Here is what my track design has evolved into. Note that the bottom (shown on previous designs) has been removed. I think that it is important to simplify the problem by separating the track into its two functions. The first function is to provide the surfaces upon which the PRT vehicle may roll and steer. The second function is to span the distance between supports. Separating the two makes sense, because the supporting, spanning role is site and weight dependent. Inside of a building, for example, a very minimal track could be hung from the building structure itself at short intervals, and headroom might be at a premium over ability to span.
In this illustration a minimal track design is shown in black, and the “wrap around” area in blue is where a supporting truss, soundproofing and outer skin can be. In the latest iteration, both the drive wheel contact area support and the top middle beam (where the steering guide wheels contact) are designed to have some variability in size, at least for the time being, as weight requirements and preferable fabrication techniques will play a role in this decision. It may be most practical, for example, to have these as separately fabricated modular parts, as they all would include rubber mounted running surfaces and some machining.
Optimum internal dimensions are 30” x 20” range, (75-77cm x 50-52cm) with drive wheels of under 21” x 7.5” wide. ( 53cm dia. by 19cm) The track dimensions allow guide wheel sizes of about 7” x 2.5” (178 mm x 64mm)
Advantages of this track include being able to handle multiple weight classes, (final specs should allow variable steel thickness) being able to accommodate vehicle speeds in excess of 60 mph (100 km/h) without requiring excessive guide wheel speeds (under 3000 rpm) being easy to fabricate, including turns and forks, with standard stock and flame cut steel (and minimal machining) ability to accommodate various propulsion means including wheel motors and LIMS, being able to accommodate slopes up to and including vertical, being able accommodate extremely tight turning radii, (with preferred drive train/motor configurations) being sized to allow use within buildings with typical ceiling heights, having a standard exterior profile which may be incorporated into a variety of truss or suspension structures.
Tradeoffs- The only tradeoff I have been required to make is size. If I were to limit speed and weight substantially, it could be made a bit smaller, but there are diminishing returns for the following reasons. Greater height allows more leverage against being twisted by inertial forces, longer wearing drive wheels, and it contributes to spanning stiffness, as well as allowing more flexibility in drive unit design. Greater width allows larger guide wheels, which then last longer because they have more, wear area and slower speeds, and equally contributes to stiffness and design flexibility.
I welcome your comments.