported systems) of being well suited for very steep slopes.  As I have pointed out in previous posts, I believe this attribute is essential to achieving flexibility in routing and station placement because it enables a completely three-dimensional transportation solution.  Such flexibility could be important for keeping costs down and increasing ridership.  I do not think that starting with the supposition that each station must handle a minimum of many dozens of passengers per hour gives the kind of flexibility that cities need.  Such pedestrian-rich station locations may not be close enough to each other to make a walkable grid of coverage and getting to such strategically placed stations might well involve more car travel than the PRT trip is likely to save.  This makes dirt-cheap stations very important.  Bare-bones ground level boarding, say, at bus stops, is an option that is out of the question with most supported systems because the ramps would be in the way.

The picture above shows a minimal station in a park. While it clearly is a low throughput design, it also would not require a lot of passengers to pay off.  Small neighborhood parks are very common in the US, often created by the real estate developers to help attract home buyers to a subdivision.  Better still, they are usually located at or near a subdivision’s entrance.  Such small neighborhood stations could exist along a routes that are important but aren’t part of a grid, say from an airport to a downtown area, or between two metropolitan areas that have grown together.  Once residents realize the benefit of such an access point and station’s capacity becomes a problem the station could be upgraded, this time based on real-world ridership numbers.   The foot-in-the-door approach to eco-friendly commuting!

This (more multi-axis) approach should also allow options that will help in the “not-in-my-front-yard!” confrontations that any new transportation infrastructure is sure to create.  For example, it enables the track to be run at a much higher altitude than systems that rely on elevators or gradual ramps.  Instead of a “take it or leave it” approach, there is the option of running the track above the tree tops if necessary.  

None of this, however, is possible without a straight-forward and inexpensive way to engineer this capability into the system.  

Here is such a method.  I have illustrated it with only the relevant wheels and engageable surfaces of the track shown.  The last post shows the track and vehicle in more detail.  (To any newbies to the site out there, I advocate direct-drive “hub motors” which rotate around electrically fed axles, so actually the whole drive system is shown!)  This design is fashioned after the rack and pinion system used by cog railways.  The trick is to make it engageable and disengageable without complicated mechanisms that would drive up costs and reduce reliability.  It uses two stretched lengths of modified roller chain as a rack, and a sprocket that is of much reduced diameter (compared to the wheels) to eliminate the need for a low gear for slow but powerful climbing.  This method adds next to nothing to the costs or complexity of the system.  Such custom links as I use here (and, indeed, whole specialty chains) are widely available because they are commonly used for material handling tasks in industrial production lines.  Here is how it engages, step-by-step.  

The forward wheels move off of the flat running surface, so they are supported by the flanges alone, which rotate separately and freely from the motorized, rubber-clad drive wheels.  For a moment the front wheels can then spin freely as the bogie is being pushed forward by the rear wheels alone.  The motor controller then increases the rotational speed of the front wheels to compensate for the smaller diameter sprocket.  (The front and rear wheels must now be synchronized at two different speeds.)  As the sprocket engages the chain there is near certainty that the teeth will not be in the exact position to mesh exactly.  To adjust for this, there is a compressible rubber cushion (shown in green) which allows the chain to “stretch.”  Additionally, it is possible to design some limited rotational play into the sprocket hub.  Since we are talking about roller chain here, any occasional slipping will not “grind the gears” causing excessive wear as would be the case in a typical rack and pinion.  Keep in mind that this transition is not expected to be taken at anything approaching normal operating speed.  Once the chains mesh with the front sprockets, engagement is kept captive by an upper bar which presses on a freely rotatable ring (blue) mounted on the wheel’s axle.  This pushes the sprocket teeth into the chain and holds them from slipping out.  Although this may seem redundant because the middle, hold-down wheels do the same thing, (push down) I added this component because I was worried that the compression of the rubber tire would allow the sprocket teeth to slip, and I prefer that rubber because of noise and vibration dampening at high speeds.  Anyway, at this point none of the track’s normal wheel support surfaces are necessary for the front wheels to pull or stay centered.  With the front wheels engaged, the rear wheels will follow a similar sequence but without any question about meshing, since the distance between wheels can be precisely set to match the chain.  Of course the whole process can happen in reverse as well, to go from chain back to ordinary track .

