Saturday, January 17, 2015

164> Papa Bear, Mama Bear, Baby Bear

As promised in my last post, I have modified the SMART PRT (Suspended Multi-axis Automated Rail Transport – Personal Rapid Transit) design yet again, this time to accommodate featherweight “pods” and enclose the bottom of the track, as well as fine-tuning certain proportions.  
There is also a secondary rationale for considering ultra-light PRT systems, which is the matter of parcel and light freight delivery. Companies such as Amazon are clearly putting heavy emphasis on speedy delivery these days, and the ability to integrate a steady stream of varying vehicles is, unlike days past, essentially a given. Couple this will the fact that such track would be many times cheaper, and a very good case can be made for exploring the matter further. 
In response to this challenge I submit the pictured multi-sized approach. In the top picture, the comparatively tiny profile of the “Baby Bear” track can be seen, which does not even reach the man’s knee. 
Before going any further, though – a disclaimer: The pictures are to illustrate component geometry only. The track is shown as if it can be simply extruded, which it can’t, and I just thickened the top of the larger sizes to show where ribs would most probably go.
Also, I’m sure that there are some newer readers who may have never considered the matter of switching suspended PRT, and who may be confused by the various end-views. To them, I offer this more complete, yet still simplified, end view and explanation.

To switch suspended PRT, the part of the vehicle that rides inside of the track (the bogie) must grip one side of the track or the other, so that when the track routing diverges, the vehicle’s drive unit (bogie) does not fall out of the track’s ever widening slot. In this end-view, the pair of steering-guide wheels on the right “clamp” into rolling engagement with the track, while the left ones spread apart to release that side. In other words the bogie, shown in blue, can be fully supported by either side of the track and so can follow either as they split apart into different routes. The weight forces of the hanging passenger cabin are shown by the three red arrows. 

It is also noteworthy that certain parts of the track are eliminated where there is no switching. In this picture, the steering guide wheels are not quite contacting anything. Side-to-side guidance is maintained by the large, counter-rotating horizontal wheels; to do otherwise would simply add wear to the smaller wheels for no reason. The actual contact rails are only at switch points and taper into contact gradually for a smooth transition. Also, particularly observant, long-time readers will note that some track parts will need to be modified or removed for tight radius turns, both side-to-side and up-and-down.
Now, back to the top pictures. In these two illustrations, BTW, the steering guide wheels are engaged as if they were approaching a “Y” in the track.

The “baby” track is sized for speeds below 30 mph, (48 km/h) with weights below 500 lbs. including vehicle and passenger/cargo. It has 8” (215 mm) solid drive wheels. (It could handle more with steel wheels and very frequent supports but this would be inconsistent with most applications) The track width is 13.5”. (343 mm) 
To the person’s top-right are the “baby” wheels within a larger (mama-bear) track. Directly below are the wheels for the “mama-bear” vehicle within the same, matching track. This size (30” or 762mm wide) is consistent with the 3.5 person vehicles that have been shown in earlier posts, weighing in at about 1300 lbs., fully loaded. The performance would be generally auto-like, with quick enough acceleration to allow fairly short on-ramps, (an often overlooked design consideration!) and speeds approaching 50 mph. (80 km/h) It is not impossible that faster speeds would be practical…Only testing will tell. 

The second picture above  illustrates (left to right, clockwise) the “mama bear” bogie in the “mama bear” track,  the “mama-bear” bogie in the “Papa bear” track, and the “Papa bear” bogie in the “Papa bear” track. This larger wheel and track would be for still higher speeds and/or loads. Not much bigger than the “Mama Bear” combo, (35” or 890mm wide) the steering guide wheels get an extra two inches of diameter while drive wheels become auto-sized. The guide wheels of heavy vehicles can also be made of longer-lasting, harder polyurethane formulation or even steel, as sound is less of an issue because such routing would typically be along highways, more than fronting homes of businesses. Being designed for long distances and for larger (GRT) shuttle vehicles, this larger sized track would not universally assume full 3D routing and would be encased in a heavier structural elements. High speed sections would require some additional interior space to allow air to slip around the speeding bogie. Some very large cities might opt for the “Papa Bear” track throughout, to accommodate faster personal vehicles designed for typically long commutes. It is, after all, only 5 inches wider and height is more a function of span/vs load than wheel size.  I am somewhat dubious about the utility of making this largest track universally “baby bear” compatible, and one approach would be to design such track to be easily convertible for this purpose, rather than to include this feature initially, like the pictures shown above. This is primarily because of the speed differences, since any quiet and smooth running 8” wheel couldn’t tolerate continuous, heavily loaded, high speed use for very long, and so must be confined areas that are appropriate for low speeds anyway. For lighter parcel delivery, however, in, say, the 25 kg load range or less, it is a different story. Here small vehicles could almost fill the track spaces between large GRT vehicles, not slow them down at all, and still be nearly silent when they get into neighborhoods… without needing new wheels every thousand miles. 

