Sunday, October 30, 2011
As many of you know, I have been advocating the standardization of key PRT technologies in order to allow PRT to be developed, produced and deployed by a consortium, rather than a single company. This, in turn, requires that this development be started on a basis of the most promising design approaches. I have concentrated my efforts on a suspended system, rather than the bottom supported approach, even though I suspect that the majority of readers prefer the latter. One key to why I think suspended systems represent the best way forward is referred to in my latest iteration of the acronym “SMART,” which is what I call this effort. (“Standardized Multi-axis Automated Rail Transport”)
As I have pointed out numerous times before, all “ground” transportation suffers from the same problem: Vehicles or people going in different directions will run into each other unless they stop and wait their turn. Going over or under solves this problem, but that solution is too expensive to deploy universally with current modes of transportation. That indispensable artery of modern commerce, the freeway, clearly shows how effective high-speed non-stop transportation can be. This is simply the result of what happens when a transportation system is modified to be multi-axis instead of existing on one plane - the ground. Unfortunately making multi-level (multi-axis) routing for large vehicles such as trucks and trains takes huge amounts of money and space. When it comes to multi-axis transport, smaller is better. Luckily, we mortals are pretty small.
A multi-axis automated rail transportation system is essentially a new infrastructure designed to do what the freeway can’t. Go to any street, to any bus stop, to any building. It would be designed to be faster and safer than driving, more energy efficient than the most advanced electric car, and expandable for a fraction of the cost of roads. Being natively multi-axis, a suspended system can be employed in areas where long ramps are undesirable (that’s basically everywhere) and the system can be elevated higher than would be practical for supported systems. This can minimize visual impact. While it is true that a supported vehicle can be made to self-bank and keep its cabin level on slopes, it is much more cumbersome to engineer. Vehicles with wheels on the bottom are just ill-suited for extremely steep travel, while hanging vehicles have no such problem. Traditional PRT designs require raised, elevator equipped stations because otherwise the entrance and exit ramps into the station would block driveways, be subject to climbing, and be visually intrusive. A native 3D system has no such restrictions. A suspended vehicle can either taxi in like an airplane or come down like a helicopter. This means that stations can be put nearly anywhere, and they can be very minimal and inexpensive. They do not require high traffic volume to pay for themselves, so they may be placed with high frequency, like bus stops rather than actual stations. This will increase ridership. The question is this: If we are going to build a whole new infrastructure, do we want it to be raised, single-level, multilevel with ramps, or natively multi-axis? A consideration of the various routing situations likely to be encountered in a widely deployed system leads me to believe that it would be better to have true multi-axis capabilities from the start. Anyway, here is the latest iteration of the SMART PRT vehicle concept. Hmm… How about “SMARTPOD?”….Sorta has a ring to it…
Unlike previous versions, the steering guide wheels have been moved outside and under the track. This shaves off about five inches from the track height, bringing it down to about 30 inches/76 cm. (less if it the track is hung from a ceiling.) What is shown here is a high-speed vehicle, (highway speeds and higher) designed for many tens of thousands of miles between tire changes. (hence the large wheels)
The wheel flanges are designed to outlast the tires in two ways. They turn independently of the wheels, so if they contact the track at a different diameter than the tires there will be no conflict. Secondly, they are only deployed during actual turns. Otherwise the bogey is centered by leaving both left and right steering guide wheels in the upright position. The upper “hold-down” wheels replace the upper steering guide wheels of previous designs, prohibiting any rotation of the bogey within the track. This design is extremely maneuverable with a turning radius of a mere 8 ft., including vertical turns. (The spacing between various track surfaces must vary, however.) The pictured design is missing most of the components of the bogie at this stage of development. The sprockets pictured are for vertical climbing, although I plan to adjust the sprocket size somewhat.
The track has been designed to be extremely easy to fabricate into sections that are straight or curved. There would be no problem finding shops willing to bid this work, even in small towns if the pipe bending is outsourced. Removal of a left or right truss section will not mean that vehicles cannot pass, although there is a small temporary rail that needs to be placed as insurance against any freak events that would make the whole vehicle sway with great force. I am still working the best way to attach sheathing, although the reader will note that there is a slight arc to the outer edges of the truss. This is to make light-weight metal or plastic sheathing more rigid.
Alert readers will notice an air scoop. At this point I am leaning toward liquid cooled motors. This greatly increases the performance-to-weight characteristics of the motors, and hub motors are ideally suited for this, as the copper coils that need cooling are stationary and accessible radially from where the wheel attaches to the frame. A simple little electric pump that is remote from the motor itself is all that is needed. No moving parts are added to the motor. The scoop is for a radiator/heat exchanger.
Finally, I want to emphasize that this vehicle has capabilities that go well beyond what is likely to be deployed early on. Nonetheless, I am designing with the future in mind so aspects that are practical today but foreclose later improvement can be avoided. Water cooling, high speeds and vertical climbing are features that might be expensive complications to first deployments. However I see little point in building an infrastructure project whose inherent design limitations will become apparent as soon as it is deemed a success. This is, in part, why I favor a full multi-axis approach. Future cities are only going to get more crowded and time is only going to get more precious.