As I see it, the principle barrier that all PRT companies face is skepticism. Who can blame city planners and transit officials? The would-be companies come to the table with claims that they can build vehicles profitably, can build city infrastructure, including bridge-like track segments, can coordinate street traffic while utilities are being re-routed, negotiate the acquisition of right-of-way where needed, create a control system for these vehicles that is safe, build stations, maintain the fleet, collect tolls, etc.
“Gee that sounds like really fascinating technology,” Transit officials say, “Let me run it up the flagpole, and I’ll get back to you…”
One way to gain the confidence of customers is to have established standards and an independent standards body. After all, you need a license to practice medicine or even do plumbing. Anyone, however, can call himself a PRT provider. Standards creation is made difficult, however, by the fact that there are so many versions of what PRT should look like. I would hope that many of these providers would reconsider the highly proprietary nature their designs. Apple computer may have survived having it’s own standard, but that is certainly the exception rather than the rule.
I cannot champion all designs at once, and so I will concentrate on my own favorite, hanging designs, and more specifically the track, which is the part that needs standardizing most. This is because PRT companies might come and go, and vehicles will wear out, but the track is a very long-term investment. Even removal would be expensive. Cities need a “plan B”. Making a standardized, non-proprietary track that is cheap, simple and as versatile as possible seems like a worthy goal.
Here you see in the foreground the basic track shape I have shown previously. Just scroll down to my June 26th and July 16th posts for reference. I had mentioned in my last post that there could be various types of specialized track, such as low profile or industrial configurations that could extend the usefulness of PRT track. As long as there is some standardization, especially the slot width, there are many potentially useful configurations.
First, note that the track here is simple angle steel. It is shown as discontinuous so that it may be demonstrated that travel can be accomplished on a single side. The light brown hangers are produced from simple steel plate by a CNC flame-cutting machine. In other words, anyone can produce such track for little more than the weight cost of steel. For anyone who wondered, now you can see why my PRT track design has those hollow running surfaces. It is for flexibility in the support and steel thickness choices.
The picture above shows how simple a slower, more limited-range bogie may be. There are two aspects in particular which are not very practical in a PRT bogie that may be used here. One is the rims on the drive wheels (green), which hold the bogie in the track like a traditional railroad car. With high speeds, continuous use and quiet rubber wheels, these flanges would wear out. An alternative, shown here in violet, is guide wheels that are small enough to fit in the slot. In PRT, such wheels would spin over 5000 rpm, and would be too prone to heating and wear. Here I have redundantly included both of these slow speed options in a single bogie, for illustration purposes. Either would be OK for the occasional cross-town trip at reasonable speeds. Also note that there are no upper guide wheels, either for steering (blue) or centering. (violet) This is because this bogie is not designed to withstand the twisting torque of low-slung heavy loads on high-speed turns.
It can be seen that for companies to move goods around a factory, sky-hook style, is quite easy and cheap. It is not necessary to build full PRT track around the warehouse. Such a system could replace forklifts and conveyor systems, adding floor space. Goods could be moved between warehouses or to stores, increasing the usefulness of PRT track, especially at night. What is lacking, of course, is the software, which would be essentially the same as for PRT.
When we ask for taxpayer or investor money to build a network, that network should be very, very useful. Having certain key dimensions and construction details standardized just makes sense for everyone. An easy-to-remember acronym like SMARTS can’t hurt either.
11 comments:
1. what prevents the bogie from rotating along the longitudinal axis? wouldn't the blue switch wheel's axle bolt would scrape along the underside of the running surface?
2. propulsion method? if your cargo isn't human, why not just use the motors for steering?
Dan The Blogger Responds-
Hello cmfseattle- I think you have a point. I may go in and do some editing… The fact is that I had other reasons for having half the track missing. To draw track in SketchUp I do one side, copy, paste and flip it. Doing that would obscure some of the bogie’s details. If the main point had been the ability to travel on one side, I would have moved the violet wheel down, perhaps even extended the angle steel downward more too. As it is, the track would have to be very tightly clamped between the blue and violet wheels. Of course the previous, taller configurations have that movement curtailed by upper guide wheels. It is true that if you used the flanges on the green wheels to center the bogie instead of the violet wheels, you certainly could not run it on half a track, although as shown, it would work OK without a load. It is also true that the half-inch clearance between the raised (blue) steering wheels and the supports (tan) is pretty tight. What can I say? I was in a hurry. One of these days I’ll load it into Google’s SVN servers and everyone will be able to play with it. I just haven’t had time to familiarize myself with that stuff.
