Saturday, November 24, 2012

148> Off-the-Shelf PRT




I was thinking, the other day, about this blog and how badly it needs a facelift, and I had a realization.  The original purpose of the site has essentially been realized.  No, I did not succeed in getting a cadre of engineers to anoint and consecrate a set of standardized dimensions under the alter of “open source.”  Nonetheless these last few posts represent what is pretty much the closing of a chapter, design-wise.  After a rather exhaustive assessment of a variety of issues, it can be said, in most instances, that there is a clear, best way to accomplish a system with the kind of capabilities I have been advocating.  I had originally hoped to create some standards for PRT, so that the business would not require a single company to be the expert in vehicle making, station building, track building, route planning , system maintenance, traffic management software, etc., etc.  What we have, actually, is a pretty good start in that direction, at least for this one type of PRT.  In my last post I outlined a bunch of “pearls of wisdom” that, if followed, outline how the capabilities of a suspended PRT system may be greatly extended.
These principles guide track design and therefore bogie design.  Since there is nobody else really trying to push the performance envelope for suspended systems, I guess I’m sort of creating the basis for such standards as I go.  What I am advocating is an open standards approach to what I call a “SMART” network. (Suspended Multi-axis Automated Rail Transport) My vision is to create the cheapest, fastest, least intrusive, most versatile, method for “air-lifting” a load from any point A to any point B without actually flying.   

At some time in the near future, this site will no longer be about getting recruits to design a better PRT system, but rather about refining and promoting those design decisions that resulted from the work already posted.  It took a very long time to do, and there are still plenty of details to nail down, but longtime readers of this site have seen the other parts of this system and know that the current work on the bogie is akin to shaping a keystone – the final piece that must fit in an arrangement of pieces that have been fashioned just for it.  Once the essential geometry is set, and the capabilities and limitations are known, it’s detail time… time to design a prototype in earnest.  Once again, my apologies to anyone who has just found this site.  I’m sure this bogie (which doesn’t even show hardware for hanging a vehicle) must be mystifying.  I will soon put the pieces together into a unified system. I promise! 




Not that there isn’t a LOT more work to be done here, on this model.  Each piece needs to be examined for redundancies, interferences, extra weight and manufacturability.  This will take days or weeks, not hours.  Still, I think the general design demonstrates that, with the right geometry, extraordinary capabilities can be achieved with a modicum of inexpensive parts.  I have had to sacrifice almost nothing in terms of speed, turning radius or climbing, which are over 100 mph, under six feet, and any angle up to 90 degrees, (straight up) respectively.

One thing that is lacking in many PRT and dual mode proposals is a practical way forward.  Often concepts are presented that are so early in the research and development stage that only a physicist can tell if they are even feasible, let alone lucrative.  Although parts of any complex machine become more specialized over time, presenting it with too many of these one-of-a-kind components too early tends to condemn an otherwise good concept to a life on the drawing board.  Since business realities demand that commercial incentive surpasses developmental risk, a budget oriented “proof of concept” design is an invaluable first step. 

 



With this in mind, this bogie design (which is a more evolved embodiment of the ideas expressed in the last post) uses “off-the-shelf” components where possible.  The motors for this model are dimensioned from the 7000 watt hub motors from Kelly Controls.  Using four adds up to a bit over 39 hp.  The upper steering guide wheels are hub motor driven scooter wheels and tires. (13”hubs, from the same source, with Pirelli Diablo tires)  The steering guide wheel is designed for continuous contact and the hub motor can be sized up to 6kw, for an additional 8hp.  Although this would compare favorably with other systems out there, it would still be a bit underpowered for commuting.  Luckily, the main drive wheels are standard low profile automobile hubs and tires (215/35-18) and so the motors can be readily swapped with higher power ones, even up to the monster (80hp per wheel) Protean motors, which would enable performance that would put most sports cars to shame.  For climbing standard sprockets are used, drilled for lug nut extensions.  The design features truck style emergency air brakes that clamp the track.  There are dual (self-diagnostic enabled) steering guide servos that work together but can work singly as long as there is power from either the track or the onboard battery.

