Thursday, July 30, 2009

44> Going, Going… Gone.

PML Flightlink has been purchased. “Who’s that?” You ask. Well, according to a yet-to-be-updated Wikipedia entry under “Wheel Motors”, it is “a UK based company that currently designs and builds the highest power density electric wheel motors in the world.”
The problem is that it appears that the new owners have discontinued the “E-Wheel” series of wheel motors, opting instead to offer custom engineered products only. That, by itself, is not such a big problem since a fleet of PRT vehicles with multiple motors/wheels each would represent a pretty big order, but now it’s pretty hard to design a system, since they took the spec sheet away. Luckily I happen to have a copy of the specs right here.

These motors were specifically made for small electric vehicles, with oversize tapered (automotive type) bearings and waterproof housings. They were designed to be run on batteries, and have regenerative braking. To those more familiar with “horsepower” it is the stated wattage divided by 746. Torque, in “foot-pounds” equals the stated Nm rating times 1.356.

These were extremely powerful motors for their size and weight. They came with standard bolt patterns so off-the-shelf wheels would fit. Anyway the present company is still in the business of wheel motors for full size vehicle conversions, since eliminating the motor, transmission, differential, etc. frees up a lot of space for batteries. They have built a 640 hp Mini Cooper, among other projects. Anyway, it was largely these amazing torque/weight numbers that made me so in love with wheel motor technology. I wish someone from the LIM (linear induction motor) camp would explain how their system could possibly compete with these kinds of numbers, since I know there are plenty of LIM believers out there.

Also speaking of LIMS, I don’t understand how they can, on one hand, describe their reaction plate being comprised of aluminum or copper over steel, and then say that steel alone will do. Why would they add it if it didn’t matter? And, assuming it does matter, how much does it matter? And I can’t help but wonder, are there actual designs out there which put the LIMS in the vehicle, or are the current designs calling for LIMS all along the track? And if they do put it in the vehicle, are they water-cooled or what?

Monday, July 20, 2009

43> Crash Tests, Anyone?

Here is a picture I drew to illustrate a point about PRT safety.
Apparently there is a doctrine which dictates how far apart vehicles must be spaced for safe stopping in case an accident. This is evidently the distant relative of some old train spacing rule. It is apparently also the basis for at least one “expert” to say that PRT can never be cost effective, because it can never have sufficient capacity on a given track to be cost effective in the city, nor fast enough to be viable in the suburbs. This argument is ridiculous on so many levels I won’t even dignify it with debate, except to spend a moment undercutting its premise, which is that PRT vehicles traveling at 45 mph, (72.5 k/h) need 3 seconds of headway to be safe. (Can you imagine auto traffic being required to maintain this kind of distance? And half of the drivers are dialing phones!) An interesting article on this subject can be found here.

Anyway, the first line of defense is, in my design at least, the eight wheels of ABS style braking power which is applied magnetically (generating electricity in the process) Linear motors are theoretically unsurpassable in this magnetic braking, as they need no wheel traction, although I believe either is system is more than adequate.

The second, emergency only, safety braking feature is a telescoping hydraulic bumper, which converts the telescoping motion into activation of brake pads which can directly grab the track itself. Such a system can be designed to make contact only possible inside the track – The cabs themselves can never collide. This would also work with rail-on-the-bottom, PRT international or Taxi 2000 style systems. In disk brakes, the “disk” is simply a circular fin that is squeezed by hydraulic brake “calipers.” In the hypothetical PRT emergency, there are plenty of fins to grab onto which are stationary parts of the track.

The third line of defense, which, admittedly, is only applicable to the system I endorse, and to a lesser extent is possible with other hanging systems like Beamways or Mister, is that shock to the passenger is absorbed by the “free-hanging” nature of the cab design. (Actually the cabs do not actually “free-hang” because of anti-sway hardware, but come pretty close)

The illustration shows how the stationary vehicle, struck from behind, has its motor unit jammed forward, yet the passenger compartment hasn’t caught up. This is cushion from whiplash for the occupants of the stationary first vehicle.

