75> Happy Tails to You....

A problem inherent in any automatic transportation system is how to avoid collisions, specifically a following vehicle hitting a leading vehicle from behind. Two factors that make PRT susceptible to rear-end collisions are the relatively tight spacing between vehicles and any autonomy given to these vehicles.

It’s my nature to want to push the envelope in terms of spacing, autonomy and speed, so naturally I’m trying to figure out how to do it safely.

Historically PRT designs have had a set line-speed. The only variation was to drop back or increment forward by a set amount, and to have a slower speed around off-line stations. This makes keeping vehicle spacing very easy, and simpler in terms of getting a product to market.  With self-banking, hanging vehicles, however, the only limit to the speed is what the passenger can handle. If a uniform speed is used, it must be one that is comfortable for passengers who are older, or less adventurous, or prone to motion sickness. The whole system gets slowed down for a small percent of potential passengers. If we are serious about creating a system that can make a profit and also compete with cars, I think we need to go as fast as is practical and comfortable for each passenger who is traveling. There may be a timid passenger in the way, but there may not. There is no system that will be full 24 hours per day, especially on the edges of the network, and optimal travel in these instances deserves consideration too. There is no rule against fast or slow lanes, passing lanes are anything else borrowed from the automotive transport world. One other point is that in tight spaces turning radii might be advantageously decreased, requiring a deceleration and acceleration. This all requires a much more robust and autonomous control philosophy than what is out there today because introduces a degree of chaos to the system, and managing that may be a challenge. Anyway, control is a very complex issue, and needs to be broken down into a number of posts, and this one’s purpose is to explore just one small aspect, that being not rear-ending a vehicle.  

           

This discussion wouldn’t be complete without mentioning the California’s PATH program. In an interesting 1997 demonstration, a tightly packed convoy of 8 Buick LeSabres traveled under automatic control at highway speeds while maintaining close headways within 10 cm. This was done with autonomous vehicles communicating with each other and with proximity sensors. There was no central control.

Because of safety issues, there needs to be extreme redundancy in any system that controls the spacing between vehicles. One idea is to create graded zones that follow each vehicle like a comet’s tail, allowing a following vehicle to ascertain the distance to the lead vehicle. The idea may be visualized as in the picture below. Each following vehicle can have behaviors that are conditional upon these zones. The colors, of course, are just for the benefit of you, the reader. How the zones are created and detected is up for grabs. 

The lead vehicle must create these zones and the following vehicle must be able to detect and react to whichever zone it is entering. While a proximity-measuring sensor would seem to do the same thing, I am interested in methods that are rely the simplest physics possible, to compliment the onboard sensors. These could be coupled with equally simple fail-safe systems. What if, for example, brakes were only NOT engaged when outside of the close range (red) zone? (Let’s assume no actual contact platooning for the moment) What about power?  What if no power is available to vehicles in yellow through red? It is at least worth pondering.

  

To create such zones, there needs to be a way to influence something along the track that can transmit the information along to the upcoming vehicle. That information needs to change in amplitude or frequency as the lead vehicle gets further away. One thought is some sort of wave-guide. For example an acrylic rod can act as a fiber-optic transmitter. Notches sawn at intervals will light up brightly, but the effect will decrease with distance from the source. Measure the brightness at such a notch and you can tell the distance from the source. The same can be done with sound or radio waves. 

Here is another very simple principle that ought to work.  

 

This works on the principle of voltage drop through lengths of wire, although actual resisters, as shown, increase the effect. The down side is that I employ an actual electrified rail to transmit the voltage to the following vehicle. Anyway, it can be seen that voltage sent by vehicle A will incrementally decrease as it gets further away. Vehicle B can measure the voltage and know its distance from vehicle A. The diodes make the electricity only flow backwards in respect to the direction of traffic. The segmented rail would create metronomic breaks in the transmission, giving an accurate means to measure velocity. 

I know. The idea of the electrified rail is impractical. Anything that is done to the track needs to be very inexpensive. Track based transmission, however, is immune to “line-of- sight” issues, so vehicles can “see” each other around curves. The other problem with all of these schemes as well as vehicle based signaling, (which would probably be the primary system, but that’s got to be a whole different post) is that a failure in the signal generation or pickup emulates the absence of a leading vehicle. A broken down vehicle must not become invisible. Ideally the whole thing needs to be reversed, so that the weaker the signal, the closer the proximity. That would be like the air brakes on trucks and trains. If there’s a failure, they engage, not the other way around. 

74> Tilted Design, Motorcycle Tires

Here is a logical offshoot of the last tilt-wheel design that I posted. It is still far from finished, lacking controllers, backup battery, brakes, etc. What is interesting about this design is that it is scaled to use standard motorcycle tires, which are speed and weight rated and specifically designed to take wear and pressure on the sidewalls. Weights ratings go to the 1750 lb. (794 kg) range and speed ratings are in excess of 175 mph. (282 k/h)

I am increasing worried, however, that perhaps one track doesn’t work for all applications. This design ties the interior dimensions to about 36” x 24”. (914 x 610 mm)  That’s not bad for long spans but is kind of awkward in buildings, under bridges, or in tunnels. While the swing-arm on the top of my designs should allow natural g-force correction and extremely steep slopes, it, too, adds to the height of the finished system. The result is very much taller than, for instance, the Skyweb Express system. 

In my brief exploration of underpasses in last week’s post, I was confronted by the disadvantage of having a tall system height (track plus vehicle) in this situation. I am not sure how many underpasses have room for both pedestrians and a fenced off Podcar lane and this troubles me. The Skyweb Express model not only doesn’t have this problem but it also appears that I may have underestimated Skyweb’s maneuverability somewhat. There is also the matter that I have several tweaks in mind that would greatly enhance their design (as I understand it) in this regard.

