49> In Search of Gridlock and Opportunity

I have, for the last couple of posts, been trying to figure out how various PRT designs would fare with limited track and stations. My quest deals with the recognition of the fact that no investors in their right minds would sponsor a full network as a trial. (I am not abandoning the possibility of private money just yet) Like it or not, we have to look for the most cash flow from the least network. This exploration has led me to recognize the fact that a few dispersed low capacity stations may not introduce passengers to the system fast enough. Paying passengers must come from somewhere. If they do not come from dozens of smaller stations, then they must come from a few larger ones.

I understand how PRT is supposed to work. It is not a hub-and-spoke, mega-station type of technology. Nobody has described PRT vehicle storage because it is not supposed to be required. But if there is any way some track can be put down, and some vehicles deployed, expansion could start from there. The “foot in the door” it seems, would need to be some situation where people are so inconvenienced that they would be happy to pay a premium to take a short ride.

So here is a building block. This is a bare-bones seven-berth station that can have a 60 second turnaround time. (In one minute all berths have been loaded and moved out, and a fresh set of vehicles has taken their place.)

This illustration shows a high-capacity station comprised of six of the seven-berth stations arranged in parallel, with three boarding scenarios. The arrows indicate foot traffic. The first (A) shows how the station could be adapted to accept a majority of passengers who are boarding. Green lights or programmable signs would direct passengers to berths. Red lights would indicate that people are disembarking from that area. The middle figure, (B) shows a balanced load between incoming an outgoing vehicles. The last figure (C) shows the station accepting large numbers of incoming passengers with few heading out. Green lights mark the three berths accepting passengers. Such a station could, with the 60-second turnaround time, process 42 cars per minute or 2,520 cars per hour. (Note; This uses the gondola design: bottom track designs would require a means to get passengers to the boarding areas without crossing tracks.)

The illustration above shows a “hub and spoke” system with the main station connected to six satellite stations. In this scenario, the time required to completely empty the main station is one minute, the same as the satellite stations. For the sake of simplicity, let us assume that the satellite stations are a half-mile from the main station and that the travel speed is 30 mph. (I originally designed this to take people from a stadium to satellite parking, so that’s why the distances are so close) The number of stored vehicles is 42, so that with the 42 in berths and the other 42 from the satellite stations, the stations would never run out of vehicles. (126 cars total)

These examples point out a few key concepts. First, it is a closed system. PRT advocates tend to see PRT as an open-ended network, with an endless supply of vehicles, which will always self-balance. (i.e. a BIG network) In this example, all stations would run out of cars in 60 seconds, were it not for the stored ones. It is only the close proximity of the satellite stations that allows replacements to get there in time. For every additional half-mile, another 42 cars are needed.

More can be learned from the example. With only 3 miles of track, it is extremely limited, yet it would still probably cost over 30 million dollars. Could it pay for itself? One thing worth considering is that the full capacity would only be utilized for, perhaps, 3 hours per day, 5 days a week. If the cost of money were, say, 10%, the daily interest alone would be $8,219. What price point and usage pattern could bring in, perhaps, $13,000. to put the project solidly into the black?

Again, I designed this for a stadium, where the time to just get the whole family into and out of the parking lot would justify some very high fares. (not to mention that 90% of the track would be on private land) After checking the schedule of a local stadium, however, I realized that these big events are so infrequent that the system would never be viable, even though it could generate upwards of $40,000. per event. I now put it forth as something to ponder only. If the main station was broken into two or three, and the system stretched a bit, it might cut driving time by 10 minutes each way for some particularly congested downtown areas. My logic was to think up a scenario where passengers would gladly pour into a super cheap station to hardly go anywhere for top dollar. Investors, after all, are not known for altruism. We can all imagine a fully-grown, distributed PRT network. Can we come up with a viable PRT seed? For, say, 30 million?

48> PRT Stations...Continued

Almost immediately after posting last week I realized that loading cars one at a time was probably not what the designers of “taxi stand” (serial) stations had in mind for crowded situations. By loading a group of PRT vehicles at once, they may depart as quickly as the leading vehicle is ready, a fact that was quickly pointed out in the comments.

In particular, alert reader Akauppi added a link to a fairly comprehensive study of the subject by Peter Muller of PRT Consulting, who pointed out that numbers of simultaneously loaded vehicles could depart in “platoons”. The study concentrated mostly, however, on what he termed “open guideway systems” such as Ultra, because of the many ways they may be maneuvered. (These systems are essentially automatic cars, and may be parked and boarded in any way a car can.) In a statement reminiscent of criticisms that I have also made, Muller states, “Captive bogey PRT systems, such as those being developed by Vectus and Skyweb Express, show little variation in station design. The stations are always off-line, and the bays are always arranged in line with each other. This lack of variation probably results from the intended relative high capacity of these systems and their inability to accommodate tight radii.”