Some readers might be concerned that the chain and sprocket are not strong enough to be used in this fashion, especially since normally at least a half a dozen teeth of each sprocket engage a chain. Each sprocket tooth, however, will have a test strength of at least 3500 lbs. The test strength of chains of the size pictured is at least 12,500 lbs. each.

Footnotes… The design as shown is based on four drive wheels, with the hold-down wheels being free-turning. This is a somewhat arbitrary decision. (The hold-down wheels make the system “half-track capable,” meaning the vehicle can travel on the either its left or right wheels alone without possibly twisting inside the track from lack of support – an essential attribute for switching tracks without the tracks themselves having moveable parts.) These hold-down wheels could just as well share propulsion and braking duties, and so could also be configured with additional sprockets and chains themselves.

Finally, A personal opinion:  I think PRT designers should take a page from the late Steve Jobs. A lot of what he did was to take existing ideas and products and redefine them by engineering them so they were a joy to the senses. He had zero tolerance for the slightly funky design choices that help rush products into the marketplace, only to limit their acceptance in the long run.  When I look at the current PRT offerings out there I see such design compromises by the boatload. We, at least in the developed world, will never fully embrace any system that is clunky, bumpy, noisy or slow! We must recognize that the bar has been set very high by a hundred years of automobile engineering and try our best not to disappoint. But then again even a Ferrari can’t rescue you from the congested city streets by going straight up!  

Sunday, October 30, 2011

130> Progress Report

As many of you know, I have been advocating the standardization of key PRT technologies in order to allow PRT to be developed, produced and deployed by a consortium, rather than a single company. This, in turn, requires that this development be started on a basis of the most promising design approaches. I have concentrated my efforts on a suspended system, rather than the bottom supported approach, even though I suspect that the majority of readers prefer the latter. One key to why I think suspended systems represent the best way forward is referred to in my latest iteration of the acronym “SMART,” which is what I call this effort.  (“Standardized Multi-axis Automated Rail Transport”)  
As I have pointed out numerous times before, all “ground” transportation suffers from the same problem: Vehicles or people going in different directions will run into each other unless they stop and wait their turn. Going over or under solves this problem, but that solution is too expensive to deploy universally with current modes of transportation. That indispensable artery of modern commerce, the freeway, clearly shows how effective high-speed non-stop transportation can be. This is simply the result of what happens when a transportation system is modified to be multi-axis instead of existing on one plane - the ground. Unfortunately making multi-level (multi-axis) routing for large vehicles such as trucks and trains takes huge amounts of money and space. When it comes to multi-axis transport, smaller is better. Luckily, we mortals are pretty small.
A multi-axis automated rail transportation system is essentially a new infrastructure designed to do what the freeway can’t. Go to any street, to any bus stop, to any building. It would be designed to be faster and safer than driving, more energy efficient than the most advanced electric car, and expandable for a fraction of the cost of roads. Being natively multi-axis, a suspended system can be employed in areas where long ramps are undesirable (that’s basically everywhere) and the system can be elevated higher than would be practical for supported systems. This can minimize visual impact. While it is true that a supported vehicle can be made to self-bank and keep its cabin level on slopes, it is much more cumbersome to engineer. Vehicles with wheels on the bottom are just ill-suited for extremely steep travel, while hanging vehicles have no such problem. Traditional PRT designs require raised, elevator equipped stations because otherwise the entrance and exit ramps into the station would block driveways, be subject to climbing, and be visually intrusive. A native 3D system has no such restrictions. A suspended vehicle can either taxi in like an airplane or come down like a helicopter. This means that stations can be put nearly anywhere, and they can be very minimal and inexpensive. They do not require high traffic volume to pay for themselves, so they may be placed with high frequency, like bus stops rather than actual stations.  This will increase ridership. The question is this: If we are going to build a whole new infrastructure, do we want it to be raised, single-level, multilevel with ramps, or natively  multi-axis? A consideration of the various routing situations likely to be encountered in a widely deployed system leads me to believe that it would be better to have true multi-axis capabilities from the start.  Anyway, here is the latest iteration of the SMART PRT vehicle concept. Hmm… How about “SMARTPOD?”….Sorta has a ring to it…