I remember in the old days I thought it would be pretty cool to be able to retrofit one road lane into four PRT lanes, packed two high and two across. One problem with that vision, however, is the need to keep people away from the track for safety reasons. This need becomes more pronounced with every incremental increase in system speed, so it really needs to be an integral part of the infrastructure from the inception. The Ultra system uses the inelegant chain-link fence strategy. Some bottom-supported systems (Vectus, Skyweb Express) use the strategy of keeping the track elevated and preventing access with the station design. Captive bogie hanging systems (such as I have been designing) have the clear advantage here, but it still seems prudent to keep the bottom slot out of reach even though it could, in theory, be very narrow, precluding, for example, insertion of an arm. How high is “out of reach?” Having given up on a combined track/vehicle height of under eight feet, (2.4 m) my next main worry is being able to fit between floors of a typical building. I will save the protracted discussion, though, of station design or optimal track height for a time when I have some illustrations prepared. Suffice it to say track height is not without consequence, so the large wheels may come at a cost. 

I have to say, though, that this design passes the “smell test” in that it appears to be a design that would be at home at very high speeds, which, of course, can be reduced. This is much better than starting with a design that has requires modifications to go fast. I also don’t see any inherent maneuverability problems in terms of relatively tight turning radii. Be forewarned though, that this design will take a while. Shown is an old version. Currently the frame (yellow) has been completely scrapped.   Simplify! Simplify! Simplify! 

73> Overwhelmed by an Underpass

I couple of weeks ago I was asked to quantify how tightly I thought a PRT vehicle would need to turn. In the case of PRT, the vertical turning radius must also be considered. (going into, cresting, or coming out of a slope) I have always considered that these radii must be fairly tight, but I had not really examined how and why I drew this conclusion.

I started my inquiry with a Google Maps starting with a place I have gotten stuck in traffic in the past. 

 

It is a place where an older road leading out of town intersected with a highway “loop” around it. Then time passed, and they built a mall and widened both roads a bunch of times. Now it’s a nightmare, but with good restaurants. Sound familiar? How would the various PRT systems compare as a solution?  The bottom picture shows the view looking east from “point B” and the smaller inset (point A) shows a small open-air bus stop, typical of the southern U.S.

The bus stop is included because it is part of the problem more than a solution.

On a typical afternoon, the traffic builds sufficiently so that it takes at least three full traffic light cycles for a bus to even reach this stop. There it blocks traffic further as passengers board - unless it just happens to reach the stop in synch with the rest of traffic stopping as well. Going straight, it blocks vehicles that might be able to turn right on the red light. If buses didn’t run through this intersection it would be better for everyone - especially the bus passengers, (who have to spend nearly ten minutes on this one intersection) but the alternative routes are nearly as bad. It seems obvious that the bus routes through here are very expensive to operate, and there is no place to fit light rail. The east/west road is as wide as will fit, and the loop was just widened - again. (Note the five-lane feeder road.)

PRT could cut through this mess like a hot knife through butter. I guess my main question is whether going over forty feet (12m) high to clear a raised highway is acceptable. As a devotee of all things futuristic, I personally have no problem with it, but will it sell at city hall? If the answer is no, it exemplifies a lot of what I have been saying about sharp curves, steep slopes, variable speeds and hanging vehicles. Hanging podcars, as I envision them, would have no problem going either over or under. The concept of a uniform line speed is challenged, however, because the PRT vehicles would need to bunch up and slow down to make the abrupt elevation drop and/or turns. I guess a two second headway would be about all we could get through per track, though.  If going over is the thing to do, the stations may need to be moved back from the intersection quite a ways, depending on how steep of a slope the system is designed for.  

I Googled around a bit, looking for other examples and found this. It is Main Street, Houston, TX as it passes under I-45. Pictured are the tracks of the new light rail.  I guess the car traffic has been largely diverted to other roads. On the face of it, it looks like they are squandering enough space to move a heck of a lot of people. Again note the need for PRT to go over or under. Actually there is virtually no way out of downtown Houston that avoids this overpass dilemma. Then there is there is loop 610 farther out, with the same thing…  And then there is the outer loop. Anyway, the situation is the same in lots of cities across the globe, so systems ought to be designed to handle the situation gracefully, whether it’s going over an underpass, or under an overpass! ;o)

72> STOP THAT!

I want to talk a bit about brakes. I am afraid that much of this has been previously discussed in the comments section, but not every reader follows the comments, and so I have to include it. First let’s clear up a little something about LIMs. (Linear Induction Motors) Proponents will point out that they make traction irrelevant. Icy surfaces will have no effect on braking. It’s like a tractor beam. I will abbreviate my reasons for leaning away from them by saying this: A motor’s efficiency depends on the close proximity of rotor and stator because magnets in very close proximity have more push and pull. With a LIM this close proximity is the between track and car, and that is very hard to precisely maintain, especially on curves. I believe a system needs to be adaptable to the space available to it. If using LIMs means not being able to corner tightly to conform to a city’s layout, I will lean toward other direct drive techniques. This is partly because I don’t see the braking issue as unsolvable.

First point. Ice. If a system has track that is directly exposed to the elements anything but LIM propulsion would seem to be problematic, especially at higher speeds. With a hanging system though, the track may be expected to remain dry except for condensation. If the running surface is to be rubber-mounted for sound and expansion reasons, however, its thermal mass is so low that it can easily and cheaply be kept at or above ambient air temperature, with a low wattage resistive wire, so that condensation would not form. Let me be clear. This is not about melting ice or evaporating moisture. Condensation will only occur if moist air is warmer then the track surface, such as if warm ocean fog is contacting track that is still cold from the night before. There are several points worth considering. One is that all activity by vehicles using the track will generate heat, and lot’s of it. Actually getting rid of the heat in (in a hanging system) would seem to be the greater problem most of the time. A second thought is that if there was a condition promoting condensation, care should be taken to design the track so that water will not drip onto the running surfaces.

