Sunday, October 25, 2009


This week I’m going to switch from low speed industrial and delivery to high-speed intercity travel. After all, once you modularize a PRT/PAT system, it opens up a lot of possibilities.

Here we have a high-speed tractor bogie, meant to act as an “engine” in the “railroad” sense of the word. By hooking one of these to a PRT bogie, (all done inside the shelter of the track) the PRT vehicle gets a big infusion of horsepower. This is directly analogous to adding engines to train cars, except in PRT the “cars” only need the engine for very high speeds. The cone part is an electromagnetic coupler with a data port in it. It uses the self-aligning qualities of a Morse taper, with magnetism and a limited travel universal joint to allow coupling and uncoupling via magnetic pole reversal. The pairs of enlarged guide wheels pivot to create a self-centering mechanism for the bogie. They are enlarged to retard the wear on both tire surface and wheel bearings that would come from high speeds and long distance travel. There are no provisions for steering shown, although they probably need them, to travel independently when needed. I would think that all small guide and steering wheels should be disengaged for high-speed travel though, because it would just wear them out for nothing. This idea would support the concept of removable, rubber mounted, guide-wheel running surfaces inside of the (municipal) track. (There are a number of other benefits to this idea) For high-speed sections these would just not be installed, leaving the smaller wheels with nothing to keep them spinning. Provisions would be required to get them up to speed before full reengagement, however.

The picture above shows how such “engines” could be used for high-speed intercity travel. Whereas the first pictures only showed the part that resides inside of the track, this picture shows an aerodynamic drag reducing “shell” that hangs down. (in blue and gray). As vehicles reach the end of the municipal track, “engines” fall in behind each of them until the system decides on a logical end point to the train. This “ad-hoc” monorail train can now travel at speeds that would be impossible for the PRT vehicles alone. Upon reaching the destination city, the train breaks apart, the PRT vehicles continue to their respective destinations, and the engines make a big U-turn and line up for a return trip. Such a scheme could (and, eventually, probably should) employ Meglev, (once public funds are as available for track as they are for roads) and I would shy away from any design commitments that unnecessarily preclude this eventuality.

Lastly, note that I have numbered my posts. Eventually I will include an index, since the vast majority of readers have found this site relatively recently.


cmfseattle said...

looks good. suggestion: "hinge" the center of the frame, place one guidance wheel at each end and one guidance wheel at the center.

Dan said...

Hi cmf…

Phssst… Be wary, wary qwiet…No, I’m not hunting wabbits….What’s that? Yep.. just as I thought…
It’s the sound of crickets...

You know, the more mechanical the concept, the fewer the comments. If I had enough time to do two sites, I’d split this one, with a more philosophical discussion site to feed a more technical design site. According to Google Analytics, the post was very well received, indeed… (best yet by far)

As for your hinge idea, it is one that I have not specifically shown, but it is a very valid approach. I have shown groups of four wheels, like a regular train, and this one was a simple four, like a car. The difference is mostly about turning radius, traction sharing, and support from half the wheels during the changing-track process. If it is hinged 3 dimensionally, like a ball-joint, it needs a set of support wheels, as well as guide wheels.

The design as shown, however, is all about speed, and I try to keep these drawings as simple as possible, illustrating one or two functions at a time. Turning radius was sacrificed in this case, as you noticed. I’m really not sure how “snakey” we want to go, though, on a bogie intended primarily for hundred plus mph speeds.

There is a logical way forward, I believe, which incorporates the massive weight, speed and maneuverability variations inherent in a truly versatile design. I am playing with the idea of track classes, (like bridge weight classes), based on speed, weight and/or function, with electronic permissions.

I guess the main point I would make to the readers, especially new readers, is that I am not really designing a system, but rather illustrating what a truly versatile standard can deliver in terms of function and performance. I want to encourage others to invent ways to make that standard more powerful and relevant. I, personally, am still working on the track, which I would like to submit, described dimensionally, with enough specificity to enable real vehicle designs to move forward without surprises.

timote said...

I appreciate thinking all kinds of applications - it is certainly better to be prepared than to lock yourself our of a market - but I'm not convinced that this the goal of PRT, at least in my head. To me, PRT is good for around town, or at most intraregion transportation.

How far and how fast are you thinking about? I'd be in favor of it for say a longer commute (going from around town to the "freeway" for 10-20 miles), but once you start talking about intercity transportation I think we need dedicated systems (rail, HSR, etc.) for that...

cmfseattle said...

a linear-taper potentiometer, set so that the midpoint of travel=straight ahead, can be used by the motor controllers, so that they behave like a differential.

is there a compelling reason to have the frame hinged along more than one axis?

intercity distances in the U.S.A. are too long for Euro-style H$Rail. Having glanced at some of the figures for CA proposals, i can't help but wonder if Doug Malewicki should have been hired as a consultant.

in France, the TGV technology was chosen over non-standard designs, because it enabled the trains to access population centers.
le aerotrain

Anonymous said...