Unlike previous versions, the steering guide wheels have been moved outside and under the track. This shaves off about five inches from the track height, bringing it down to about  30 inches/76 cm. (less if it the track is hung from a ceiling.) What is shown here is a high-speed vehicle, (highway speeds and higher) designed for many tens of thousands of miles between tire changes. (hence the large wheels)
The wheel flanges are designed to outlast the tires in two ways. They turn independently of the wheels, so if they contact the track at a different diameter than the tires there will be no conflict. Secondly, they are only deployed during actual turns. Otherwise the bogey is centered by leaving both left and right steering guide wheels in the upright position. The upper “hold-down” wheels replace the upper steering guide wheels of previous designs, prohibiting any rotation of the bogey within the track. This design is extremely maneuverable with a turning radius of a mere 8 ft., including vertical turns. (The spacing between various track surfaces must vary, however.) The pictured design is missing most of the components of the bogie at this stage of development. The sprockets pictured are for vertical climbing, although I plan to adjust the sprocket size somewhat.  

The track has been designed to be extremely easy to fabricate into sections that are straight or curved. There would be no problem finding shops willing to bid this work, even in small towns if the pipe bending is outsourced.  Removal of a left or right truss section will not mean that vehicles cannot pass, although there is a small temporary rail that needs to be placed as insurance against any freak events that would make the whole vehicle sway with great force. I am still working the best way to attach sheathing, although the reader will note that there is a slight arc to the outer edges of the truss. This is to make light-weight metal or plastic sheathing more rigid.

Alert readers will notice an air scoop. At this point I am leaning toward liquid cooled motors. This greatly increases the performance-to-weight characteristics of the motors, and hub motors are ideally suited for this, as the copper coils that need cooling are stationary and accessible radially from where the wheel attaches to the frame. A simple little electric pump that is remote from the motor itself is all that is needed. No moving parts are added to the motor. The scoop is for a radiator/heat exchanger.
Finally, I want to emphasize that this vehicle has capabilities that go well beyond what is likely to be deployed early on. Nonetheless, I am designing with the future in mind so aspects that are practical today but foreclose later improvement can be avoided. Water cooling, high speeds and vertical climbing are features that might be expensive complications to first deployments. However I see little point in building an infrastructure project whose inherent design limitations will become apparent as soon as it is deemed a success.  This is, in part, why I favor a full multi-axis approach. Future cities are only going to get more crowded and time is only going to get more precious.   

Friday, October 14, 2011

129> Emergency!

Do a PRT vehicles need a way to for people to escape in an emergency?  Many seem to think so, in that I am aware of a number of systems that have stated evacuation procedures.  This is problem of elevated track, since obviously if the vehicle is on the ground one can just get out, so long as the doors can open.  It is particularly difficult with suspended vehicles or systems that employ track that is too narrow to walk on.  This is unfortunate, because the very real advantage of being minimal and out of the way becomes a disadvantage in this case.

All of this begs the question of what can stop a PRT system in the first place.  The historically contemplated mode of failure is some sort of systemic computer problem.  In a system with completely centralized control, a system outage would stop all traffic.  Yet Google and others have demonstrated autonomously piloted automobiles.  If all PRT vehicles can be sufficiently autonomous to find their way to a station, then that would seem to rule that problem out.  Advances in battery technology have made it much easier to have ample on-board backup power to get to a station, so a systemic power failure wouldn’t seem to pose a problem either.

Then there is the in-vehicle failure.  It should be noted that two such failures could trap all vehicles between the two and that a single such failure requires that all vehicles must be able to operate in reverse.