About smooth surfaces – One thing that has been pointed out is that smooth metallic running surfaces do not provide much traction in the first place. I would offer this. There is only so much braking that you want to subject a passenger to, except for emergencies. I submit that on a smooth dry surface there will be sufficient traction to reach the braking limits that would be acceptable from this comfort standpoint. So the traction issue is a safety/extraordinary event issue that will never happen anyway.

All brakes, including linear and rotary motor magnetic braking systems, will be overwhelmed by being undersized, and they will all certainly be undersized to handle “brick wall” stops instantly, traction or no traction. For this reason a back-up system is needed. The obvious solution is to directly engage the track with brake shoes in some manner. Such a system would not be used for routine braking, lest there be wear to the track over time. But for emergencies, extreme braking power is quite feasible.

This brings up another issue. Passenger restraints. I personally favor a padded waist restraint bar if it can be incorporated gracefully. I would like to discourage movement about the cabin, so that it (the cabin) can hang semi-freely, rather than have this motion be 100% simulated. We don’t need kids intentionally “rocking-the-boat” so-to-speak.

There is another safety feature that is sometimes mentioned which bears consideration. There is no reason to supply power to the track directly behind any vehicle. Having no power would seem to be a pretty good defense against malfunctions of headway distances. I can’t say that I have worked out the details, but it is worth noting that if there is no electrical draw, switching on and off can be repeated with very little wear. (no sparking, etc.) I would like to see what inventive minds could do with the concept.

I do not think it is unreasonable to consider that each vehicle should have several rangefinders to determine how it is spaced between others. Such devices are commonplace these days. They come with cameras and are showing up on cars as a way to help drivers not back into things. With a homogonous fleet and guaranteed vehicle-to-vehicle alignment, I think self-spacing and impending-collision detection systems are very doable.

With a hanging system, safety should be almost a none-issue. In post 43 I illustrate how the bogies from which the cab hangs can be spaced to prevent those cabs from hitting each other, and how the swinging action can help absorb shock. Another idea would be a sort of airbag idea for bogies, shown below.

 

In the event of an immanent collision, the cylinder would quickly extend, filled by gases created by a measured explosive charge. Collapsing is much more difficult, however, as the gases are trapped in the cylinder until they leak out. Such devices could be both forward and backward facing, so they would hit each other in an impact. The U-shaped ends are fitted with a strap or cable and are designed accommodate misalignment, especially on curves. As they compress, resistance would increase. This is akin to safety “crumple zones” in cars but much more controllable. A key advantage to such a system is the relatively long length of the combined compressive strokes. Adding length reduces the G-forces acting on the passengers.

This is coupled with the forward swinging motion of the “gondola” shown in post 43. The preferred deceleration profile would gradually increase G-forces that swing the cabin forward, so that at the time of impact passengers would be being pushed into their seats rather than out of them, as would be the case with any bottom supported vehicle. This, coupled with the methods mentioned above, should create a system that can be demonstrated to be extremely safe, despite smooth track and fairly hard wheels, which are desirable from a mechanical efficiency point of view.

71> Switching Tracks

 

Here is a little project that is still under development. I would have preferred to have solved all of the problems with it before posting, but I have had precious little time to devote to my PRT “hobby” lately, so I’ll go with what I’ve got.

The design is inspired by a very innovative aspect of the MISTER system as shown most clearly near the end of this video, Mister not only doesn’t require switches in the usual railroad sense, it doesn’t even need the connecting track to touch the main line.  One great aspect of this scheme is that it gives remarkable flexibility in routing, even after a line is finished, because a branch can be added with little or no disruption to the existing track.  

 

While I have taken a general track design approach that is much more similar to the designs worked out by PRT pioneer Dr. J. E. Anderson, (but turned upside down) I still wanted to maintain the possibility of track that could be added to with minimal disruption. The bogie designs I have been working on all share the quality of being able to completely support a PRT vehicle from either their left or right sides, like the MISTER system. I cannot claim the ability to add a switching point without any service interruption whatsoever, but the track shown may have either side removed and still be functional, if supported properly. Sections of such track could be used at points where future expansion plans might require branching. This would include entrance and exit points for sites of possible future stations. The trick, design-wise, is to build a box beam with the bottom element removed, without greatly weakening the structure. The main trusses must remain parallel to each other and square to the overall structure, yet removable. 

 

  

The use of turnbuckles (shown below) evolved from a realization that the chances of getting this thing to fit together while hanging it from a crane were pretty close to zero, yet I had wanted cross members to stiffen those areas of the structure. In theory the turnbuckles could bend the plates enough to get the assembly started, exerting forces shown by the arrows. They then could be loosened, the plates bolted, and then retightened.  

 

After assembly the cross bracing is continuous, as shown below. 

I now believe the better course would be to have rigid bracing with permanently angled plates, but that involves a total redraw, and this series of pictures illustrates the general idea well enough, I think. I would also note that most designs can be greatly simplified after some careful study, but this project has not reached that stage.

 

70> Speaking of....

The other day I was looking over Jerry Schneider’s excellent ITT website for anything new and a link caught my eye. (It had the word “New” in red Italic, right after the title)
It turned out be a site that hadn’t been updated since 2003, so I guess it’s just new to the ITT site. Anyway, the hanging system described therein bares a striking resemblance to the system I have been piecing together. So much so, that I emailed the designer out of courtesy, telling him he deserved credit for a lot good ideas that many people (including me) thought were mine. A lot of what I have come up with has evolved as this blog has progressed and my thought processes have been fairly transparent. Yet it appears I could have just gone to this guy’s site and lifted almost every idea from him. So much for original thinking. Anyway the guy’s name is Tad Winiecki and he apparently started a motorcycle gang once that Unimodal (SkyTran) founder Doug Malewicki joined. Tad thought Doug’s designs were pretty unfriendly to handicapped and elderly, (That’s for sure) so he started playing around with his own designs. Particularly intriguing is his concept for creating track from roll-formed steel. Anyway, Tad, I really didn’t steal your ideas…Honest!

