Sunday, March 22, 2009
There is a problem that I have yet to solve with the gondola-like design I have proposed for PRT vehicle design. It is the problem of balancing the load. When two heavy people sit together, if the “pod” simply hangs by gravity alone, it will be very far out of level.
Let me back up and state the advantages of the design. The first is turning speed. If an ordinary vehicle makes a sharp turn at high speed, it creates sideways G-forces. The answer to this has always been to avoid such turns by designing the road with only gradual curves. (Consider the real estate consumed by a “cloverleaf”) Sometimes the roads are banked somewhat. The problem with gradual curves is that they are very unwieldy (design-wise) in an urban environment. With city streets generally designed with sharp corners, gradual curves have to use the airspace above valuable corner real estate. Right-of-way issues will be untenable. Highly banked track has drawbacks too, such as being banked only for a certain optimum speed, and adding expense to every curve and corner network-wide.
The second advantage is a quicker acceleration and deceleration rate. Any driver who has owned a compact car or a car with bad brakes or has tried to save gas by hardly pushing the petals knows that limiting acceleration and deceleration too much is a recipe for late arrival. If the name of the game is passenger throughput both acceleration and deceleration should be robust enough that having the vehicle be able to rock forward and back to minimize G forces would be desirable.
The third is steep slopes. In order to descend to street level without blocking driveways, or even just for versatility in a hilly town, handling steep slopes is a must.
Then there is the issue of passenger comfort and safety. The gondola design creates a means by which all G-force is diverted downward, toward the floor of the vehicle. This greatly enhances passenger comfort, safety and saves a lot of otherwise spilled coffee.
So the unsolved question is this; How do we keep the advantages of a free-hanging vehicle while not having it tilt from an uneven load? Note that making the vehicle wheelchair friendly tends to mean other seating is further from the center of gravity, making the problem worse.
So that’s the problem. If you have an idea, please post it, if it involves a picture, email it to me and I will post it for you.