The obvious countervailing argument is that those “open guideway systems” fail to address one of the obvious benefits of most PRT systems, that being reduction of roads. We are rapidly coming to a time when we will have electric cars. Does separating precious real estate for less nimble automated ones really solve anything? Isn’t a separate road less efficient than just widening the one that’s already there? Well that’s a different subject, so I will return to what he terms a “captive bogey” system. (Pod on top of a rail.)

I did have one idea on this subject, which I have not seen, and that is this. The necessarily elevated stations, such as is required by the PRT International and Skyweb Express systems, must include an elevator (for the disabled) a feature I have criticized in the past as not being repeatable throughout the suburbs, for cost reasons. I think it noteworthy, however, that such a system, in the inner city, may have a very small footprint at sidewalk elevation. The sheltered area below the station might actually be an asset, as it could house news or food stands, or other sidewalk vending, at a natural spot for pedestrians to congregate. (No, that’s not the idea.) The idea is this. The “offline track” can be further split in two with the elevator in the middle, its structure supporting both tracks and a common boarding area, which needn’t cross any track. It would look something like this.

In this picture the large E is the elevator, which has two doors, ED1 (elevator door 1) and ED2. This is how it would work. The elevator, at street level, would open ED2 and passengers would be lifted to the boarding area, and ED2 would reopen, letting them board. ED2 would close and ED1 would open to let arriving passengers into the elevator, which would descend to street level and open (ED1) to let arriving passengers leave. ED1 would then close and ED2 would open, starting the process anew. Back on the boarding level, green and red lights, or even gates would be indicating the available vehicles, starting at the front of the line. The vehicles could move out as a platoon or the front vehicle could start out when ready. Once passengers have disembarked the vehicles on one of the tracks, the now empty vehicles in the arrival area would move up (to the boarding area) as a group.

In a hanging (gondola) system, a similar design can be used at street level, without the elevator. Very highly trafficked areas could have an elevated level as well, so that the station would, by the berth count illustrated, be capable of 12 simultaneous loadings and 16 unloadings.

Finally, here is a depiction of dual docking track described above, but with the “saw tooth” boarding scheme favored by Mister and Ultra. (fig. 1) Note that passengers may either board or disembark from any berth. The saw tooth design, being inherently parallel, gains less from splitting the track into two than does a straight line (serial) arrangement.

Actually the long, narrow footprint of a single row of berths probably fits better into the available space of most sidewalk environments. (fig. 2) Each vehicle may leave immediately after boarding, but both departing and docking vehicles may have to wait for each other because this system requires backing up into potential traffic to leave the station. A good way to control traffic would be alternate between groups of vehicles entering the station and groups leaving, (like the previous example) rather than a pure “first come, first serve” basis. In Muller’s study, he suggests that all vehicles can pull out together, ignoring the issue of vehicles not being ready at the same time. I would suggest perhaps three at a time. (In fairness, he showed a three-berth station) I should also note that with a gondola design, with no slots in the floor to step into, open-air stations could be extremely cheap, and therefore positioned with much more frequency than other station designs I have considered, and therefore could be made with fewer berths. (I am a big fan of cheap stations) Going back to the original, hypothetical three-station loop, however, it would seem that “platooning” is increasingly advantageous as traffic increases, but is a drawback if the traffic is minimal in “saw tooth” stations. Note that in this system, the berths are not exactly equal. Vehicles in the front berth, for example, would have little problem leaving but when empty the front berths could have slower vehicle replacement times. The opposite would be true for berths in back. Optimal traffic management for very busy stations would seem to be relatively complex. It is not immediately apparent to me if the saw tooth design would have better throughput than the dual track strategy outlined above, but I think it would out-perform the single line “serial” designs (PRT International, Vectus) with ease. I would also point to the variation of the saw tooth design I pictured in the last post, would not require platooning but requires rapid elevation changes in the track to avoid pedestrian/vehicle interference. It would seem to call for a comparatively large station, if the number of berths was, say, less than eight, but would be a very compact and efficient way to arrange a dozen or more berths.

In conclusion, I would reiterate the observation of the last post, that in order for PRT to be a valuable transportation alternative in initial limited and trial situations, high capacity stations are a must. In these posts I have explored the ideas of boarding and departing in groups and splitting the offline track as a means of increasing station throughput. I have not exhaustively studied every possible way to achieve simultaneous parallel “processing” of passengers, but it seems that PRT can have passenger turnover rates approaching group transit alternatives.

