Comments on the LeviCar Proposal and Related Issues
Francis D. Reynolds, PE
On September 13, 2004 E.V. WORLD published an article by Joshua Zev Levin, Ph.D. titled "The Perfect Synthesis, a proposal to mate GMs AUTOnomy Skateboard concept with MagLev train technology." That article, which is now in the Dualmode Debate section, should be read before this article.
I was delighted to read Josh's article. There seems to be no magic bullet that will rapidly turn on the coming dualmode transportation revolution. Getting attention for this most-promising concept has turned out to be a slow and difficult process. Each article such as his that we manage to get published helps to spread the word.
As our Internet host, Prof. Jerry Schneider commented, Josh's concept is similar to my own HiLoMag dualmode transportation concept, but I also see significant differences. I would like to comment on those differences.
Some of our colleagues are proposing dualmode systems that would use wheels of one form or another to support the vehicles in both modes. Josh, I, and others strongly prefer maglev for the high-speed automatic guideway mode, and pneumatic-tired wheels for the street mode. I have evaluated other forms of guideway vehicle support, but have always come back to maglev, as one might guess from the acronym "HiLoMag."
Maglev trains are the chief application for magnetic-levitation technology to date, and most lay people are unaware of its great promise for use in other applications. Many of us feel that maglev trains will never be a significant solution to our transportation problems, not because of the use of maglev but because the whole concept of "trains" is obsolete, except for slow heavy freight. Coupled trains served the world very well a century ago. But with the advent of the automobile, the airplane, and more recently advanced electronics, computers, and maglev, there are now much better ways to design and build transportation systems than trains, whether the trains run of rails or float on magnetism.
We believe dualmode is the best solution for the foreseeable future, since it combines the advantages of trains, cars, and airplanes, yet gets rid of their worst disadvantages. The main problems in getting a worldwide dualmode system will not be technical but sociological. Technological changes in society are always difficult to achieve because people tend to adhere to the past and fear change.
High-speed automatic switching can be easily accomplished by using the same simple concept that has been used for switching in the Morgantown, West Virginia, People-mover system since the 1970s. Back then we called it the "guide right or guide left" concept. The Morgantown single-mode system uses pneumatic-tired wheels not maglev, and the system speed is only 30 mph or some such low velocity. But its basic guidance concept is ideal for the automatic switching of maglev or any other kind of surface transportation cars at any speed.
The Morgantown guideway system has a fence-like guide rail at each edge of a traffic lane. A physical arm is extended out from each car, on one side of the car or the other, but never on both sides at the same time. A roller at the end of each arm rolls against the guide fence on one side or the other, and thereby senses the current position of the car. It is like a blind driver sticking his arm out of the car window, feeling a wall beside the road as it passes by, and steering accordingly.
I was an engineering manager in the development of the Morgantown system, but wasn't associated with the steering engineering group, so I am not familiar with all of the steering details. Those cars may have an electric augmentation or power steering system, but in theory they wouldn't even need that. The variation in force between the roller and the fence as the car deviated slightly from one side or the other of the centerline of the guideway could mechanically steer the car though a conventional automotive-type steering linkage.
Those are the basics of the guidance system to keep the vehicles on the road. The switching is achieved by the same system in an equally simple manner. Since only one arm can extend at a time, if the right arm is out the vehicle follows the right guide fence, and vice versa. But where the guideway splits into two branches, the left guide fence moves left along with the left branch, and the right fence or guide rail follows the right branch of the guideway. So if the left arm of a car is extended the car will follow the left branch of a switch, and vice versa. Nothing moves or happens in the roadbed, all of the action is in the individual cars. I believe this is called a "passive" switching system by some people.
In my HiLoMag concept I moved the guide fences in to the center of the guideway lane, lowered them way down so that these "lateral guide rails" are essentially flush with the maglev surface. The "arms" are now in the form of a small toggle mechanism that reads one or the other guide rail. Here instead of steering the front wheels as automobiles and Morgantown cars do, the guidance-and-steering forces are directly obtained by the interaction with the guide rails. Adequate forces can be easily supplied by moderately strong guide rails; the lateral forces on the vehicles are small due to their magnetic levitation, and the use of optimum bank angles (superelevation). Laterally oriented inductive maglev is incorporated in the guidance system so there is no physical contact anyplace at operating speed. For the details please read Jerry's website at http://faculty.washington.edu/jbs/itrans/hilo2.htm under "Guidance and Switching," and study the accompanying diagrams, Figures 3. and 4.