As to your other points… One of my text revisions explained that the bogie was simplified for easy inspection of the basic interoperability principles. I included a little hexagonal box for steering control, but no computer/motor controller. The motors would be in the wheels. I guess I should go back and label them as such. As far as steering, if you mean what I think you mean… (And I think you mean steering like in a little “Bobcat” loader where it steers like a tank, i.e. by making the right or left wheels go faster) then I would say this. It would work at slow speeds indoors, not so much at high speeds and on frozen condensation, since that method requires predictable, yet limited tire slippage to work. However, that subject opens a whole host of issues, one being the electronic direct drive equivalent of a car’s differential.. After all, outside wheels should always turn faster than inside wheels when cornering, regardless of steering method. Could motor rotation alone produce reliable steering? Maybe, but I wouldn’t design around the idea. Don’t forget, one point is that such bogies can venture out into the larger network, maybe doing upwards of 10,000 miles per year, at up to 35 mph. This could open new warehousing and distribution models as well as encouraging public/private partnerships for network expansion. We don’t want them crashing.
Anyway, thanks for the alert eye….
yeah, sorry, i posted before absorbing all the info. i do like how you adapted anderson's switch (tm). to use motor steering, you'd probably need an articulated bogie, but i think that having the wheel sets farther apart would be desirable anyway.
I have some familiarity with the design of warehouses for retail distribution. I could see PRT being highly desirable for dispatching deliveries to stores (perhaps even stores within malls).
Less compelling, but still potentially desirable would be inbound deliveries from vendors. There are distribution techniques that would benefit from many small deliveries from vendors that are made impractical due to the fixed cost of a driver and an expensive vehicle.
I have a hard time imagining a PRT network compatible system being used within a warehouse or factory, except as an interface between the location and the outside world. This is simply because using the PRT standard would be using a generalized tool for a specialized task. A specialized tool would likely accomplish whatever result with lower cost in space and capital than the PRT standard.
I'm not trying to rain on your parade; I'm just providing a perspective.
I do, on the other hand, see PRT as having the potential to change logistics pretty significantly.
Hello, Afransen. Thanks for commenting…by the way, esteemed readers, I have had a small break in my schedule. Often just getting a post out is all I have time for. Right now I have had my computer on “standby” whenever not in use, because I don’t know if it will ever boot again if I turn it off. Do not be surprised if I am temporarily silenced some time in the near future. My hardware and/or work obligations could easily conspire to make that happen.
Anyway, Afransen, since we seem to pretty much agree on everything except your third paragraph, let me fill in my perspective a bit.
I think one generalized tool, the forklift, is a pretty inefficient way to get stuff from, and around a warehouse. I can’t tell you how many hours I’ve spent waiting for the forklift to come and load me up, often with something I can put in the truck of my car. Sometimes they bring me the whole pallet, get fifteen items off, and drive the whole thing back again.
In steel shops, they use overhead cranes, which are basically beams that move back and forth (sideways to their length) overhead. A little trolley moves along the beam with a winch. It’s a skyhook. Plates of steel can be leaned on end, and the operator can clamp a plate of steel and bring it the cutting table. Thousands of sheets can stored in a fairly small warehouse this way. Out in the yard, they need to be stacked flat with lots of space between the rows because they must be forklifted. If operations are in multiple buildings the crane must lay the sheet down on a forklift blades for transport taking a few guys on each end of the trip. Other items that benefit from vertical storage include many building materials, like glass, marble and granite slabs, door and window units. I would think all would benefit by being able to be “sky hooked” to various phases of the finishing process as well as to a truck or even a final destination. You might also be interested in Wikipedia’s description of a “stacker” crane, (a concept I was planning to reveal to the world as my own invention until five minutes ago…) which could be extended beyond the warehouse with a PRT style control system and a track interface.
I have been in a production cabinet factory where components were moved about, assembly-line style all by hanging. This was particularly handy in the finishing department where components were sprayed and baked, all while hanging. In this case multiple destinations were handled by multiple rows of passing hooks with each row going to a different place, for example drawer fronts to be painted vs. drawer fronts to be stained, or laminated.
I can’t help but imagine there would be uses where complicated sorting is required, because bogies could read a bar code and take something to exactly where it belongs thousands of feet away. I have seen some insanely complicated conveyor systems to do that sort of thing. True 3D routing takes much less floor-space. Cost of floor-space dictates location. Location dictates travel times….
No, skyhooks are not a cure-all, but I would bet they find plenty of “in-house” uses.
Also, I think it is worth considering the degree to which warehousing itself is a product of big-vehicle, scheduled delivery. If products can flow like water out of a tap, who knows what warehouses would be like… I guess smaller and more local?
Anyway, stay tuned for my next post. It deals with the product delivery end of things.
Freight carried on PRT systems will most likely spend most of its journey on existing transport modes. This means that a standardised pallet or container for freight needs to be totally acceptable to operators of existing modes.
A container that fits on PRT will be relatively small, making automated transfers essential to be economic
A standardised Small Automated Container is what I have in mind.
(Email me at MAIT@john-greenwood.co.uk)
Dan The Blogger Responds-
Thanks John, your observations mirror my own. I am writing this after just posting on many of the same issues. You bring up good points on security and theft etc. Definitely worth considering..PS. I put MAIT on the link list, which I hope to completely re-do one of these days with better descriptions of the sites...hope it sends some traffic your way..
