Friday, May 6, 2011

123> Thoughts on Track Size and Switching

Well, I’m up in New England again, away from the modern world, and probably posting this from the town library.  I have gotten to see both the Atlantic and Pacific oceans in this past month, and had a fair amount of time to think along the way.  And there is something bugging me.  It’s the track.  It’s too big.  I mean, take a look at this.

This is a now defunct “Santa’s Village” out in California.  True, it is supported every 20 ft. or so, and true, it went VERY slow…  But still, does PRT track need to be THAT much beefier? 

The answer is no, if you ask Asko Kauppi. (known to many of you as the frequent contributor to this site “akauppi”.)  His vision of PRT, shown below, runs on nothing more than a pair of pipes.

 True, it may not go very fast, handle steep slopes in ice storms, or draw power from the track.  But still, it can be argued, it would provide very decent mobility in most situations – and at a fraction of the track cost.  Could such a minimal track ever work in America?  Certainly, in certain circumstances.  But we Americans like to get places fast, and there’s a lot of ground to cover in our sprawling cities.  So my designs speak more to the needs of the longer distance commuter market.  Yet I think there are several important lessons to be learned from the design. 

First, it runs on a “half-track”.  That eliminates half of the cost right there.  What is a “half-track” you ask?  Funny that it should come up now, because I recently was mentioned in a “Transport Innovators” posting regarding switching for suspended PRT.  The fact that the viability of switching suspended vehicles was not all-together settled, in the minds of some, led me to re-examine the issue, if for no other reason, than just to explain the concepts in a more understandable way for my readers.  I decided to use primarily illustrations rather than words, and opted to put it all into a single picture.  (Suitable for framing! lol)  Be sure to click on it to enlarge.

 I would emphasize that the last picture is probably the most important, because it holds the key to understanding most of the mechanical drawings on the subject.  (found through patent searches, etc)  I would also point out that most systems do not anticipate the inertial forces that would require so many wheels as the last picture would imply.  I know from experience that some end up being included solely for the possibility of a freak, powerful blast of wind just as the vehicle is switching tracks.  Steep slopes also contribute to the need for the wheels to completely capture the track at all times.  So when I refer to a “half-track” I am speaking about an arrangement such as in the first illustration. 

Asko’s design is not the only one that runs on a “half-track.”  Ollie Mikosza’s “MISTER” system is a suspended system that pioneered the concept for PRT.  There are some new visualizations  for his system, and it appears that he has abandoned the structurally superior but complex triangular truss design in favor of the sleeker, much easier to build three-tube design that is universally favored by rollercoaster makers. 
So why not just go with the MISTER/rollercoaster style track?  I have several concerns.  First is the fact that it is open to the weather.  Ollie seems sure that snow and ice are not a problem but I’m a natural skeptic. There is also the matter of limited surface area for traction and braking, and the matter of noise.  I will say right now that these are largely higher speed or higher load issues, and not necessarily a problem with the MISTER system as it is designed.  I am curious, though, about how to safely carry the electricity to run the vehicles in an open track system.  In the case of Asko’s BM One design, the vehicles are battery powered. This obviously cuts track costs and there is no shock hazard.

Anyway, I have, so far, opted for a covered design.  I am not sure, though, that it ALL must be covered. For example, the track as I have specified it seems over-designed for many “last mile” applications.  Consider, for example, a large residential subdivision where there would be little or no through- traffic and speeds would be very low.  Perhaps a central loop would put all within walking distance.  It occurs to me that perhaps a vehicle could get around such an area on battery power alone, and that a cheaper, lighter, open “half-track design might be appropriate.  So far I have designed to include highway speeds and even faster.  Could such a vehicle also operate on a stripped-down, ultra-cheap half-track?  I will be devoting considerable time to this question…from my Yucatan hammock.

 Oh! And speaking of hanging around in the woods… Take a look at what was hanging over that little structure I am building when I arrived! One tiny little oak tree saved the project. It took a lot of cable to lay that sucker down in the driveway. And yes, that’s me, in all of my country scruffiness.


