Here is a little project that is still under development. I would have preferred to have solved all of the problems with it before posting, but I have had precious little time to devote to my PRT “hobby” lately, so I’ll go with what I’ve got.
The design is inspired by a very innovative aspect of the MISTER system as shown most clearly near the end of this video, Mister not only doesn’t require switches in the usual railroad sense, it doesn’t even need the connecting track to touch the main line. One great aspect of this scheme is that it gives remarkable flexibility in routing, even after a line is finished, because a branch can be added with little or no disruption to the existing track.
While I have taken a general track design approach that is much more similar to the designs worked out by PRT pioneer Dr. J. E. Anderson, (but turned upside down) I still wanted to maintain the possibility of track that could be added to with minimal disruption. The bogie designs I have been working on all share the quality of being able to completely support a PRT vehicle from either their left or right sides, like the MISTER system. I cannot claim the ability to add a switching point without any service interruption whatsoever, but the track shown may have either side removed and still be functional, if supported properly. Sections of such track could be used at points where future expansion plans might require branching. This would include entrance and exit points for sites of possible future stations. The trick, design-wise, is to build a box beam with the bottom element removed, without greatly weakening the structure. The main trusses must remain parallel to each other and square to the overall structure, yet removable.
The use of turnbuckles (shown below) evolved from a realization that the chances of getting this thing to fit together while hanging it from a crane were pretty close to zero, yet I had wanted cross members to stiffen those areas of the structure. In theory the turnbuckles could bend the plates enough to get the assembly started, exerting forces shown by the arrows. They then could be loosened, the plates bolted, and then retightened.
After assembly the cross bracing is continuous, as shown below.
I now believe the better course would be to have rigid bracing with permanently angled plates, but that involves a total redraw, and this series of pictures illustrates the general idea well enough, I think. I would also note that most designs can be greatly simplified after some careful study, but this project has not reached that stage.
The other day I was looking over Jerry Schneider’s excellent ITT website for anything new and a link caught my eye. (It had the word “New” in red Italic, right after the title)
It turned out be a site that hadn’t been updated since 2003, so I guess it’s just new to the ITT site. Anyway, the hanging system described therein bares a striking resemblance to the system I have been piecing together. So much so, that I emailed the designer out of courtesy, telling him he deserved credit for a lot good ideas that many people (including me) thought were mine. A lot of what I have come up with has evolved as this blog has progressed and my thought processes have been fairly transparent. Yet it appears I could have just gone to this guy’s site and lifted almost every idea from him. So much for original thinking. Anyway the guy’s name is Tad Winiecki and he apparently started a motorcycle gang once that Unimodal (SkyTran) founder Doug Malewicki joined. Tad thought Doug’s designs were pretty unfriendly to handicapped and elderly, (That’s for sure) so he started playing around with his own designs. Particularly intriguing is his concept for creating track from roll-formed steel. Anyway, Tad, I really didn’t steal your ideas…Honest!
Speaking of SkyTran, I have long thought that the combination of PRT and high-speed levitated travel was an odd one. Whereas the concept of going fast in podcars is nothing new, it seems to me that the “bread and butter” of PRT is in neighborhood travel. The acceleration and deceleration distances, and rounded corners of a high-speed track would seem incompatible with city layouts and traffic dynamics. Inductrack technology assumes the need for wheels at startup. I would submit that it would be best to just use those wheels for most urban use, not because wheels are better, but because the track would be so over-priced for its low-speed function. That being said, the Inductrack technology is pretty remarkable. As I understand it, in a nutshell, it involves an unpowered bed or track on which a permanent magnet studded sled will levitate as long as it is kept moving. I believe a breakthrough aspect is this; it seems that to varying degrees there exists a “magnetic friction” which is produced as repelling magnets are drawn across each other. Apparently “Inductrack” is very efficient at controlling this effect. Although Mr. Malewicki sees this invention as useful for PRT, and NASA is interested in it for launching rockets, I see another use. It seems to me that they have invented the perfect magnetic bearing. I don’t know how it would miniaturize, but for large scale or platter type configurations it would seem to be ideal. I would be interested in how it would work in wind generators for example.