What is regrettable is that the Mama Bear track isn’t smaller and cheaper – more of a mid-point between the larger and smaller sizes. Unfortunately once you can physically over-pack a vehicle with weight, (as is unpreventable with the interior cabin space required by disability laws) you can theoretically load each vehicle just as much, and as long as there is the remote possibility of a sudden stopping of traffic, where suddenly such loaded vehicles are bumper to bumper, applying all of that weight to a span, or even all applying emergency brakes at once on a curve, (thus pulling the track forward and sideways and down) … there is the need for some pretty beefy track, at least that is how it will be regulated. 

Ironically, the baby bear track can be small because it is small… If track and vehicles are cheap enough, it becomes easy to pay for, even without heavy ridership, which permits longer headways and slower speeds, so everything can be lighter-duty. Of course the “baby bear” can’t exist as a transit system alone, since it does not meet the criteria mentioned above. The Mama and Papa Bear systems need to really pack the tracks and run as fast as possible to pay their way, especially until the business model proves itself and costs begin to drop. This kind of traffic is best promoted by providing a certain degree of comfort…And comfort adds…you guessed it… weight. In PRT, there is no such thing as a free bowl of porridge!

Next step - Adapt this wheel geometry to actual stock steel, practical fabrication methods and truss design, as well as to finally address the long-neglected issue of “third rail” placement.


qt said...

Like it.

One question. You may have addressed this earlier, but is the overloading-a-big-cabin problem unavoidable? For example, with load sensors in the bogie--too much weight and the pod won't go?

If there isn't a legal or reliability issue, this might be worth the extra complication if it let you make the mama-bear track enough lighter or cheaper...

Lee Sprecker said...

What determines the size of the ‘drive’ wheels? If you had two bogies for each POD and 4 wheels driven in each bogie would the wheels be smaller or is it a function of the speed required? The ‘Mama’ and ‘Papa’ tracks look to be the same size but different size drive wheels so is it just a function of load? What weight limit do you propose for Papa and Mama? I thought that your earlier switching design was much simpler. With a ‘control’ wheel on the top to guide the bogie onto the straight track or lower that one and raise one to switch. Why are you going to this complex device? Is the track dimension about 3’ X 4’ as it appears in your drawing? Could it be narrower?

Dan said...

Dan The Blogger offers his apologies to qt! He has just discovered that Google has started automatically sending notifications of comments (such as the above) directly to his spam folder for some reason.

It’s a really good question, qt. I will go one further by wondering aloud if there is even any way to avoid some kind of weight sensor. Luckily, it shouldn’t add much cost or complexity and could come in handy. The million dollar (and highly subjective) question is, “What is the ideal weight limit of the “flagship” vehicle?”
My thoughts came partially in response to the PRT designer I mentioned at the opening, who was considering an ULTra-sized cabin. You can slip an extra 500 lbs. into one of those pretty easily.
I have to defer, more or less, to J. E. Anderson on this one. Having read his assessment of the problem, both mechanically and aesthetically, I was impressed that he was very conscious of the need to make track as skinny as possible, and I started from there. I tried to shave off more, but couldn’t. It is really sort of a sweet spot. It is where two truckable sections can be bolted together on sight and hoisted to span almost all intersections (5-6 lanes) for vehicles that are (rightly) compact but just shy of being cramped and claustrophobia inducing. That baby track, BTW, would need more height to span more than, say, 30 ft.
I know some would prefer a still smaller, cheaper, greener, solution; and, to use the analogy of taxi services, there are even bike-powered rickshaws. With my investor hat on, though, these solutions don’t look like they will ever sweep away Yellow Cab, and my money is on that somewhat greater degree of comfort and speed. It is more universally acceptable to riders and faster speeds mean more fares quicker. For those who don’t mind a slower, stripped-down vehicle and are traveling solo or as a pair, there can always be featherweight vehicles that can run on the baby-bear track, and there may well be a vibrant niche market for such systems in certain locales or circumstances. The lower cost would be pretty much matched by a lower throughput of passengers, though.

Dan said...