REPULSION vs. ATTRACTION MAGLEV
I agree with Josh that a repulsion form of maglev will be far superior for dualmode guideways than any of the attraction-maglev concepts. One major reason for using repulsion maglev is that full-speed automatic switching is then a cinch, but I haven't seen nor been able to invent a way to switch attraction-maglev vehicles at full speed or anywhere near it.
Why not? Note that attraction-maglev vehicles wrap around the sides of the guideway. That is necessary for them, because the vehicle is above the roadbed yet it must somehow be "attracted" upward. The only way we can do that is to put the part of the vehicle containing the maglev elements below the part of the roadbed containing the maglev so that the magnetic force can pull the vehicle up. That is accomplished by providing the vehicles with structural wraparound skirts or "saddlebags" as I like to call them. These saddlebags must extend down below part of the guideway in order to accomplish their purpose. If turning were attempted with such a configuration the saddlebags would interfere with the guideway.
But with repulsion types of maglev, the magnetic force pushes the vehicle up directly without the need for a 180-degree magnetic-force-direction reversal. So repulsion maglev is the only way to go if we want a high speed switching system. No saddlebags to interfere.
Please study this concept if you have had any concerns about the feasibility of switching closely following individual cars independently of each other at high speeds. The simple basic facts of this steering concept seem to be missed by a lot of people, even after they read or hear about it. This well proven concept has been around for decades if not centuries, but I still hear people say that there is no way to independently switch closely spaced vehicles automatically at high speed. We do it manually in our automobiles billions of times a day, and computerized systems are a lot more capable and precise than humans are in areas such as this.
Josh used the term "maglev monorails" a number of times in his article. I have trouble with the semantics there. High-school physics tells us that a car hanging below a guideway of some kind, such as a funicular or cable car system, is stable because the points of support are above its center of gravity. But most vehicles are supported above a roadbed of some kind, and are made adequately stable by three or more points of support separated both longitudinally and laterally. The center of gravity of the vehicle is of course roughly centered between those lower support points, which can be wheels, maglev, air-bearings, etc.
A "monorail" isn't truly a single rail, and cars could not balance on top of a single rail unless they are gyroscopically stabilized. What we have been misled to accept as a "monorail" is effectively two or more integrated rails with vertical separation (instead of horizontal) in order to provide roll stability. Monorail cars are normally saddle-shaped so they can have part of their weight below the top of the rail assembly, which adds to the stability. But for a car to be stable in roll on a true single rail its saddlebags would have to hang way below the rail, and we would actually have a suspended car.
Monorail guideway systems offer the advantage of somewhat less visual intrusion, but I have yet to be shown that a monorail system can be less expensive, safer, or technically superior, all factors considered.
The saddlebags of monorail vehicles would prevent high-speed switching just as the saddlebags inherent in attraction-maglev cars would. For full-speed switching we need repulsion maglev with the vehicles levitated above at least two laterally separated maglev "rails" or magnetic-flux-field "tracks." The avoidance of "monorails" won't prevent us from putting the guideways up in the air if we want to, however. Trestles and "elevateds" have been used for over a century. I am convinced that our coming guideway system will be elevated in some places, sometimes in tunnels, and sometimes at the surface, just as our highway and railroad systems are now.
LINEAR SYNCHRONOUS MOTORS
Josh made no reference in his article to the propulsion of the maglev cars on the guideways. I tend to think of "maglev" as the support for the vehicles, and consider the propulsion (which is usually some form of linear electric motor) as a separate system, but one usually closely associated with if not integrated with the maglev. For important reasons that have been expounded upon in my and some other articles in this website, I strongly favor the use of linear Synchronous motor (LSM) propulsion on the guideways, instead of linear induction motors (LIM).