Speaking of wind generators, on his Jpods website, Bill James raises the possibility of covering PRT track with solar panels to power the “podcars”. (Yes, I am trying to warm up to the term after it was pointed out to me that podcars produces better search results than PRT.) Anyway the concept of supplying energy along the track rather than “piping” it in has a certain appeal, although I would question some of Mr. James’ premises. One thing that I learned years ago is that the energy “density” of solar radiation is not all that great. Far greater is the energy density of wind, although the fact that it cubes in power every time the wind speed doubles also means the reverse – as the wind slows, the extractable energy falls off a cliff. None-the-less in windy parts of the country it’s there for the taking. Here is a picture that caught my eye recently.
The concept of having the transmission towers produce energy themselves is rather poetic, don’t you think? Part of the problem with wind generation has been that it is often not generated near where the users are. If PRT starts going between cities, the reverse will be true. The track will need power away from the city. Perfect for periodically placed wind generators.
Speaking of cubing wind energy – One sure way to get increased wind speed is to go up. Here is a concept with nothing to do with PRT but that every PRT advocate will appreciate. Lighter-than-air wind generators. So big they increase wind speed just by forcing air to move around their shear size.
Oh, yeah. Speaking of towers, I couldn’t help but notice this one, holding up this PRT track.
Who published this anyway? Beamways? Very Nice. This form of bridge is called a “cable-stayed” bridge and is quite distinct, structurally, from suspension bridges like the Golden Gate, which have cables anchored in the ground. This style is just made for PRT…er… Podcars. It is even wind generator ready.
First a reiteration of the big picture. Designing a PRT system as logically as possible must start with a track that won’t put unnecessary limits on future usefulness of the system. Unfortunately, in an effort to get a product to market, most PRT venders have produced designs that fall short of having the potential to do anything but be small players in the transportation mix. Current systems, by and large, are not versatile enough to be used for anything other than supplemental vehicles in very densely populated city areas. That may be a perfectly fine business model, but the resultant designs fall far short of embodying PRT’s transformative potential. Where would the internet (for example) be today if it relied on proprietary networking cables rolled out according to the business plan of a single company for specific, cherry-picked markets? Standards based PRT track design is sorely needed.
I recently posted bogie design with tilted wheels. The purpose of design effort was not so much the bogie itself, but to see if such a design would require modifications to the track profile. Actually it has, but only slightly. The general design first described in post 39 has stood up to many challenges (outlined in subsequent posts) including multiple weight classes, speed ranges, station types, freight and industrial uses, propulsion types, turning radii and pitch angles, etc. What remains to be done is to explore braking and traction issues, to address the issue of forking (adding) track with minimal deconstruction, and general track construction methods.
All of that being said, here are some explanations regarding that tilted wheel design. First of all, it is a response to the challenges of high speed. The design makes no sense for anything less than, say, 30 mph. It gets much more attractive at speeds over 80. The rationale is this. At very high speeds the guide wheels really get a workout. In order to provide a smoother ride and make less noise, all wheels should be made of a material with some give. (rubber or plastic, not steel) Such materials wear out, especially on very small wheels. The bearings, too, take a beating. Centering the bogie without guide wheels is a challenge, however, because of issues that are particular to the remedies. Flanges on wheels can wear and heat up. Having a wheel running in a trough generally means that all wear occurs only on a very limited ring around the wheel. The same is true if the trough is in the wheel. (Pulley wheel profile) While this can be tolerated to a degree, the issue is most acute on the drive wheels, which support the full weight of the vehicle. V-shaped wheels in a V groove wear rapidly because the wheel has multiple diameters contacting at once. This creates wheel slippage.
In the illustration below it can be seen that the angled wheels, through gravity, work to minimize any contact with the flange, which has a radius to minimize friction wear, and could be made of a harder material. The inserted detail shows how the bogie becoming off-center causes the entire wheel (and whole vehicle) to be lifted against gravity.
These drive wheels are characterized by their large diameters, which have plenty tread surface to distribute the wear, and revolve at slower speeds than smaller wheels would. It is assumed that these wheels would use tapered roller bearings, like cars, and so cannot tolerate very high rotational speeds like ball bearings, but can better support the vehicle weight and the sideways “thrust” forces associated with fast tight turns.