The striking vehicle, in so far as other braking methods have failed, as a last resort, lifts it’s own weight, absorbing that many lbs. (kilos) to dissipate the last of the energy stored in the vehicle’s momentum. The passengers, like children on swing set, are lifted and pressed into their seats until reaching a natural or, in a worst case, cushioned, apogee, and then swung back down. This is just one more unappreciated advantage of a hanging system.

Thursday, July 16, 2009

42> Design Time!

A few posts back I revealed what I consider to be the most logical track design. Notably absent was any description of the drive units that would inhabit this track, so here is what I’ve got. I know that the parts as shown are held together by flimsy, non-braced plates that extend into areas where they do no good, among other issues. It is, however, mostly a drawing to identify and re-route interferences. (Areas where multiple parts are expected to occupy the same space) It is also about as far as I have gotten in “SketchUp”, Google’s free 3D drafting software. It is not ready to post for you, the readers, to work with yet, because I didn’t break it into editable components. This exercise has, however, revealed how stunningly simple the mechanics are, with “wheel-motors” as the propulsion, since there is no need for power transmission. The wheels just turn, with up to 20 hp each.

The system I envision uses the basic eight-wheel architecture of an ordinary railroad car. The first illustration is of one half of a one half, to show the details that would otherwise be hidden. Red arrows indicate the rotary to linear (cam) movement that controls the steering. The second illustration shows how a mirror image assembly completes the (half) unit. The plates in yellow are the structural elements from which a PRT “pod” would hang. It would be suspended between a pair of the double units pictured. Such an architecture would enable very tight station maneuvering in 3D, while distributing weight over a large area, (for the cheapest track) The four-wheel (half) units, as pictured, could be used as is, in factories or distribution centers, or even on the grid, (for light delivery) with weight loads in the 40-170 kg. range.

This final illustration shows a cam mechanism that could be used to alternately raise and lower he steering guide wheels. Two servomotors operate the camshaft jointly, yet either can operate it separately, because of the ratcheting mechanisms. If either motor fails, the unit can operate normally yet the failure is immediately detected by the encoders.

Saturday, July 11, 2009

41> The Future Revealed!

I have been slipping into the fringe… That’s right, out of the main stream, into the ranks of the eccentric, into the world of the worshipers of the untried and untested… Beware!
I am thinking the unorthodox, have thought the unorthodox, and am beginning to believe! (Scary music and goose bumps ensue)
“What is this unholy philosophy?” you ask…trembling..
“It is this.”
“PRT can and should behave like ordinary traffic. Like ordinary drivers. It should react to the open road like a kid on spring break, unless, of course, Grandma’s on board. Slow traffic should stick to the slow lanes, stay off the highways.”
“No, wait ... Not independent drivers…”(the author closes his eyes as if communing with the great beyond) “Starlings! Schools of fish! Yes, That’s it! Traffic should behave communally. Like drivers who can read each other’s minds, and create ad hoc teams to punch through traffic, like a bubble in a witches brew…”
Think about it. Right now, the prevailing methodology is to slow the whole system down so that a vulnerable few don’t get frightened or motion sick. Everyone else has to take a little longer to get there. I understand that safety is a huge issue. Yet millions are being spent to research ordinary cars “driving by wire” as it is sometimes called. Now I might be a little crazy, but that’s nuts. Speed and switching control while captive in a rail is one thing, but turning your car over, on a real, 3D freeway to a computer is something way higher on the “crazy scale”. Or perhaps not… Modern passenger planes can take off and land unassisted, so what is the big deal?
The possibilities and ramifications are many to this philosophy. For example, passengers can be screened for speed preferences before boarding, or can have their personal preferences set upon creating an account. Now say, for example, 1st and 2nd avenues run North-South, and there are multiple PRT vehicles approaching the area, seeking North-South passage. Why not create a temporary fast and slow lane to accommodate those passenger preferences? Let the speed demons take 1st and the slowpokes take 2nd. This particular arrangement can dissolve as fast as it was created, while circumstances create other opportunities to snake through congested areas.
This obviously takes a much, much higher order of complexity in software control than the ordinary systems that have been developed so far. It is equally obvious that this approach is the future of PRT control, enabling the most efficient use of any given track infrastructure.
The author opens his eyes, séance complete, future revealed! (Wink wink.) You heard it here first, folks… ;o)
All kidding aside, there has been a shift away from centralized control in a variety of communication and control architectures in recent years, as individual “nodes” become endowed with greater and greater processing power. As for PRT, the original concept was to have a fleet of vehicles moving at exactly the same speed. Merges within congested areas would be accomplished by only slight speed changes, or presumably the merge would be called off. The claim of “non-stop” travel was a bit disingenuous, because the trip was to only begin once there was space on the track. In other words, the waiting would be done at the station instead of on route. Now the question is how, with every PRT “pod” having redundant Pentium class processors, can that computing power be employed to prevent traffic congestion in the first place? Although this may all seem very far down the road, I think it does have some bearing on the physical systems, including optimal track layout, station design, and vehicle capabilities.