Speaking of SkyTran, I have long thought that the combination of PRT and high-speed levitated travel was an odd one. Whereas the concept of going fast in podcars is nothing new, it seems to me that the “bread and butter” of PRT is in neighborhood travel. The acceleration and deceleration distances, and rounded corners of a high-speed track would seem incompatible with city layouts and traffic dynamics. Inductrack technology assumes the need for wheels at startup. I would submit that it would be best to just use those wheels for most urban use, not because wheels are better, but because the track would be so over-priced for its low-speed function. That being said, the Inductrack technology is pretty remarkable. As I understand it, in a nutshell, it involves an unpowered bed or track on which a permanent magnet studded sled will levitate as long as it is kept moving. I believe a breakthrough aspect is this; it seems that to varying degrees there exists a “magnetic friction” which is produced as repelling magnets are drawn across each other. Apparently “Inductrack” is very efficient at controlling this effect. Although Mr. Malewicki sees this invention as useful for PRT, and NASA is interested in it for launching rockets, I see another use. It seems to me that they have invented the perfect magnetic bearing. I don’t know how it would miniaturize, but for large scale or platter type configurations it would seem to be ideal. I would be interested in how it would work in wind generators for example.

Speaking of wind generators, on his Jpods website, Bill James raises the possibility of covering PRT track with solar panels to power the “podcars”. (Yes, I am trying to warm up to the term after it was pointed out to me that podcars produces better search results than PRT.) Anyway the concept of supplying energy along the track rather than “piping” it in has a certain appeal, although I would question some of Mr. James’ premises. One thing that I learned years ago is that the energy “density” of solar radiation is not all that great. Far greater is the energy density of wind, although the fact that it cubes in power every time the wind speed doubles also means the reverse – as the wind slows, the extractable energy falls off a cliff. None-the-less in windy parts of the country it’s there for the taking. Here is a picture that caught my eye recently.

The concept of having the transmission towers produce energy themselves is rather poetic, don’t you think? Part of the problem with wind generation has been that it is often not generated near where the users are. If PRT starts going between cities, the reverse will be true. The track will need power away from the city. Perfect for periodically placed wind generators.

Speaking of cubing wind energy  – One sure way to get increased wind speed is to go up. Here is a concept with nothing to do with PRT but that every PRT advocate will appreciate. Lighter-than-air wind generators. So big they increase wind speed just by forcing air to move around their shear size.

 

Neat eh? (photo courtesy of MAGENN Power Inc.)

Oh, yeah. Speaking of towers, I couldn’t help but notice this one, holding up this PRT track.

Who published this anyway? Beamways? Very Nice. This form of bridge is called a “cable-stayed” bridge and is quite distinct, structurally, from suspension bridges like the Golden Gate, which have cables anchored in the ground. This style is just made for PRT…er…  Podcars. It is even wind generator ready.

 

69> About That Angled Wheel Design...

First a reiteration of the big picture. Designing a PRT system as logically as possible must start with a track that won’t put unnecessary limits on future usefulness of the system.  Unfortunately, in an effort to get a product to market, most PRT venders have produced designs that fall short of having the potential to do anything but be small players in the transportation mix. Current systems, by and large, are not versatile enough to be used for anything other than supplemental vehicles in very densely populated city areas. That may be a perfectly fine business model, but the resultant designs fall far short of embodying PRT’s transformative potential. Where would the internet (for example) be today if it relied on proprietary networking cables rolled out according to the business plan of a single company for specific, cherry-picked markets?  Standards based PRT track design is sorely needed.

I recently posted bogie design with tilted wheels. The purpose of design effort was not so much the bogie itself, but to see if such a design would require modifications to the track profile. Actually it has, but only slightly. The general design first described in post 39 has stood up to many challenges (outlined in subsequent posts) including multiple weight classes, speed ranges, station types, freight and industrial uses, propulsion types, turning radii and pitch angles, etc. What remains to be done is to explore braking and traction issues, to address the issue of forking (adding) track with minimal deconstruction, and general track construction methods. 

All of that being said, here are some explanations regarding that tilted wheel design. First of all, it is a response to the challenges of high speed. The design makes no sense for anything less than, say, 30 mph. It gets much more attractive at speeds over 80. The rationale is this. At very high speeds the guide wheels really get a workout. In order to provide a smoother ride and make less noise, all wheels should be made of a material with some give. (rubber or plastic, not steel) Such materials wear out, especially on very small wheels. The bearings, too, take a beating.  Centering the bogie without guide wheels is a challenge, however, because of issues that are particular to the remedies. Flanges on wheels can wear and heat up. Having a wheel running in a trough generally means that all wear occurs only on a very limited ring around the wheel. The same is true if the trough is in the wheel. (Pulley wheel profile) While this can be tolerated to a degree, the issue is most acute on the drive wheels, which support the full weight of the vehicle. V-shaped wheels in a V groove wear rapidly because the wheel has multiple diameters contacting at once. This creates wheel slippage.

In the illustration below it can be seen that the angled wheels, through gravity, work to minimize any contact with the flange, which has a radius to minimize friction wear, and could be made of a harder material. The inserted detail shows how the bogie becoming off-center causes the entire wheel (and whole vehicle) to be lifted against gravity.

These drive wheels are characterized by their large diameters, which have plenty tread surface to distribute the wear, and revolve at slower speeds than smaller wheels would. It is assumed that these wheels would use tapered roller bearings, like cars, and so cannot tolerate very high rotational speeds like ball bearings, but can better support the vehicle weight and the sideways “thrust” forces associated with fast tight turns.