In the illustration above note that the running surfaces have been replaced by half-round, or bull nosed rails. (shown in white) While it is obvious that such a design would greatly increase wear on both rails and wheels, such a profile also allows an extremely tight turning radius. My thinking is that at very slow speeds, such as for station maneuvers, the wear will be a minor factor. After all, by definition, the sharper the turn, the slower the speed and the less distance traveled. What about medium turns? One thing that occurred to me is that such inserts could provide a banking angle, which would treat the bogie like it was going straight. With wheel motors the wheels toward the outside of the curve can be made to rotate faster, facilitating (if not actually causing) the turn. This is a work in progress…I don’t have all of the answers at this time.
This all raises another very interesting point. In the last post, it was pointed out that the steering guide wheels would come into and out of contact with running surfaces as needed, so they would not spin and wear unnecessarily. Here we have described other running surfaces that are not of a continuous, unchanging profile. There are other situations as well, such as very steep slopes, which might call for special “sticky” rails or other inserts. Having various inserts has a lot of advantages. They may be replaced and upgraded. They can be precisely finger-jointed to allow for thermal expansion to eliminate the repeating noise and vibration associated of expansion joints in train tracks and some roads. They allow one basic structural track profile to perform many functions without modification. They can be made of materials (such as stainless steel) that are too expensive to be used structurally. They can be rubber mounted for noise and vibration control. It becomes easier to add a diverging or converging track to a previously completed one when the running surfaces are modularized into precisely sized components. One interesting application for inserts is the technique used by Disney to detect any breaks in the tracks of their rides. They fill the tracks with compressed air. If there is any break or crack the pressure drops and they know it immediately and can stop the ride.
Finally, a note about the fifth wheel shown below; (in the center of everything else) There are several possible functions for such a part, from centering and holding down the bogie to additional braking, power and traction. Such a part can eliminate the possibility of wear on the wheel flanges altogether on straightaways. The truth is, however, that to do the design I had to either add it or not. Because it is easier to take it out than add it later, I added it. It could, in theory, prevent extraordinary forces, such as extreme cross winds or earth tremors from lifting the bogie inside of the track. It has a smaller diameter than the main drive wheels but it supports no weight, so ball bearings would suffice and wheel-wear would also be minimal. It is largely redundant, I know, but this is all a work in progress, and, as I mentioned before, it is really all about the track anyway.
This is off-topic. The regularly scheduled post will be along in a day or two.
Having a bit of a soapbox to stand on, I realize, has some advantages. I want use mine now to share an idea that’s been in the back of my mind for a couple of years now. The situation in Haiti illustrates a problem that occurs again and again the world over. It is the problem of distributing aid. Specifically it is the dependence of aid agencies on having a top-down system, where airports must be secured, warehouses must be secured, roads must be secured etc, all before food can get to people in need.
The traditional wisdom is that the aid packages cannot be parachuted in, for fear of crushing people and/or causing riots. As a guy who loves to design, giving up the whole idea drives me crazy.
The problem is distributing the aid fairly and evenly. In many cases gangs steal the aid by hijacking the trucks or taking over the warehouses. Often conflict prevents aid workers from getting to affected areas. In Haiti, there are villages that will be cut off (by road) for some time. Surely there must be some way to get food and water to the people directly.
I submit that the distribution problem is actually a packaging problem. If individual portions of food and water could be dumped from a plane in a form that would not clobber the people below, they would self-distribute on the way down. Long brightly colored ribbons would make them easy to find. When a maple tree drops its seeds, they disperse by means of papery little wings that make them gently spin to earth. Can’t we do the same for a food bar and a half a cup of water? Think about it. You can’t hoard what you have to search out to collect, and small amounts aren't worth stealing. In many cases the children in these disasters watch helplessly as their parents struggle to get the family through. This would give them a chance to go on an Easter egg hunt and be heroes. There would be no favorites, at least in terms of social position or gender.
People could also be encouraged to migrate away from unsanitary conditions. If the drops occur north of town, people will pick up and go to where the food shows up.
I guess in one way this IS related to PRT. The key is to think small. The problem of making something safe to drop from a few thousand feet becomes exponentially harder as the weight increases. This strikes me as similar to the nasty tendency to think big with transportation, or at least not take small vehicle mass transit PRT seriously. It just seems that if you mention moving ten people instead of one or two, suddenly you are taken much more seriously. Small is counter-intuitive.