I won't address the merits or drawbacks of the bogie design (because I'm not really qualified) but I will say that I think PRT pods are poorly suited for long-distance (100+ mile) travel.

For travel at that duration/distance (intercity), I would like to be able to stand up, walk around, use a Dining Car or a restroom. I dont see how you could do such things in a pod or a train of pods.

High speed training would be useful for longer commutes, however.

My current commute, for example, is 32 miles - all freeway. It is only manageable because I travel at relatively high speed for practically the whole distance.

The ability to get in a pod & enter a high-speed corridor where travel was at 100+ mph, would actually shorten that commute & relieve me of a great deal of early morning stress as well.

Dan said...

Dan The Blogger goofed...
Hi folks, Rather than respond in order I want to jump straight to the comment by Anonymous;
You are absolutely right, Anonymous. The bathroom thing, in particular, is pretty much of a deal killer for long distances. It really just never occurred to me…
Hi Timote, long time…. I guess you and Anonymous are pretty much on the same page here, and you can add my vote. Locking the passengers into a situation where they can’t get off and there are no facilities is a deal killer, at least without scheduled stops. It raises the question of how far is too far, as well of a bunch of other questions regarding the best way to address those longer commute times, with their preferred higher speeds.

There are other problems as well. I wonder, for example, about sharing vehicles between cities. Whoever owns them might very well be local and probably wouldn’t really want them too far away from the maintenance facilities. Furthermore, the advantages of point-to-point service between cities is not that great in the event that both cities have PRT networks. That is because, assuming there is a GRT shuttle, (with bathroom) between the cities, the vehicles on the receiving end can swarm to meet the incoming GRT, so that passengers need only walk a few feet. Their destination info can be transferred automatically.

Anyway, I guess it’s back to the ol’drawing board. I guess the general concept might have utility for freight, however. I do want to emphasize, though, that I am mainly trying to settle on track dimensions. The various systems I have been showing of late are mostly just to help envision what kind of uses might be found for the track, so I can see if the track would need to be modified. In particular, for example, the guide wheels can only be as big as the track is wide if they are to be internal, raising questions about bearing wear. The little guide wheels that give the versatility in urban situations are too small to be left engaged at high speeds. Does freeway speed require a whole different track and bogie design? If so, how do I need to modify the basic PRT track to enable compatibility?

Cmfseattle, About your potentiometer observation; I am not sure I get your concept fully, as a potentiometer generally controls voltage and the controllers would be primarily adjusting frequency to change speed, not voltage. Of course frequency can be controlled by voltage and vice versa.. I fully agree that the motors can act as a differential. I have generally assumed that each vehicle, maybe each bogie, would have a full computer, save the peripherals and the hard drive (use flash memory instead) and that it would inform the controllers as to what to do. I have also assumed that the track would inform the computer, presumably by some form of encoder technology… I wrote a bit about it in post #20. Linear encoders need not be optical. Anyway I think the principles and technologies of servo motor control pretty much apply here, but there needs to be a separate feedback loop for each side to get the differential effect.

That video clip is disturbing... Great Halloween stuff, especially when followed by the next YouTube suggestion, the “Destruction of Aerotrain”….

cmfseattle said...

you only have to average >60mph to be competitive with over-the-road delivery. bathroom/rest stop sidings spaced every 20 miles or so (~15mins @ 90mph) would be manageable. especially along mountainous terrain, you'd want maintenance eqpt. depots anyway.

the potentiometer is just a cheaper alternative to mapping the guideway: when the front guidewheel pushes on that half of the bogie, the angle between the front and back bogie halves determines the ratio of left-wheels speed to right-wheels speed.

Dan said...

I see what you mean... I have only lightly toyed with not mapping it. I guess it depends on how autonomous the bogies are. If they can run ordinary cars on a freeway by computer, I suppose such mapping might be avoidable. I think we would want something to act as sign posts however, to inform of up-coming traffic,sharp turns,etc.

cmfseattle said...

i remember that you thought Anderson's control system did not make the vehicles autonomous enough.

2 points:
- today, vehicles are too autonomous, which is the cause of congestion.
- today, personal computers are not reliable enough.

most of our problems with both transportation and computers revolve around unpredictability.

the requirements are simple: A to B safely and quickly. the methods should be as simple and reliable as possible.

Bruce Attah said...