It seems to be an overhead crane is more versatile than something using your PRT standard. An overhead crane can reach any x-y coordinate along its track, often running the whole length and width of a shop. Your PRT standard would only be capable of reaching points directly under a section of guideway.
Forklifts for anything palletized would also tend to blow PRT out of the water. Smaller boxes that are conveyor friendly would have a hard time using your PRT standard.
All I'm saying is that for these kinds of tasks, there already exists systems that are more highly tailored to that purpose. The network effect is not that strong for transport within a structure. The real opportunities are for transport between sites.
"I can’t help but imagine there would be uses where complicated sorting is required, because bogies could read a bar code and take something to exactly where it belongs thousands of feet away. I have seen some insanely complicated conveyor systems to do that sort of thing."
The sorting I'm talking about is taking, perhaps, 3000 distinct kinds of items, and sorting them in 300 or so buckets, placing them on pallets following some rules about grouping similar products together within the buckets and putting heavy items on the bottom and lighter items on top. This can be accomplished quite efficiently with very little in the way of equipment, usually just some forklifts and motorized pallet jacks. It requires sophisticated IT systems, as well as the ability to precisely phase in the arrival of products from vendors. PRT could make that last bit quite a bit easier, the rest, I have my doubts.
"Also, I think it is worth considering the degree to which warehousing itself is a product of big-vehicle, scheduled delivery. If products can flow like water out of a tap, who knows what warehouses would be like… I guess smaller and more local?"
Actually you might be surprised. Logistics is basically a trade-off in transportation cost and facility cost. High transportation cost makes it easier to justify more facilities to serve a given need, where if transportation cost were zero and lead times were acceptable, the need would generally be served by one location, so long as the size of the facility was still within the range of increasing economies of scale.
Imagine the postal service. Why are there so many post offices? Because transportation costs are high. If they were much lower, it would likely make much more sense to send all the mail for a large city or perhaps even a state to one sortation facility.
Dan The Blogger Responds-
Thanks Afransen…
About the crane. My PRT standard allows the crane to reach any XY coordinate in the building and any XY coordinate in other buildings as well. This is because the crane’s trolley part can connect to track that leaves the building. Within any building it is functionally identical.
As far as your other points are concerned, I think we are talking past each other a bit here. I am trying to develop a track standard that will not be seen as having shortcomings a hundred years from now. This forces me look deep into a future that includes vast operational networks of PRT track, and “backwards engineer” from there, to make sure no major potential is left unexamined. The track must not preclude possible future uses.
Your arguments seem more routed in a more immediate future. I doubt you mean to suggest that manned, 2 dimensional warehousing and sorting will forever trump 3 Dimensional automatic sorting and warehousing; I, conversely, do not mean to suggest these changes could occur anytime soon, just that they probably will, eventually. I acknowledge that I haven’t replaced the forklift/pallet paradigm with anything I have described. That is or future engineers to do.
Your comment on the post office logistics is spot-on, in today’s world, or even a generation ahead. But still further out, in a future, track-networked world, the reduced cost of transportation you site might be secondary to ability to immediately and automatically dispatch mail (or a similar delivery) to within a block or two of its destination via micro-deliveries, (straight from the airport.) It’s more of a pipeline model and would lead to many more, and smaller, post offices (or warehouses.) I would argue most of the factors that contribute to “efficiencies of scale” are mitigated by the nature of a PRT network. Otherwise we had better buckle up for bigger buses and “light” rail. Thanks again for a thought-provoking post.
Forgive me for being rather present-focused in terms of distribution logistics.
As far as the dominance of the pallet-forklift paradigm of goods transportation, it's worth noting that we do not even have a global standard (or continental, within North America) pallet design. The pallet model faces direct competition from 'roll cages', which are quite common in Europe, with the advantage being that they do not require any equipment to move.
I guess I'm trying to impart to you my impression of how logistics will develop in the future. Recent techniques using sophisticated, well-designed (but still relatively cheap) information systems combined with human labour can often beat the pants off of a physical system with minimum human involvement. Also not that every facility has a fixed cost in the unproductive land around the perimeter, offices, washrooms, cafeterias, training rooms, insurance, taxes, utilities, maintenance personnel and managers. This is a large part of the driving force to fewer locations rather than more. Another part is inventory. PRT can certainly help to reduce the concern about inventory, but I am not so convinced about those other fixed costs. Even if we manage to replace human labour-based systems with automated physical systems, this only serves to increase fixed costs per location, as each location will need to have at least one highly skilled technician on-site or on-call to deal with any technical problems. This is a lesson that seems to run against popular wisdom, which is why I thought I should share it here.
The same is true for post-offices. Until we can have freight delivery direct to your door, I think freight-capable PRT would serve to drive centralization in order to reduce capital requirements and reduce sorts. A model I am seeing develop around where I live is for retail post offices to be set up as a counter in a grocery store or pharmacy, and increasingly the private couriers are taking advantage of this as well, delivering to these locations rather than going door-to-door in a neighbourhood.
Grateful ffor sharing this
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