Similarly the idea of moving tons of food aid with thousands of little parachutes or whirly-gigs sounds ridiculous, until you consider that, as a society, we are already the kings of over packaging. We mass-produce and (over) package little items by the millions every day. These aid items just need to be highly compactable for transit, but, when falling, have enough drag to fall at speeds too slow to be dangerous. Is that really so hard? Not if you think small. Heck, I’m pretty sure my kid’s packaged lunches are almost ready to go as is! Think origami, and plastic that you can fold and will spring back. Think tails with multiple wind catching discs that stack tight for shipping. Let’s solve this problem before the next big disaster, shall we?
Here is a little detail of the bogie design I posted last week
I embrace the “in vehicle” switching philosophy, which is found in designs by J. Edward Anderson and others. I can see little logic for moving the track, as is the case for ordinary trains. This design, however, has generally involved a “bi-stable” guide wheel positioner, wherein one steering guide wheel always remains engaged. This prevents a situation where the vehicle is neither directed left nor right, and so crashes into the middle of splitting tracks. The problem, however, is that if the vehicle is going at high speed, maybe with no turns in sight, the small steering guide wheels end up racing for no reason. An obvious remedy for this is to have the engaging “fin” within the track be discontinuous. That way, one wheel set will still be in the engaged position, for safety, but it will not have any running surface to engage to with, at least when on the straightaway. There is no needless spinning.
In the picture above the running surfaces for the steering guide wheels are shown in blue. Because of expansion and noise, the running surfaces should be finger-jointed and rubber mounted, so making them discontinuous and tapering them into and out of contact position is not a problem. (This detail is not shown)
This results in a different problem, however, also exacerbated by higher speeds. The steering wheels, if not engaged, cease spinning. Then, upon re-engagement, they would have to go from zero to thousands of RPMs in an instant, which would tend to tear them up. They must, therefore, be caused to spin prior to engagement with the running surface, and preferably at exactly the correct speed.
There may be some motor and controller out there what would work, but my guess is that it would be very, very expensive, and way over-built. These wheels need only spin. They don’t actually need to drive anything, even thought the monster shaft size would be consistent with delivering the power of a midsize motorcycle. I say make our own.
The “motor” shown above is a simplification. Additional electromagnets can be added. Now I don’t know a whole lot about digital electronics but I have bread-boarded some simple circuits and I know that if there is a source of pulses (such as the encoders I discuss in post 20) the frequency can be easily manipulated by simple means such as a J-K flip-flop, (a basic building block chip, available on Ebay, for example, for about 20 cents) This output can trigger a $5. solid-state relay and Voila! A simple motor. Again, I am sure someone else could come up with a much more refined design but I think the principle is sound. Maybe I should market this idea to Boeing or Airbus. Ever see how those landing wheels smoke when they hit ground?
We, as a community of PRT advocates, are, sadly, a painfully small group. This blog is now quite easy to find on Google, but the fact is there just aren’t that many people looking. The collaborative design infrastructure included on this site is pretty useless if there are no engineers who are interested. It’s been forty or so years and still PRT is a curiosity that few know about or take seriously. There is no dialog, no buzz, relatively speaking, though there is a bit of a comeback underway.
In my last post I asked for nominations for best video. All of the submissions, save four, were promotional corporate videos for particular systems. These tended to portray the advantages of a PRT system as the advantages of their own proprietary solution. One of those four, posted in a comment by alert reader cmfseattle, was a rudimentary mash-up of three promotional clips. It “got me to thinkin’…”
The problem as I see it is that the case for PRT is a multifaceted one, and not well suited to sound-bite evangelism. Sure, there’s “On Demand”, “Point-to-Point”, and “No sharing, No waiting,” but that’s all true of everyone’s cars as well. The advantages of PRT, as shown in the various promotion videos, often emphasize a comparison to other forms of mass transit. The ordinary audience doesn’t care which form of mass transit is best. Many never ride it anyway. The only, (quite predictable) result of this type of sales pitch is to get the light rail companies up in arms. Because the videos try to be upbeat and optimistic, the countless negative consequences of failure to act must be minimized. (That will be a trick for any PRT video)
We need an audio/visual approach to PRT advocacy very, very badly. When someone wants to explain PRT to a friend they should be able to say, “Look up “PRT” on YouTube,” and that person would get the whole message in a few minutes and walk away a believer. I wish we could get a Michael Moore or Al Gore to do a real documentary, but that is actually “Moore” than we need. (Sorry, I couldn’t help myself…) Heck, we don’t even have a generic PowerPoint presentation. A well constructed, 5-10 minute narrated mash-up of pictures and clips could do more to advance PRT than anything else I can think of. A picture is worth a thousand words and often a video is worth a thousand pictures. Every group on the planet has promotional videos except us. And it’s really not that hard.