I also believe that a mix of both high capacity and very inexpensive suburban stations or stops is required to have a system capable of reducing commuter traffic, and that most current PRT designs do not meet this test. I hope that consideration of these station alternatives will prompt a reexamination of PRT vehicle design, especially with regard to both vertical and horizontal turning radii.

Alert read cmfseattle sent us this link to an article written by Bill James, (Jpods) a fellow who has come up with some designs (track and bogey), which are so much like mine it’s spooky. (And he seems to have done it first, but who is counting?) What is very cool is his trademarked term for PRT, the “Physical Internet.” Very descriptive, don’t you think? Let’s agree on something just that versatile and unstoppable.

47> Serial vs. Parallel

In my last post I brought up the idea of GRT as a way to get the first PRT track built because one of the problems with PRT is that it becomes less compelling with fewer stations. I think it is legitimate to ask, “At what point (in terms of scale) is PRT cost effective and profitable?” Is it worth building a mile of track with just a couple of stations?

This type of question got me to thinking about station design. Below (left) is a drawing showing the typical station usually associated with PRT. The vehicles wait in line for passengers, and then leave. In my example, they get off at one area and enter further down the line, cutting “turnaround” time. The problem with this design is that the whole station throughput is dependent on how fast the passengers enter the pods and seat themselves. In a very minimal system, this could limit the number of paying customers on the track.

On the right is a station with parallel berths for boarding, allowing the throughput of the station to be much higher. My original question was how minimal a system could be, and I will demonstrate my points with the following formula, where H is the headway between vehicles, T is the turnaround time, or the time I takes to enter a vehicle, get seated and get up to speed, and N is the number of stations.

Let’s consider the case, for example, of a system that could financially “break even” at 6 cars a minute, on (24 hr) average (10 second headway), but that means, for example, that the headways must be far closer during peak times, say, 2 seconds. Now let’s assume that the city wanted to start with only small triangle of track between 3 stations. If the stations were configured as in the left hand illustration, and the turnaround time (T) was, say, a minute, then it can be seen that H = 60secs divided by three, which is 20 seconds. Therefore the minimum headway is 20 seconds, or ten times as much as is required to break even. It can be shown that with the taxi-line style stations, it would take 30 stations to achieve the desired traffic throughput.

The second (right hand) illustration shows how parallel docking areas can be configured to allow multiple boardings at a time. In such a configuration the berths may be considered as separate stations, as far as the formula is concerned, but even with the additional berths the number of stations needed to break even is over 7. In a situation where the customer really only wants a 3 station loop, the stations had better be able to accommodate 10 berths each and the foot traffic had better be there to require them, or the project will lose money.

I think that there are important design implications to consider here, first and foremost being the importance of rapid boarding.

I, off-hand, do not recall seeing parallel boarding schemes in any illustrations other than the Mister System. Because of the slots that would be in the floor on most bottom track designs, I wonder how parallel boarding would even work, although two berths would be easy, because the elevator could be positioned between the tracks. In any case, designers should consider ways of speeding the boarding process as much as possible for limited system designs.

46> Many Vehicles, One Track

Here’s something to think about. In this picture, the vertical blue lines represent payload capacity, something like 50 to 75 kg per line. I originally started drawing this picture to explore weight distribution of possible track compliant vehicles, but then I realized that I had better share a bit of thinking first.

The baskets (A) represent something that could be used in manufacturing or for baggage handling. It’s not PRT, but it is a possible avenue to a proving ground and test track. A successful system would be a great confidence builder for the hardware, software, and the company that installed it. Having a demonstration project (that you get paid for) seems like something worth considering. (Currently the “state-of-the-art” technology involves conveyor belts or other floor space intensive systems, with laughable forking and destination sorting technologies.)

Cargo containers (B) can be similarly used, including outdoors or across town, if necessary. Cargo can be loaded and scheduled to depart automatically, so it can travel in the middle of the night, eliminating the cost of drivers working nights or being stuck in traffic in the day and, naturally, saving gas and payroll. Cargo containers could also be programmed to take the “long way” to their destinations to reduce network congestion, (for a reduced rate, of course). These would be great for moving mail between substations, for example.

The small “pods” (C) represent what would be best for 95% of rides taken, being designed for two or less passengers. These small vehicles could be pretty fast, passenger profile permitting, and would therefore be competitive with cars for longer commutes time-wise. Although current models generally assume identical velocity, these models also assume very limited networks. It should be noted that no system will be full of vehicles 24 hours a day, and that in a more comprehensive network, routes can be dedicated to faster or slower traffic dynamically.