In this design the steering guide wheels are not on rocker arms, like in the earlier design.  Although the rocker design does seem to offer smoother engagement, this supposed advantage assumes a continuous rail to engage upon.  If the steering guide wheels are positioned first, with the contact rails being tapered to make contact after that, this is smoother still.

About the upper steering guide wheels: First, the matter of wear.  After all, they are soft rubber, relatively small, constantly engaged, and contacting at an angle.  I would first note that tires for scooters and other two wheeled vehicles have heavy sidewalls so that riders can lean into turns, which is an extreme torture test compared to pushing into the smooth steel of the “diamond” guides.  With the new (counter-rotating) lower guide wheel geometry and wider drive wheels the forces exerted on the upper wheels is minimal.  Also, engagement between the wheel and guides need not be continuous, or at least not under significant pressure.  I envision the contact being primarily on the crown of the tire most of time but, unlike scooter use, there is no driver, second rider, or vehicle weight on them.  A good finished design will enable the whole wheel to be swapped so that the tires can be changed on a bench instead of on the vehicle. Lastly, the tires are relatively cheap and specialized wheels will eventually evolve.  These should be good for well over ten thousand miles as they are.   All tires should probably have ribbed or foam reinforcement inserts, giving them the ability to run properly even if deflated.  After all, tires are hollow primarily as a cushion against uneven road surfaces, which, of course, does not apply here.

About the emergency brakes – This aspect has had the least amount of thought at this point, but I wanted to explore where the hardware would fit, so I put a crude system in place.  The idea is that the lower brake shoes engage first, pulling the bogie into the track and compressing the tires a bit before the upper shoes make contact.  We don’t want to have the brakes make the tires lose traction. The brakes are spring activated, and disengaged by compressed air.  Another concern is clamping only on one or the other side of the track on switches.  As it stands, such a one-sided drag might tend to pull the bogie off course.  I am still mulling that one over.  The geometry enables some kind of bumper activated system and/or a passenger activated one well.

I know it is very difficult to understand a system from a few pictures, but there is only so much that is worthwhile to show at this point.  An exploded view would be helpful, but most of the parts will still be evolving for a while yet.  Another issue to consider is that the ordinary way such parts are made on an industrial scale is by punching and stamping.  These processes are used to cut out a shape from metal sheet and form it into a 3D shape, which stiffens it in the prescribed manner.  This requires huge machines and matching heavy steel male and female surfaces to squeeze the plate between, often at high temperatures.  Such a process is impractical for small scale production, so we are left with making everything out of plate and profiled stock, such as tubing or angle steel.  This compromises proportions and weight tremendously, and is one reason why I think that such manufacturing should be separate from the PRT business per se.  In any case, any designs herein will be constrained by processes that can be done on a small scale, often by hand, but hopefully with shapes also suitable for mass production.  I can say from experience that, at a certain point, it is better to simply start making the thing, because the prints inevitably prove themselves short-sighted, and every change creates a ripple effect.

Well, that’s it for now, but for this closing thought.  On Thanksgiving morning, on I-10, (the principle southern road across the US) there was a massive pile-up due to fog.  Over a hundred cars and trucks were involved, scores were injured and two died.  The highway was closed for nine hours.  This is a system that seems unworthy of the times, if you ask me.  We live in a world awash in cheap sensors and amazing computing power. Yet all of that heavy machinery was being controlled by people blinded by fog and in too much of a hurry to slow down.  This is a systemic problem that needs a systemic solution. We need an app for that!
 

9 comments:

akauppi said...

Great write, Dan!

Congratulations on reaching a certain step in the project! We need that - ability to show that progress has been done, and in ways where we don't need to re-question the earlier findings too much. Step, step, step ....

On the "one-sided emergency braking" issue, just consider not doing emergency brake on switches.

On part manufacturing/design, I think you know 3d printing? I had my first parts (spare parts for a lamp) done recently, but the technology is getting ready to serve also your needs. It allows designs that would not be manufacturable in conventional ways. Metals are available as material. MakerBot 2 Replicator is the current state-of-the-low-end I think, check it out here: https://store.makerbot.com/replicator2.html

And thanks for the great ending on a sad story. You are right. Our cars need better sensors, and our transport planners need better alternatives.

