Friday, May 6, 2011
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.