The full size “pods” (D) can be used for families, people with bikes, baby carriages, the disabled, people with luggage, etc. These would have the “standard,” more gentle and slower ride, and employ greater headway between vehicles. Because there are societal benefits to traveling with a bike, or traveling in groups, or enabling the disabled, etc., I think that this class of vehicle should be subsidized and be more numerous within the network than ridership statistics alone might dictate.

The last, labeled (E) is a GRT or “Group Rapid Transit” vehicle and is designed for downtown or shuttle environments. It cannot ascend or descend steep slopes, and is designed for more expensive, high capacity stations. It designed to run profitably in simple loop or “back and forth” configurations such as between airport terminals, and, most importantly, could get the first PRT compliant track built. GRT can skip stations without passengers, like a city bus, but it can also have the intelligence to coordinate with other such vehicles to match passengers and destinations. This, and their small size, compared to buses or trains, means that no passengers have to sit through more than a couple of quick stops. After more loops are completed PRT vehicles can be added as needed, and the GRT vehicles retired or converted to night delivery use. (Or perhaps they will be found to have continuing utility within the system. I am not aware of any studies involving GRT and PRT sharing track, and really have no opinion, at this time, one way or the other.)

Most people are linear thinkers. The linear thinkers among us will see all of these vehicles as a hopeless distraction. I, on the other hand, usually look forward and imagine an optimal embodiment and environment, and then backtrack from there. This enables a viewing of possible pathways to a desirable outcome that cannot be had otherwise. It’s like cheating at solving a maze by starting at the end, so if I seem to fluctuate, sometimes, between reality and sci-fi, that is the madness behind the method…I mean, “the method behind the madness.”

45> A Critique of PRT International’s Design Approach

In my last post I ended by wondering out loud about whether anyone significant was actually endorsing the vehicle-mounted linear motors. After I thought about it, I remembered a slide in the PRT International streaming lecture, and so I have just listened again to Ed Anderson’s explanation of the various design trade-offs from his perspective.

Let me be clear, first of all, about one thing. I would love to see any PRT, including the design embraced by PRT international, implemented by some city, somewhere. There’s a lot to skepticism to disprove and much to learn. I also have great respect for Dr. Anderson and his work, and sympathize with the position he is presumably in, having investors to answer to. He has to, for their benefit, defend the exact design choices that moved forward, even as technologies change over time. Some “sound-byte” logic and “glossing-over” is to be expected anytime the politics of business is in play. That being said, it drives me nuts, and so here I am again. The last time I went off on this poor guy was only a few months ago. Of course, with 30% new readers each week, and an average viewing of only about two minutes, most readers won’t know the difference, and so, if you are new to the site, you’ll find some pretty smart people have weighed in on this general topic in the past, if you are interested…

First though, I think it is worth noting that there is a fundamental difference in vision that leads to the design differences. There is no need for PRT International, or any other PRT vendor, to have a product that will work in every city. Indeed there is strong incentive to create the simplest design that will work for the most profitable situations. Even if the design is useless for 95% of a city’s transit needs, it is only the lucrative 5% that is of interest to the PRT vendor anyway. If that seems cynical, I would point out that I think those numbers are very high compared to light rail. My environmentalist friends, however, should brace themselves for disappointment at the limited scope of change that PRT will bring, at least short term.