I discussed with a guy who'd been managing roads in Papua New Guinea recently (I didn't even know they had roads there!). What dawned to me is that with PRT one can make "roads" all through a jungle, in seeming harmony with the wild life (less maintenance, too).

- Asko

Anonymous said...

Congratulations! May I recommend that you move/copy this work to Facebook page, to get more public traction.

Dan said...

Dan The Blogger regrets the passing of the “Recent Comments” feature. That was a 3rd party add-on, was always buggy, but now doesn’t work at all. Maybe they’ll get it fixed – who knows! Now on to the comments posted by alert readers akauppi and anonymous…

Akauppi, I am still waiting for a good, clean-evaporating/burning wax for such a device, so that the results can be cast in metal by the “lost wax” method. They make little 3D wax printers for jewelry - maybe the same wax would work. I have friends who run CNC mills, and actually those machines change tools and remove material so fast it’s almost the same thing if the shape can be cut from a block. I must say, though, that the Makerbot would be killer for making a scale model of a PRT vehicle.

Your BubbleMotion design strikes me as singularly well suited for the eco-tour business. Track-support base-plates could probably be designed to employ anchors that corkscrew right into the forest floor, and everything could be brought in by helicopter. Yeah, I think you need to immediately get a project going in the cloud forests of Costa Rica. And you’ll need a guy on site, right? Habla Espanol!

Oh yeah - the braking. Actually the bogie is always locked to one side or the other, so it really doesn’t matter if the brakes pull unevenly. The bogie can’t derail. I don’t know what I was worried about.

Sorry, Anonymous. I don’t have a Facebook page and likely won’t get one anytime soon. Nor do I tweet.
I guess I just don’t want to have anything else to keep up with. The problem is that besides having a lot more going on in my life than when I started the blog, I am spending a whole lot more time designing. These renderings that I post are the result of some serious hours for what is supposed to be a “hobby.” Luckily I enjoy it!

Juho Laatu said...

There are many possible tracks towards open standards. So far the work has been mainly your personal work with some comments from others. Another approach would be to have an open organization with open participation of individuals (I note that you already said that finding those people is not easy). Third alternative could be based on a joint effort of some key companies. And a fourth one, a project with open participation by all interested companies.

(Since the name of your blog already assumes open standards I skip all closed, semi-closed and one company based standardization approaches.)

My point is that if you want the standards to be implemented one day, it would be good to get all the relevant companies involved as early as possible. And assuming that you want all (this type of) PRT systems to be based on one standard, it is even more important to get the companies involved early (to find an agreement before the commercial competition starts, and to allow the participants to take a lead on the market).

Currently there is no widespread interest among the companies. But it is possible to gradually raise their level of interest and invite them to participate or at least follow the work. Open standardization with companies with various interests would likely lead to some problems, compromises etc. but that may be needed anyway to reach the targets of open and leading standards.

Juho Laatu said...

Building a prototype would surely make the system more credible. In addition to a full scale prototype I'd be interested also on a miniature model. That could demonstrate that the system works as a whole.

I don't know if you lean in the direction that the vehicles would operate independently, with no communication with the system and the other vehicles, or if you assume that the system would have a central role in controlling the routes and timing.

Especially in the latter case also those "soft" parts may need standards and demos to make the system credible.

Also software simulations would be interesting (and some have already been done).

Dan said...

Juho, I am going to be writing a post on standards shortly, so I will confine this to a couple of points that seem most relevant. When it comes to standards and companies, the first motivation on their part is to lock out the competition. What would really defeat our purpose is if they file patents to help them do it. Still worse, they might do just that and then sit on it. I think those kinds of standards (as in ISO standards) are premature anyway. This is different from trying to establish standard ways of doing things – best practice solutions. These would be the logical (and even-handed) starting point for more formal standards anyway.

As for building a prototype, I’ve got a problem. I’ve given up my shop and don’t expect to have a new one of any consequence until I fully move to the New England. So far, only duplicate hand tools have made the journey from Texas. Other than that I’d be just the guy to do it.