OK Lee, Let me take a shot at all of this…

Wheel size influences the ride, such as how noisy or how much vibration there is. If the track is to be capable of crossing itself, it would need to span the slot it is crossing. Wear is a major issue, as larger surface area translates into longer life. There is also heat, as a large diameter wheel has longer to cool before it hits the surface again. A lot depends on the material used… Harder tends to last longer but transmits more vibration and noise. Soft wears out faster. Rubber on steel produces a silky ride and rubber tires have decades of engineering behind them and are very cheap for their performance. These vehicles need to be putting on massive mileage every day.

I’m not crazy about the mechanical complexity of 8 wheel designs. Because the track needs some height or it would “fold” under weight, the question can be turned around... “Why have a bunch of small wheels instead of fewer, larger ones?” (I might add that large diameter, for wheel-motors, equals more torque.) I would use double bogies, however, for very large GRT in the Papa Bear track if there was a case to be made for such a vehicle.

There is no particular weight limit for “Papa Bear.” It is a profile that can have as much beef around it as required. Mama Bear would be generally designed for about 1500 lbs., vehicle and load, although this too, is flexible, as the structure is external.

The design you liked, I liked too, or I wouldn’t have designed it! However, A] there doesn’t need to be ANY top guiding wheel so it is just a waste, B] concave/convex wheel solutions involve multiple diameters and so some diameter must slip (friction, heat, wear) unless the wheel and track actually meet at only two points, narrowing all wear to two tiny rings on each wheel. Just not good mechanics for high speed, robust, low maintenance design. The current design is actually no more complicated – it is still just two moving assemblies - I think you are fooled by the fact that all of each side does not move in unison. This design incorporates CRISS-CROSSED members between upper and lower steering guide wheels. When the lower RIGHT goes up, so does the upper LEFT. It is still just two wheel-holding assemblies that go up and down. This design, you will note, securely “hooks” the bogie to one side or the other against gravity, whereas the other did not. If there were a “blow out” with the previous design it would disengage the upper guide wheels. This is impossible with the present design. Using the “ceiling” for any smaller bogie means that that ceiling cannot be raised for a bigger bogie to fit. This applies to 3rd rail and communications as well, so there are plenty of reasons to put stuff on the sides, if you want a versatile system.

The double, counter-rotating wheels are a game-changer, in terms of performance, but having the steering guide wheels external to the track (exposed to weather, projecting noise) was a step backward, IMHO, so I wrapped the track around them. To make the track narrower, I would have to reduce these guide wheel sizes, which are consistent with preferred load/speed/hardness. It is about 36” wide I think, but we are talking about something that spans 80 ft. and carries thousands of pounds… Get too narrow and the whole thing will twist sideways so it can sag easier!

Lee Sprecker said...

I have concerns with the idea of multiple track designs. This will add much complexity to the development of a system. In this case I think ‘one size fits all’ applies. If the track is designed for a total POD weight of 2000 lbs with the POD itself weighing 1000 lbs and a maximum of 1000 lbs load then all uses would be designed within these limits. I select 1000 lbs for passenger use around a POD designed to carry 4 people and a wheelchair or two bicycles or two ‘shopping’ carts. With five possible passengers at 200 lbs average each or 4 at 200 lbs average each and two bicycles or two ‘shopping’ carts 1000 lbs seems to be a good size. OK, don’t like my numbers then what ‘works’ for you and why?
For carrying freight the POD would have less weight as there would be no air heating and cooling required, there would be no seats etc so the freight POD might weight only 800 lbs and can carry a 1200 lbs load. That is a good sized load. I do not see why there would be a need for different sizes of track. 10 freight PODs would carry 12,000 lbs. That is 6 tons of goods delivered to 10 businesses with only 10 PODs. That seems to be a respectable amount in a small space.
For distribution from warehouses to stores the warehouse will load many pallets of goods onto a truck. The truck will drive to several businesses dropping off one or more pallets at each business. Then the truck drives back to the warehouse empty. If each pallet was loaded onto a POD (with a weight limit of 1200 lbs each) at the warehouse and unloaded at the business there would be great savings for all. Yes the PODs would return to the warehouse empty but it costs a lot less to move 10 empty freight PODs than a truck and driver. No ‘special’ loading sequence of pallets, so they can be unloaded at the correct store easily. No truck and driver wading through traffic to get to the businesses and waiting for someone to bring a forklift to unload the pallet(s).
I feel sure that a system can be developed to automatically load and unload a pallet from a freight POD on a ‘siding’ (like railroads used to do) at the elevated level and lower it to ground or freight door level. All of the movement can be done at night when the system is not as busy and this will provide an additional source of income to the system. Several freight PODs to one business or one POD to smaller businesses.
No I do not see PODs delivering your mail, pizzas or packages but they can deliver the bulk mail from a distant airport or major distribution station to the local post office for local delivery. FedEx can deliver the bulk pallets of packages to a local delivery point. All of this at night when the system passenger traffic is slow. Giving a discount for travel (for all) at night can develop extra income when the system might not be used very much for passengers. No problem with those late night ‘drunk drivers’ on the road if they take the ‘POD system’. Bank robbers will like the night discount and speed of their getaway until they discover that they have been sent to the police station.
A 1200 lb load is substantial and of course several PODs would carry as much as a truck. I do not think you need to have multiple track designs. What do you think? Can we make the 2000 lbs total POD weight a ‘design standard’? Let the Pod designer decide how much his/her POD will weigh. If they design the ‘Baby Bear’ it will work fine on the ‘Papa Bear’ track. No need for a track ‘lite’ option. Dan what do you think the outside dimensions for this design track ‘standard’ would be?
OK then let’s move on to the bogie!