I, on the other hand, believe in the network effect, and see any limitations, especially budgetary, as potentially lethal. The spread of the railroad, for example, was transformational in a way that is similar to the internet. Both would have been economically viable on some scale, even if the build-out costs were, say, ten times as much. But both designs proved versatile and cheap enough for a massive, world-changing implementation, wherein the existence of the network itself created whole new businesses. That’s what I like to think about. PRT 2. All that having been said, here’s what I don’t like about the PRT International approach.
1. First there is inability to go up and down steeply or sharply. This has spin-off disadvantages galore. It’s not just the cost of raising the stations, but the political cost of lowering the track so the stations don’t have to be so high. Ed Anderson points out that, for a given track height, a hanging system is more visually intrusive. When track has to be kept low to keep station costs down, that is a concern indeed. He can never really contemplate raising the track way up, which is probably the best way to address local opposition to a proposed track segment. Also, although it is never ruled out, it is pretty obvious that bringing one of his pods to ground level is not very likely to happen. In other words, access to the system from a bus stop or private parking lot is pretty well abandoned. Again these limitations are not particularly important in the urban configurations he is designing for.
2. Second is the linear motor. I just believe “wheel” or “hub” motors are better, and that if they had it to do over, they would use them instead. The Linear Induction Motors (LIMs) have major efficiency drops with anything but very close “near contact” with the track, which must be outfitted, for it’s entire length, with a “reactor” plate. How much does that drive up the cost of the track? Also keeping the LIM close creates limitations on track design, specifically on sharp turns up or down. (As in, say, dropping down to a station from a higher track level) This is, again, is not much of a limitation if you are only talking about getting around downtown, and your cost basis is already less than the competition.
3. Then there is the issue of needing to bank turns. This includes the track on either side of the turn itself. In a truss system this has got to be expensive, especially on tight turns constricted by landowners not willing to cede right-of-way. Again, in an urban environment, competing with massively expensive systems like light rail, this is not such a big issue. If it can’t go fast or make sharp turns, so what? Neither can the competition. It’s an issue if you want the fixed part of the system “dirt cheap” so it can be massively expanded, however. Or if you see your ultimate competition as the automobile, not light rail, or if your ultimate objective is green prosperity through mechanical efficiency rather than moving on to the next big contract.
4. Finally there is the issue of stuff getting into the track. If on the ground there are serious potential problems ranging from flooding to peoples feet getting stuck. Even raised there is the potential for freezing rain being blown in and accumulating, or the more exotic sandstorm. In the PRT International presentation, the position of the LIM facing downward indicates that the reactor plate sits directly under the track’s slot, where debris would enter. I will be the first to say, I am certain that this is not news to them, and that a remedy has been engineered. But it is one other advantage to a hanging system, with the slot on the bottom.

In conclusion, I believe that the PRT International/Taxi 2000 type design has limitations that would need to be overcome before it would find wide acceptance in anything other than inner city use. This is largely because what seems to be the simplest, most straightforward design has the unintended consequence of simplifying the cars at the expense of the track and stations. Therefore the design has less chance of achieving the “network-effect,” one of PRT’s primary advantages over other forms of mass transit. The design has very little utility for the delivery of freight, so this is one potential loss of revenue, especially at night, when the track would be largely empty anyway. (limited routing precludes freight anyway) The use of LIMs doesn’t seem to solve anything worthy of modifying the whole track for, because there is no reduction in moving parts. I believe wheel motors to be more efficient both as propulsion and brakes, and, unlike the LIMs, they are sealed.

However, as anyone who has studied my designs well knows, a truly flexible, very inexpensive system involves many other tradeoffs as well. In particular, the tradeoffs for cheap track and stations involve some pretty sophisticated engineering on the vehicle side. In practice the daunting challenge of any PRT vendor will be to become a bridge builder, vehicle manufacturer, and public works contractor, all at once. Starting with a very simple design is, in practice, essential.

In the US at least, transportation projects involving road “improvements” follow a totally different path than mass transit, being drawn up years in advance and being triggered by road usage reports. There is currently no business model for entering that market with PRT. Mass transit involves a more holistic approach, cracking the door for more “out-of-the-box” thinking, giving the opportunity to PRT vendors to air proposals. I do not want any of my criticisms of current designs to give pause to any transit authority official or city planner anywhere. Period. I believe they will work, as promised and engineered, and probably well beyond expectations, for the stated purpose. I just hope companies like PRT International, if they start making money, put some of it into developing a product for commuters.

44> Going, Going… Gone.

PML Flightlink has been purchased. “Who’s that?” You ask. Well, according to a yet-to-be-updated Wikipedia entry under “Wheel Motors”, it is “a UK based company that currently designs and builds the highest power density electric wheel motors in the world.”
The problem is that it appears that the new owners have discontinued the “E-Wheel” series of wheel motors, opting instead to offer custom engineered products only. That, by itself, is not such a big problem since a fleet of PRT vehicles with multiple motors/wheels each would represent a pretty big order, but now it’s pretty hard to design a system, since they took the spec sheet away. Luckily I happen to have a copy of the specs right here.

These motors were specifically made for small electric vehicles, with oversize tapered (automotive type) bearings and waterproof housings. They were designed to be run on batteries, and have regenerative braking. To those more familiar with “horsepower” it is the stated wattage divided by 746. Torque, in “foot-pounds” equals the stated Nm rating times 1.356.