 

In the illustration above note that the running surfaces have been replaced by half-round, or bull nosed rails. (shown in white) While it is obvious that such a design would greatly increase wear on both rails and wheels, such a profile also allows an extremely tight turning radius. My thinking is that at very slow speeds, such as for station maneuvers, the wear will be a minor factor.  After all, by definition, the sharper the turn, the slower the speed and the less distance traveled.  What about medium turns? One thing that occurred to me is that such inserts could provide a banking angle, which would treat the bogie like it was going straight. With wheel motors the wheels toward the outside of the curve can be made to rotate faster, facilitating (if not actually causing) the turn. This is a work in progress…I don’t have all of the answers at this time.

This all raises another very interesting point. In the last post, it was pointed out that the steering guide wheels would come into and out of contact with running surfaces as needed, so they would not spin and wear unnecessarily.  Here we have described other running surfaces that are not of a continuous, unchanging profile. There are other situations as well, such as very steep slopes, which might call for special “sticky” rails or other inserts. Having various inserts has a lot of advantages. They may be replaced and upgraded. They can be precisely finger-jointed to allow for thermal expansion to eliminate the repeating noise and vibration associated of expansion joints in train tracks and some roads. They allow one basic structural track profile to perform many functions without modification. They can be made of materials (such as stainless steel) that are too expensive to be used structurally. They can be rubber mounted for noise and vibration control. It becomes easier to add a diverging or converging track to a previously completed one when the running surfaces are modularized into precisely sized components. One interesting application for inserts is the technique used by Disney to detect any breaks in the tracks of their rides. They fill the tracks with compressed air. If there is any break or crack the pressure drops and they know it immediately and can stop the ride.

Finally, a note about the fifth wheel shown below; (in the center of everything else) There are several possible functions for such a part, from centering and holding down the bogie to additional braking, power and traction. Such a part can eliminate the possibility of wear on the wheel flanges altogether on straightaways. The truth is, however, that to do the design I had to either add it or not. Because it is easier to take it out than add it later, I added it. It could, in theory, prevent extraordinary forces, such as extreme cross winds or earth tremors from lifting the bogie inside of the track. It has a smaller diameter than the main drive wheels but it supports no weight, so ball bearings would suffice and wheel-wear would also be minimal. It is largely redundant, I know, but this is all a work in progress, and, as I mentioned before, it is really all about the track anyway.

68> Haiti and Thinking Small

This is off-topic. The regularly scheduled post will be along in a day or two.

Having a bit of a soapbox to stand on, I realize, has some advantages. I want use mine now to share an idea that’s been in the back of my mind for a couple of years now. The situation in Haiti illustrates a problem that occurs again and again the world over. It is the problem of distributing aid. Specifically it is the dependence of aid agencies on having a top-down system, where airports must be secured, warehouses must be secured, roads must be secured etc, all before food can get to people in need.

The traditional wisdom is that the aid packages cannot be parachuted in, for fear of crushing people and/or causing riots. As a guy who loves to design, giving up the whole idea drives me crazy.

The problem is distributing the aid fairly and evenly. In many cases gangs steal the aid by hijacking the trucks or taking over the warehouses. Often conflict prevents aid workers from getting to affected areas.  In Haiti, there are villages that will be cut off (by road) for some time. Surely there must be some way to get food and water to the people directly.

I submit that the distribution problem is actually a packaging problem. If individual portions of food and water could be dumped from a plane in a form that would not clobber the people below, they would self-distribute on the way down. Long brightly colored ribbons would make them easy to find. When a maple tree drops its seeds, they disperse by means of papery little wings that make them gently spin to earth. Can’t we do the same for a food bar and a half a cup of water? Think about it. You can’t hoard what you have to search out to collect, and small amounts aren't worth stealing. In many cases the children in these disasters watch helplessly as their parents struggle to get the family through. This would give them a chance to go on an Easter egg hunt and be heroes. There would be no favorites, at least in terms of social position or gender.

People could also be encouraged to migrate away from unsanitary conditions. If the drops occur north of town, people will pick up and go to where the food shows up.

I guess in one way this IS related to PRT. The key is to think small. The problem of making something safe to drop from a few thousand feet becomes exponentially harder as the weight increases. This strikes me as similar to the nasty tendency to think big with transportation, or at least not take small vehicle mass transit PRT seriously. It just seems that if you mention moving ten people instead of one or two, suddenly you are taken much more seriously. Small is counter-intuitive.

Similarly the idea of moving tons of food aid with thousands of little parachutes or whirly-gigs sounds ridiculous, until you consider that, as a society, we are already the kings of over packaging. We mass-produce and (over) package little items by the millions every day. These aid items just need to be highly compactable for transit, but, when falling, have enough drag to fall at speeds too slow to be dangerous. Is that really so hard? Not if you think small. Heck, I’m pretty sure my kid’s packaged lunches are almost ready to go as is! Think origami, and plastic that you can fold and will spring back. Think tails with multiple wind catching discs that stack tight for shipping. Let’s solve this problem before the next big disaster, shall we?

67> Motorized Steering Guide Wheels

Here is a little detail of the bogie design I posted last week

I embrace the “in vehicle” switching philosophy, which is found in designs by J. Edward Anderson and others. I can see little logic for moving the track, as is the case for ordinary trains. This design, however, has generally involved a “bi-stable” guide wheel positioner, wherein one steering guide wheel always remains engaged. This prevents a situation where the vehicle is neither directed left nor right, and so crashes into the middle of splitting tracks. The problem, however, is that if the vehicle is going at high speed, maybe with no turns in sight, the small steering guide wheels end up racing for no reason. An obvious remedy for this is to have the engaging “fin” within the track be discontinuous. That way, one wheel set will still be in the engaged position, for safety, but it will not have any running surface to engage to with, at least when on the straightaway. There is no needless spinning.