NUMBER OF GUIDEWAY LANES
Josh proposed multiple maglev lanes. More lanes would be wonderful if we have enough money for such luxury, but most of us feel that, at least initially, system cost is going to be a major constraint. A sizable part of my own effort on dualmode has been preliminary design studies to achieve very high capacity per maglev guideway lane, in order to reduce system costs. The capacity of a single track or lane is of course determined by the speed of the vehicles and the minimum clearance distance or headway (if any) between vehicles. I believe a single lane of a HiLoMag type of system will be capable of handling the traffic of about ten highway lanes at sixty miles per hour; and at 200 mph (325 kph) a single HiLoMag guideway lane would carry the traffic of thirty-three highway lanes. We can certainly build a lane of maglev for less than we can build ten highway lanes, so we might argue that we can save money in the long run by building a dualmode system, and gain all of the advantages of dualmode for free. (Yes, I know I am grossly oversimplifying a very complex matrix of problems). Another advantage of fewer lanes, which will probably be more important than cost in many areas, is narrower guideway corridors. When we propose to intrude in a dense area with an additional transportation path, even a narrow lane raises major opposition, let alone a wide series of lanes.
CHOICE OF REPULSION MAGLEV TYPE
Josh Levin seemed to refer to only the Danby-and-Powell-invented superconductivity-repulsion Maglev 2000 system. Because of major logistics problems and high costs on the required cryogenic system, and the high cost of superconducting alloy for the coils, my guess at this time is that the Richard Post / Lawrence Livermore Labs. "Inductrack" repulsion maglev system with permanent "rare-earth" magnets in Halbach arrays is going to win out in the long run. Of historical interest, Robert Goddard (yes, the liquid-rocket inventor) invented and patented a repulsion-maglev system in 1910. I don't know the details of his system, but we can safely say that it used neither superconductivity nor super permanent magnets.
TRUE DUALMODE vs. PALLETED CARS
Let's talk about the requirements for running vehicles on the streets and highways as well as on the automatic guideway system. Josh and I are proposing quite different configurations to meet those requirements. He proposes car bodies that will accommodate people (or freight), plus maglev-equipped bogies to mate with the bodies and carry them as guideway cars. And he specifies different bogies, with pneumatic-tired wheels, to temporarily convert the bodies to cars that can be driven on the streets and roads.
What Josh called "chassis" or "bogies," have been called by many different names, but the commonly used name for them in this group is "pallets." Other dualmode debaters and I have talked long and sometimes heatedly about pallets for years. But to the best of my knowledge we always assumed vehicles which were self-sufficient for manually driven street and road travel, but which used pallets to adapt them to travel on the guideways. Josh added another kind of pallet, a street pallet, making three different units necessary for any trip that uses both the streets and the guideways. Four units total would be needed if the trip starts on the streets and ends on the streets.
I have been a strong advocate of what we call "true-dualmode cars," cars permanently equipped to travel in both modes. I have conceded however, that some guideway pallets will be necessary in order to use street-mode-only vehicles on the guideways during the transition period when few true-dualmode cars would be available. And guideway pallets will be needed for carrying special loads, such as boat trailers, on the guideways.
With the addition of street pallets we now have four different configurations to compare: A system using true dualmode cars is one. A system using guideway pallets to carry street-mode-only cars is another. A system with street pallets to carry guideway-only cars is a third. And the fourth option, the one Josh proposed, is the use of stripped passenger-car bodies or freight containers that would need one kind of pallet to travel on the streets and another kind of pallet to travel on the guideways.
I foresee arguments for and arguments against each one of these four configurations. My gut feel is that true dualmode cars will prevail in the long term, but the factors to be weighed against each other are far too many and much too complex for hasty decisions. Much study, debate, and experience will be necessary; universally accepted truths will be slow in coming. Time will tell. I am reminded of the development of the airplane, where the questions were asked, "Which is best, the conventional or the tail-first (canard) configuration?" "Which is best, the monoplane, biplane, or triplane? ---- wood and cloth or metal? ---- the inline engine or the radial? ---- liquid cooling or air cooling? ---- reciprocating engines or jet? ----turbulent flow or laminar?
Last modified: October 07, 2004