Saturday, April 25, 2009

30> Active Wheels

Back in my January 30 post, I brought up the concept of the “motor in the wheel” design. I like the idea a lot because it has no more moving parts than a LIM (linear Induction Motor) but is all contained in a neat little package, as opposed to having to provide miles of “reactor plate” in the track. Also, the tolerance between the rotor and stator parts of the motor can be very small. With a LIM these spaces would be a challenge to maintain, effecting efficiency. Check out this excellent simulation by Paul Nylander (http://bugman 123.com)

video

Oops. Bloggers' videos don't loop so it doesn't go 'round- Check out the web site...There's lots of neat stuff..

I found motor in wheel suppliers for bicycle conversions, and conveyor belts (drum motors) but I missed the obvious search words “wheel motor” until I ran into this interesting innovation from Michelin.



Anyway, I found a UK company, PML that produces a range of “wheel motors” sized for vehicle use. I have not had a chance to consider the various choices or to work them into a design, but they appear to be sufficiently small as to enable the many wheel, split carriage design I favor. (lots of traction, very tight turning radii, both up and down and side to side)

Designs will be forthcoming.

Wednesday, April 22, 2009

29> Thinking Outside the Box on Earth Day



Happy Earth Day, readers. Actually it is more like “Earth Evening”, right now.
I would like to punctuate my PRT posts with a personal note. As of the May 1st I will be leaving Texas and blogging from my land in New Hampshire, where, bit by bit, I am taming the land. There I live the greenest of lives. It brings out the Thoreau in me. (If “Walden”was required reading in every high school, we wouldn’t be in this environmental mess) Anyway, bear with me if I’m slow to post or respond, as there is no internet, phone, not even cell phone, on the land.. I must go to the town library for internet. I will spend about half of my time there until mid fall.

Pictured is my sole source of electricity, other than my car. These (3) 15W solar cells can be pivoted from the ground to aim directly into the sun. I started with a deformed tetrahedron made from six lengths of conduit strung together like beads with galvanized wire. Pipe brackets, some 1x4s, some steel cable, and an afternoon, and Voila! Total cost to put these collectors 30 ft. in the air? Less than $75. Now That’s Green. What's this got to do with PRT? Not much, but, hey, this is a mid-week post...about green..ah heck, I was looking for an Earth Day photo and just felt like sharing thus one.

So, my friends, on this Earth Day, let’s resolve to think “outside the box” to imagine a cheaper, faster, more reliable, more comfortable, more acceptable PRT design. (cheezy tie-in)

And one more thing, do not assume I know the latest PRT news. I was so busy with my land last summer I missed the Ithaca conference because I didn’t even know about it. I was only an afternoon’s drive away. So post those links folks! And don’t be afraid to comment on something that is a bit off-topic if you believe it would be of interest to the readers of this blog. Give me your suggestions! Mother Earth and I thank you.

Saturday, April 18, 2009

28> An “Ah-Hah!” Moment



In the post dated 3/22, I posed the question about what to do with an unbalanced load. I got the answer that I didn’t want, that the cabin couldn’t hang freely, but rather needed an active mechanical positioning system to correct the problem. Unfortunately, the beauty of the gondola design is that it minimizes errant G forces within the cabin by free hanging, so having an active system to correct for “level” would seem to be counter-productive. I think I have solved the problem. First let’s look at a little picture (above) I did to explain how to stop a passenger compartment from swinging too freely. If a vehicle swings too freely a turn or a gust of wind could get it swinging back and forth like a swing set. Pictured are two hydraulic/pneumatic cylinders tapped to work in both directions. (Sorry they look like car shocks, personal clip-art)
The cylinders are connected by hydraulic fluid lines with valves. When the valves are fully open, the “gondola” swings freely. When fully closed it doesn’t swing at all. The valves can then be adjusted for best performance. My guess is that a small bubble of air in the system will enhance performance. Note that two pair of such cylinders are needed, one for front to back swing control and one for side-to-side control. These would be integrated with any other suspension system.

Here is the “Ah-Hah!” part. The unbalanced load creates a difference between the (loaded) cabin position and the position that the cabin should take from (unoccupied) gravity. But this gravity is not necessarily down. It is whatever the forces of momentum make it. Therefore a simple “out of level” detector will work continuously during a journey, because it won’t just detect down, it will detect gravitational force and an active system meant to detect a severely unbalanced load can be added to a free-swinging system. It can straighten out a weight-tipped cabin while still allowing the cabin to swing.