In the picture above the running surfaces for the steering guide wheels are shown in blue. Because of expansion and noise, the running surfaces should be finger-jointed and rubber mounted, so making them discontinuous and tapering them into and out of contact position is not a problem. (This detail is not shown)
This results in a different problem, however, also exacerbated by higher speeds. The steering wheels, if not engaged, cease spinning. Then, upon re-engagement, they would have to go from zero to thousands of RPMs in an instant, which would tend to tear them up. They must, therefore, be caused to spin prior to engagement with the running surface, and preferably at exactly the correct speed.

There may be some motor and controller out there what would work, but my guess is that it would be very, very expensive, and way over-built. These wheels need only spin. They don’t actually need to drive anything, even thought the monster shaft size would be consistent with delivering the power of a midsize motorcycle. I say make our own.

The “motor” shown above is a simplification. Additional electromagnets can be added. Now I don’t know a whole lot about digital electronics but I have bread-boarded some simple circuits and I know that if there is a source of pulses (such as the encoders I discuss in post 20) the frequency can be easily manipulated by simple means such as a J-K flip-flop, (a basic building block chip, available on Ebay, for example, for about 20 cents) This output can trigger a $5. solid-state relay and Voila! A simple motor. Again, I am sure someone else could come up with a much more refined design but I think the principle is sound. Maybe I should market this idea to Boeing or Airbus. Ever see how those landing wheels smoke when they hit ground?

66> "Luucy! We Got Some "splainin" To Do!"

We, as a community of PRT advocates, are, sadly, a painfully small group. This blog is now quite easy to find on Google, but the fact is there just aren’t that many people looking. The collaborative design infrastructure included on this site is pretty useless if there are no engineers who are interested. It’s been forty or so years and still PRT is a curiosity that few know about or take seriously. There is no dialog, no buzz, relatively speaking, though there is a bit of a comeback underway.

In my last post I asked for nominations for best video. All of the submissions, save four, were promotional corporate videos for particular systems. These tended to portray the advantages of a PRT system as the advantages of their own proprietary solution. One of those four, posted in a comment by alert reader cmfseattle, was a rudimentary mash-up of three promotional clips. It “got me to thinkin’…”

The problem as I see it is that the case for PRT is a multifaceted one, and not well suited to sound-bite evangelism. Sure, there’s “On Demand”, “Point-to-Point”, and “No sharing, No waiting,” but that’s all true of everyone’s cars as well. The advantages of PRT, as shown in the various promotion videos, often emphasize a comparison to other forms of mass transit. The ordinary audience doesn’t care which form of mass transit is best. Many never ride it anyway. The only, (quite predictable) result of this type of sales pitch is to get the light rail companies up in arms. Because the videos try to be upbeat and optimistic, the countless negative consequences of failure to act must be minimized. (That will be a trick for any PRT video)

We need an audio/visual approach to PRT advocacy very, very badly. When someone wants to explain PRT to a friend they should be able to say, “Look up “PRT” on YouTube,” and that person would get the whole message in a few minutes and walk away a believer. I wish we could get a Michael Moore or Al Gore to do a real documentary, but that is actually “Moore” than we need. (Sorry, I couldn’t help myself…) Heck, we don’t even have a generic PowerPoint presentation. A well constructed, 5-10 minute narrated mash-up of pictures and clips could do more to advance PRT than anything else I can think of. A picture is worth a thousand words and often a video is worth a thousand pictures. Every group on the planet has promotional videos except us. And it’s really not that hard.

It all starts with a great “storyboard.” The narrative is generally written below empty boxes, which can then be filled in with sketches or descriptions of what the viewer might see during those words. This is often done on a white board, because there is a whole lot of erasing and brainstorming involved. It does, however, make creating a coherent presentation much easier by preventing most effort from ending up “on the cutting-room floor…” (For you youngsters, that’s from when film was cut and spliced by hand.) Once a good storyboard is created, the “boxes” can be “filled” with specific images and video clips, presumably from the web, and the rest is relatively easy and cheap video editing. Speaking of editing, one thing I thought was a stumbling block is that the Flash file format used on YouTube. Yesterday, however, I downloaded a free program called “Any Video Converter” which makes downloading YouTube content a breeze and can convert files to any file format you can think of. This is a good thing for PC users because Windows Movie Maker (comes with Windows) seems (for me at any rate) to prefer WMV files over AVIs. (We will take a moment now to allow Mac users to smirk……. Thank you.)

Anyway, perhaps this site might be a useful vehicle for such a project to be done collaboratively. I do have, after all, the infrastructure in place. Just a thought.

Oh yeah, about that tilt wheel design…

I guess I’ll explain it later. Happy 2010, folks.

65> The Efficiency of Absence and Angled Wheels

Before everyone’s eyes glaze over from too much shoptalk, I would like to ask for nominations for the best videos to explain PRT to a complete newbie. It is time for me to update my “About This Blog” sidebar, and I want people who stumble on this site to go away believers without me having to waste a lot of space trying to explain it.

Speaking of the sidebar, I see my “Recent Comments” list is still blank - at least on my computer. If anyone is getting the list, or knows how to fix this widget, let me know. It would really help keep threads alive.

As most of you know, I am trying to finalize the design of the most cost effective, versatile PRT track design for suspended systems. Unfortunately, this entails exploring every conceivable use, limitation and bogie design. Higher speed. Tighter turns. Steeper slopes. Industrial. Freight. Heavier loads. Cheaper Stations. Manufacturability. Longer Spans… “Pod” designs may evolve, but the track stays, so we need to get this right. I have taken the approach that the running and guidance surface dimensions are a somewhat separate issue from the structural truss, and that these surfaces can basically be surrounded by a support structure. Inside, for example, most structure is no longer needed, because the running surfaces can be supported (hung) at frequent intervals. Anyway, it mostly comes down to the bogie design.

I have, lately, been working on a problem inherent to rail based PRT designs - the shear number of wheels required per bogie. Here I show an older bogie design with 18 wheels.

