Friday, June 26, 2009

39> Progress on the Track

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.


qjmic said...

Dear Sir,

I had a look at your blog last week, I use to search for solution in my own little corner, and what a pleasant surprise to find that other people work on the same concept, with similar ideas.

I've studying town bus transportation of my little 120k people city of Besançon / France (So excuse my poor English..), I collect data's from bus system web site (number of lanes, capacity...) and also I use to take buses or follow it wit my car.

My conclusions are :
Motorized 10T box with 35-50 people capacity under half fill, and sometimes only one or two people on board at the end or start of the lane (except lane witch end at the market center !), when one people want to stop, every other people of the bus stop.

Cabs don't need to be motorized when stop.
Possibility to hire cab for half day (shopping) ans call back when needed (as VIP with car and driver), no time to reach a car place in center of town.
"0" gaz emission (authorities put on place bikes... 200 rainy days by year, old people...).

There are 2 kind of people
People who have ideas and no money or no power.
People who earn money with actual configuration are afraid with new concepts even if this is our future.

About your switching track system :
In case of arriving by on of the two tracks with vertical axis roll in bad position and mechanism malfunction, it can be dangerous, the switching must be "forced" by the track when cab arrives from one of the two Y branch with bad configuration or malfunction as shown on patented drawing.
Good exercises to invent, but, all was already invented, and take care at mechanical function, reliability and industrialization costs.

I saw on the net an other system (in use) using twin inverted U track ton keep the cab under the track during switching track crossing, also with lateral switching provided by the cab itself, it was a pendular train, not personal system.
I see that you know Vectus PRT,,the more industrialized and advanced project.
The main lack of this project is the need of heavy structure to board (more heavy if track is 3 meters above the street).
You link also to beamway witch dream about a global system (town and countryside), if you consider a global trip between A point to B point, you often need to take one bus or taxi, one train, and another bus, even if our train (TGV) is fast(320km/h commercial use), taken in account time transfer, boarding, unsynchronized schedules, the average speed downed to under 200km/h.

I like to drive my car, but every day the same travel to go to work...
I always get job at an average of 40 kms from my home, with suburbs area, with travel time from 20mn to one hour.
With a PRT system, you can take time to look at the landscape or read a book or work (with my laptop), if travel time could be taken in account as work time, it can enable daywork reducing and enable time saving with family !

Sorry, unsorted comments.
About me : / My blog (in French) just the beginning !


Bengt Gustafsson said...

Beamways system is not designed for high speed operation. It may get a bit above 50 km/h which is its design goal, but would never be able to get above 90 km/h or thereabouts due for instance to wheel rpm restrictions.

I don't see how gjmic could get this impression from the website...

Dan said...

Dan the Blogger Responds-

Qjmic, I’m glad you enjoy the site.

About buses. The same is true in my little town of 6 million. It drives me crazy when huge mostly empty buses block the street to let a person off, especially streets without a turning lane. With one car waiting to turn and the other lane being taken by the bus, the road becomes useless.

About 2 kinds of people – I don’t really blame anybody. People are afraid to start things that might fail and make them look foolish. They fear for their jobs. The real problem is that there is no foolproof way for them to make money, win or loose, on PRT. (At least in the U.S.) People make money on buses, light rail, street expansion, etc. even if those things don’t solve the problem. It is their job to keep adding more, so that is what they do.

About switching. The illustration (June 7) was admittedly misleading. I was trying to show the role of the various wheels. In the “older posts” link, there is a post from Dec. 08, with a drawing showing an older version of the “in car” switching, which shows how the vehicle can never fall out of the track. I know that, in that picture, the support seems to float in thin air, but that is because it is a sectional view. Also, I have not fully detailed the safety features of my switching scheme for the sake of simplicity.

Bengt, I’d love to know how my track design compares with what you envision for Beamways. Almost by definition, track profile would be the starting point for a standard.

Also, to clarify a point for my readers, I am not really designing a system, high-speed or otherwise, at this point, although it must seem like I am. I am trying to identify the key structural elements that all systems (including high speed) must incorporate, in order to create a set of common standards and definitions and to identify key components and functions. Once that is done, these elements can be offered to the open-source community for refinement and incorporation into a defined system architecture. Private companies could then, at their discretion, use this architecture or parts of it, and use these standards and definitions to facilitate communication with subcontractors and customers alike.

akauppi said...

You haven't mentioned temperature expansion anywhere, but I guess it's not really a problem with your proposed two-layer track system (outer supporting and inner active). Actually, it's rather a benefit for such a design.

You can have the gaps between support rail structure and active rail structure in different locations, and the use of multiple wheels (as you have) will make the bypass supposedly unnoticeable.

Temperature expansion for steel needs a gap of some two inches every 100m (heh, messing you with mixing the units, am I?). That is rather much.

Dan said...

Yeah, Akauppi, I don't think it's an issue. Notice that the track is hollow under the drive wheels so that the active surface can be finger jointed while the interior is doweled or otherwise pinned into alignment. As for the sides, I can imagine various alignment means, and, you're right, a benefit is that it's an alignment/expansion problem only since track segments are independently supported within the outer truss.