These were extremely powerful motors for their size and weight. They came with standard bolt patterns so off-the-shelf wheels would fit. Anyway the present company is still in the business of wheel motors for full size vehicle conversions, since eliminating the motor, transmission, differential, etc. frees up a lot of space for batteries. They have built a 640 hp Mini Cooper, among other projects. Anyway, it was largely these amazing torque/weight numbers that made me so in love with wheel motor technology. I wish someone from the LIM (linear induction motor) camp would explain how their system could possibly compete with these kinds of numbers, since I know there are plenty of LIM believers out there.

Also speaking of LIMS, I don’t understand how they can, on one hand, describe their reaction plate being comprised of aluminum or copper over steel, and then say that steel alone will do. Why would they add it if it didn’t matter? And, assuming it does matter, how much does it matter? And I can’t help but wonder, are there actual designs out there which put the LIMS in the vehicle, or are the current designs calling for LIMS all along the track? And if they do put it in the vehicle, are they water-cooled or what?

43> Crash Tests, Anyone?

Here is a picture I drew to illustrate a point about PRT safety.
Apparently there is a doctrine which dictates how far apart vehicles must be spaced for safe stopping in case an accident. This is evidently the distant relative of some old train spacing rule. It is apparently also the basis for at least one “expert” to say that PRT can never be cost effective, because it can never have sufficient capacity on a given track to be cost effective in the city, nor fast enough to be viable in the suburbs. This argument is ridiculous on so many levels I won’t even dignify it with debate, except to spend a moment undercutting its premise, which is that PRT vehicles traveling at 45 mph, (72.5 k/h) need 3 seconds of headway to be safe. (Can you imagine auto traffic being required to maintain this kind of distance? And half of the drivers are dialing phones!) An interesting article on this subject can be found here.

Anyway, the first line of defense is, in my design at least, the eight wheels of ABS style braking power which is applied magnetically (generating electricity in the process) Linear motors are theoretically unsurpassable in this magnetic braking, as they need no wheel traction, although I believe either is system is more than adequate.

The second, emergency only, safety braking feature is a telescoping hydraulic bumper, which converts the telescoping motion into activation of brake pads which can directly grab the track itself. Such a system can be designed to make contact only possible inside the track – The cabs themselves can never collide. This would also work with rail-on-the-bottom, PRT international or Taxi 2000 style systems. In disk brakes, the “disk” is simply a circular fin that is squeezed by hydraulic brake “calipers.” In the hypothetical PRT emergency, there are plenty of fins to grab onto which are stationary parts of the track.

The third line of defense, which, admittedly, is only applicable to the system I endorse, and to a lesser extent is possible with other hanging systems like Beamways or Mister, is that shock to the passenger is absorbed by the “free-hanging” nature of the cab design. (Actually the cabs do not actually “free-hang” because of anti-sway hardware, but come pretty close)

The illustration shows how the stationary vehicle, struck from behind, has its motor unit jammed forward, yet the passenger compartment hasn’t caught up. This is cushion from whiplash for the occupants of the stationary first vehicle.

The striking vehicle, in so far as other braking methods have failed, as a last resort, lifts it’s own weight, absorbing that many lbs. (kilos) to dissipate the last of the energy stored in the vehicle’s momentum. The passengers, like children on swing set, are lifted and pressed into their seats until reaching a natural or, in a worst case, cushioned, apogee, and then swung back down. This is just one more unappreciated advantage of a hanging system.

42> Design Time!

A few posts back I revealed what I consider to be the most logical track design. Notably absent was any description of the drive units that would inhabit this track, so here is what I’ve got. I know that the parts as shown are held together by flimsy, non-braced plates that extend into areas where they do no good, among other issues. It is, however, mostly a drawing to identify and re-route interferences. (Areas where multiple parts are expected to occupy the same space) It is also about as far as I have gotten in “SketchUp”, Google’s free 3D drafting software. It is not ready to post for you, the readers, to work with yet, because I didn’t break it into editable components. This exercise has, however, revealed how stunningly simple the mechanics are, with “wheel-motors” as the propulsion, since there is no need for power transmission. The wheels just turn, with up to 20 hp each.

The system I envision uses the basic eight-wheel architecture of an ordinary railroad car. The first illustration is of one half of a one half, to show the details that would otherwise be hidden. Red arrows indicate the rotary to linear (cam) movement that controls the steering. The second illustration shows how a mirror image assembly completes the (half) unit. The plates in yellow are the structural elements from which a PRT “pod” would hang. It would be suspended between a pair of the double units pictured. Such an architecture would enable very tight station maneuvering in 3D, while distributing weight over a large area, (for the cheapest track) The four-wheel (half) units, as pictured, could be used as is, in factories or distribution centers, or even on the grid, (for light delivery) with weight loads in the 40-170 kg. range.