With a direct drive (hub motor) system, like I advocate, mechanical failure is exceedingly unlikely.  After all, the only moving part is the wheel itself, so there is no drive train to break down. Each wheel turns on its own.  In-vehicle control or communications failure?  It would seem that there are a number of remedies for these possibilities as well, the most obvious being a redundant backup system.  After all, the cost of computer boards these days is hardly worth mentioning.   I suppose a last resort would be to pulse the motors very slowly (this will make them incrementally turn a few degrees with each pulse) without the computer systems.  The steering guides would be set to exit at the next ramp, and the vehicle would emit a beacon to alert other vehicles.  All of this could be triggered with simple relays or even manually. Furthermore, at least in the designs I am contemplating, the vehicles’ bogies, which are located inside the track, have bumper/coupling means.  They can both push and pull other vehicles.

Then there is the possibility of a break in the track, say from an earthquake or large truck collision.  This is a psychological barrier as much as an actual threat, in that the idea of flying off a broken track into free fall is a particularly frightening vision.  With good brakes and the right software, it seems like thus too should be manageable, unless there are multiple breaks in the track, cutting off whole sections from a station.  Such a case, it should be mentioned, would foil almost all evacuation plans, even if the vehicles were riding atop a wide causeway, unless it is one with very frequent exit stairs.  I might  mention here the break detection system employed by Disney for their rollercoasters:  The pipes that comprise the track are filled with compressed gas. A reduction in pressure means that there might be a break.   I would also add that with a hanging system, one of the advantages is that stations do not require lengthy ramps or elevated stations.  This would favor stations being positioned with more frequency, reducing the number of potentially stranded passengers. 
Then there is fire. With the motors being separated from the vehicle as they are in a suspended system,

even if there were a large amount of flammable materials in the motor, (which there aren’t) there

is still no way it could catch the cabin on fire. What about the cabin itself? This presents the one tricky
problem.  How do you stop some idiot with boxes of papers and a lighter from starting his own fire? One obvious, but partial, remedy is to have a smoke detection system which automatically sends the vehicle to the next stop.  I suppose that there is also the possibility of some release of noxious fumes from a power supply or other computer component overheating or burning out. The fact that computers are ever-shrinking and
requiring less and less power seems to indicate that this won’t be a problem. I suppose, also, that it possible that a passenger might spill a bottle of ammonia or puncture an aerosol can. The need for emergency outside air seems far-fetched, but is worth at least considering when weighing design options. 

So it seems like a catastrophic earthquake, multiple separate vehicle failures, or a very foolish passenger are the main causes that would require evacuation, so long as the vehicles are at least semi-autonomous and have robust back-up power. That and simple human psychology. Perhaps there needs to be a way to evacuate passengers simply to make the system more saleable. After all, the fire and police departments might see this as just another potential drain on resources. And of course there is the law. Perhaps some well-meaning politician has put “public safety first” and created a legal hurdle. If there is such a statute, I am not aware of it, but of course this would vary between countries. 

If there absolutely must be an evacuation means, for a hanging system I can see a few possibilities.
One is to have some sort of extra rail all along the track where emergency vehicles could travel, unimpeded by stalled vehicles, getting access to all.  This is cumbersome to engineer well, but is at least worth contemplating.

Another solution is to have a means to lower the cabin or parts of it. This could be done with a very small winch, since it doesn’t need to raise the cabin fully loaded or be in any particular hurry. With gravity assisting, cables could be lowered with the most minimal of motors, or even by gravity alone. The tricky part is how far such a system could or should go before wind starts becoming a factor. Even with telescoping scissor-action stabilizers, diagonal cabling and every other means, there is still a problem if you go high enough. There is also the matter of limited choice as to what is below. Is the terrain level? Is it the middle of a highway?  In the end Bubbles and Beams video, the vehicle leaves the system via an elevator of sorts, which is little more than a pole and some cables. The arrangement looks a bit flimsy, at least for going up and down on a regular basis. Going down in an emergency, however, is a whole different matter. Perhaps such poles could be placed periodically or some of the support poles themselves could be so equipped.