Andrew F said...

Hey Dan! Sorry for my absence lately. We just had a federal election up here in Canada that has been diverting my attention.

I guess my question about a slimmed-down half-track for low-speed residential areas, etc. is how much savings might be achieved for a given amount of route km when you will still need some form of station periodically. Is a 50% cost savings on the guideway possible? It could help an initial system to reach critical mass with less capital up-front (though these light-duty guideways may have to be replaced if demand rises sufficiently).

On the bright side, the need for a battery ought not to be a problem, as it seems sensible to have some form of battery backup onboard the vehicle in the event power is interrupted on the main guideway--as long as you don't expect the vehicle to be able to travel more than a few kms on battery power.

Dan said...

IF you were only going to go fairly slow –
IF you didn’t mind if a particularly bad freezing rain could possibly shut the section down -
IF you didn’t electrify the track –
IF you had no complaints with putting support posts fairly close together and there were no buried utilities to deal with –
IF you did not have any telephone poles, (or wire drops coming from them) to move,
Then I would imagine the savings well would be over 50%. That’s track alone though, not vehicles nor stations, and I worry that cities might not plan ahead and create future choke points to save a buck.

akauppi said...

Some correction concerning our BM One effort.

We plan to go 45kmph on the "half track" and more if the vehicle is supported from both sides (but that is the exception, half track being normal mode of operation).

Freezing rain shouldn't be a problem, but that is shown once we reach field trials. Weather conditions are particularily hard to simulate but we'll be getting basic simulation results within this year. If the simulations were to show the project cannot be done, it probably won't.

For steeper slopes, BM One has track assisted ascent like the SF cable cars. And then there's vehicle elevators for vertical.

Distance of support posts is one of the parameters we're toying around in the simulations. It's a compromise with track sturdiness and a few other parameters.

Existing poles in many cases can be merged with the track (in Finland, mostly lighting since telephone cables go underground). This offers additional benefits at least in connection with pedestrian/cycle lanes because of even lighting (not every 20m) and less 'wasted' light.

As a general solution, I am not suggesting "half track" would be good for every design. Things need to be made simple - that is the main guideline that helps make them reliable and priceworthy. Making a separate "half track" mode to something which by its own design is not, sounds to me like going the opposite way (more complexity, more cost).

This is of course only words and gut feelings at the moment. We'll likely share the simulation results once we get them out. If anyone wishes to haste this, there's a funding round coming up in Jun/Aug via Venture Bonsai:

You should be able to join, regardless of your home country. Ask me for more (and sorry Dan for the commercial plug here).

Dan said...

Dan The Blogger responds...
45 mph? How do you brake? Clamp the tracks somehow?

Anonymous said...

45 km/h (28 mph). Should have typed that "kph", right? :)

Braking is simply negative acceleration. The same engine should be able to do it. As to emergency break, we might have clamps.

Personally, I think the brick wall / emergency break issue has traditionally received too much attention in the PRT world. It's a feature that shouldn't really be needed, ever. It must be there, like emergency fall preventors in elevators or evacuation rocket in human rocket launches. Only, it shouldn't dictate designs.

I don't want to go too much into details, yet. I think it's best to get real hardware under one's feet and then answer the questions (or just take the ride). ;)

Dan said...

OK. That makes a huge difference. As a guy who has designed, built, and then used a lot of machinery until it broke, wore out, or didn't, my best guess is that the "pulley wheel" design starts to get impractical a bit over your proposed speed. Also there are some new polymers on the market that out-perform the old urethane wheel materials. Either way though, soft wheels mean quietness,(Pipe is notorious for noise) and better traction,(spread out contact area) but will wear quickly with the pulley wheel design (angular slippage)and small diameter (less total wear area)

With the harder plastic wheels there is more noise, (less cushion) particularly at track expansion joints, with much reduced contact area, (less traction) and wear that tends to hollow a groove on that contact area.

Luckly, at 28 mph you should be fine, although you might find that the multiple wheel arrangement that I show in the last picture might prove better even at those speeds. Not that you need my advice, but, after all, this is sort of an engineering oriented site! We like wheel material/design issues!