This final illustration shows a cam mechanism that could be used to alternately raise and lower he steering guide wheels. Two servomotors operate the camshaft jointly, yet either can operate it separately, because of the ratcheting mechanisms. If either motor fails, the unit can operate normally yet the failure is immediately detected by the encoders.

41> The Future Revealed!

I have been slipping into the fringe… That’s right, out of the main stream, into the ranks of the eccentric, into the world of the worshipers of the untried and untested… Beware!
I am thinking the unorthodox, have thought the unorthodox, and am beginning to believe! (Scary music and goose bumps ensue)
“What is this unholy philosophy?” you ask…trembling..
“It is this.”
“PRT can and should behave like ordinary traffic. Like ordinary drivers. It should react to the open road like a kid on spring break, unless, of course, Grandma’s on board. Slow traffic should stick to the slow lanes, stay off the highways.”
“No, wait ... Not independent drivers…”(the author closes his eyes as if communing with the great beyond) “Starlings! Schools of fish! Yes, That’s it! Traffic should behave communally. Like drivers who can read each other’s minds, and create ad hoc teams to punch through traffic, like a bubble in a witches brew…”
Think about it. Right now, the prevailing methodology is to slow the whole system down so that a vulnerable few don’t get frightened or motion sick. Everyone else has to take a little longer to get there. I understand that safety is a huge issue. Yet millions are being spent to research ordinary cars “driving by wire” as it is sometimes called. Now I might be a little crazy, but that’s nuts. Speed and switching control while captive in a rail is one thing, but turning your car over, on a real, 3D freeway to a computer is something way higher on the “crazy scale”. Or perhaps not… Modern passenger planes can take off and land unassisted, so what is the big deal?
The possibilities and ramifications are many to this philosophy. For example, passengers can be screened for speed preferences before boarding, or can have their personal preferences set upon creating an account. Now say, for example, 1st and 2nd avenues run North-South, and there are multiple PRT vehicles approaching the area, seeking North-South passage. Why not create a temporary fast and slow lane to accommodate those passenger preferences? Let the speed demons take 1st and the slowpokes take 2nd. This particular arrangement can dissolve as fast as it was created, while circumstances create other opportunities to snake through congested areas.
This obviously takes a much, much higher order of complexity in software control than the ordinary systems that have been developed so far. It is equally obvious that this approach is the future of PRT control, enabling the most efficient use of any given track infrastructure.
The author opens his eyes, séance complete, future revealed! (Wink wink.) You heard it here first, folks… ;o)
All kidding aside, there has been a shift away from centralized control in a variety of communication and control architectures in recent years, as individual “nodes” become endowed with greater and greater processing power. As for PRT, the original concept was to have a fleet of vehicles moving at exactly the same speed. Merges within congested areas would be accomplished by only slight speed changes, or presumably the merge would be called off. The claim of “non-stop” travel was a bit disingenuous, because the trip was to only begin once there was space on the track. In other words, the waiting would be done at the station instead of on route. Now the question is how, with every PRT “pod” having redundant Pentium class processors, can that computing power be employed to prevent traffic congestion in the first place? Although this may all seem very far down the road, I think it does have some bearing on the physical systems, including optimal track layout, station design, and vehicle capabilities.

40> PRT: The Best Idea that Nobody Knows About

OK, Almost nobody, not counting the intelligent and insightful readers I am presently addressing…We have a problem here. And it needs to be addressed head-on. The problem is this. Great ideas don’t rise into actual day-to-day reality simply by being great ideas. The most brilliant innovations will lie dormant until their time has come, and not a day earlier.

So what makes an innovation an “idea whose time has come?" Pressure. Pressure of public opinion. Pressure of greed. Pressure to do the right thing. Pressure from loved ones. Pressure from above. Pressure from below. Political pressure, Peer pressure. The pressure to make the safe choice.

We don’t have a better idea problem. We have a pressure problem. More specifically, we have a complete lack of pressure to change the status quo on the people who could make it happen. The people who control transportation control existing forms of transportation. They control roads, bridges, buses, and trains. Those are their tools. Carpenters use nails and surgeons use scalpels. Our transportation people use the tools they know. PRT is not, currently, one of those tools.

This is an extremely hard lesson to learn for intellectual, inventive, types. We, (yes I count myself also) tend to think that any great idea should be instantly embraced, as though the entire populous is in a constant, active search for a better way. The problem is that humans are more generally in a search for a way to avoid the pressures that are put upon them.