A variation on that theme is something I am currently working on. It would involve a fold-out platform or seat which the track support poles could be fitted with. This could be lowered via a cable running inside of a channel.

I can also envision such cable-inside-of-a-channel lowering means that can be mounted to the underside of the track, so they could swing down.  Even rudimentary (very narrow) ladders could swing down in this way. 

This all then brings up to more questions:  How often along a track would escape equipment be appropriate?  If money were absolutely no object, there is no end to the clever things that could be miraculously folded into the track.  There is also the matter of the equality of escape means.  If there were ladders integrated into the support poles where would that leave the elderly or disabled?  Where do you draw the line between stairs and ladders and ramps?

If this all seems a bit extreme to you, join the club. I really think that having some control autonomy with onboard backup power is enough, but I may suffer less acrophobia/claustrophobia than most.  Still it needs to be figured out. If there is a “safety” feature that can packed into the package, can you imagine any elected official NOT electing to include it?  Or can you imagine anyone buying a system in which such matters haven’t been adequately addressed?

Finally, a note to my readers. Lately I have been designing more and blogging less.  Originally I had hoped that with enough readers, I might get some help in the design work.  It appears that isn’t going to be the case, so I will no longer chase readership with frequent posts.  This blog was never about entertainment, after all. As designs progress, they become more difficult to explain.  There is huge difference (in the amount of time involved) between an “artist’s conception” and something that can actually be built.  I am a guy who builds things, so I am not content to just leave things at that early stage of development. This does not mean I won’t ever post opinion or general interest stuff. I will when something comes to me.  Better to have quality than quantity, if readership numbers are not the object. Currently I am in the middle of a whole new bogie and track design, something which I have worked on almost daily. These things take lots of time!

Thursday, September 8, 2011

128> Learning from Roller Coaster Design


I have previously written about how we need a three dimensional approach to transportation, and one of the main themes I have returned to, design-wise, is of a PRT system that can be routed with minimum of restrictions – a track that can go up or down steeply or around curves tightly, coupled with a vehicle to match. 

It is very tempting to model raised track after bridges.  After all, in most cases, that is essentially what we’re dealing with.  But bridges, as we know them, weren’t really designed for the task at hand. Bridges for ordinary vehicles are necessarily gradual in any curvature because vehicles are generally heavy, and so have great momentum, or are not running on tracks, so they may skid off course.  With a vehicle that is both light and locked onto rails, turning radius or elevation changes can be taken at speeds that are as fast as passenger comfort will allow.  In the past, it was necessary to keep all vehicles going at a single, constant speed.  At least from a computer/control standpoint, that is no longer the case.  If there’s a place where only a hairpin turn will work, the entire system need not be held hostage to the speed for that turn.  In the case of empty vehicles, it makes little sense to run the vehicles unnecessarily.  Garaging the vehicles in shaded (or even climate controlled) storage locations could be advantageous, but would be particularly so if its feeder track, from where it diverges to where it rejoins, is as compact as possible.  Staging, garaging, and repairing vehicles takes space, and space is expensive.  I have seen little in current PRT designs that acknowledges this reality.  As a matter of fact, little attention has been paid to the amount of track involved in acceleration/deceleration lanes for stations.  Perhaps this is because the systems have traditionally been designed to be slow.  Unfortunately, going even reasonably fast opens a whole can of worms, design-wise.  But a really smooth, quiet and fast ride is what will make believers out of the passengers.  A slow, clunky implementation is what will ensure that PRT doesn’t catch on.    
Here are some thoughts regarding actual construction of track:  First of all, the track will no doubt be made in sections in a fabrication shop and trucked to the site, where it must fit together. Any on-site welding, if any, will be minimal, especially considering that expansion joints will be required between sections or groups of sections. Steel can expand nearly an inch per hundred feet between record temperature lows and highs for many areas. 