I have written quite a bit on control in the earlier posts. You might check out posts 20,75,76, 77, 98,105.
Bottom line - I like the “unbreakable” nature of autonomous control, but certain aspects, like traffic management need addressing more globally. Merging certainly should not be done autonomously, but to the degree it is centralized, the system becomes more fragile and inflexible. Autonomous vehicle control software, like Google’s, is really a game changer, imho, as is the proliferation of “cloud” based technologies. Remote sensors with Ethernet – based machine control is an emerging industrial technology that is getting to be “off-the-shelf” these days. The technologies are evolving so fast it’s pretty hard not to put if off!

Juho Laatu said...

> When it comes to standards and companies, the first motivation on their part is to lock out the competition. What would really defeat our purpose is if they file patents to help them do it.

Yes, but I guess you want to get them involved one day, and therefore one can not avoid getting also their needs involved in the process one day. If they are outside the project, they may work against the project.

I support the idea of avoiding patents in the the PRT standards. In PRT this is important also for practical reasons since the business case for widespread PRT is not easy even without the patent problems. I think your project has been excellent since it has listed so many ideas, that are as a result now outside the patentable zone.

It is also possible to have standards bodies with rules that aim at making the standard free of patents, and that limit the use of existing patents. The rules may force all participants to offer their possible patents to others on some agreed terms. Often it is better to get companies (with interest in patents) inside the standards body rather than leave them outside (and invite them to kill the project with their patents because they see this project as competition to their own approach).

It is not possible to avoid all patents (e.g. implementation details just outside the specs). But one can plan the IPR environment and make the best of it. In this case the target would be to find a consensus on one set of specs and a patent free(ish) policy. Companies must understand that the target of the project is to create an ecosystem where high number of participants helps in building a credible PRT system, and thereby brings hopefully lots of business to all. This means that there will be also competition, but that competition and patent fights should not take place inside the core standards that must be open and free to all (or at least to all members, or to all companies that treat your company the same way). One can also agree on reasonable and non-discriminatory licensing (maybe covering areas outside the core specs).

My message is only that planning and timing must be right also on the IPR questions. If you expect the PRT system to become viable business some day, better start standardization and tie the companies together well before that date, and start developing and finding consensus on the specs (among all interested parties) so that they are ready when they are needed.

So far all the PRT systems have been based on one company and proprietary specifications. Open and uniform standards would be the next step. Companies should be interested if they believe in the planned scenario.

Dan said...

Since essentially every dimension I show is for a reason, it is all obvious and not patentable after the fact, like you said. If someone can show advantages stemming from different, proprietary methodologies, more power to them. I really have no vested interest, one way or the other, so long as the world eventually gets a really effective system up and running so it can prove its worth. Perhaps you see a downside that I am missing, but it seems to me that if they highjack the design and fail it would still be better than the design remaining unexplored in obscurity. At this point there are so many hurdles between what we have and an air-tight business model, I think we have plenty of time. Companies, after all, have a mandate to generally stay within their core competency. Until we figure an angle that is a win-win for them, there’s not a lot of point in knocking on doors. Eventually, though, actual interfaces between trades and physical subassemblies need to be established to clarify everyone’s job. That’s a point where I could certainly see some sort of open source style licensing agreement to help to ensure quality, forward compatibility, etc. I guess what I am saying is that I am wary of going to companies prematurely, just to throw out ideas to see what sticks. Odds are nothing, and you decrease the chance of future cooperation.

Juho Laatu said...

Yes, I agree that there is no point in knocking the doors of the companies prematurely. But if and when we can see a good common an open standard based path, then that approach should be proposed to the companies. The probability of different companies taking their different paths and blocking each others out e.g. by using IPR is quite high. Open standards can make PRT more successful earlier than multiple competing closed approaches can. That's why it would help to make the right moves at the right time (when the concept is mature and there is a sensible path, but no fierce competition yet) and invite companies to a path that would benefit all of them. I mean that standards do not emerge naturally by themselves but they need to be planned and driven.