Anonymous said...

Thanks, Dan for the solid advice. :)

There are indeed some new materials that can come to help, but obviously the auxiliary rail mechanism is one that either makes or breaks the whole concept. All people I've discussed it with do however think it can be done.

Juho said...

Cheap and light tracks are important to make PRT systems fly, and to make them feasible not only in some best hot spots but for general use everywhere. There are many possible approaches. My first scenario was a railroad track style (or any inverted T shape) suspended system. That is not a half-track approach but simple anyway.

Simple tracks may add some complexity to the bogies, so one has to find the best balance between the track and bogie cost (and size and reliability etc). A T shape track (and other types too) can be protected from weather (and electric shocks and birds) using an additional cover. The cheapest tracks (e.g. private tracks) may be built without such cover.

In general it is good if the basic standard allows many kind of implementations, maybe for light and heavy weight vehicles, for high and low speed, weather proof, indoors, with and without electricity etc.

Dan said...

Dan The Blogger’s got a lot on his plate…

Hi guys, I just stopped in to say I’ve been helping my elderly relatives with a surgery and recovery, while dealing with the reconstruction from a burst water pipe in their home. As if that wasn’t enough, I’ve got a whole new bogie/switching scheme that has come out of these discussions, (but it’s not ready to show yet) and to crowd my brain yet further, I am developing a new home wind generator, designed around the concept of stackable units that spin around a stretched cable. Power-producing spinning beads!

Juho, as for that inverted “T” design… As I am sure you know, there are trolleys made to fit on the inverted T-shaped bottom of I beams, usually equipped with a chain hoist, to serve as an overhead crane. What I do not understand, however, is how you propose to allow switching on such an arrangement. Presumably the matched horizontal surfaces of the inverted T are your running surfaces; I do not see any way to make that track profile alone hold a vehicle captive during switching, unless you want to have the track itself pivot to accomplish this. If you modify the T to have wheel captivating surfaces on either side, so that the vehicle may choose to hold onto one side or the other during switching, then you indeed have created a situation where you are traveling on a “half-track” during that transition. Or am I missing something?

Jenny Brien said...

Comparing the santa's Village track to the BM One renderings, it's clear that the latter is a great deal less visually intrusive. If it were my street or park I much rather a track at 3.5 metres with top-riding pods over a 7 metre high track with gondolas.

Dan said...

Hi Jenny, thanks for commenting… I am not sure I agree with you, but you are not the first person to say that. In fact PRT guru J.E. Anderson is on your side, and he supposedly did a study where the majority agreed with your assessment. I do not know the details of the study, however. Specifically I do not know if it only considered runs of track or if it looked at the system as a whole, including stations. Stations bring up the matter of ramps. One advantage to the hanging design, if it is articulated, is that vehicles can come down to ground level without needing long ramps, which represent additional visual clutter, (not to mention getting in the way.) Such ramps invite climbers and if there are electrical lines involved, there are those additional safety issues. The BM One design pays for its sleek track by forgoing line power and shielded communications in favor of batteries and wireless. Nothing is free.

It is also more difficult to make very long spans for track that supports vehicles from the bottom, because any cables tend to be in the way. And of course longer spans mean less support posts to look at. Of course these factors may be surmountable with the right designs. One additional challenge is in the fact that systems that rely on gravity to stay on the track tend to have that track exposed to snow and ice. Slopes may require some additional anti-skid hardware which, although probably minor from a visual standpoint, is still part of the system. Suspended designs are generally more shielded from the weather.

I would also note that the Santa’s Village system was pretty ugly from the start. The vehicles were supposed to be bees and originally had wings.

It may be that with all things considered the bottom supported designs would still be favored visually, perhaps by a majority; I really don’t know. But there is a bit more to that debate than can be addressed with these pictures alone.

Anonymous said...
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Miko said...

Hi! I'm just going to join this conversation a few years after it started. My concern with the half-track solution is that MISTER/Metrino claims to have it patented. akauppi, are you concerned about intellectual property issues?