High speed PRT is a good idea. PRT that can do 100 mph will be able to offer a better service than passenger trains on almost any route. IMHO, bathroom stops are not a problem. On a trip of up to about 3 hrs (around 300 miles), 99 out of 100 passengers will not require a stop, and those who do will be able to pause the movie they're watching, touch the "bathroom stop" button on the screen in front of them, and within five minutes arrive at a station with smarter and more comfortable facilities than they would be likely to find on a train. Trains are required to make a difficult trade-off: they must either go long distances without a stop (for speed), or sacrifice speed and energy by making intermediate stops (for connectivity). This means they often cannot serve small towns, for instance. There are numerous closed stations and thousands of miles of disused right-of-way in rural areas for that reason. PRT could economically serve many of those routes, as well as serving busier routes more flexibly than a train can. Quicker, too: Over a route that has several intermediate stops, a PRT system that operated at 100 mph would probably be faster than a train whose nominal operating speed was 125 mph. On many routes, trains are obliged to run at average speeds as low as 50 mph, due to the frequency of intermediate stops. High speed PRT would completely blow such train services away.

Dan said...

Dan The Blogger Responds-

Hi cmf, I think that more autonomy equals more scalability with less complexity. Look at ants or bees. As per the computer issue: There are processors and OSs that are made to never crash, and that’s an option. However, with sufficient commoditization, computer components get so cheap that 4 and 5 way redundancy becomes an option. If 3 of 5 (minimum) processors all need to agree, and each is 99.999 percent reliable, the chance of 3 malfunctioning all at once is pretty much nil. In my experience 99% of computer problems come from software conflicts, a general purpose OS, add-on graphics boards or components with moving parts. (hard drive) I don’t know enough about computers to do anything but make an educated guess, but I would think that a lot of these software and hardware “hairballs” could be stripped out of commodity systems fairly easily. The hard drive could be replaced with flash, for example. I wonder about Linux or BSD for an OS that could be gutted of extraneous code-clutter… Anyway it’s really not my field, but the memory, boards and processors are really cheap…

Hi Bruce, Thanks for the (European?) perspective. In the US there is very little popular experience with higher speed trains at all. I have never, personally, been on one, so I appreciate you bringing up this perspective. (I used to third class trains in Mexico in the seventies and I do remember that all or the stops made even short trips take forever) I think you bring up a very good point with regard to the bathroom issue. As long as platooned vehicles can couple and decouple at speed and on route, the service to communities, (and their restrooms) is quite practical. This is a good reason to consider this capability as essential for long trips. I had previously seen the platooning as something that would happen at either end of an essentially uninterrupted and uninterruptible journey. Your way makes more sense. There are a couple of other issues however. In my scenario, the power for high-speed comes from engines that attach to the less powerful but more versatile bogies used for city travel. Detaching the “engine” would not be necessary for a rest stop or drop-off but might be to enter a city network. I can see that empty vehicle and engine management could get to be complex with more and more places to strand the fleet. I don’t see these problems as insurmountable though. Thanks for your most valuable contribution!

Bruce Attah said...

I hear that in the US, when they talk about "high speed rail", they usually mean 90 mph. In Western Europe and East Asia, they mean about 160 mph or higher. In China these days, anything slower than 217 mph ain't worth talkin' about, apparently. Still, the vast majority of interurban passenger rail services in these regions offer trip speeds between 50 and 100 mph, which I think a suitably engineered PRT system could easily beat. So I think it's great that you're thinking seriously about how the guideways, bogies and drivetrains for high speed PRT might be designed.

Ryan Baker said...

First, I'll mention that my inclination is toward thinking that transferring from PRT to a High Speed Rail system is going to be a better way to go. For one, the energy efficiency of such a system should be much higher. There are some trade offs in convenience. The value of PRT's main convenience (intelligent routing) is much reduced in this situation since there is a long direct route. On the other hand the train's conveniences (bathrooms) are enhanced. Lastly, you have the personal space topic, and this will just depend on preference. Many people will prefer an atmosphere where some social interaction can take place, other's will prefer greater privacy, and many people will be ambivalent.

So.. all that said, I will offer up some ideas to improve upon this concept.

For bathrooms, I'd imagine there would still be rest stops along the way. Individual bogies can still leave the train without an outrageous cost and since it won't happen often I think you can consider that a reasonable solution.

To the topic of sharing vehicles between cities, are you aware of companies like TTX that share rail cars between rail companies? It's likely regional or national entities would fulfill that role. I think a bigger question, at least early on, may be comparability of systems. You've talked about that in other entries, but I'd mark it as probable there will be some initial clashes in implementation compatibilities.

If you push ahead with the concept of moving individual bogies, you should consider using the space in the aerodynamic shells for lightweight freight.

To Bruce's comment (expect he won't see this though), I can see the possibility that some smaller areas might be better served by PRT, and then others by GRT, but with two large point to point destinations I'm pretty sure there will be sufficient cause for a full High Speed Rail connection, unless we develop some kind of evacuated tube transport that bogies can transfer to.

an-148 said...

another problem that could show up with highspeed is bird strike: unless every gondola has expensive hardfaced windscreen, there would be the need to include a motorized bullet nose in front of the platoon: it can be made of transparent material, to allow a panoramic view, at least to the first rider .