Although it is possible to bend any shape of structural steel, pipe is by far the least troublesome, at least when it comes to complex curves, where the steel must bend, at once, both up or down and sideways.  Squared stock, having a top and bottom that should remain level and sides that should remain plumb, presents a challenge that does not exist with round pipe.  Squared profiles can be produced with precision from welded flat stock however, although that is a lot of welding.  Pipe joints can easily accommodate expansion with a tightly fit inner sleeve that is only welded on one side.  The outer, running surfaces can be angle-cut or even finger-jointed to ensure a smooth ride.   

Presumably track would be assembled on some sort of scaffolding – a big jig that would establish the endpoints and angles while supporting the pieces for welding.  Pipe bending is an imprecise business, as there is some tendency for steel to spring back. Requiring radii of absolute precision is a recipe for very high costs, so any design should accommodate this fact. 

Luckily, such challenges have been faced before by the makers of roller coasters, and I think that their design conclusions apply here as well.  In the top picture, it appears that the large pipe may actually be many segments of straight pipe with only the small pipe being actually bent, although we can’t be sure.  That certainly is a possibility for eliminating some bending altogether. Note the periodic bolted flanges. This universal connection scheme greatly simplifies assembly in the field. I have looked for, but not found, expansion joints.  I believe this is because the loops and curves can enlarge in terms of radius, eliminating the need.  This system is clearly not as strong as it would be with the same weight of steel used in a triangulated truss design, but the simplicity of fabrication more than makes up for it.  Actually, triangulated trusses are not unheard of in roller coasters, as my Google image search revealed, but I think the point here is that with sufficient support they can be removed.  Consider, for example, the track as it approaches the docking area.  Depending on the situation, the track might curve in complex ways, while supports might be quite closely spaced.  Here you would need no triangulating trusses, and, indeed, they would be all different lengths and an unnecessary complication.  A straight run over a highway, on the other hand, would call for a stiffer design. In that case the trusses would be all the same length and can be easily added.  The picture below shows variations with and without trusswork. My apologies if the design looks a bit half-baked… It is a work in progress. 

The idea of standardized, modular lengths brings up a question.  How long should the sections be and why? At the moment I am leaning toward shorter lengths for curves than I had originally thought, principally because I worry that longer lengths might not easily fit together in the field. (It looks like the roller coaster designer concurs.)  Also shorter lengths would seem to be more versatile, enabling a number of transition options. For example, a higher speed turn might incorporate several radii so as to not be too abrupt. Straight sections, I suppose, could be designed around what would fit on an 18 wheeler.  A pair of trailer length segments, bolted together, would easily span a four lane road with a turning and bike lanes.   

The problem reminds me of the slot car set I had when I was a kid.  I had several types of curved and straight track, all in short lengths, and these could be assembled into any number of layouts.
Finally, one advantage to dividing the track into “bite-size” pieces is that it would be easier to put a price tag on this whole thing. There is very little guidance on how much PRT hardware will cost, especially broken down in terms of stations, track, and vehicles. At least this would be starting point for the infrastructure part of it.

Friday, August 12, 2011

127> Really, Really Fast

As anybody does much design work knows, you can always do better. Second guessing one’s own designs is something that is best not rushed, however. So here I am starting from scratch once again, with fresh eyes and a few different conclusions.

There are several considerations that motivated me to rework the bogie design. First, I think I put too much emphasis on a system that could use off-the-shelf tires, even at high speeds. This led me to motorcycle tires. Actually, though, what is the function of a tire? It is for vibration dampening, shock absorption, and traction. Since we are talking about running on smooth (finger-jointed?) steel, it is mostly just traction that we’re worried about. The problem here is that to achieve it, tires create a flat spot where the tire meets the road. Taking the wheel “out of round” in this way increases rolling resistance. In other words, it wastes energy. Any emergency stopping should undoubtedly be done by clamping the track, and no standard tread design is going to climb very steep slopes anyway.  Finally, I suspect that it would be easy and cheap to outsource, even in small quantities, a solid rubber tire designed specifically for PRT. 

