Sunday, December 27, 2009

65> The Efficiency of Absence and Angled Wheels

Before everyone’s eyes glaze over from too much shoptalk, I would like to ask for nominations for the best videos to explain PRT to a complete newbie. It is time for me to update my “About This Blog” sidebar, and I want people who stumble on this site to go away believers without me having to waste a lot of space trying to explain it.

Speaking of the sidebar, I see my “Recent Comments” list is still blank - at least on my computer. If anyone is getting the list, or knows how to fix this widget, let me know. It would really help keep threads alive.

As most of you know, I am trying to finalize the design of the most cost effective, versatile PRT track design for suspended systems. Unfortunately, this entails exploring every conceivable use, limitation and bogie design. Higher speed. Tighter turns. Steeper slopes. Industrial. Freight. Heavier loads. Cheaper Stations. Manufacturability. Longer Spans… “Pod” designs may evolve, but the track stays, so we need to get this right. I have taken the approach that the running and guidance surface dimensions are a somewhat separate issue from the structural truss, and that these surfaces can basically be surrounded by a support structure. Inside, for example, most structure is no longer needed, because the running surfaces can be supported (hung) at frequent intervals. Anyway, it mostly comes down to the bogie design.

I have, lately, been working on a problem inherent to rail based PRT designs - the shear number of wheels required per bogie. Here I show an older bogie design with 18 wheels.


True, half of them need to fully disengage to switch tracks, but still 9 per side seems like a lot. In post 54 I show a much simpler configuration, with railroad style flanged wheels and little guide wheels that fit between the two halves, but this design is unworkable for high speeds. Post 56 shows a high speed-bogie, but with no steering wheels, so do not be confused. As you can see from the picture below, PRT’s acrobatic unpowered cousin, the roller coaster, requires many wheels as well, and would require still more if designed to switch tracks via steering guide wheels. 

In railroads, they cut the number of wheels from 16 to eight by adding a flange to each wheel. The problem is that the flange creates friction with the track which would tend to overheat and wear it out at high speeds, smaller wheel diameters, or if it were made of some material other than conductive, strong (but loud) steel. To minimize wear, the designer must keep the wheels perpendicular to the rail surface, hence the 24 wheels per roller coaster car.


Some years ago, while arguing over a design detail of a piece of factory equipment I was designing with a machinist friend, I came up with this axiom. “There is nothing more efficient than absence!” I have returned to that thought many times since. So how can I get some of these darn wheels to be absent? Without flanging the wheels or track?  While steering guide wheels can be disengaged for straight runs, guide wheels for centering the bogie cannot. One thought is to wedge the bogie in the track with angled wheels. Here is what I drew to help me think.




Could this line of thinking mean I need to take my track design completely back to the square one, after all of these months of exploration? The verdict is still out, and I have some more mature designs to share at a later date, which require some fairly lengthy explanation. But it is Sunday, and I’m in the middle of remodeling my bathroom, so I will bid you all a Happy New Year.  




8 comments:

cmfseattle said...

3 PRT systems in 3 minutes

Austrans - Wheels and Rail

Self-steering railway bogie
United States Patent 5730064

Anonymous said...

"While common belief dictates that the wheels are kept on the tracks by the flanges, the flanges in reality make few contacts with the track, and when they do, most of the contact is sliding."
http://en.wikipedia.org/wiki/Rail_adhesion#Directional_stability_and_hunting_instability


A steering mechanism might be useful to eliminate some wheels.

Dennis said...

Trying to figure out what to do with all the wheels must give you occasional thoughts of using maglev for zero wheels.

Dan said...

Dan the Blogger is back-
Cmfseattle, great work. I don’t know how you find this stuff. That patent will be worth studying from what I have gathered so far. The video though, starts a lot better than it finishes, with skips, uneven sound and ugly test track footage. I love most of “Bubbles and Beams”, but I find the elevator and that vehicle being up to the challenge of cross-country road travel a bit much. (and it doesn’t show any controls or give explanations) I have considered doing my own “mash-up.” I guess I’d need screen capture and video editing software and a bunch of free time. Perhaps I will just take the best videos and just post them all together, maybe with descriptions. Of course I could also link to sites like “Get on Board” on the side board as well.

Of course while I’m at it I ought to index all of the links you (and a few others) have posted. I can’t tell you how many times I’ve lost one that I wanted to recheck…Alas, so much to do – so little time.

Anonymous, That’s an interesting link that I hadn’t seen. I had read that there was a radius leading up to the flange, and that it didn’t contact much. Under “rail profile” they show a worn piece that looks pretty bad though… I also read somewhere, a while back, that high speed is notoriously tough on the flange and rail, and I do not want to be tied to steel wheels for sound and vibration reasons but that’s a whole different subject. A soon to be posted design has a radiused flange that is really just for extraordinary forces. The tilted wheels further protect it (the flange) from wear, but that’s for a future post. I have to pace myself.

Dennis, the answer is yes. I am particularly intrigued by Unimodal’s Inductrack, which, amazingly, uses no power, save the motion of the bogie itself. It seems, though, that this inevitably leads back to track based linear motors to get that motion without a “third rail” power strip. That is way too expensive to use as the foundation of a geographically extensive network. I wish I had a better feel for how much horizontal square footage is optimal for how much weight with maglev – I would seriously consider bumping the track dimensions for a possible future retrofit, although I think I’m generally OK in that respect. In the meantime, though, it appears that the “easy sell” is track that could double as a bike or golf cart track “if this PRT thing doesn’t work out.” Heck, nobody can even sell a third rail system, let alone something with miles of embedded electromagnets.

The whole concept of a new network on top of our old road network is a real leap of faith in the first place. Once at least one city has, say, 500 PRT vehicles, the new (corporate) name of the game will be smoother, faster, quieter, and the politicians will line up to bring home PRT pork. Maglev will have its day… In the meantime we still have a (ug!) 25 mph (40k/h) speed record to break and we have to pray that Ultra doesn’t have problems with snow and ice. It looks like a long road ahead. – Oh yeah, and I really haven’t seen much on maglev track switching…

akauppi said...

I'm equally interested to see, if there are any nice PRT videos out there. Personally, I may be picky but I know of none.

Vectus has money-made presentation videos, but they are soooo sterile. :) And then there are the amateur-made videos that speak out 1980's PC loud.

With today's technology, we should be able to do better, and most importantly, the expectation level of Internet general public expects it.

The best video would be of actual PRT in service. :D

Dan said...

We could really use a good documentary-style promotional film. One problem with existing clips is that each company touts the advantages of PRT as their own. That reduces those substantial advantages to just another ad. We, as a society, are either skeptical of, (or tune out completely) anything that sounds like a sales pitch.

A second problem is that issues like land use, the environment, productivity, equality for non-drivers, dependence on foreign oil, (to name a few) do not lend themselves to happy little sound bites. The films are too short to fully frame either problem or solution.

You are absolutely right that, in this era, the bar has been raised, especially for animations. The guys with working systems have the advantage. They can just shoot footage. Maybe we need to pass a collection plate or get some college students to do it or something. No, we need “Industrial light and Magic” or “Dreamworks.” Where IS Hollywood in all of this? You would think PRT would be able to garner at least one high profile champion…

cmfseattle said...

high-profile PRT champions?

Richard Garriott

Larry Page

mountain view + google + NASA + SkyTran = High-$peed Rail

maybe.

Dan said...

Dan the blogger strokes his beard reflectively-
This I did not know....