Thanks, RacingManiac, excellent reference. I do not know if this is the correct link
tf1 wrote:what advantage(s) do you see from going to a spherical wheel?
C'mon, how could you expect me to answer that?
OK, let's reinvent the wheel, then. I will play "devil's" advocate, because the wheel is like 3,000 years old and it is undefeated. You could say that modern wheels have only 100 years, but they certainly have advantage.
* "Conventional" wheels have only 2 degrees of freedom, wich means you can vary only your speed and the radius of the curve. The more obvious advantage is the ability to move with 3 degrees of freedom, which means you can rotate or move laterally the car, which in turn implies the ability to have any slip angle you wish, or none at all.
If you have seen the movie, maybe you remember when "our hero" is followed by a truck full of robots? The truck is moving sideways.
* The difference is a little deeper: to know the trajectory of a non-holonomic
system, like cars and bicycles, you need to know the history of his path.
On the contrary an holonomic
system trajectory is independent of its momentum or its velocity: it depends only on his coordinates and time, like, for example, a pendulum. This, in turn, means that lateral movements are not limited to parking manouvers: you can do lateral movements at any speed.
Again, if you have seen the movie, you may remember that "our hero" decides to drive manually, when, distracted, he almost hit a truck in the back: he then procedes to move the car laterally at, I do not know, 300 kph in Hollywood speed units, and the car does not slip much sideways (you could have exactly zero under/oversteer and
rotation for the entire manouver).
* If, actually there is no need for an slip angle to exist for the car to displace laterally or even rotate, you do not need to create friction between the tire and the road to take a curve: essentially you could do all the time what rally pilots do when they slide, pushing the car with the engine in the desired direction. Think of an office chair with spherical wheels.
This should extend the life of the wheel "thread" enormously. For example, I did not see any flat tyres in the movie.
* Finally, they are totally cool. For example, the hub caps have a funny hexagonal design that suggest the need for the rigidity of the entire assembly over the wheel and the maximum space for air to flow. Notice the huge air intakes on the rear and
front wheels and how they mix with the body. This is what made me think about air bearings. Besides, this thing was designed by Audi, apparently, in a sort of "semi-serious" mood about how cars could look in 2035. Or in 1935...
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