It all starts with a great “storyboard.” The narrative is generally written below empty boxes, which can then be filled in with sketches or descriptions of what the viewer might see during those words. This is often done on a white board, because there is a whole lot of erasing and brainstorming involved. It does, however, make creating a coherent presentation much easier by preventing most effort from ending up “on the cutting-room floor…” (For you youngsters, that’s from when film was cut and spliced by hand.) Once a good storyboard is created, the “boxes” can be “filled” with specific images and video clips, presumably from the web, and the rest is relatively easy and cheap video editing. Speaking of editing, one thing I thought was a stumbling block is that the Flash file format used on YouTube. Yesterday, however, I downloaded a free program called “Any Video Converter” which makes downloading YouTube content a breeze and can convert files to any file format you can think of. This is a good thing for PC users because Windows Movie Maker (comes with Windows) seems (for me at any rate) to prefer WMV files over AVIs. (We will take a moment now to allow Mac users to smirk……. Thank you.)
Anyway, perhaps this site might be a useful vehicle for such a project to be done collaboratively. I do have, after all, the infrastructure in place. Just a thought.
I would love to hear from you. I might even include your thoughts in a future post. (Only with your permission of course) Just email me- danverhoeve@gmail.com.
Want to download editable copies of the designs pictured in this blog? These (generally done in Google’s free 3D program“SketchUp”) are now available at our design collaboration site,http://code.google.com/p/openprt/Instructions for sharing, improving and updating designs via SVN are also posted there, under “Downloads.”
ABOUT THIS BLOG
Everyone knows that automobiles, as we know them, cannot continue to be the primary way the world commutes forever. There is the emergence of an enormous commuting class in the developing world, but it’s not just that there will not be enough fuel. The cost will be so high as to humble the world’s great powers, and be the cause of future wars. The impact on Global warming will be catastrophic. The health effects for residents of large cities is already significant. The lost productivity caused by grid-locked traffic currently takes a big bite out of our standard of living that we don’t even recognize. It will only get worse. Clearly something needs to be done. The problem is that there is, currently, no alternative. The car now offers the only real transportation system which has a prayer of offering a traveler a nearly straight line, nearly non-stop, essentially door-to-door journey. (I am leaving out bicycles and motorcycles, and scooters and Segways, etc. because they can all be problematic in bad weather, for older persons, etc.) Enter the PRT, or PERSONAL RAPID TRANSIT. . Though promising in theory, this concept has failed to deliver, and I think I know why. The problem is that the PRT systems developed thus far were developed not to solve this great world problem, but rather to create a business. This bias toward profit has poisoned the decision making process and created products with limited usefulness. I am not against profit. It is just that there has been too little emphasis on what a city wants and too much on what the corporation wants to offer. The system needs to be designed as a versatile, practical set of solutions, not as a product offering that reflects the strength and weaknesses of the company offering it. Proprietary or patented specifications and single source suppliers can only discourage a city government from taking the leap of faith needed to make PRT a reality. Enter this blog. This is but a timid first step on what could be a world-changing journey. What if the complete specifications for a working PRT system were developed and continually improved via posting online? What if the system was modular, with all of the various parts and pieces being individually ready to be out-sourced to the lowest bidder? What if the next company interested in being a PRT provider didn’t have to re-invent the wheel? What if the next city government considering PRT could have easy access to the thoughts and experiences of their peers in other cities? What if all the concerns - environmental, macro- and micro-economic, political, technical, fiscal, legal, even psychological- could be so completely vetted that cities world-wide could institute PRT programs with confidence and competence? So get on board, spread the word…and let’s change the world!