Secondly, there is the matter of flanged wheels. I don’t like flanges for hard and fast use because I if they are of a hard material, they will make noise and vibration. If they are of a soft material, the area making angular contact will wear quickly. This is because a flange is in effect, a wheel with more than one diameter. Since any given diameter will make a wheel travel just so far per revolution, if wheel portions with more than one diameter make contact at the same time, one or the other must skid to compensate. Thus you have designed-in a wearing surface. Position-locking angular contact can be made with equal diameters however. Consider the example of a rounded pulley wheel on a square bar. There, two point contact can be made and, if the materials are hard, there is little frictional tradeoff. Anyway, I have softened my position to consider using flanges because they so simplify the mechanics involved. There are better plastics these days, (such as Dupont’s Hylene) and with large diameters and geometries that minimize load, it’s worth a look, even for continuous high speed applications.  
Another matter that I have been recently considering more is the matter of aerodynamics of the bogie itself. If the bogie takes up all of the room inside of a box beam track, then it must push all of that captive air in front of it. Any bogie design must take this into account, and obviously smaller is better.
The design shown fits into a track with and internal height of about 20” (500mm) high. This is where I may have gone a bit overboard. You see, I wanted to fit the wheels with a commercially available hub motors and although I have seen many Chinese offerings from companies I have never heard of, these don’t even come with technical data sheets and are hard to design around. Unfortunately, western motor manufacturers seem to only want to design for a very large customer base, and really haven’t tried to get into the direct-drive vehicle business, so I was left with a somewhat oversized British offering. 

Protean motors are very powerful wheel motors which are designed to fit on ordinary cars with minimal modification or loss of power. Since I don’t want to design track that is too small to transport people at speeds they have already become accustomed to, and I don’t want to design a system that will constantly require wheel changing, these 16” offerings seem like a reasonable top end, as far as rim diameter goes. This does, however, make it into one heck of a hotrod. 
The Protean wheel motors, you see, produce (together) up to 320 HP continuously. (240 KW) These motors ARE the wheels, of course, so there is zero drive-train loss. So the thing can pretty much go as fast as we want. (For comparison a Tesla Roadster goes 125 mph (0-60 mph in 3.9 seconds) pulling  a roadworthy steering and suspension system, a transmission, and a 450kg battery pack at “only” 288 HP. (185 KW) So we are talking fast. Very fast.  Note that a motor’s power draw is proportional to the work it does, not its potential, so you still use very little power while cruising if the vehicle and bogie are well designed aerodynamically. In the pictures these motors are seen in green. 

The geometry that I am exploring in this design centers around eliminating upper guide wheels by having the vehicle press against a “ceiling” within the track to eliminate tipping or derailing when turning off of the main track onto a fork. The steering guide wheels are angled and flanged to fit more compactly. These guide wheels could also be external to the track, something that I have avoided for noise reasons, but my fears may well be overblown on that issue. Anyway, I have shaved a few inches from the track girth and, well, made a rocket.

Tuesday, July 26, 2011

126> A Few Good Destinations

In the early days of PRT, back when governments and multinational companies were first eyeing the idea, the whole concept was so futuristic that it was plenty enough to envision a standard vehicle, track and station and multiply them around into a grid, and call it a system. Back then it was a question of whether those new computers were capable of reliably and safely managing traffic flows.  As I was introduced to the concept, there would be a station every block or so, so that it would not be too long of a walk to get to one. The track would be one-way and you could get anywhere by circling around. Thinking back, maybe this just wasn’t good enough, and nobody realized it.  

Personally, I have had a very hard time trying to shoehorn the cities I know into such a scheme. It would be great if the funds were there to actually make such a comprehensive grid, but since they are not, it becomes a question of giving the most bang for the buck. But the systems that were designed for the grid model may not exactly fit the new roles. Moving away from a grid model has implications for the track, the vehicles, and the stations.  

