20> Podcar Control and Encoders

I’ve been wanting to start a conversation about PRT control for some time, so I thought I would start with this primer on motor control.

I don’t know a whole lot about brushless motors, other than that brushes are the means regular motors use to time the advance the magnetic fields ahead of the advancing rotor. With modern electronics, however, motors do not require mechanical means to achieve this timing. Triggering the magnets electronically offers great precision. Instead of “full-on, full-off”, magnetic forces can be ramped up or down; the motor’s rotation can be advanced or reversed, even held frozen.

Whereas in theory one could always know just where the shaft is, rotation-wise, under load the actual rotations or speed could differ from what is expected. One answer is the optical encoder.

My thanks to ikalogic.com for the logic diagram and shaft encoder pic. I just glanced at the site, but it looks educational. Sorry about the resolution. Click on the image to enlarge it.

The key is the C shaped “electric-eye”. (optocoupler) As holes in the disk align with the beam, a logic pulse is created. In the third picture, I depict how the same principle could be used to inform a PRT system on a pod-car’s position (and speed) along the track.

Some thoughts:
1. The track can be fitted with the PRT equivalent to traffic signs. Unlike drivers, PRT vehicles will follow their instructions to the letter. “Signs” in the track can trigger precise deceleration rates for upcoming turns, acceleration rates for merging, etc.
2. These “traffic signs” can be dynamic, reflecting real-time data.
3. The track itself should also receive data from the PRT vehicles. Track segments can “know” their traffic counts, for example, to upgrade or downgrade their availability factor, for routing decisions. It would seem that the process of merging would be the result of direct cross talk between cars and track.

There’s a lot more to be said about the division of control responsibilities, so I’ll save that for a separate post.

15> The "Podcar" and the PRT Dream

First, I HATE the term “Podcar” or “pod”. Unfortunately, Since the PRT thing in Ithaca last summer, it seems that a lot of “PRT” Googling results in this awful term. Are people who ride “pods” considered “Pod-People”? (Anyone remember that movie?) Anyway, I use it here in the title solely for the cynical reason that it might bring in some (Googled “POD”) readers, and some of them might become contributors to the cause. I would like to reiterate that cause now, as many people might tend to scan the site, without realizing it’s purpose, which is buried in the end of the “About this Blog” section
The ultimate dream would be to realize the world’s first large-scale open-source mechanical, software, legal, environmental and social engineering project, with a full set of blueprints, contracts, position papers, environmental studies, etc. provided by the masses, for the benefit of humanity and the planet. A “Wikipedia” of how to build a truly 21st century transportation system with local talent and resources, with a hefty “how –to” section on every possible situation. A framework by which primitive “model T” iterations of PRT are skipped, leading to successful and ever more efficient and beneficial implementations worldwide.
But on a much more humble scale, a bunch of us are “second-guessing” each other, on the topic of the day, or week, and our thoughts are being archived in the “cloud.” Anything we say may provoke a design breakthrough, or cut off some bone-headed approach that would only be a setback. In other words, it’s all good, as long as we get enough contributors to be a real resource that can, at least, be found.
I am not free to work toward this full time, but it is my passion. I wish I could post daily, but I can’t. I have many more ideas than I have posted so far, but I have to meter them out. I don’t want the best ideas buried too deep. So to any readers out there- Please post your thoughts about anything I write or any comments you read. Please spread the word! At some point I will start an email campaign to known advocacy groups and academia, but I need a blog gushing with comments, arguments, and ideas. If we, the people, reach a definable consensus, that is powerful stuff. It is the stuff of dreams.
Last but not least . Enjoy the illustration. I would like to note, however, the motor units shown don’t represent any particular design based on inner parts, size of the inner workings or anything else, for that matter. It’s hard enough just making them look shiny. But sometimes a picture says a thousand words, (and one blog address). I wanted to get this out sooner rather than later.