I think you are discounting this out of hand.
Philster, have a looksee here.
I couldnt link the website for some reason so I shall C and P. Its from the Axon-Cable site.
"Slips rings are usually used when there is a need for a continuously rotating electrical connection between static (1)and mobile (2) components -for example a support and a rotating radar antenna. However, in many military or space applications an electrical connection with only a maximum of one rotation is required. For these instances a slip ringsolution is too expensive so the AXOTWIST™ solution deve-loped by AXON’ is ideal. "
According to the guys who develop the stuff, you need slip rings to accomplish a continous rotating coupling.
Tower cranes also come to mind.
Never mind, I was misremembering, as I realized shortly after I posted that. What I was thinking of is the antitwister, which would work but would require our wheeldebeest to roll over its “cord” once every two rotations of the wheel, which might be awkward. You’d also have to dispense with the axel, perhaps mounting the wheel in a fur-lubricated “fender”, or some such.
Their side legs. The Mulefa are built a little strangely. They’re diamond shaped with a leg at the front, a leg at the back, and a leg on either side. Only the front and back legs hold the wheels, the side legs push them on.
There are also naturally occuring roads on the Mulefa world (I can’t remember what caused them), which made wheels convenient.
Two hours, ten minutes too late (by Straight Dope Time). Solvitur circumtorquendo.
Elenia25 asked,
Insects are six-legged and walk with a continuous selection of alternate tripods. It is fast, efficient, and very stable.
Sometimes people just write nonsense. I’ve read that only mammals yawn – when I’ve seen snakes and birds do so; that only humans make tools – we know what happened to that one; and, just today, that only primates throw things – by an author who a few pages before described how a wild fox picked up a ball, tossed it 16 feet in the air, and chased after it to catch it again. She also described ravens kicking snow down on passers by, and then cawing in “laughter.” I myself have seen magpies dropping flowers on a squirrel as though to tease it. Stephen Jay Gould talks about old scientists’ tales, such as the oft-repeated one that raccoons can’t salivate. Caveat lector!
Mona in Toronto
I don’t see any post two hours ten minutes ahead of mine. And if you’re referring to the axotwist, that only allows for finite rotations, whereas the antitwister allows for arbitrary rotations.
But does it have a beard?
Wow, this thread went for 49 posts before it finally went sexual… pretty amazing!
The most fundamental reason for animals not evolving wheels has been omitted so far! As a fundamental principle of evolution, a mutation must occur. AFAIK, there have been no mutations to produce wheels so far.
IF such a mutation had occured, then the selective process could have proceeded.
But we often forget that evolution is the selection of mutations that occur…and think that evolution has an intelligent choice going on.
There is no intent driving evolution…just the cold hard selection process of chance mutations…most of which are deleterious.
Sorry. But then I’m just a plant evolutionary botanist.
Only on the calendar day you were two hours, ten minutes too late to make. It’s a very cleverly-drawn hoax, and an excellent illustration of why hour high-school geometry teacher told you that you can’t use a diagram to prove a theorem.
I just held my headphones and cord in the manner illustrated on the page I linked, and rotated the headphones over a hundred times without imparting any net twist to the cord. Perhaps you’d like to explain how this was possible, if the antitwister is a hoax?
And I still don’t see what I was two hours and ten minutes late for. Would you care to be more explicit?
Also if you’d bothered to read the link to Cecil’s answer to Marie’s question you will see that Cecil mentioned this method of rotating-without-twisting-the-umbilical himself. :rolleyes:
Ouch! Friction at high speeds?
Perhaps not a hoax, but more or less a joke. As the article points out, the thing only works if the disk is magically suspended in mid-air, with neither any means of support above or below or any mechanical drive to keep it rotating (though I suppose it could be combined with a turbine – or pinwheel rockets).
The “question mark” shape is confusing the issue. If the disk is turned the other way, you will see that the only way to achieve the “antitwister” effect is to keep enough slack in the cord to gather up a loop and throw it over the disk once for every rotation. With great effort (and considerable vibration, stress, and wear in the operation), I suppose there are imaginable ways that the thing can, somehow or other, be engineered, but the possibility of it being arrived at by biological evolution is effectively zero.
April 1.
“Now we have to kill him.”
After B.C. seens a clam walking along on two little legs.
–Do I get a virtual prize? A leather medal? A statue carved in butter?
Many one-celled animals move by cilia or flagella. For years, scientists thought that these were hairlike, flexible structures. (“Cilia” means eyelash and “flagellum” means little whip.). Many animal cells have cilia as well. Our lung passages are lined with ciliated cells that move soot, dust, and germs to the top of the trachea. A single cigarette paralyzes them for an hour.
But better microscopes revealed that they are stiff little corkscrews which rotate lke propellors. The rest in an embedded “ring bearing” in the cell wall. They are powered by differences in ionic charges
Here’s a quote from some biology notes:
Peritrichous bacteria have more than one flagellum, and the flagella rotate independently of one another:
- 95% of the time the flagella rotate counterclockwise
- 5% of the time the flagella switch directions and rotate clockwise
- When all the flagella are rotating counterclockwise, the flagella are bundled together and the bacterium travels in a straight line (swims)
- When one flagellum switches direction, the bundle disassociates, and the bacterium tumbles
- alternate swimming and tumbling result in a three-dimensional random walk
Read more here: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/prostruct/flag.html
For you evolution fans, bacterial flagella are more primitive than those of eukaryotic cells:
http://www.health.adelaide.edu.au/Pharm/Musgrave/essays/flagella.htm
For even more information on flagella, one might consult this learnëd treatise.
This is a similar mechanism to that in peristalsis, although applied to a “rigid” body rather than semi-fluid food and waste. It would certainly be possible for a biological mechanism to be designed to do this; however, I think it is physically unlikely that anything the size of a rodent or larger would have any need for it. The limiting factor is that the starting torque for a wheeled vehicle is high. Although the rolling resistance is lower than for any other type of transportation method (i.e. it requires no lifting, sliding, or tumbling of the main body, just the interia of the wheels) you first have to get up enough speed to get the thing moving, and with the mechanism which Chronos describes, the mechanical advantage is against you by a ratio of the axle diameter to the wheel diameter. You could reduce that by having your peristaltic driver work at the upper rim of the wheel, but then the speed is higher (for the same angular velocity) requiring quicker action.
Add to that the fact that now your “foot” (area exposed to the ground at some point) is several times the surface area of a walking foot, and most most nomadic mammals use the very resource-intensive hoof to protect their foot; your wheeled animal would have many times that much material invested in a hoof, and a single break or serious spall would immobilize it.
Wheels are good on flat pavement, more or less constant speeds, over relatively long distances. None of these are conditions that appear in the natural, unmodified world in significant proportions. Even creatures that migrate over long distances generally move in spurts and fits, not a continuous, steady pace. For stop and go movement, wheels are actually slower than legs. (At ten yards, in a race between a man, a horse, and an F1 car from a dead stop, the man wins.) For movement over uneven or roughened ground, it is clear that legs are superior.
It’s a good thing we have these slow, unwieldy legs; if we were naturally accustomed to traveling much faster we’d have been building bypasses along time ago and you know how that ends up.
Stranger