Saturday, July 4, 2009

40> PRT: The Best Idea that Nobody Knows About

OK, Almost nobody, not counting the intelligent and insightful readers I am presently addressing…We have a problem here. And it needs to be addressed head-on. The problem is this. Great ideas don’t rise into actual day-to-day reality simply by being great ideas. The most brilliant innovations will lie dormant until their time has come, and not a day earlier.

So what makes an innovation an “idea whose time has come?" Pressure. Pressure of public opinion. Pressure of greed. Pressure to do the right thing. Pressure from loved ones. Pressure from above. Pressure from below. Political pressure, Peer pressure. The pressure to make the safe choice.

We don’t have a better idea problem. We have a pressure problem. More specifically, we have a complete lack of pressure to change the status quo on the people who could make it happen. The people who control transportation control existing forms of transportation. They control roads, bridges, buses, and trains. Those are their tools. Carpenters use nails and surgeons use scalpels. Our transportation people use the tools they know. PRT is not, currently, one of those tools.

This is an extremely hard lesson to learn for intellectual, inventive, types. We, (yes I count myself also) tend to think that any great idea should be instantly embraced, as though the entire populous is in a constant, active search for a better way. The problem is that humans are more generally in a search for a way to avoid the pressures that are put upon them.

This brings me to the picture. To creatures who try to avoid unwanted pressure, guilt is a strong motivator. It is extremely easy to continue to do the wrong thing as long as everybody else does it too, and our eyes are diverted from the truth. Hence the popularity of gas guzzling SUVs. The act depicted here prompts the witness to consider the hidden environmental cost of every gallon of gas.

This idea came to me because I realized that I could not visualize the “tons” of carbon dioxide that environmentalists where talking about, so I decided to find out just what the volume of that CO2 from burned gasoline was. After finding that out, (4.867 cubic meters per gallon) I needed a vessel to put it in, and naturally chose a balloon, and figured the radius to come to 1.051 meters.

Since it is easier for me to make a faux image than a real one, I had to find pictures of big balloons, and I quickly found the world of advertising balloons, and a thought came to me. The demonstration of volume of CO2 is better done in person than an image on the web. A single person standing (like in the picture) by a busy road could reach thousands. An organized campaign could reach millions. It also occurred to me that the balloon companies could, perhaps, be enticed to donate the balloons for free, especially if their own name appeared on the balloon, big enough for cameras to pick up. (Technical note, before someone orders one, the balloon as shown could spin as to be unreadable, because it needs two point tethering)

Just a thought folks, from a man who would like to turn up the pressure. By the way, wear T-shirts saying, “P.R.T.” “Look It Up.” (or something like that)

P.S. My apologies to my metric using friends abroad, I’m short of time today as it is “Independence Day” here in U.S., So, to my fellow Americans, happy Fourth of July!

Remember, it is your patriotic duty to point out stupid national behavior, no matter how common. For each of us to dump that much Carbon Dioxide on a daily basis is nothing short of insane. Every one of us can help create the pressure for change, even if it is simply to say something to a friend. Better yet, email the above picture to someone you love.