This brings me to the picture. To creatures who try to avoid unwanted pressure, guilt is a strong motivator. It is extremely easy to continue to do the wrong thing as long as everybody else does it too, and our eyes are diverted from the truth. Hence the popularity of gas guzzling SUVs. The act depicted here prompts the witness to consider the hidden environmental cost of every gallon of gas.

This idea came to me because I realized that I could not visualize the “tons” of carbon dioxide that environmentalists where talking about, so I decided to find out just what the volume of that CO2 from burned gasoline was. After finding that out, (4.867 cubic meters per gallon) I needed a vessel to put it in, and naturally chose a balloon, and figured the radius to come to 1.051 meters.

Since it is easier for me to make a faux image than a real one, I had to find pictures of big balloons, and I quickly found the world of advertising balloons, and a thought came to me. The demonstration of volume of CO2 is better done in person than an image on the web. A single person standing (like in the picture) by a busy road could reach thousands. An organized campaign could reach millions. It also occurred to me that the balloon companies could, perhaps, be enticed to donate the balloons for free, especially if their own name appeared on the balloon, big enough for cameras to pick up. (Technical note, before someone orders one, the balloon as shown could spin as to be unreadable, because it needs two point tethering)

Just a thought folks, from a man who would like to turn up the pressure. By the way, wear T-shirts saying, “P.R.T.” “Look It Up.” (or something like that)

P.S. My apologies to my metric using friends abroad, I’m short of time today as it is “Independence Day” here in U.S., So, to my fellow Americans, happy Fourth of July!

Remember, it is your patriotic duty to point out stupid national behavior, no matter how common. For each of us to dump that much Carbon Dioxide on a daily basis is nothing short of insane. Every one of us can help create the pressure for change, even if it is simply to say something to a friend. Better yet, email the above picture to someone you love.

39> Progress on the Track

Here is what my track design has evolved into. Note that the bottom (shown on previous designs) has been removed. I think that it is important to simplify the problem by separating the track into its two functions. The first function is to provide the surfaces upon which the PRT vehicle may roll and steer. The second function is to span the distance between supports. Separating the two makes sense, because the supporting, spanning role is site and weight dependent. Inside of a building, for example, a very minimal track could be hung from the building structure itself at short intervals, and headroom might be at a premium over ability to span.

In this illustration a minimal track design is shown in black, and the “wrap around” area in blue is where a supporting truss, soundproofing and outer skin can be. In the latest iteration, both the drive wheel contact area support and the top middle beam (where the steering guide wheels contact) are designed to have some variability in size, at least for the time being, as weight requirements and preferable fabrication techniques will play a role in this decision. It may be most practical, for example, to have these as separately fabricated modular parts, as they all would include rubber mounted running surfaces and some machining.

Optimum internal dimensions are 30” x 20” range, (75-77cm x 50-52cm) with drive wheels of under 21” x 7.5” wide. ( 53cm dia. by 19cm) The track dimensions allow guide wheel sizes of about 7” x 2.5” (178 mm x 64mm)

Advantages of this track include being able to handle multiple weight classes, (final specs should allow variable steel thickness) being able to accommodate vehicle speeds in excess of 60 mph (100 km/h) without requiring excessive guide wheel speeds (under 3000 rpm) being easy to fabricate, including turns and forks, with standard stock and flame cut steel (and minimal machining) ability to accommodate various propulsion means including wheel motors and LIMS, being able to accommodate slopes up to and including vertical, being able accommodate extremely tight turning radii, (with preferred drive train/motor configurations) being sized to allow use within buildings with typical ceiling heights, having a standard exterior profile which may be incorporated into a variety of truss or suspension structures.

Tradeoffs- The only tradeoff I have been required to make is size. If I were to limit speed and weight substantially, it could be made a bit smaller, but there are diminishing returns for the following reasons. Greater height allows more leverage against being twisted by inertial forces, longer wearing drive wheels, and it contributes to spanning stiffness, as well as allowing more flexibility in drive unit design. Greater width allows larger guide wheels, which then last longer because they have more, wear area and slower speeds, and equally contributes to stiffness and design flexibility.

I welcome your comments.

38> The 16th Rule

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

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

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

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

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

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

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


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

37> Coming …Soon?

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

36> BACK TO DESIGNING

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

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

35> Troubled

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

34> Access for the Disabled

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

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

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

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

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

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

32> I Just Can’t Let This Stand Unchallenged

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

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

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

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

31> Fired Up!

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

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

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

30> Active Wheels

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



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

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



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

Designs will be forthcoming.

29> Thinking Outside the Box on Earth Day

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

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

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

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

28> An “Ah-Hah!” Moment

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

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

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