Here are some typical situations that may exist outside of any downtown grid; The freeway commute - this calls for a relatively fast vehicle and outlying stations with lots of parking. The “strip”-  This is where eateries and retailers have reached a critical mass so that the  whole stretch of road has become like one long mall. It probably would call for two-way track that does not interfere with signs and driveways. Stations should be minimal footprint, perhaps designed specifically for private property, such as in the parking lot of a major retailer. Major destinations – Areas such as a museum district, a major hospital complex, or stadium need access to the system, although there may not be enough in the budget to put stations every half mile between them and other destinations. These call for large stations and a system with distributed automobile parking, since it is unknown where a visitor’s origin is, but it is likely that the first leg of the journey was from outside the system.

I think that each of these scenarios is extremely typical and each plays to the strengths or weaknesses of a given system design. True, these introduce design complexities that are much greater than what a PRT company would ideally want to tackle. But what is the choice? Try to interest cities in a “one-size-fits-all” system? 

In the end it is each city’s specific layout that must be addressed. Perhaps rather than a grid mentality, what is called for is a destination mentality. How can the most important destinations be served with the least amount of track and stations? That, after all, would seem be the best value proposition from the city’s standpoint. Yeah, I know... None of this really plays to PRT’s strengths. But PRT track is also cheaper and less disruptive to install, and being raised so as not to block crossing traffic is a huge bonus. So perhaps PRT can prove itself with less track and stations than the network we would like to see. 

A couple of points: First, parking. It seems pretty obvious that most people will have to park their cars to use the system. Maybe there are a few older cities out there that are teaming with pedestrians who live very close in. But for most of us, the construction of arterial highways has created a suburban landscape of car dependent homeowners and apartment dwellers. This calls for assessing each of the out-lying station’s potential to be a gateway to the system, and therefore a place to store the car in the meantime. Will merchants be willing to share parking in exchange for being convenient to the riders? Probably not in areas where people would want to park for the whole workday. Bottom line – Any system will need sufficient parking to support enough passengers to make the system viable. That potentially means thousands of parking spaces. It is likely that some stations will essentially be parking lots. Land costs are not inconsequential, so parking ends up becoming a factor in routing.
Another point is that in a landscape of very limited funding, shuttles (GRT) must be reconsidered. If the system is centered around serving the most important destinations, then it stands to reason that more people will be sharing a common itinerary. This has implications for track size, although we must avoid anything too big to be visually acceptable. The track I have shown in previous posts is about as big as I would want to risk. I think it is noteworthy, though, that technologically it is a simple matter to keep heavier vehicles spaced further apart than lighter ones to minimize weight concentrations on the track. I would keep it under six passengers anyway.  Such vehicles would simply share track with the PRT vehicles and move between high capacity stations. These would be “express” shuttles, so if your destination isn’t a main terminal, you would use PRT, which could service all destinations.

A last point about stations. I have opted for a suspended design mostly because such a system can drop to ground level and ascend with a minimum of station related hardware and track. Neither long ramps nor elevators are required, which is of paramount importance in a stripped down, budget starter system. A suspended system would also seem ideal for parking lots since PRT vehicles could go directly to your car yet there would be no track to cross.  
In a “destination oriented” design, the point would be to enable the rider to eliminate the lion’s share of driving from his/her day-to-day routine. The idea is to make all of one’s normal destinations available and convenient to the rider – shopping, dining, entertainment, etc. A well thought-out system could provide traffic relief that would ripple throughout the city’s side streets, not just the roads that parallel the track. This is because it would cut out what would otherwise be individual outings in the car. A few choice stations, (and some very lucky merchants!) would make most driving unneccessary.  Also, I cannot help but consider such a proposition from a tourism point of view. To some cities this is a very big deal. And, being elevated, it’s naturally scenic! 

So how stripped down could a system be? I guess I can imagine a single convoluted loop as a starter, but every city is different. Finally, I would add that there MUST be a way to branch track without a long shutdown. Any prospect of skipping over areas can only be temporary. Success will mean a demand for stations all along the track, so adding stations must be easy to do.  I posted a design for a branchable box-beam track in post 71.

Sunday, June 26, 2011

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…

Tuesday, May 24, 2011

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.