 

True, half of them need to fully disengage to switch tracks, but still 9 per side seems like a lot. In post 54 I show a much simpler configuration, with railroad style flanged wheels and little guide wheels that fit between the two halves, but this design is unworkable for high speeds. Post 56 shows a high speed-bogie, but with no steering wheels, so do not be confused. As you can see from the picture below, PRT’s acrobatic unpowered cousin, the roller coaster, requires many wheels as well, and would require still more if designed to switch tracks via steering guide wheels. 

In railroads, they cut the number of wheels from 16 to eight by adding a flange to each wheel. The problem is that the flange creates friction with the track which would tend to overheat and wear it out at high speeds, smaller wheel diameters, or if it were made of some material other than conductive, strong (but loud) steel. To minimize wear, the designer must keep the wheels perpendicular to the rail surface, hence the 24 wheels per roller coaster car.

Some years ago, while arguing over a design detail of a piece of factory equipment I was designing with a machinist friend, I came up with this axiom. “There is nothing more efficient than absence!” I have returned to that thought many times since. So how can I get some of these darn wheels to be absent? Without flanging the wheels or track?  While steering guide wheels can be disengaged for straight runs, guide wheels for centering the bogie cannot. One thought is to wedge the bogie in the track with angled wheels. Here is what I drew to help me think.

Could this line of thinking mean I need to take my track design completely back to the square one, after all of these months of exploration? The verdict is still out, and I have some more mature designs to share at a later date, which require some fairly lengthy explanation. But it is Sunday, and I’m in the middle of remodeling my bathroom, so I will bid you all a Happy New Year.  

64> The ULTra Architecture - Continued

In the last post I touched on the idea that vehicles such as ULTra could be driven by “joystick”. This idea of driving by electronic controls (as opposed to the current practice of having actual mechanical connections between the pedals, steering wheel and the engine and brakes,) is not new. The use of electrical motors and regenerative brakes starts us down that road, which leads to the “skateboard concept.” (scroll down to post 50 for a picture)

Let’s take this line of thinking a step further. If the Ultra vehicles are guided by some kind of laser system that centers them on the track (with accuracy of less than a centimeter, I understand) such a system could presumably be fitted on private, steerable cars as well. An example of a steerable car which could presumably be easily modified for the ULTra control system is this Michelin concept car. The idea is that you drive your car to a ramp (or car “elevator”) and driver control is switched off and automatic control is switched on. Voila! You are now in a fully automatic PRT system until you are dropped off.

That Michelin video raises an important point however. People are really in love with their cars. The very best selling point of this electric car seems to be its muscle. Then there is the addition of luxurious creature comforts, such as adjustable seats, high-end music, etc. It seems to me that private vehicles will always become more and more loaded with features and power until something or someone steps in to halt it. Electric vehicles, in themselves, are not without environmental costs. The electricity they use must be generated, and this, itself, generally involves combustion. The prospect of hundreds of millions of Chinese cars being recharged by way of coal (their principle source of energy) power plants is truly frightening. Coal is, of course, 100% carbon, so there is no fuel on earth that is worse for global warming. Anyway, the point is that there would need to be some kind of societal decision as to how much to limit the power and weight (and therefore luxury) of these vehicles. We can’t afford a guideway network for Hummers. Because any vehicle on the system would need to be meticulously maintained, (combined with the necessary luxury limitations noted above) perhaps some type of leasing model would be the way to go.

This scenario does not eliminate “ordinary” PRT operations. Fully automatic “taxis” could still populate the track. PRT vehicles could come down to ground level and use a special lane to get to stops which cannot be served by raised stations. This would, of course, create the same interferences with vehicular and pedestrian traffic that plague other forms of surface transportation.

The main problem with the whole idea is the same problem that plagues all supported PRT systems. All supported systems inherently discourage true point-to-point travel compared to hanging systems. If they come to the ground they interfere with other traffic and pedestrians. Ramps must be fenced off for safety and are ugly. Stations must be positioned so that ramps won’t block driveways. If elevators are used to raise the passengers or lower the vehicle, the station is considerably more expensive. This is a big deal if you consider the economics of the network. I believe that in many cities the ridership figures are such that a great percentage, maybe even most, of the city would go unserved by the PRT network unless simple “bus-stop” type boarding areas are employed. I think this is a point worth repeating. It is a very big problem if the cost of stations precludes their use in large areas of a city. PRT needs the “network effect” to fulfill its promise as a transformational technology. Of course this is just money problem. If the government wanted to switch some road funds into PRT that would be a different matter. From a business perspective though, there will always be a number of riders under which it becomes unprofitable to create local service.
For the time being I remain very wary of any system that can only take the “low hanging fruit” to market.
Merry Christmas!

63> ULTra – Architecture and Iteration

There has previously been, in my mind at least, some question about whether ULTra is really PRT. After all, the 40 km (25mph) speed is hardly “rapid”. And the distances that passengers will be willing to travel at those speeds are somewhat limited as well, although I suppose they are far enough to be legitimately called “transit”.

I started writing this post with a number of negative suppositions. I have previously criticized the ULTra design for being little more than a golf cart, and wondered aloud what the advantage of automating such a vehicle really was. Actually I was about to call for ATS (The company that makes ULTra) to consider a purchase of company like Taxi 2000, or PRT International, as a way forward out of the constraints of it’s present design limitations. I am forced, however, to reconsider.