Dan said...

The capacity you envision is large for the probable payload. With average vehicle occupancy in the 1.2 -1.4 persons per car range, basing the vehicle and track on 5 plus passengers means you’ll be moving a lot of unneeded container space around almost all of the time. In mechanical design, Weight begets weight begets more weight! Also 5 people and a (probably electric) wheelchair seems like a whole lot for a mere 1000 lb. vehicle. Fully loaded, it will take some big motors to get it up to speed and on-ramps should be commensurately longer or line speed slower. Turns should be more gradual, and elevations would be more flattened. Obviously, track is larger throughout your system, and is more than what I would generally recommend. Good news, though… This is what “Papa Bear” was designed for!

I question your take on freight. I think that the kind heavy cargo delivery you speak of would be just as well be left on the ground. (Although never say “never!”) I was thinking more of smaller custom and rush deliveries that pay better, like fetching a sold out item from another store branch while a customer waits, or facilitating same day or “almost to the door” delivery for the likes of Amazon.
The reason for different track sizes is optimization. “One-size-fits-all” can result in a poor fit for everybody, and cities have so far found PRT to be just that. This whole blog has been dedicated. in part, to remedying this sad situation!

Papa-Bear track is optimized for pods like you describe but it is also great for longer-haul higher-speed trips along freeways. It is not designed to get into the “nooks and crannies” of a city, (like under an overpass, or into a strip center) so there are less choices for station location. Cities would have to buy more land, move more underground utilities, divert more traffic, etc. The fastest way to nix a PRT proposal, in my opinion, is come with a system that requires the city to jump through a lot of hoops.

But if cities want primarily sub-highway-speed PRT, they can do it all, much more economically and flexibly, with Mama Bear. This track enables basically any style station, any track layout, highly compact vehicle storage, and is the perfect choice where space, minimum cost/disruption is a premium, while still offering a “civilized” ride. This is the suggested mainstay. The vehicles just happen to be able to run in the heavier, faster track insofar as they don’t hold up traffic. If a city wants to connect with an airport or a Park-and-Ride, and anticipates that this may become a main artery, the city can install the larger track in anticipation of a future shuttle service but it can be used for ordinary PRT in the meantime, thus promoting network expansion.
As for Baby bear, the space in the track where it fits is empty anyway. It does not need to be built-out in any way, and costs nothing to reserve it for future innovatators. I have to confess, though, that I paid a little extra attention to this empty channel because my friends up at Shweeb-Can, who endorse the SMART platform, have been working on a motor-assisted, switchable version of their pedal-powered vehicle. And we are far from alone in seeing potential for feather-weight transport. After all, like Bill James, (JPods) says, “It costs less to move less!”- and the most profitable freight, by far, is in the feather-weight category. Anyway, you can ignore Baby Bear if you don’t like it. Part of my job here is to propose new ideas and hold a light to such design possibilities so as to promote innovation and a better understanding of the many ripple effects, both problematic and promising, that such proposals bring about.

qt said...

Glad the weight-sensor thought shows potential. I thought of it mostly because I got the impression that you'd have preferred a smaller Mama Bear track and settled for the present size due to the overweight problem. And it occurred to me that elevator companies have been dealing with that for a long time (as I tried to get upstairs in a big hotel during certain science-fiction conventions, for instance...).

It sounds, though, like you prefer Mama Bear as she is. My mistake if so. I certainly won't argue size optimization with you--you've clearly done your homework and I haven't. If I've pointed out a potentially useful mod, that's a feather in my cap anyway.