Here’s how it works. A simple tilt detector like this
mercury switch (similar to those found in a pinball machine) determines that the cabin is tilted and the motor (pictured in blue) activates a screw jack to adjust the level. This process is purposely a bit slow, say 3 seconds. During a trip, the cabin will swing somewhat freely. (dampened by the hydraulic system) Any variation from the cabin floor being perpendicular to gravity or G forces will activate the motor, which will contribute to G force mitigation in a minor way during velocity changes and banking, but will principally keep the “gondola” level during constant velocity straight-aways and during “docking.” I have to say that this is a very immature, out of proportion design, posted as a conceptual drawing only.

Saturday, April 11, 2009

27> Designing For The U.S. Market

One thing I need to express is that, as an American, I cannot help but design for the U.S. market. Back in the 50s, then President Eisenhower spearheaded the construction of the U.S. interstate “super” highway system, and state and local governments quickly followed suit. By the late sixties suburban communities were popping up like weeds far from city centers, because without traffic lights and driveways greater distances were now commutable.

Fast-forward a generation and we have the great American suburban sprawl. Instead of a single “downtown” there might be ten. There are few pedestrians, because nothing is within walking distance. Traffic is not just confined to one direction. It is everywhere and may be worse thirty minutes from downtown than downtown itself.

Such a situation demands something much more ambitious than the little projects that the world has seen so far. It requires thousands of kilometers/miles of rail per city and speeds that are consistent with long commutes.

Obviously, no project can start on such a grand scale, but I believe any system that has a chance of adoption in the U.S. must be scalable to meet these needs. That means the cheapest possible track, the cheapest possible stations, and the fastest possible vehicles, designed for rides up to thirty minutes. That means a smooth ride is a must. The system, including stations, must have a minimal footprint. The station design, for example, promoted by the MISTER system is great, but only for about 10% of the stations, because, as I have said, there are no pedestrians. The sidewalks are empty but the streets are full.

Going fast means banking on corners or slowing for them, or clipping them (buying right-of –way) for larger radius turns. Banking track means more expense, complex engineering, and more specialization is required of the track builder. Perhaps there is a simple track design to do this but I have (so far)opted for the self-banking gondola design to address this issue. I am also inclined toward adaptable vehicle speed architecture rather than a set cruising speed. Empty vehicles should be very fast, traffic permitting, since there is nobody on board to get motion sick.

The U.S. transportation system is broken and needs to be fixed, and no little downtown “people mover” project is going to change that fact, just like light rail won’t nor will more buses, but that’s for a different post.

Finally, a question for my readers – In those systems with linear motors, what are the provisions for a power interruption? I was surprised to find that In the Taxi 2000 design they envisioned special “tow truck” type vehicles. Any thoughts on stranded passenger protocol?

Friday, April 3, 2009

26> Linear Induction Motor Tractor Unit


Here is a simple conceptual drawing of how Linear Inductions Motors (LIM) could be employed in a tractor unit for a gondola style Personal Rapid Transit (PRT) vehicle. Shown is a simplified track encasement, without outside structural support. The 3.2mm (1/8”) gap between is maintained by making internal rails (shown in orange) and the reactor plate (blue/green) both setscrew adjustable. With tight radius turns, the gap will be uneven and perhaps somewhat larger, but this diminished power and efficiency will not materially affect performance. By having two units in tandem closer gaps can be maintained. This design is compatible with the switching protocol illustrated earlier. The LIMS on one side must be turned off during switching, so the pod cannot accelerate strongly through the switching process. There are four LIMs. The proportions shown are consistent with the (Baldor) # LMAC16123D99. (12”x16”) (30.4 x 40.6 cm)

The performance of each are as follows. Each weighs 105 lbs. (48kg) and can produce up to 190 lbs. (845N) of pull (15% duty) and 38lbs. (169N) continuous. That’s a total of 760lbs. (3380N) max total, and 152 lbs. (676N) of continuous pull. The motors (total) weigh 420lbs. (190.5 kg)

The downside is this. These figures are for 60 Hz, 460 volt, 3 phase current. The maximum velocity for these LIMS at 60 Hz. is only about 15 mph. It is unclear how much pull would be sacrificed for additional speed, which is achieved by increasing the frequency of the AC current beyond 60 Hz.

Most past models for PRT have assumed speeds of about 30 mph. (48 kph) That may be fine for short haul downtown environments, but that’s where trolleys, shuttles and even light rail are most competitive. The urban/suburban sprawl typical of many cities (especially American) requires considerably more speed because of the distances involved.