I have been selling the ULTra designers short, I now believe, and this is why.  Many of the aspects I don’t like about ULTra are truly intermediary. They will not stop ULTra from becoming much better (and more versatile) in future iterations. It seems that the designers over at ITS have a motto of extreme simplicity and conservatism. Anything else is kept “close to the vest”.   Here is one example. The traditional steering, (as opposed to track constrained steering) at first glance, would seem to have all of the negatives of cars. It would skid on ice, for example. Safety issues would seem to prohibit any kind of speed with an automated guidance system. The idea of a track would seem SO much better than trying to center the vehicle with lasers and sensors. So why didn’t they do it? Well for one thing, tracks are less versatile, because they prohibit the vehicle from being able to move freely on any paved surface. But it is mostly, I believe, because they didn’t need to. Tracks would offer the potential of much higher speed but they don’t need speed. It’s only an airport “people-mover”. But the fact is that a track or guide rail is still perfectly compatible with ULTra. They just chose not to use one, for now. Lasers can be turned off, but you can’t easily pull up the tracks. Therefore lasers win. If and when speed becomes an issue a simple rail that sticks up under the center of the vehicle could be added, with minimal modifications to the vehicle.

One interesting aspect of ULTra is that it could presumably be driven away by a human operator, using a plug-in video game style controller. This would seem like a natural way for mechanics to move vehicles around a maintenance facility, for example. That raises intriguing questions about dual-mode, doesn’t it?

Don’t be too put off by the weight. They are using the old, heavy, lead-acid batteries. But once again, the only trade-off has been to design-in some extra space. They can upgrade to Lithium-Ion or even third rail at any time. It was explained to me that track electrification was deemed too costly, but I can’t help but wonder about partial electrification, so that the batteries could get some on-route charging. The possibility of easily swappable batteries also comes to mind.

I also hate the track, especially as seen from below. That would seem to be a hard sell for city streets.  This, also, is not really an issue that can’t be much improved. There is nothing that says that the track must be massive concrete, for example, although noise could become an issue of the track was pure steel. There is a gradation between rails and roads. If redundant road area (anything not in line with being directly under the wheels) is removed you are left with a pair of very narrow beams – seems pretty much like a pair of rails to me. ULTra can theoretically drive on such “rails”.

I guess the lesson here is to beware of false choices. This does not just apply to Ultra. I was bemoaning the huge turning radius of the Anderson designs and a similar thought occurred to me. There is nothing inherent in the concept that prohibits tight turns. It I just that it necessitates a more complex bogie than is called for in the current business plan. 

It is easy to look at a system from afar and the hard choices that have been made and to rap them up as defining that system, rather than see them as a collection of business decisions. ULTra is not a clunky, slow, heavy vehicle on an ugly, massive roadway. ULTra, like other systems, is an architecture first, and the rest of it is a means to salable iteration of that vision. This architecture, I am finding, is surprisingly tweekable.

62 > Mission and Miscellanea

First on the agenda, readers may note that our “Recent Comments” feature has disappeared. It was rather peculiar. I was on the phone with someone asking if it was just my machine, which it was, and then he refreshed his screen and it was gone for him too. It turns out that it’s a third party “widget” and I have left a cry for help on their site. We’ll see what happens.

I have recently included an index under the search box. It is very incomplete at this point. It is actually a link to post number 0, so if you find I have a glaring omission you can say so in the “comments.” I will try to periodically delete these comments as I address the issues to which they refer.

I want to clarify something. I have shown a lot of different designs since this site started and one might be tempted to think I am just throwing them out there, to see what sticks, or that every design cancels the one before it. One might think that I am inventing and improving “my system.” This is not exactly true. Actually what I have been doing is trying to verify a “best” suspended track design and finalize its dimensions. My reasoning is that while a PRT provider could go out of business and vehicles may come and go, wear out or be improved piece-by-piece, the track will stay until someone tears it down. We cannot know what technologies or configurations will be desirable or employable in, say, 30 years. (Or how the city’s transportation needs might change) We can, however, create a design that is as flexible as possible. This flexibility can include the ability to accommodate different neighborhood types, vehicle weight classes, speeds, special purpose vehicles, propulsion types, and station types, turning radii and slopes, while being easy to construct, deconstruct, and connect to.

I do not think it is altogether coincidental that the two active PRT platforms run on a road-like surface, which can be used for other vehicles if the projects or companies fail. It is simply insurance for the buyer.

Therefore one of my aims is to provide a track profile that is not entirely incompatible with the various PRT technologies available. I would like to see a track that could be readily adapted by one or more PRT venders, so that the track expense does not represent a total financial and political risk. In this respect I diverge from most would-be providers, who require absolute faith in both their proprietary products and their companies. (Most of which are not scaled for any actual contract) I hate to say it, but this seems extremely naive. Is it any wonder that their proposals don’t carry much currency with those entrusted with the public’s money? We, in America at least, have seen many of our pillars of industry and finance file for bankruptcy in the last couple of years. Do these “companies” actually think that they can scale up to manufacture vehicles, lay track, and manage an untried network all at once? More importantly, do they think they can sell that scenario? There’s a clock named after this kind of optimism.

My approach, again, (43% of this site’s readers sample as new, so I repeat myself with purpose) is this. Standardize the basics. Document consensus. Establish common ground.

Where do the companies promoting bottom-supported PRT fit in with all of this? It is my intention to eventually examine these systems as well, with an eye toward addressing any major shortfalls constructively. (Readers will note that in Post 48 I suggested a way to double the throughput of a small-footprint elevated station for almost no additional expense, for example).

A common pitfall in design stems from starting with a set of assumptions and continuing from there. The more you invest in those initial design assumptions, the less likely you are to consider that, perhaps, you were wrong in the first place. I have invested a good deal of time exploring suspended systems, and almost none with the supported designs. Perhaps my original objections can be easily addressed. How can one tell without actually going back to square one?

Finally, there are a couple of obvious flaws in the classification system I suggested last week. One is the use of the letter “x” for both spacers and to mean “Does not apply.” A minus sign would be seem to be a good alternative. Also, (as pointed out by an alert reader) the term “articulation” is not self-explanatory. It does indeed refer to tilting the cabin with respect to the track to adjust for slopes and curves. Pitch and Roll are aviation terms. In the system I did not allow space for both Pitch AND Roll articulation. This, as you can see, is a work in progress.