Saturday, February 19, 2011
As many of you know, I have never been a big fan of dual mode. The problem is simple. If a vehicle is light enough to be part of an effective elevated PRT system, it is too light to be a robust road vehicle. Conversely, if it is sturdy and comfortable enough to not seem ridiculous as a car, it would require a track that would be unacceptably massive and costly. You tend to either have a bad car or bad PRT or both. Yet if you thread the needle just right, they are off by tantalizingly little . Lithium based batteries, ever-shrinking computing power, carbon fiber technologies and miracle plastics are nudging things forward, but what is needed is something really dramatic. Something to knock off half of the weight form the start.
The other day I was thinking about all of this, or at least how to transport people that last mile. I was considering bicycles, scooters, and Segways, and wishing for something that would have a roof to keep the rain out. I was even considering what technology would be involved in matching PRT to a Segway, instead of the other way around. I even have a picture to prove it.
It was around then that I decided to do an image search for a rain-proof Segway, and I stumbled onto something that had passed beneath my radar when I first heard about it. It is the EN-V concept car, which, as it turns out, which may well be the “best-yet” dual mode platform. It is a joint venture between GM and Segway, and it does two things that really reduce the weight problem. First of all, it runs on two wheels instead of four. Roadworthy tires and wheels are heavy, after all, especially if you include durable shocks and springs. This vehicle also lacks a mechanical steering wheel and all associated linkages. Like the ULTra, it is self-navigating, or at least, “drive by wire.” That brings up the intriguing notion of having the vehicle drive itself back to the station after dropping off a passenger. The side-by-side, two-wheel arrangement enables steering without any pivot assembly, and also allows 360 degree rotation in place, something that might add considerable flexibility in station design.
The relationship between the EN-V and PRT seems symbiotic: PRT can’t go the “last mile”, and the EN-V can’t go all that far. The EN-V’s shortcomings in speed and battery life could be rectified by an electrified track. Equally promising is that the EN-V weighs in at under 500 kg, and that is for a version with a much bigger battery and motor than would be required for dual mode use. Also, as long-time readers well know, I have my doubts about how good of a PRT vehicle can be designed and constructed by any fledgling company without seriously deep pockets for R&D. GM and Segway have dumped a lot of money and knowhow into this project. They have based the vehicle on what they call the “Puma” platform, which is literally just that… a versatile, self-balancing platform slung between two wheels.
I really think this combination deserves some serious consideration, more than I have time for within the context of a single post. Look forward, therefore, to more on this subject in days to come.
Here are some related videos: This short clip shows the “Puma” platform without the passenger compartment.
This second video shows a bare-bones version in action as well as a simulation of a city street designed for using the vehicle as an ULTra-like PRT.
The EN-V comes in three flavors, as shown in action in these vids.